I
“EFFECTS OF MANDIBULAR CANINE INTRUSION OBTAINED
USING CANTILEVER VS BONE ANCHORAGE: A COMPARATIVE
FINITE ELEMENT STUDY”
By
DR. AFSHAN SAMAN WAREMANI
Dissertation Submitted to
Rajiv Gandhi University of Health Sciences, Bengaluru, Karnataka
In partial fulfillment of the requirements for the degree of
MASTER OF DENTAL SURGERY
IN
ORTHODONTICS AND DENTOFACIAL ORTHOPAEDICS
Under the guidance of
DR. NAUSHEER AHMED M.D.S.
Associate Professor
Department of Orthodontics and Dentofacial Orthopaedics
Government Dental College and Research Institute
Bengaluru - 560002
Karnataka, India
(2016-2019)
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LIST OF ABBREVIATIONS USED
VII
(In alphabetical order)
Sl.No Abbreviation
Full Form
1. CT Computed Tomography
2. FEM Finite Element Method
3. fig Figure
4. gm Gram
5. mm Millimeter
6. µmm Micro millimeter
7. MBT McLaughlin, Bennet, Trevesi preadjusted
edgewise bracket system
8. MPa Mega Pascal
9. N Newton
10. PDL Periodontal Ligament
11. i.e. That is
12. 3 D Three Dimensional
13. TMA Titanium Molybdenum alloy
14. SS Stainless Steel
15. TAD Temporary Anchorage Device
16. TiAlVn Titanium aluminium vanadium alloy
17. AD Anno domini
LIST OF TABLES
VIII
SL.NO PARTICULARS PAGE NO
1. Material properties of the members 48
2. Amount of force on the x-axis produced with the toe-ins
tested 48
3. Amount of intrusion of crest node and root node
Displacement along y axis 48
4. Labial/lingual movements of crest and root node
Displacement along z axis 48
5. Stresses in canine periodontium 49
6. Alveolar bone stress around canine 49
LIST OF GRAPHS
Sl.No PARTICULARS PAGE NO
1. Amount of intrusion of crest node and root node
Displacement along y axis
46
2. Amount of intrusion of crest node and root node
Displacement along y axis
46
3. Stresses in canine periodontium 47
4. Alveolar bone stresses around canine 47
LIST OF PHOTOGRAPHS
IX
SL.NO PARTICULARS PAGE NO. 1. CT Model of the mandibular arch
Fig
77
2(a) Model of the bone from canine to the second molar 77
2(b) Mesh form of the teeth 78
2(c) Teeth with 1.5mm offset of the canine 78
3(a) Canine tooth and its periodontium 79
3(b) Periodontium of the dentition 79
3(c) alveolar bone with sockets 80
4(a) Teeth with bracket and wire 80
4(b) With 4 different toe-in bends of cantilever i.e 0,4,6,8
degrees (Zero from left side).Assembly with
Cantilever arrangement
81
4(c) model in ansys software 81
5(a) mini-implant model with 1.2 mm diameter and 6mm
length
82
5(b) model with elastic chain placed from mini-implants
to canine
82
5(c) model with mini-implant 82
6(a) (Vector plot for beam element)Analysis Results for 0
degree :
83
6(b) (Vector plot for beam element)Analysis Results for 4
degree
83
6(c) (Vector plot for beam element)Analysis Results for 6
degree
84
6(d) (Vector plot for beam element)Analysis Results for 8
degree
84
6(e) (Vector plot for beam element)Analysis Results for
mini-implant
84
7(a) displacement along Y and Z axis (model with 0º toe-
in)
85
7(b) displacement along Y and Z axis (model with 4º toe-
in)
85
7(c) displacement along Y and Z axis (model with 6º toe-
in)
86
7(d) displacement along Y and Z axis (model with 8º toe-
in)
86
7(e) displacement along Y and Z axis (model with mini-
implant
87
8(a) stress in the Canine peridontium (0º toe-in)
87
8(b) stress in the Canine peridontium (4º toe-in) 88
8(c) stress in the Canine peridontium (6º toe-in)
88
LIST OF PHOTOGRAPHS
X
8(d) stress in the Canine peridontium (8º toe-in)
89
8(e) stress in the Canine peridontium (mini-implant) 89
9(a) stress in the alveolar bone (0º toe-in) 90
9(b) stress in the alveolar bone (4º toe-in) 90
9(c) stress in the alveolar bone (6º toe-in) 91
9(d) stress in the alveolar bone (8º toe-in) 91
9(e) stress in the alveolar bone (mini-implant) 92
10(a) effects on the molar (0º toe-in) 92
10(b) effects on the molar (4º toe-in) 93
10(c) effects on the molar (6º toe-in) 93
10(d) effects on the molar (8º toe-in) 94
10(e) effects on the molar (mini-implant) 94
11(a) stress changes in posterior segment (0º toe-in) 95
11(b) stress changes in posterior segment (4º toe-in) 95
11(c) stress changes in posterior segment (6º toe-in) 96
11(d) stress changes in posterior segment (8º toe-in) 96
11(e) stress changes in posterior segment (mini-implant) 97
ABSTRACT
XV
Title: Effects of Mandibular Canine Intrusion Obtained Using Cantilever versus Bone
Anchorage: A Comparative Finite Element Study
Background and objectives: This study was conducted to assess and compare the
effects of mandibular canine intrusion obtained, by using cantilever having different
compensatory toe-in bends and with mini-implants using 3D finite element method
Materials and Method: 3D models of the mandibular right quadrant were created
using FEM. Brackets and molar tubes were modelled with 0.022 x 0.028-in slots and
0o of tip and torque with a base wire of 0.021 x 0.025-inch. In the first model
mandibular canine intrusion was produced using a cantilever loop (17x25 inch TMA)
and having different compensatory toe-in bends (0º, 4º, 6º and 8º). In another model
intrusion was done using two mini-implants placed buccally, on either side of canine
in the interdental bone. Force was applied using an elastic chain. The amount of pure
intrusion and associated labial tipping of canine that occurred in both the models was
assessed and compared using FEM analysis.
Results: Pure intrusion of the canine was produced by both the 6º toe-in as well as the
mini-implant, but the amount of intrusion with the 6º toe-in was higher. The labial
tipping of the canine was also reduced in these two models. The highest amount of
periodontal ligament stress was observed around the canine root with a 0º toe-in bend.
In the posterior segment, the molar displayed a slight tendency for extrusion and distal
crown tipping
Conclusion: The intrusion mechanics using cantilever, simulated in this study may
achieve pure mandibular canine intrusion with minimal labial tipping when a
compensatory toe-in of 6º is incorporated into the cantilever. The molar displayed
slight extrusion and distal tipping
Key words: arch wire; bracket; cantilever; intrusion; FEM; mini-implant
INTRODUCTION
1
EFFECTS OF MANDIBULAR CANINE INTRUSION OBTAINED
USING CANTILEVER VS BONE ANCHORAGE: A
COMPARATIVE FINITE ELEMENT STUDY
INTRODUCTION:
A deep overbite is a malocclusion, which is commonly encountered in an orthodontic
practice. Severe deep bites (overbite >5 mm) are found in nearly 20% of children and
13% of adults, representing about 95.2% of vertical occlusal problems. A deep bite
malocclusion overlies a variety of hidden skeletal or dental discrepancies.
Accordingly, a deep bite should not be approached as a disease entity, and should be
seen as a clinical manifestation of an underlying skeletal or dental discrepancy.1
Deep bite can be divided as dentoalveolar in nature or skeletal due to growth of the
jaws.2 A skeletal deep bite could result from a discrepancy in the vertical position of
the maxilla, the mandible, or their cant. Excessive maxillary and mandibular alveolar
heights have been reported in deep bite cases. At the most basic level of analysis, the
skeletal and dental components that appear to be consequential in affecting overbite
change are (1) maxillary skeletal displacement, (2) mandibular skeletal displacement,
(3) maxillary dental change, and (4) mandibular dental change.3
Few studies, which have dealt with the components of skeletal deep bite, showed that
the gonial angle was the highest shared skeletal factor in deep bite malocclusion.
Ceylan and Eroz studied some components of deep overbite and one of the significant
findings was that the gonial angle was the smallest in the deep bite group, also the
INTRODUCTION
2
study showed that the vertical component of mandibular growth has a more
remarkable effect than the rotational component and that the mandibular skeletal
changes were twice as important as the mandibular dental changes and about 2.5 times
as important as the maxillary changes in inducing overbite changes.1
Regarding dental deep bite, a deep curve of Spee and an increased buccal root torque
of the maxillary incisors were proven to be correlated with deep bite malocclusions.
The over-erupted maxillary and mandibular anterior alveolar basal heights and the
under-eruption of the maxillary and mandibular posterior segments were also shown
to have positive correlations with deep bite malocclusions.1The exaggerated curve of
Spee has been shown repeatedly, to have a main role in developing dental deep bites.
This finding reflects the importance of the mandibular dentoalveolar factor in deep
bite malocclusions, emphasizing the need for extruding the mandibular buccal
segment and intruding the mandibular incisors in most deep bite mechanotherapies.
Andrews, found that the curve of Spee in subjects with good occlusion ranged from
flat to mild, noting that the best static intercuspation occurred when the occlusal plane
was relatively flat. He proposed that flattening the occlusal plane should be a
treatment goal in orthodontics.4
Correction of deep bite is often a challenging step in orthodontic treatment. Deep bite
cases that are untreated can cause increased anterior crowding, maxillary dental
flaring, periodontal problems, and temporomandibular joint problems and can
interfere with lateral and anterior mandibular movements. Deep bite can be treated
orthodontically by intrusion or flaring of the incisors, extrusion or passive eruption of
the buccal segments, or a combination of these. Although, extrusion of the posterior
dentition is an effective method of bite opening in growing patients, it is not indicated
INTRODUCTION
3
in patients with normal incisor display or normal or long lower facial height, its
stability is questionable in non-growing patients with average to low mandibular plane
angles. Intrusion of the maxillary incisors is undertaken in patients with excessive
incisor and gingival display and a large interlabial gap. Considering these facts,
mandibular incisor intrusion is the most suitable deepbite treatment for adults with
normal incisor and gingival display and a normal or high mandibular plane angle. 5
Intrusion refers to the apical movement of the geometric center of the root (centroid)
in respect to the occlusal plane or a plane based on the long axis of the tooth. Labial
tipping of an incisor around its centroid produces pseudo-intrusion as it influences the
vertical incisal edge position.7Although this pseudo-intrusion gives clinical impression
of deep overbite correction, it should not be confused with the genuine intrusion.
Recently, several researchers have focused on the effect of aging on anterior tooth
display and on how treatment mechanics change the perception of age. Sarver,
Ackerman and Zachrisson drew attention to the importance of lower incisor intrusion
in deep bite patients with reduced upper incisor display to preserving a youthful
appearance. Lower incisor intrusion can be accomplished using different arches, such
as a reverse Spee arch, a three-piece intrusion arch, or a utility arch. Even though
intrusion can be achieved successfully with all of these appliances, incisor
proclination during intrusion and unwanted distal tipping on posterior anchorage teeth
are inevitable.9
Although continuous arches provide rapid correction through both incisor proclination
and majorly posterior extrusion, the extrusion of posterior teeth is not always stable,
especially in adult patients. Intrusion using segmental arches not only provides
INTRODUCTION
4
accurate prediction of forces or moments but also predominantly produces incisor
intrusion with molar extrusion to a lesser degree thus minimizing counteracting side
effects. The use of temporary anchorage devices for lower incisor intrusion have been
described in a few case reports, and the effects were limited to the mandibular anterior
area.9,10
Approximately 50% of patients with deep bite have anatomically extruded mandibular
canines. Because simultaneous orthodontic intrusion of the 6 anterior teeth can cause
undesirable effects in the posterior anchorage segment, segmented intrusion of the
mandibular canines should be considered when levelling the curve of Spee.11
A few reports have described the methods for individual intrusion of the canines. A
technique described by Ricketts et al involved using the utility arch after complete
incisor intrusion as a stabilization arch and gently tying an elastic band from the
canine bracket to a step-down bypass segment in the utility arch.6 In another study
reported by Marcotte, suggested the use of a cantilever from the auxiliary tube of the
first molar to the canine bracket slot. Burstone, in a study, also described a method for
individual intrusion of the canines that included a slight compensatory toe-in bend to
deliver a lingual force for controlling the tendency of buccal crown tipping of the
canine.11
Since Creekmore and Eklund initially performed maxillary incisor intrusion using a
vitallium screw inserted just below the anterior nasal spine, many clinicians have tried
to intrude the incisors with absolute anchorage. Recently, implant-anchored
orthodontics has led to the development of new orthodontic treatment strategies.
These implants provide stationary anchorage for various tooth movements and even
make it possible to move a tooth in more than a direction which was impossible with
INTRODUCTION
5
traditional orthodontic methods. Miniscrew anchorage is especially useful for tooth
intrusion, because it can apply a low, continuous force of a set magnitude without
causing reciprocal movements of other teeth.14
In conventional mechanics, cuspids are traditionally intruded by means of arch wires
with second order bends or bypass bends associated with elastics and using the
neighboring teeth for anchorage. In these cases, the extrusive component of the
anchorage units cannot be avoided. Another alternative is the use of segmented arch
wires relying on posterior teeth for anchorage. When one wishes to intrude a cuspid
tooth while keeping its axial inclination, the buccal insertion of two mini-implants is
recommended, one on the mesial and one on the distal region of the tooth targeted to
be intruded.15
In this case, mini-implants emerge as an excellent alternative as they provide efficient
anchorage, requiring no tooth support and with no esthetic compromise. Additionally,
patient cooperation is less required. Mini-implants have been used in the orthodontic
office with increasing frequency in cases where an inadequate number of dental units
stand in the way of an effective anchorage, or even only to simplify orthodontic
mechanics and make it more predictable.15
Mini-implant anchorage is especially
useful for tooth intrusion, because it can apply a low, continuous force of a set
magnitude without causing reciprocal movements of other teeth.14
Finite element method was first developed in 1956 in the aircraft industry. This
method has since been in widespread use not only in aerospace engineering, but also
in civil engineering. The finite element method is an extremely effective technique for
INTRODUCTION
6
the treatment of problems of plane stress and plane strain. The first three dimensional
FEM study in dentistry appeared in 1974, where J.W.Farah and R.G.Craig did finite
element stress analysis in a restored first molar.16
Finite element analysis has been
applied to the description of form changes in biological structures (morphometrics),
like area of growth and development. Finite element method is also useful for the
study of structures with inherent material homogeneity and potentially complicated
shapes such as dental implants. The mechanical behaviour of the orthodontic wires
and different design of brackets and its contact problem can be well modelled and
simulated by the finite element method. Advantages are that extensive instrumentation
is not required, complex larger problems can be split into smaller problems,
FEM enables the evaluation of biomechanical effects such as stress and strain on
human body parts that are difficult to access without causing harm to subjects,11
it is a
completely non-invasive procedure, three dimensional models can be generated,
actual physical properties can be simulated and external environment can be simulated
and the operator can repeat the study as many times as possible.16
In orthodontics, finite element method has been used to clarify the stress distribution
causing root resorption, to evaluate the risk of adverse events during technical
procedures, and to verify and devise new mechanics. Orthodontic treatment requires
adequate management of the mechanics and attention to biology in order to achieve
efficient tooth movement. Recently, finite element analysis has provided a visual
image of the effects of an orthodontic force on the tooth and its supporting structures.
It also serves as a useful tool to simulate different loading systems and evaluate the
initial effects in the dentoalveolar structures to better understand biomechanics.17
INTRODUCTION
7
A finite element model is constructed by dividing solid objects into several elements
that are connected at a common nodal point. Each element is assigned appropriate
material properties corresponding to the properties of the object being modelled. The
first step is to subdivide the complex object geometry into a suitable set of smaller
‘elements’ of ‘finite’ dimensions. When combined with the ‘mesh’ model of the
investigated structures, each element can adopt a specific geometric shape (i.e.
triangle, square, tetrahedron, etc.) with a specific internal strain function. Using these
functions and the actual geometry of the element, the equilibrium equations between
the external forces acting on the element and the displacement occuring at each node
can be determined.18
Uncontrolled canine intrusion in the treatment of deep bite may lead to buccal crown
tipping and thus to increased mandibular intercanine width, and it could also increase
the chances of orthodontic treatment relapse.19
Buccal crown tipping control is
important because excessive buccal tipping of the canine may increase the risk of
gingival recession or bone resorption, especially in patients with a history of
periodontal disease and bone loss.33
The proclination of these teeth could also lead to
abfraction lesions because the canines receive additional loads when mandibular
lateral excursions are performed.41
Therefore, there is still a need to improve the
clinical approach for intruding the mandibular canines while adequately levelling the
curve of Spee.11
The purpose of this study was to use the finite element method to simulate and
compare the effects of intrusion of mandibular canine obtained using segmented
mechanics with a cantilever having different compensatory bucco-lingual activations
(toe-in bends) and with bone anchorage using mini-implants.
OBJECTIVES
8
OBJECTIVES
The objectives of this finite element study are:
1. To simulate the segmented intrusion of mandibular canine with a cantilever
and to evaluate the effects produced by different compensatory bucco-lingual
activations (toe-in bends) on the canine and the posterior teeth.
2. To simulate the intrusion of mandibular canine with mini-implant and evaluate
the effects on canine and the posterior teeth.
3. To compare the results and effects produced by cantilever and mini implant on
the mandibular canine and the posterior anchor teeth.
REVIEW OF LITERATURE
9
REVIEW OF LITERATURE:
A study was conducted to explore the different components of deep bite
malocclusion and determine their actual contributions in its development. Dental
and skeletal measurements were made on lateral cephalometric radiographs of 124
patients and analysed. Results showed that a deep bite malocclusion is multi-
factorial having definite dental and skeletal components. The gonial angle was
found to be the highest contributing skeletal factor confirming the importance of
the growth and angulation of the ramus. Among dental components a deep curve
of Spee was the highest contributing factor, confirming the importance of
intruding the mandibular incisors in deep bite mechanotherapy. The study
concluded that a thorough analysis of all deep bite components reduces the
clinician's bias toward predetermined mechanics in treating deep bite patients and
allows for better individualized treatment planning and mechanotherapy 1
A longitudinal study was conducted to analyse the multidimensional nature of
overbite changes that occur during adolescence. The study used cephalograms of
181 untreated children (102 males, 79 females) taken at ages 10 and 15. Four
major components like maxillary vertical displacement, mandibular vertical
displacement, upper incisor vertical change within the bone and lower incisor
vertical change within the bone were measured. The results showed that although
the average overbite changes between 10 and 15 years were minimal (0.2 mm),
variation ranged from 2.4mm of bite opening to 5.6 mm of bite deepening. Despite
the large discrepancy between maxillary and mandibular skeletal displacement,
overbite remains relatively stable, supporting the notion of vertical dentoalveolar
REVIEW OF LITERATURE
10
compensatory mechanisms. The multivariate model suggests that mandibular
changes, specifically vertical growth and rotation, are more important than
maxillary changes in determining overbite changes. Also important clinical
approaches can be developed in the treatment of developing open/deep bites. 3
A study was conducted determine the curve of Spee by examining its development
longitudinally in a sample of untreated subjects with normal occlusion from the
deciduous dentition to adulthood. Sixteen male and 17 female subjects were
selected and the maximum depth of the curve of Spee was measured. The depth of
the curve of Spee was measured on their study models at 7 time points from ages 4
(deciduous dentition) to 26 (adult dentition) years. The result showed that the
occlusal plane in the deciduous dentition is relatively flat and the largest increase
in the maximum depth of the curve of Spee results specifically from, the eruption
of the mandibular permanent first molars and incisors relative to the deciduous
second molars. During the mixed dentition stage, the curve decreases slightly and
then remains relatively stable into early adulthood. The study concluded that there
are no significant differences in maximum depth of the curve of Spee between the
right and left sides of the mandibular arch or the sexes 4
A retrospective longitudinal study was done to investigate the long-term stability
of deep overbite correction with mandibular incisor intrusion with utility arches in
adult patients. Pre-treatment (T1), post-treatment(T2) , and 5-years post-retention
(T3) lateral cephalograms of 31 patients (range, 24.1-30.9 years) with Class II
Division 1 malocclusion and deep bite, treated by maxillary first premolar
REVIEW OF LITERATURE
11
extraction and mandibular incisor intrusion, were traced and measured. The
treatment protocol included intrusion of the mandibular incisors to correct the
deep bite and extraction of the maxillary first premolars to correct the overjet. In
the maxillary arch, after alignment and retraction of canines, the upper incisors
were retracted by 0.017 x 0.025-in beta titanium alloy archwires with mushroom
loops. In the mandibular arch, utility arches (0.016 × 0.022 inch) Blue Elgiloy
wires, activated to exert 40 g of force, were used for incisor intrusion. The mean
active treatment time was 2.7 years. Significant decreases in overjet and overbite,
significant retroclination and retraction of the maxillary incisors, and significant
increases in protrusion, proclination, and intrusion of the mandibular incisors were
observed at T2. At T3, there were statistically significant but clinically
unimportant increases in overjet, overbite and extrusion of the mandibular
incisors. With mandibular intrusion utility arches, 2.6 mm of true incisor intrusion
was obtained. The study concluded that deep bite treatment with mandibular
incisor intrusion with utility arches was effective and appeared to be stable in non-
growing patients.5
A study was conducted to measure the amount of true incisor intrusion attained
during orthodontic treatment. Abstracts were selected and from these, original
articles were retrieved, and their references were hand searched for missing
articles. The results showed that twenty-eight articles met the initial inclusion
criteria, but 24 were rejected because they did not quantify true incisor intrusion or
factor out normal growth impact when required. The remaining 4 articles showed
that true incisor intrusion is attainable but with large variability depending on the
appliance used. The mean estimates of intrusion and 95% CI were 1.46 mm (1.05-
REVIEW OF LITERATURE
12
1.86 mm) for the maxillary incisors and 1.90 mm (1.22-2.57 mm) for the
mandibular incisors. The study concluded that true incisor intrusion is achievable
in both arches, but the clinical significance of the magnitude of true intrusion as
the sole treatment option is questionable for patients with severe deep bite. In non-
growing patients, the segmented arch technique can produce 1.5 mm of incisor
intrusion in the maxillary arch and 1.9 mm in the mandibular arch. 7
A study was conducted to compare the dento-facial effects of mandibular incisor
intrusion using mini-implants with those of a conventional incisor intrusion
mechanic, the utility arch. Twenty-six deep-bite patients were divided into two
groups. In group 1 the mandibular incisors were intruded using a 0.16 x 0.22–inch
stainless-steel segmental wire connected to two mini-implants. In the second
group, mandibular incisor intrusion was performed using a conventional utility
arch. Lateral cephalometric radiographs were taken at pre-treatment and at the end
of intrusion. Thirty landmarks were identified to measure 23 linear and 20 angular
measurements and compared. The results showed that the duration of intrusion
was 5 months for group 1 and 4 months for group 2. The study concluded that
pure upper incisor intrusion could be achieved using a segmental arch to the
incisors when it is supported by two mini-implants that are placed between the
lateral and canine teeth. Also the incisor intrusion that was achieved using TAD
supported segmented archwire was no different than the movement achieved by
the conventional intrusion utility arch. 9
A study was conducted to compare the efficacy of overbite correction achieved by
conventional continuous arch wire technique and the segmented arch technique as
REVIEW OF LITERATURE
13
recommended by Burstone. The sample consisted of 50 adult patients having low
angle, deep bite malocclusions and were at least 18 years old. Twenty-five patients
were treated with a continuous arch wire (CAW) technique with a pre-torqued and
pre-angulated bracket system. The other group were treated with the segmented
arch technique. An intrusive force of 10 to 15gms per tooth was used. Results
showed that the treatment period of the Burstone group was 4 months longer than
that of the continuous arch wire group. Incisor intrusion with little extrusive
movement in the molar area, however, is found with the segmented arch technique
as recommended by Burstone. This study concluded that the arch leveling
technique, according to Burstone, can produce genuine intrusion of the incisors
with little vertical effect in the molar area in adult patients 10
A finite element study was conducted to evaluate the effects of mandibular canine
intrusion produced using cantilever loop with different toe in bends and the
subsequent effects on the posterior teeth. A finite element study of the right
quadrant of the mandibular dental arch together with periodontal structures was
modelled using Solidworks software. All bony, dental, and periodontal ligament
structures from the second molar to the canine along with brackets and molar
tubes were graphically represented and modelled. A 0.021 x 0.025-in stainless
steel base wire and a 0.017 x 0.025-inch titanium-molybdenum alloy cantilever
was also modelled. Discretization and boundary conditions of all anatomic
structures tested were determined with Hypermesh software and compensatory
toe-in bends of 0, 4, 6 and 8 degrees were simulated with Abaqus software. The
results showed that there was a tendency for buccal crown tipping of the
mandibular canine when a passive 0 degree toe-in was simulated. The amount of
REVIEW OF LITERATURE
14
this buccal tipping tendency decreased as the amount of compensatory toe-in
increased. When a compensatory toe-in of 6 degree was simulated, the buccal
crown tipping tendency was completely eliminated. The stress produced in the
PDL of the posterior teeth used as dental anchorage was minimal and the anchor
molar showed a tendency for distal crown tipping and extrusion. This study
proved the need of incorporating compensatory toe-ins to prevent undesired buccal
or lingual crown tipping of the mandibular canines during intrusion with a
cantilever. 11
A study was done to describe the One-couple orthodontic appliance systems. One-
couple systems are capable of applying well-defined forces and couples to effect
controlled tooth movement during treatment and consist of two sites of
attachment: one in which the appliance is inserted into a bracket or tube where
both a couple and force is generated, and one at which the appliance is placed as a
point contact where only a force is produced. Appliances with long interbracket
spans between two points of attachment have low load deflection rates and deliver
relatively constant forces and moments as the teeth move toward their desired
locations. Moreover, in two-tooth systems where the appliance is engaged in the
bracket of only one tooth and tied as a point contact to the other tooth, the force
system created is statically determinate which means that the forces and moments
that the wire will apply to the teeth are easy to discern clinically. This makes tooth
movements more predictable. A couple is created only at the tooth in which the
wire is engaged but forces exist at both attachment sites acting in opposite
directions because the appliance is in static equilibrium. By applying tile basic
laws of equilibrium, one-couple appliances can be designed and adapted to
REVIEW OF LITERATURE
15
perform numerous functions like canine extrusion, midline movement, anterior
intrusion, and anterior extrusion. The large range of activation of these wires
means that tooth movement will proceed even without frequent monitoring and
appliance adjustment. The actions of such appliances are highly predictable and
any unwanted side effects can be localized and easily monitored during treatment.
The simplicity and flexibility afforded by one-couple orthodontic appliance
systems make them an attractive choice in clinical situations where maximal
control of tooth movement is desired. 12
A case report illustrates the successful treatment of over-erupted mandibular
incisors and excessive mandibular curve of Spee with the indirect use of
miniscrew anchorage and segmented wires. A 22 year old female patient
diagnosed with a severe Class II Division 1 malocclusion, deep overbite and
excessive curve of Spee was treated. After initial levelling and aligning,
Miniscrews (length, 9 mm; diameter, 1.5 mm) were placed into the buccal alveolar
bone at the mandibular premolar extraction sites to achieve en-masse intrusion of
the mandibular anterior teeth. A 0.016-in × 0.022-in utility archwire was installed
and ligated to the mandibular miniscrews and intrusive force of 50mg was applied
to the anterior segment to be retracted. A cephalometric evaluation immediately
after the intrusion procedure detected intrusion of 5.0 mm without molar
extrusion. This report concluded that the indirect use of miniscrews is an efficient
method for intruding over-erupted mandibular incisors.14
REVIEW OF LITERATURE
16
An FEM study was done to determine the most desirable force system and loading
conditions required to achieve effective molar protraction from an interdental
miniscrew with minimal side-effects. The variation of force delivery was
simulated through changes in the height of a miniscrew, length of a molar
extension arm, and incorporation of a lingual force. CBCT data from a 27-year-old
male patient with missing mandibular right first molar, brackets, molar tubes,
mini-screws and protraction appliances were modelled with finite element
software. A total of 80 loading conditions were simulated by altering the extension
arm length (2–10 mm), miniscrew height (0–8 mm), and magnitude of protraction
force from the lingual side (0–1.5 N). Results showed that in this specific FE
model of mandibular molar protraction, a long extension arm (8–10 mm) was
necessary to eliminate mesial tipping when a protraction force was applied. The
most ideal force system in the model appeared to be the longest extension arm (10
mm) and the addition a lingual force half or equal magnitude of the labial force
(0.5–1 N). The height of the miniscrew was not critical to achieve translation
during mandibular molar protraction; although, a more occlusal position of a
miniscrew may help reduce mesial tipping with a long extension arm 17
A study was conducted to examine the success rates and find factors affecting the
clinical success of screw implants used as orthodontic anchorage. Eighty-seven
patients (35 male, 52 female; mean age, 15.5 years) with a total of 227 screw
implants of 4 types were examined. Results showed that the overall success rate
was 91.6%, with a mean period of force application of 15 months. Therefore, it
was concluded that screw implants can be used for orthodontic anchorage
predictably and consistently in routine orthodontic practice. Mobility at the
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17
mandibular implant sites, and inflammation were the factors associated with screw
implant failure in this study. The study concluded that to minimize failure,
clinicians should attempt to reduce inflammation around the screw implants,
especially for screws placed on the right side in the mandible. 20
An FEM study was conducted to specify the required toe (º) of the vertical
segment of a cantilever from the distal aspect to achieve pure intrusion of a
mandibular canine with a segmented arch in lingual orthodontics. The geometrical
model of a mandibular canine tooth was developed and the mathematical equation
was devised to evaluate º (positive value: toe-in, negative value: toe-out) based on
certain input parameters. To determine this numerical study by finite element
analysis (FEA), total eight different positions of point of force application (Pf) on
bracket top (occlusal) surface were considered based on different values of input
parameters In FEA, the results were displayed in the form of instantaneous
movement of a mandibular canine due compression and tension of PDL. From the
distribution pattern, it was clear that the equivalent stress was concentrated at apex
which leads to maximum bone remodelling in that region. Hence, it signifies the
intrusive nature of mandibular canine movement. Thus, the values of the required
vertical segment toe of a cantilever from the distal aspect of a mandibular canine
were verified with FEA. The range of an intrusive force within the biological limit
of a mandibular canine was found to be 20–30 g. The study anticipated that the
pure intrusion of a mandibular canine with a segmented arch in Lingual
orthodontics will be achieved quiet efficiently and rapidly. 21
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A study was done to provide equivalent E and v pairs suitable for finite element
modeling of a tooth, periodontal ligament, and bone complex by using a reported
crown load-displacement relationship as the criterion. In any finite element
analysis, 2 mechanical parameters of the PDL are needed: Young’s modulus (E)
and Poisson’s ratio (v). Previous studies have reported quite different values of E
and v. Especially, E values were reported in a large range, from 0.01 to 1,750
MPa. CBCT images of a selected maxillary central incisor with the 2 neighbouring
teeth were used to create a finite element model. The PDL was created
surrounding the roots by dilating the roots with 1 voxel (0.25 mm). The PDL,
teeth, and bone were assembled to create a virtual tooth, PDL, and bone complex
called the solid model. The solid model was then imported into software (version
12.1; ANSYS, Canonsburg, Pa) for meshing and analysis=-+ for v = 0.35, E =0.71
MPa for = 5 0.4, and E = 0.47 MPa for v = 0.45 can be used for finite element
modelling of the tooth, PDL, and bone complex. 22
A three-dimensional finite element study was designed to investigate the stress
levels induced in the periodontal tissue by orthodontic forces. A three-dimensional
model of the lower first premolar was constructed on the basis of average
anatomic morphology and consisted of 240 iso parametric elements. Principal
stresses were determined at the root, alveolar bone, and periodontal ligament
(PDL). In all loading cases for the bucco-lingually directed forces, three principal
stresses in the PDL were very similar. At the surface of the root and the alveolar
bone, large bending stresses acting almost parallel to the root were observed.
During tipping movement, stresses non-uniformly varied with a large difference
from the cervix to the apex of the root. On the other hand, in case of translatory
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19
movement, the stresses induced were either tensile or compressive at all occluso-
gingival levels with some difference of stress from the cervix to the apex. It was
inferred that the pattern and magnitude of stresses in the periodontium from a
given magnitude of force were markedly different, depending on the centre of
rotation of the tooth. 23
A study was developed to directly and accurately measure orthodontic tooth
movement in a group of human volunteers. A 3D computer model of a maxillary
incisor tooth was simulated, which was subjected to an orthodontic load. An
apparatus of laser was used to sample tooth movement every 0·01 seconds over a
1-minute cycle for 10 healthy volunteers, whilst a constant 0·39 N load was
applied. This process was repeated on eight separate occasions and the most
consistent five readings were taken for each subject. The data gleaned by this
method were used to validate the 3D FEM model. This was formed of 15,000
four-noded tetrahedral elements. Tooth displacements ranged from 0·012 to 0·133
mm. An elastic modulus of 1 N/mm2 and Poisson’s Ratio of 0·45 was derived for
the PDL. Strain analysis, using the model, suggested that a maximum PDL strain
of 4·77×10-3 was recorded at the alveolar crest, while the largest apical strain
recorded was 1·55 ×10-3. The maximum recorded strain in the surrounding
alveolar bone was 35 times less than for the PDL. This FEM model validated that,
the PDL is the main mediator of orthodontic tooth movement 24
A study was undertaken to investigate the stress components (S1 and S3) that
appear in the periodontal membrane, when subjected to transverse and vertical
loads equal to 1 N and to quantify the alteration in stress that occurred as alveolar
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20
bone height was reduced by 1, 2.5, 5, 6.5, and 8 mm, respectively. Six three‐
dimensional (3D) finite element models (FEM) of a human maxillary central
incisor were designed with different alveolar bone height. When, there is absence
of alveolar bone loss, a tipping force of 1 N produced stresses, which reached
0.072 N/mm2 at the cervical margin, up to 0.0395 N/mm2 at the apex and up to
0.026 N/mm2 sub‐apically. When, 8 mm of alveolar bone loss is present, the
findings were −0.288, 0.472, and 0.722 N/mm2, respectively. Without bone loss,
an intruding force of the same magnitude produced stresses of −0.0043, −0.0263,
and 0.115 N/mm2, respectively, for the same areas and sampling points. In the
presence of 8 mm of alveolar bone loss the findings were −0.019, −0.043, and
0.185 N/mm2 for intrusive movement. The study showed that alveolar bone loss
caused increased stress production under the same load compared with healthy
bone support. Tipping movements resulted in an increased level of stress at the
cervical margin of the periodontal membrane in all sampling points and at all
stages of alveolar bone loss. The study concluded that the increased stress
components were found to be at the sub‐apical and apical levels for intrusive
movement. 25
A 3-dimensional finite element study was undertaken to determine the types of
orthodontic forces that cause high stress at the root apex. A three dimensional
model of a maxillary central incisor, its periodontal ligament (PDL), and alveolar
bone was constructed on the based on the average anatomic morphology. The
maxillary central incisor was chosen, as it is more prone to apical root resorption.
The material properties and 5 different load systems (tipping, intrusion, extrusion,
bodily movement, and rotational force) were tested. The analysis showed that
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21
purely intrusive, extrusive, and rotational forces had stresses concentrated at the
apex of the root. The principle stress from a tipping force was located at the
alveolar crest. For bodily movement, the stress was distributed throughout the
PDL; however, it was concentrated more at the alveolar crest. The study
concluded that, intrusive, extrusive, and rotational forces produced more stresses
at the apex and bodily movement and tipping, produced forces concentrated at the
alveolar crest and not at the apex. 26
A study was undertaken to analyse the distribution of the stress on dental and
periodontal structures when a simple tipping dental movement or torque
movement is produced. A tri-dimensional computer model based on the finite
element technique was used for this purpose. The model of a lower canine was
constructed based on the average anatomical morphology and 396 isoparametric
elements were considered. The three principal stresses (maximum, minimum and
intermediate) and Von Misses stress were determined at the root, alveolar bone
and periodontal ligament (PDL). In loading cases for the bucco-lingually directed
forces, the three principal stresses were very similar in the PDL. The study
concluded that the dental apex and alveolar crest zones are the areas that suffer the
greatest stress when these types of movements are produced 27
A study was done to examine the relationship between intrusion with low forces
(25 gm) using utility arches in the bioprogressive technique of upper and lower
incisor teeth and root shortening. Thirty-eight cases were selected and by means of
a modified computer program, the lateral cephalograms (T, and T,) for each
patient were digitized. For each patient intrusion was measured as the length from
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22
the incisal edge of the upper incisor to the palatal plane of the maxilla and from
the incisal edge of the lower incisor to a line from gonion to the lowermost point
of the inner border of the symphysis. For the measurements from the intraoral
radiographs, all incisors were measured along tooth’s longitudinal axis for total
tooth length, crown length, and root length. Root shortening was found to average
1.64 mm for maxillary incisors and 0.61 mm for mandibular incisors subjected to
intrusive force. No relationship was found between the amount of root shortening
and of intrusion achieved. A prolonged treatment time was significantly correlated
to root shortening. This study concluded that control of treatment time is of
importance especially when intrusion in the maxilla is performed. 28
A study was done to analyze the changes of biomechanical characteristics of
micro-implant-bone interface by establishing a 3D finite element model of stress
variation of micro-implant anchorage-assisted intrusion of orthodontic teeth molar.
ANSYS software was used for modelling. Pure titanium micro-implants were
implanted into the alveolar bone, leaving 3 mm outside the alveolar bone. Von-
Mises stress and displacement (mean displacement and peak displacement) under
the five tilt angles of 30°, 45°, 60°, 75°, and 90° were calculated by applying 200 g
of horizontal force. Under the 200 g of horizontal force, the Von-Mises stresses
and the mean displacements decreased with the increase of the special tilt angles.
Under the 200 g of horizontal force, all peak displacements of different tilt angles
were relatively small. The study concluded that, the micro-implants can maintain
certain stability under a horizontal force of 200 g 29
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23
A study was done to investigate the 3D position of the center of resistance of 4
mandibular anterior teeth, 6 mandibular anterior teeth, and the complete
mandibular dentition by using 3D finite-element analysis for establishing actual
clinical treatment plans by observing the initial displacement pattern of the teeth
groups subjected to horizontal and vertical forces. After the alveolar bone was
formed along the curvature of the cemento-enamel junction (CEJ) at a distance of
1 mm below the CEJ,16 a 3D finite-element model of the 14 teeth of the complete
mandibular dentition, periodontal ligament, and alveolar bone was created
ensuring left-right symmetry. A 200-g retraction force was applied to the 4
mandibular anterior teeth group, 6 mandibular anterior teeth group, and complete
mandibular dentition group. The forces were applied 0 mm, 5 mm, 10 mm, 15
mm, and 20 mm apically from the center of the incisal edge of the mandibular
central incisors to the lingual direction. The results of this study showed that the
position of the center of resistance of the 4 mandibular anterior teeth group was
13.0 mm apical and 6.0 mm posterior to the incisal edge of the mandibular central
incisors. The position of the center of resistance of the 6 mandibular anterior teeth
group was 13.5 mm. apical and 8.5 mm posterior to the incisal edge of the
mandibular central incisors. The position of the center of resistance of the
complete mandibular dentition group was 13.5 mm apical and 25.0 mm posterior
to the incisal edge of the mandibular central incisors. The study suggests that
miniscrews be placed distal to the lateral incisor in the 4 mandibular anterior teeth
and distal to the canine in the 6 mandibular anterior teeth 30
A study was done to compare 4 strategies for image-based model generation of the
PDL on the finite element simulation results and, thereby, to assess the sensitivity
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24
of simulation results to modeling assumptions during segmentation and meshing.
Two methods(1 and 3) were based on approximating early on the geometry of the
PDL (by using prescribed thicknesses), whereas methods 2 and 4 were entirely
image based. Mapped meshes of 8-noded hexahedral elements with 3 elements
across the thickness of the PDL were generated to create 3 models with different
prescribed constant thicknesses 0.1 mm (model 1a), 0.2 mm (model 1b), and 0.3
mm (model 1c). The locations of the 2 most significant stress maxima and the 4
most significant stress minima correspond to the 4 modelling strategies. This
shows that, qualitatively, the stress distribution in the PDL is remarkably
insensitive to the modelling and reconstruction techniques for low orthodontic
forces. The predicted values of tooth intrusion were not significantly affected by
the PDL’s thickness. The study inferred that if tooth intrusion is to be used to
determine the material properties of the PDL, then a robust and accurate
reconstruction of the PDL is a prerequisite. 31
The purpose of this FEM study was to investigate the relationship between
moment to force (M/F) ratios and the center of rotation by use of the finite element
method (FEM). A 3D finite element model of the upper right central incisor was
made comprising the tooth, PDL, and alveolar bone and consisted of 1184 nodes
and 908 solid elements. A 100-g lingual force was applied at the midpoint of the
labial surface of crown, 5.25 mm from the incisal edge. The relationship between
the M/F ratio at a crown point and where the tooth moved was determined. The
center of resistance was located at 0.24 the root length apical to the alveolar crest.
Results showed the M/F ratios at the midpoint of the crown were - 9.53 for root
movement, - 8.39 for translation, and - 6.52 for crown tipping. The study showed
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25
that very small difference in the M/F ratios produces clinically significant changes
in the centers of rotation, showing that the center of rotation is very sensitive to the
M/F ratio difference, particularly as movement approaches translation 32
A series of orthodontic procedures were performed on adult patients in an attempt
to intrude elongated teeth with varying degrees of periodontal damage for the
purpose of studying the results clinically and radiographically, thus evaluating the
influence of treatment on the periodontal status. Sample comprised of 30 patients,
five men and 25 women, aged 22 to 56 years. In 24 patients migration of incisors
had been noted in relation to progressing periodontal disease. Four different types
of appliance were used for correction of the overbite by intrusion. One patient was
treated by use of an edgewise appliance with a J hook for intrusion, adapted for
100 gm per side. Four patients were treated by use of 0.016 x 0.016-inch edgewise
utility arches, three patients had intrusion adjustments bent into a loop of a 0.017 x
0.025inch stainless steel wire. All other patients were treated with a base arch
intrusive mechanism. The study showed that the utility arch and the base arch
seemed to result in both the largest intrusion and the largest gain in bony support.
33
A study was done to show a new radiographic method developed for measuring
changes in root length. With this method, orthodontic intrusion was investigated as
a potential cause of apical root resorption of maxillary incisors. The study had an
experimental and a control group each consisting of 17 patients. The experimental
subjects had a treatment plan that called for 2.0 to 4.0 mm of overbite correction.
The appliance consisted of a 0.017 x 0.025-inch TMA intrusion arch from the
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26
maxillary tube of the maxillary right first molar to the maxillary left first molar. A
lateral cephalometric and periapical radiograph were taken before and after the
intrusion phase to measure changes in position of the central incisor and root
resorption. Intrusion was carried out for a mean duration of 4.6 months. The
average amount of intrusion was 1.9 ram, and the mean rate of intrusion was 0.41
mm per month. The control group had a mean resorption of 0.2 mm after an
interval of 4.3 months. In this study, the method used for intrusion was found to be
effective in reducing overbite, while causing only a small amount of root
resorption 34
A study was done to evaluate the clinical usefulness of miniscrews as orthodontic
anchorage. Seventy-five patients consisting of 116 titanium screws of 2 types, and
38 miniplates were retrospectively examined. Each patient was given a
questionnaire that included a visual analog scale to indicate discomfort after
implantation. The results showed that miniscrews had a high success rate of
approximately 90%—the same as miniplates and large titanium screws, and they
provided sufficient anchorage immediately after placement surgery for any
orthodontic tooth movement. In addition, miniscrews placed without a
mucoperiosteal incision or flap surgery significantly reduced the patient’s pain and
discomfort after implantation. The study concluded that miniscrews have suitable
characteristics as orthodontic anchorage.35
A study was done to investigate the effects of incisor intrusion obtained with the
aid of miniscrews. Miniscrews are used as a stable anchorage unit in orthodontics.
They have small dimensions and can be placed in interdental areas where
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27
traditional implants cannot be inserted. Eleven patients (three males and eight
females; mean age: 19.79 ± 4.79 years; mean overbite: 5.9 ± 0.9 mm) with a deep
bite of at least 4 mm, excessive gingival display on smiling and normal vertical
dimensions were treated. Two miniscrews 1.2 mm in diameter and 6 mm in length,
were placed distal to the maxillary lateral incisors and forces applied for intrusion.
The upper incisor intrusion was achieved in 4.55 ± 2.64 months. The mean rate of
intrusion was 0.42 mm/month. The mean overbite pre-treatment was 5.54 ± 1.38
mm. The mean intrusion of the upper anterior segment was 1.92 ± 1.19 mm (CR-
PP distance) and the mean change in overbite 2.25 ± 1.73 mm. the study
concluded that true intrusion of upper incisors can be achieved using miniscrew
anchorage. 36
A study was done to analyze the stress distribution patterns in a conical self-
drilling type of miniscrew implant system and the surrounding osseous structures,
with no ossseointegration, for 2 implant materials—Ti6Al4Vn alloy and implant-
grade stainless steel—under horizontal and torsional loading. A numeric approach
was used to investigate how the load transfer at the bone-screw interface changes
for miniscrew implants made of different materials and for different directions of
loading. Results showed that the maximum stresses occurred in the cortical bone
surrounding the neck of the implant at 6 and 8.5 MPa for horizontal and with
stress values for the stainless steel model considerably greater than those for the
titanium alloy model. The values obtained for stainless steel were 19.6 and 17.2
MPa; those for titanium alloy were 11.7 and 8.3 MPa. The results demonstrated
that a conical type of miniscrew implant with a length of 10 mm and a diameter of
2.0 mm composed of either stainless steel or titanium alloy can safely resist the
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28
high levels of orthodontic force. Implant-grade stainless steel and Ti6Al4Vn alloys
are suitable materials for miniscrew implants 37
A study was done to compare and evaluate the extrusive forces and torquing
moments on the posterior dentition generated during anterior intrusion with
different intrusion techniques in the maxillary and mandibular dental arch. Seven
wire specimens were used for each of the following intrusive arches: Utility arch
0.016× 0.016” Blue Elgiloy, Utility arch 0.017× 0.025” TMA, and Burstone
Intrusion arch 0.017 ×0.025” TMA. Simulated intrusion from 0.0–3.0 mm was
performed on the Orthodontic Measurement and Simulation System (OMSS). The
forces and moments were recorded in all three planes of space at 0.1 mm
increments and the values at 3.0 mm for all wires were used for all statistical
evaluations. The results showed that at 3 mm vertical displacement of the incisors,
the Utility intrusion archwires recorded mean extrusive forces in the range of
1.59–2.10 Newton. The Utility 0.016× 0.016-inch Blue Elgiloy exerted higher
force than the Utility 0.017×0.025-inch TMA. The recorded magnitudes for the
Burstone 0.017×0.025-inch TMA intrusive arches were 1.30–1.56 Newton. The
study concluded that the upper Burstone 0.017×0.025-inch TMA intrusion arch
exerted the lowest forces ⁄ moments on posterior teeth. The highest forces were
generated by the 0.016×0.016-inch Blue Elgiloy utility arch and the highest
moments by the lower 0.017×0.025-inch TMA utility arch.38
A study was done to investigate the roles of bone quality, loading conditions,
screw effects, and implanted depth on the biomechanics of an orthodontic mini-
screw system by using finite element analysis. A 3-dimensional bone block model
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29
integrated with a mini-screw was constructed with a computer-aided design
program to simulate a mini-screw implanted in bone as an orthodontic anchorage
unit. The analysis showed that both stress and displacement increased with
decreasing cortex thickness, as cancellous bone density played a minor role in the
mechanical response. The study concluded that a wider screw provided superior
mechanical advantages. The exposed length of the miniscrew was the real factor
affecting mechanical performance. Both bone stress and screw displacement
decreased with increasing screw diameter and cortex thickness, and decreasing
exposed length of the screw, force magnitude, and oblique loading direction. 39
A finite element study was done to evaluate the influence of placement angle and
direction of force on the stability of miniscrews. Three-dimensional finite element
models were created to represent screw placement angles of 30, 60, 90, 120, and
150 degrees. Bone models were also created using FEM and simplified to
dimensions of 20 mm in length and width, and 15 mm in height for evaluation.
The screws were modelled as a titanium alloy miniscrew with an elastic modulus
of 110 gigapascals (GPa) and Poisson’s ratio of 0.34. The screws were inserted to
a depth of 8 mm up to the collar of the miniscrew. The contact between the bone
and the screw was defined as a frictional interface with a coefficient of friction of
0.37. The interface between the miniscrew and the bone elements was fixed and
the traction force was fixed at 2 N, which is the approximate orthodontic force
applied to a miniscrew. Von Mises stresses were evaluated for miniscrew
insertions into bone model at 30, 60, and 90 degree angles. The finite element
analysis showed cortical bone stress in both 0 and 30 degree direction of force was
greatest for screws placed at 120 and 60 degree angles and least for 90 degree
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30
angle. Trabecular bone stresses were 35 and 35.1 MPa for 60 and 120 degree
angles, respectively at 0 degree direction of force, and 33.4 and 34 MPa for 60 and
120 degree angles, respectively at 30 degree direction of force. The trabecular
bone stress for 90 degree angle was 5.6 MPa at both directions of force. The study
concluded that insertion of miniscrews at angles less than or greater than 90
degrees to the alveolar process bone might decrease the anchorage stability of the
miniscrew.40
A study was done to determine risk indicators for the aetiology of abfractions
(cervical wedge-shaped defects) on teeth using dental and medical variables
obtained in a population based sample. Medical history, dental, and socio-
demographic parameters of 2707 representatively selected subjects 20–59 years of
age with more than four natural teeth were checked for associations with the
occurrence of abfractions. The estimated prevalence of developing abfractions
generally increased with age. The following independent variables were associated
with the occurrence of abfractions: buccal recession of the gingiva, occlusal wear
facets, tilted teeth, inlays, toothbrushing behaviour. The first premolars had the
highest estimated risk for developing abfractions, followed by the second
premolars maxillary and mandibular canines. The results of this analysis indicated
that abfractions are associated with occlusal factors, like occlusal wear, inlay
restorations, altered tooth position and tooth brushing behaviour. This study
delivers further evidence for a multifactorial aetiology of abfractions. 41
A clinical study was undertaken to analyze adult skeleto-dental changes induced
by a reverse curve mushroom archwire. Lateral cephalograms from before
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31
treatment and immediately after bite opening were evaluated from 8 female adult
patients with a mean overbite of 3.9 mm. 6 linear and 5 angular measurements
were selected for cephalometric analysis. Alignment was performed by using
progressively larger cross-section round mushroom archwires placed on lingual
brackets. After completing alignment, a reverse curve mushroom arch was
engaged into the occlusal slot of the lingual bracket and tied back at the first
molar. The results showed that there was highly significant reduction in overbite
with a resulting post-intrusion overbite of 2.0 mm. Some lower incisor
proclination was seen, which was not of significance. The inclination of the
occlusal plane was increased by 1.68 and the lower anterior face height was not
significantly increased. The study inferred that the use of a reverse curve
mushroom archwire is capable of intruding the lower incisors with minimal side
effects on the posterior teeth.42
A study was conducted to investigate whether levelling the curve of spee, using
two orthodontic treatment techniques, produces stable results on a long-term basis.
All patients had Class II malocclusion with an overbite of 50% or greater, a
mandibular plane angle less than 32°, and a curve of spee 2 mm. The records used
consisted of dental casts taken at T1, after orthodontic therapy (T2), and at
postretention (T3). All subjects in both the groups were treated with fully
preadjusted fixed orthodontic appliances with 0.018-in slots. The curves of Spee
were measured on the left and right sides of each set of mandibular models. The
results showed that both techniques produced highly significant reductions in the
curve of spee (T1 to T2). Statistically significant, but clinically insignificant,
postretention relapse of the curve of spee occurred (T2 to T3). For both
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32
techniques, a statistically significant difference was seen in the incidence of the
relapse of the curve of spee between patients who were completely levelled post-
treatment and those who were not. The study did not find a correlation between
pre-treatment curve of spee and relapse in any of the other occlusal traits studied 43
A study was done to determine the reactions in the pulp and dentine following
experimental orthodontic tooth movement performed under controlled conditions.
The material consisted of seventy clinically intact premolars from children 10 to
13 years of age. Thirty-five of the teeth were extracted without treatment and
served as control. The remaining thirty-five received fixed orthodontic appliances
which initiated continuously acting intrusive forces. The intrusive force was
recorded, at the start of the experiment and immediately before extraction of the
teeth. The force applied varied from 35 to 250 grams for the different teeth, and
the experiments lasted from 4 to 35 days. The appliance consisted of a spring
which was attached to the molars and activated against the first premolar. The use
of such appliances resulted in intrusion of the teeth, but since the spring was
engaged on one side of the tooth only, a certain tipping movement would also
occur. All the teeth went through the same histologic procedure. The results
showed that alterations in the normal histologic structure of the pulp and dentine
were noted both in the untreated control material and in the experimental material.
The pulp alterations in the experimental material were always most pronounced in
the coronal portion, gradually decreasing toward the apical region. Forces above
150 to 200 gm invariably resulted in stasis in the pulp vessels, as judged by the
presence of brown pigment from deteriorating erythrocytes. The width of the pre-
dentine zone was often reduced in those teeth in the experimental series which
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33
showed severe vacuolization of the odontoblast layer. Teeth which had completed
apex exhibited more severe changes than teeth with open apices, and the
magnitude of the force was also important. The resorption observed in dentine was
related to the magnitude of the force and the duration of the experiment 44
A study was done to elucidate relationships between the dental roots and
surrounding tissues in order to prevent complications after placement of a
miniscrew. Cross sections of human jaws were analyzed in 20 mandible and 20
maxilla. Resin blocks were prepared and cut serially at 1 mm intervals from the
cervical line to the root apex and images of each section then were obtained at a
resolution, the interroot distance, buccolingual bone width, cortical bone
thickness, mucosal thickness were measured. The results showed that the interroot
distance increased from anterior to posterior teeth and from the cervical line to the
root apex in both the maxilla and the mandible. The study concluded that the
safest zone for placement of a miniscrew is between second premolar and first
molar, from 6 to 8 mm above the cervical line in the maxilla, and between first and
second molars, less than 5 mm from the cervical line in the mandible. In the
maxillary, the regions for which a miniscrew of 8 mm is recommended are a
buccal installation between central incisor and canine (from 9 mm above cervical
line), between first and second premolars (from 3 mm above cervical line), and
between second premolar and first molar (from 3 mm to 4 mm above cervical
line). In the mandible, the regions for which a miniscrew of 8 mm is recommended
are between canine and first premolar (from 9 mm below cervical line), between
first and second premolars (from 5 mm to 8 mm below cervical line), and between
first and second molars (from 2 mm to 3 mm below cervical line).45
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A study was conducted to compare the skeletal and dental effects of 2 intrusion
systems involving mini-implants and the Connecticut intrusion arch in patients
with deepbites. Forty-five patients (26 women, 19 men) fulfilling the criteria were
selected and divided into 3 groups with 15 subjects in each group. The
Connecticut intrusion arch group, comprising 6 men and 9 women, had intrusion
with Connecticut intrusion arches; the implant group, comprising 6 men and 9
women, had intrusion with a mini-implant system. The initial intrusive force of the
Connecticut intrusion arches was 60 g, and it was checked and reactivated
monthly after controlling the intrusive force. In the implant group, 0.018 × 0.025-
in brackets were placed on the patients’ 4 maxillary incisors.. Aligning and
levelling were not performed. A passive 0.016-in round segmental archwire was
placed to maintain the initial position of the 4 maxillary incisors. Two self-drilling
mini-implants were inserted into the alveolar bone and intrusion force was
delivered by nickel-titanium coil springs. Results showed that the mean amounts
of genuine intrusion were 2.20 mm (0.31 mm per month) in the Connecticut
intrusion arch group and 2.47 mm (0.34 mm per month) in the implant group.
Both systems led to protrusion and intrusion of the maxillary incisors, and
protrusion and extrusion of the mandibular incisors. Although movement of the
maxillary molars led to loss of sagittal and vertical anchorage during intrusion of
the incisors in the Connecticut intrusion arch group, these anchorages were
conserved in the implant group. The overall success rate was 90%. 46
A study was done to determine whether the size of the maxillary buccal segment
influences the amount of steepening, extrusion, or narrowing of the buccal
REVIEW OF LITERATURE
35
segments, or the rate of intrusion that occurs with maxillary incisor intrusion. 40
patients included in the sample were between 9 and 14 years of age needing
maxillary central and lateral incisor intrusion of at least 2 mm. Patients in the long
buccal-segment group had maxillary buccal segments that included the canines,
both premolars, and the first molars. In the short buccal-segment group, the buccal
segments consisted of only the maxillary first molars. Patient records were taken
at the beginning and end of maxillary incisor intrusion. Results showed that both
groups had about the same amounts of incisor intrusion. In the long buccal-
segment group, a small decrease in maxillary arch width was observed; in the
short segment group, a small increase was found. In both groups, the buccal
segment steepened in the short buccal-segment group almost 14° more than in the
long buccal-segment group. Both groups had small amounts of extrusion of the
buccal segments. The axial inclination of the anterior segment changed (proclined)
more in the long buccal segment group. There was no difference in rate of
intrusion between the long and short segment groups 47
A study was done to examine the effect that varying the position of an occlusal
load would have on the stress contour in the cervical region of a lower second
premolar using a two-dimensional plane strain finite element model. A two-
dimensional finite element model was generated of a lower second permanent
premolar. The outline of the tooth, amelodentinal junction and pulp were
represented. The periodontal ligament was assumed to be 0.3 mm wide, and the
dimensions of the surrounding compact and cancellous bone were derived from
standard texts. The model was loaded using seven different loading positions. The
first six loads used a single 500 N load distributed at various points radially around
REVIEW OF LITERATURE
36
the crown. The maximum principal or first principal stress in the buccal and
lingual enamel in the cervical region was sampled along two horizontal planes.
The first plane A-A was 1.1 mm above the amelo-cemental junction while the
second plane B-B was 2.2 mm above the amelo-cemental junction. This study
showed that varying the position of the occlusal load produced marked variations
in the stresses found in the cervical enamel. Loads applied to the inner buccal and
lingual cuspal inclines, that mimic the loading produced during lateral excursions
of the mandible, produced the highest stresses and these were of the correct order
of magnitude to initiate enamel failure 48
MATERIAL AND METHOD
37
MATERIAL AND METHOD
The Finite Element Method (FEM) is a precisely constructed three dimensional
mathematical method that is majorly used in engineering studies. It helps solve large
numbers of equations based on the shape of complex geometric objects and their
physical properties to calculate structural stress, and also has the advantage of being
applicable to any solid of irregular geometry that contains heterogeneous material
properties. The finite element analysis provides the orthodontist with quantitative data
that can yield an improved understanding of the reactions and interactions of
individual tissues and helps evaluate different loading conditions in order to optimize
the biomechanics delivered.
It involves the graphical simulation of a structure in a computer to form a mesh which
explains the geometry of the designated structure. This mesh is further divided into a
number of finite elements by a process of discretization or subdivision. The elements
are further connected at intersections called nodes. Thus a complex structure is formed
by discretization and formation of elements, which can be arranged in two or three
dimensions.
Steps involved in the finite element model preparation:
1. Construction of the geometric model of the structure
2. Conversion of geometric model into finite element model
3. Material properties and data representation
4. Loading the configuration
CONSTRUCTION OF THE MODEL
A geometric model of the mandibular segment from the right second permanent molar
to the right permanent canine was created through CT scan and converted to three
MATERIAL AND METHOD
38
dimensional step file format through reverse engineering technique (fig.2a, 2b). All
teeth (elastic modulus 20 GPa; poisson’s ratio 0.3) were modified until the proper
crown-to-root ratio was obtained. The posterior teeth from the second molar to the
first premolar were levelled, and the canine with its surrounding alveolar bone (elastic
modulus 345 MPa; poisson’s ratio 0.3) was extruded by 1.5 mm. Further, it was
converted into finite element format through a meshing software ANSYS (fig.2c).
Two 3- dimensional solid models were constructed and periodontal ligament (elastic
modulus 0.71 MPa; poisson’s ratio of 0.4) modified with 0.20-mm linear thickness
uniformly. After all bony, dental, and PDL structures were graphically represented,
brackets and molar tubes were modelled with 0.022 × 0.028-in slots and 0º of tip and
torque. The brackets were placed on the facial axis of the tooth. The first molar
auxiliary tube had a 0.018 × 0.025-in slot. A 0.021 × 0.025-in base wire was also
modelled to passively fill the second molar tube, the first molar main tube, and the
premolar bracket slots to simulate the posterior anchorage segment. This passive fit of
the base wire into the posterior appliances was achieved because of the pre-levelling
and alignment. All brackets and tubes, and the base wire were assumed to be
composed of stainless steel (elastic modulus of 200 GPa; poisson’s ratio 0.3) In the
first model (fig. 4a, 4c) a cantilever with a cross-section of 0.017 × 0.025 inch and the
properties of titanium-molybdenum alloy (elastic modulus 69 GPa; poisson’s ratio 0.3
) was simulated. The posterior end of the cantilever was fitted inside the first molar
auxiliary tube, and a helix 3 mm in diameter was constructed mesially to be flush to
the tube. The horizontal segment extends mesially to the area corresponding to the
interproximal contact point between the first premolar and the canine. At this point, a
90º bend was modelled occlusally, comprising a vertical segment that ended at the
level of the uppermost portion of the canine bracket. Finally, another 90º bend was
MATERIAL AND METHOD
39
made to generate the final segment of the cantilever, which was in contact with the
upper part of the canine bracket. Another model constructed had two self-drilling
mini-screws of dimension 6 mm in length and 1.6 mm in diameter (Ti6 Al4,113.8 GPa
elastic modulus , poissons coefficient 0.3) inserted buccally at 90º angulation 40
, in the
interdental area ,one at the mesial aspect of the mandibular canine i.e. between the
canine and lateral incisor and the other at the distal aspect of mandibular canine i.e.
between the canine and the first premolar (fig. 5b, 5c). In this model, the mandibular
right segment from the canine to the 2nd
molar will be modelled with metal bracket
0.022 x 0.028 inch slot. A straight 0.019” x 0.025” stainless steel archwire will be
fashioned and placed alongside the canine’s buccal surface immediately below the
bracket to prevent undesirable lingual root torque. Intrusive force to the tooth will be
applied using an elastic chain from the mini-screws to the canine bracket.
Model 1(a) - model having a cantilever loop with a toe in of 0º for intrusion of canine
Model 1(b) - model having a cantilever loop with a toe in of 4º for intrusion of canine
Model 1(c) - model having a cantilever loop with a toe in of 6º for intrusion of canine
Model 1(d) - model having a cantilever loop with a toe in of 8º for intrusion of canine
Model 2 – model with two mini-screws placed buccally and mesial and distal to the
canine for intrusion of canine
CONVERSION OF GEOMETRIC MODEL TO A FINITE ELEMENT MODEL
After the geometric model construction, discretization was done to transfer the model
into a number of finite elements (smaller bodies or units with pentahedron,
MATERIAL AND METHOD
40
hexahedron or rectangular structures) and nodes which are the intersecting points
between two or more elements. Nodes are the points at which the degrees of freedom
are defined, which in turn determine the number of ways a node is allowed to move.
This procedure is carried out towards making the model more suitable for numerical
evaluation and implementation on digital computers. The boundary conditions of the
anatomic structures tested were performed using ANSYS software to create a finite
element model. Version (14.0)
MATERIAL PROPERTIES AND DATA REPRESENTATION:
In this study the periodontal ligament, alveolar bone, teeth, brackets, molar tubes, arch
wire, miniscrew, and cantilever were modelled. The arch wire, bracket, buccal tubes
are considered to be made of stainless steel and these structures were modelled as
being homogenous and isotropic. Also the cantilever was considered to be made up of
titanium molybdenum alloy and the implant was considered to be made of titanium
alloy. The properties of the anatomic structures and the materials used in this study
were based on the elastic modulus and poissons ratio. The PDL had hybrid meshes
with pentahedron and hexahedron elements, which provided more accurate
estimations of the stresses on these structures. The diversity of the mesh was
important because the PDL was being evaluated for stress in this study. The other
materials had pentahedron elements, and each element had 6 degrees of freedom, thus
they could move and rotate in any direction within the space. Eventually, each
pentahedron element had 6 nodes, and each hexahedron element had 8 nodes. The
interactions present between the brackets and wires were determined using beam
elements. The remaining contacts between the elements of different objects were
MATERIAL AND METHOD
41
made by rigid contact interactions, in which phases from the different materials
remain without relative displacement between them. Three reference axes (X,Y,Z)
having the mandibular canine as the reference point were used for cantilever
activation:
(1) X -axis for the mesio-distal aspect
(2) Y-axis for the occluso-gingival direction, and
(3) Z-axis for the bucco-lingual aspect
EXPERIMENTAL CONDITIONS (METHODOLOGY)
In the first constructed model a cantilever was used for intrusion of the canine (fig.
4a,4c). It was placed from the molar tube extending till the canine bracket and pre-
activated with a 35º tip-back. This offset applied a force of 0.02 N on the Y-axis
(mesio-distally) and 0.37 N (occluso-gingivally) on the Z-axis of the canine. This was
achieved by prescribing a displacement vector at the bottom of the cantilever, which
was in contact with the canine bracket. After achieving this position, the cantilever
was caught by a rigid link. Thus, all of the energy accumulated at the offset was
transmitted to the bracket and then to the tooth.
The following compensatory toe-in bends were simulated in this experiment: 0º, 4º,
6º, 8º each applying a force of 0.01 N, 0.052 N, 0.082 N, 0.12 N, on the X-axis
(bucco-lingually) respectively (fig. 4b). The activation of each simulated
compensatory toe-in was equivalent to the magnitude of the force in the x-axis
inferred from the visualization correspondent to the force that each toe-in produced.
Therefore, the force variation was only in the x-axis. Also the resultant counter-effect
produced by the cantilever with different toe-in’s, on the anchor molar causing its
MATERIAL AND METHOD
42
movement along the Y-axis (mesio-distally) and along Z-axis (occluso-gingivally)
was determined.
In the second model (fig.5a, 5c) two mini-screws were placed at angulation of 90º
buccally in the interdental bone on both the mesial and the distal sides of the canine,
and an intrusive force of 0.147 N was applied onto the tooth using an elastic chain
extending from the mini-screws to the canine bracket. A straight 0.019” x 0.025”
stainless steel archwire was fashioned and placed alongside the canine’s buccal
surface immediately below the bracket to prevent undesirable lingual root torque.
In the first model, the amount of pure intrusion of canine was measured by the
movement of the tooth along the Z-axis, and the amount of buccal crown tipping that
occurs due to different compensatory toe-in bends of cantilever was measured along
the X-axis. Also the counter-effect on the posterior anchorage system and stress
changes in the alveolar bone and periodontal ligament surrounding the canine and the
molar tooth were assessed. In the second model canine intrusion was achieved using
two mini-screws placed on either side of the target tooth with an elastic chain from the
miniscrews to the tooth. The effects of this intrusion on the surrounding alveolar bone
and periodontal ligament were measured. The results obtained from these two models
were evaluated and compared using the three dimensional finite element analysis
using ANSYS software.
RESULTS
43
RESULTS
The values of pure intrusion produced by two finite element models were obtained. In
the first model (fig 4a,4b) intrusive forces were applied by a cantilever with different
toe-in bends (fig 4c) and in the other model, force was applied using mini-implants
(fig 5b). The result of the analysis is called ‘post processing’. Stresses and the
displacements are calculated and represented in coloured bands, different colours
representing different stress levels and different values for maxillary molar
displacements.
Red colour area of the spectrum indicates maximum principal stress, followed by
orange, yellow, green and blue representing the reducing levels of stress. White colour
of the spectrum represents the least level of stress.
Two nodes, the tip of the buccal cusp (crest node- no. 128046), and the apex of the
root (root node- no. 129160) were selected for evaluating the movement of the canine
along the Y-axis indicating intrusion and the Z-axis indicating tipping of the tooth in
the labial or lingual direction.
When intrusive forces were applied by the different toe-in bends of the cantilever and
with the mini- implant, the amount of displacement of the crest and root nodes of the
mandibular canine model that occurs along the Y-axis was measured and tabulated in
table 3. The displacement of the canine along the Y-axis due to 0º, 4º, 6º and 8º toe-in
bend of cantilever is represented in the fig 7(a), 7(b), 7(c) and 7(d) respectively. The
displacement of canine due to forces applied by the mini-implant is represented in fig
7(e).
RESULTS
44
In the first model with 0º toe-in bend of cantilever, the amount of crown movement as
depicted by the blue dots was 0.949μmm apically , and the root movement as depicted
by the red dots was 0.184μmm apically (table-3, fig 7a), the 4º toe-in bend showed
3.056μmm apical movement of crown and 2.456μmm apical root movement ( table-3,
fig 7b), the 6º toe-in showed crown movement of 5.486μmm apically and root
movement of 5.027μmm towards apex (table-3, fig 7c), the 8º toe-in showed apical
crown movement of 7.31μmm and apical root movement of 7.37μmm (table-3,fig 7d).
In the second model the amount of crown and root displacement along the y axis
produced as a result of forces from the mini-implant were 1.9μmm and 1.6μmm
towards apex respectively (table-3, fig 7e). The amount of intrusion obtained by the 8º
toe-in bend of the cantilever was found to be the highest among all models and the
least value was produced by the cantilever with 0º toe-in bend (graph-1).
The amount of labial/lingual tipping of the canine was evaluated by the movement of
the crest node and the root node along the Z- axis and represented in the table 4. The
figures 6(a), 6(b), 6(c), 6(d), 6(e), illustrate the movement of the crest and root node.
The amount of labial displacement of the crest node that occurred with the 0º toe-in of
the cantilever was 3.71μmm while the root node moved lingually by 3.21μmm (table-
4, fig 6a), 4º toe-in bend produced 3.59μmm labial displacement of the crest node and
the root node moved lingually by 1.59μmm (table-4, fig 6b), 6º toe-in bend produced
0.67μmm labial movement of crest node and 0.65μmm movement of root node
lingually (table-4, fig 6c). The opposite effect was seen with the 8º toe-in bend of
cantilever which produced a lingual displacement of both the crest node and the root
node by 3.01μmm and 2.4μmm respectively (table-4, fig 6d). The amount of labial
displacement of crest node produced by the forces from mini implant was 0.048μmm
RESULTS
45
while the root node moved lingually by 0.036μmm (table-4, fig 6a). The results
showed that in the mini-implant model least amount of tipping of the canine tooth
occurred on application of intrusive forces, whereas the maximum amount of labial
tipping of canine was seen with the model having a cantilever with 0º toe in bend
(graph-2).
The counteracting effects on the molar produced by the cantilever were illustrated in
the figures 10(a), 10(b), 10(c), 10(d). The molar tooth in all the models showed slight
extrusion and distal tipping of the crest node which represented the tip of the mesio-
buccal cusp. The implant model however did not display any significant molar
counter-effects (fig 10e).
The periodontal stresses around the root of the canine produced by the intrusive forces
applied from the cantilever and the mini-implant were illustrated by the figures 8(a),
8(b), 8(c), 8(d), and 8(e) respectively. The red areas showed maximum stress
distribution whereas the blue areas showed minimum stress distribution. The
maximum stresses were evaluated and tabulated in table 5.
The 0º toe-in cantilever model displayed maximum stress (0.0024 MPa, fig. 8a , table-
5) in the periodontium of the canine followed by the cantilever model with 6º, 8º and
4º of toe-in the the decreasing order (table 5). The least amount of stress was seen in
the mini-implant model (0.000340 MPa, fig. 8 e, table-5, graph-3).
The stresses occurring in the alveolar bone around the canine were also evaluated and
tabulated in table 6. The maximum stress values were obtained in the implant model
(0.0039MPa, fig. 9e, table 6), followed by the 6º, 8º, 4º toe-in cantilever models (fig.
9b, 9c, 9d, table-6 ) while the least amount of alveolar bone stress was seen with the
cantilever with 0º toe in bend (0.0016MPa, fig. 9a, table-6, graph-4).
RESULTS
46
GRAPH 1: AMOUNT OF INTRUSION OF CREST NODE AND ROOT NODE
DISPLACEMENT ALONG Y AXIS
GRAPH 2: LABIAL/LINGUAL TIPPING OF CREST AND ROOT NODE
(DISPLACEMENT ALONG Z AXIS
RESULTS
47
GRAPH 3: PERIODONTAL STRESSES AROUND CANINE
GRAPH 4: ALVEOLAR BONE STRESSES AROUND CANINE
RESULTS
48
TABLE 1: MATERIAL PROPERTIES OF THE MEMBERS:
Member Elastic Modulus Poison’s ratio
Tooth 20GPa 0.3
Periodontal Ligament 0.71Mpa 0.4
Bone 345Mpa 0.3
Stainless steel Wire 200Gpa 0.3
Titanium –Molibdium alloy 69Gpa 0.3
Implant 110Gpa 0.33
TABLE 2: AMOUNT OF FORCE ON THE X-AXIS PRODUCED WITH THE
TOE-INS TESTED
Toe in Force in the y axis (N)
0º 0.01
4º 0.052
6º 0.082
8º 0.12
TABLE 3: AMOUNT OF INTRUSION OF CREST NODE AND ROOT NODE
DISPLACEMENT ALONG Y AXIS (µmm)
0 degree 4 degree 6 degree 8 degree Implant
Crest node -0.949µmm -3.056µmm -5.486µmm -7.31µmm -1.9µmm
Root node -0.184µmm -2.456µmm -5.027µmm -7.37µmm -1.6µmm
RESULTS
49
TABLE 4 : LABIAL/LINGUAL MOVEMENTS OF CREST AND ROOT NODE
DISPLACEMENT ALONG Z AXIS
0 degree 4 degree 6 degree 8 degree Implant
Crest node 3.71µmm 3.59µmm 0.675µmm -3.01µmm 0.0485µmm
Root node -3.219µmm -1.59µmm -0.65µmm -2.4µmm -0.0365µmm
TABLE 5: STRESSES IN CANINE PERIODONTIUM
0º toe-in 4º toe-in 6º toe-in 8º toe-in Mini-
implant
Stress 0.002443 0.00194 0.002361 0.002069 0.00034
( MPa)
TABLE 6: ALVEOLAR BONE STRESS AROUND CANINE
0º toe-in 4º toe-in 6º toe-in 8º toe-in Mini-
implant
Stress 0.001603 0.002215 0.003581 0.003192 0.003994
( MPa)
RESULTS
50
NODE NUMBERS
CREST : 128046
ROOT : 129160
Number of elements
Number of nodes
Model 1
790774
172545
With Implant
817659
177001
NODAL SOLUTIONS
1. 0º toe-in cantilever model
2. 4º toe-in cantilever model
RESULTS
51
3. 6º toe-in cantilever model
4. 8º toe-in cantilever model
5. Mini-implant model
DISCUSSION
52
DISCUSSION
A deep bite is a complex orthodontic problem that is a common feature of many
malocclusions. It consists of a variety of skeletal and dental factors. A decrease in
vertical skeletal growth, axial inclinations of the upper and lower anterior teeth,
vertical positions of the anterior and posterior teeth, and loss of periodontal support
are among the factors that contribute to the development of deepening of the bite.
Correction of a deep bite is an important part of orthodontic treatment due to the
potential deleterious effects on the temporomandibular joint, the periodontal health
and facial aesthetics.9
A deep overbite is typically corrected by intrusion of the anterior teeth or extrusion of
the posterior teeth.14
In patients with an excessive gingival display and a normal
vertical dimension, incisor intrusion is the treatment of choice.9 A study by burstone
concluded that it is much easier to intrude lower incisors because of their smaller root
mass and the common presence of a curve of Spee in the lower arch. 8
Deep bite is often corrected using continuous or segmented arches. Melsen et al.
(1989) indicated that the segmented arch technique is the treatment of choice for
patients with elongated incisors or periodontal bone loss.5 A study done by Varlik et al
concluded that deep bite treatment with mandibular incisor intrusion with utility
arches was effective and appeared to be stable in non-growing patients.33
Weiland et
al showed that segmented arch mechanics can produce genuine intrusion of the
incisors with little vertical effect in the molar area in adult patients.10
However, during anterior intrusion with the segmented or the continuous technique,
the posterior teeth are subjected to a vertical force, which tends to extrude them and a
DISCUSSION
53
moment or torque, which in the upper arch will steepen the occlusal plane and in the
lower arch flatten it. According to principles of static equilibrium, the magnitudes of
the posterior extrusive and anterior intrusive forces are equal. If intrusive forces are
kept low, occlusal forces tend to negate the eruptive tendency of the posterior teeth.38
Most of the deep bite cases have anatomically extruded mandibular canines, and the
treatment plan often involves the intrusion of the incisors and the canines. As
simultaneous orthodontic intrusion of the 6 anterior teeth can cause undesirable effects
in the posterior anchorage segment, segmented intrusion of the mandibular canines
should be considered when levelling the curve of Spee. 8,11
Intrusion is defined as the apical movement of the geometric center of the root
(centroid) in respect to the occlusal plane or a plane based on the long axis of the
tooth. Labial tipping of an incisor around its centroid produces pseudo-intrusion,
Conventional intrusion mechanics frequently cause labial tipping of incisors, a
situation which does not always give favourable treatment outcomes.8
Orthodontic appliances such as the cantilever, spring, etc. deliver relatively constant
forces owing to the large inter-bracket distance between two points of attachment. In a
two-tooth system, if an appliance is engaged in the bracket slots of both the teeth, it
generates a force and a couple at both the brackets resulting in a two couple statically
indeterminate system 13
But, if an appliance is engaged in the bracket slot of one tooth
and tied as a point of contact on the bracket of another tooth, then this force system is
called as a one-couple system because a couple acts only at the bracket slot where an
appliance is engaged. One couple system is statically determinate as equal and
DISCUSSION
54
opposite forces act at both the attachment sites (engaged and tied) to maintain the
static equilibrium of an appliance.12
In this study a cantilever was fabricated with 0.017×0.025 inch TMA wire and one
end was inserted into the molar auxiliary tube and the other end was placed over the
canine bracket to create a one couple statistically indeterminate system (fig. 4a). The
one-couple system produces the reactive force as well as the couple on the molar tube
which try to displace the molar tooth. This can be minimized by engaging an archwire
from second molar tube to first molar tube and extending further through brackets
slots of first and second premolars to generate posterior teeth anchorage segment.
Thus, posterior teeth will act as a one complete anchorage unit, making the effects of
couple and reactive force significantly lower than the effect of force on the canine. A
study done by Kojima and Fukui showed that the addition of the second molar to the
anchorage unit decreases the reactive forces on the posterior anchorage system and
also increases the amount of anterior intrusion.50
Hence in our study the posterior
segment was consolidated with 0.019x 0.025inch stainless steel wire from the
premolars to the second molar teeth.
Many studies have been done to intrude the mandibular canine individually but are
often faced with the problems of unwanted labial tipping of the concerned tooth.
One technique was described by Ricketts et al and involved using the utility arch after
complete incisor intrusion as a stabilization arch and gently tying an elastic band from
the canine bracket to a segment in the utility arch which had a step down.6 Another
technique was reported by Marcotte, and burstone 8 who suggested the use of a
cantilever from the auxiliary tube of the first molar to the canine bracket slot.
DISCUSSION
55
However, these techniques do not include a method for controlling the buccolingual
inclination.8,11
Hence in our study a cantilever loop was used to intrude the mandibular
canine. The cantilever was tested with 0,4,6,8 degree toe-in bends which were
incorporated to determine its effectiveness of each toe-in bend in controlling
unwanted labial tipping of the mandibular canine on application of intrusive forces
(fig. 4b).
Creekmore and Eklund initially performed maxillary incisor intrusion using a
vitallium screw inserted just below the anterior nasal spine, and since then many
clinicians have tried to intrude the incisors with absolute anchorage.14
The
development of mini-implants in the past years has enabled efficient anchorage,
requiring no tooth support and with no esthetic compromise whatsoever. Additionally,
no patient cooperation is required.15
Miniscrews have a high success rate of
approximately 90%, which is the same as miniplates and large titanium screws, and
they provided sufficient anchorage immediately after placement surgery for any
orthodontic tooth movement.14
Many studies have been done to intrude the incisors and canines using mini implants.
A study done by Telma martin et al showed that pure cuspid intrusion can be achieved
by the use of elastic forces applied from two mini implants placed on either sides of
the labial surface of canine root. The unwanted buccal tipping was prevented by the
placement of a rigid 0.019x0.025 inch stainless steel wire on the labial surface of the
crown just below the bracket.15
A study done by esen aydogdu et al concluded that
pure incisor intrusion could be achieved using a segmental arch to the incisors when it
is supported by two mini-implants that are placed between the lateral and canine teeth.
DISCUSSION
56
Also the incisor intrusion that was achieved using TAD supported segmented archwire
was no different than the movement achieved by the conventional intrusion utility
arch.9 A study by Ishihara et al showed that the indirect use of miniscrews is an
efficient method for intruding over-erupted mandibular incisors.14
Omur Polat-Ozsoy et al conducted a study which investigated the effects of incisor
intrusion obtained with the aid of miniscrews and showed that mini screw mechanics
produce pure intrusion of the incisors.36
A study by Singh S, Mogra S showed that
Implant-grade stainless steel and Ti6Al4Vn alloys are suitable materials for miniscrew
implants.37
Letizia Perillo conducted a finite element study to evaluate the influence of
placement angle and direction of force on the stability of miniscrews and found that a
mini screw placed at 90 degree angulation to the alveolar bone surface provided good
anchorage.40
A study by Kyung-Seok Hua et al showed that in the mandible, the
regions for which a miniscrew of 8 mm is recommended are between canine and first
premolar (from 8 mm below cervical line), between first and second premolars (from
5 mm to 8 mm below cervical line), and between first and second molars.45
In this FEM study mandibular canine intrusion was attempted using two mini implants
composed of titanium and with a diameter of 1.5mm and length 6mm. The implants
were placed on either side of the mandibular canine labial surface at a distance of
8mm from the alveolar crest and angulated at 90 degrees. To control any undesirable
effect a straight 0.019 x 0.025inch stainless steel archwire could be fashioned and
placed alongside the cuspid’s buccal surface immediately below the bracket.15
(fig.5b,
5c)
DISCUSSION
57
The phenomenon of tooth movement in response to an applied load was first reported
nearly 2000 years ago (Celsus, 1st century AD). Although teeth are moved routinely
in orthodontic practice, it is still the case that there is much to learn about the exact
ongoing changes in the biomechanical loading of tissues and the precise mechanism of
tissue response following force application. To better understand the biomechanics of
tooth movement, a variety of methods have been used like theoretical mathematical
techniques, photo-elastic systems and laser holographic interferometry. However,
such techniques have the disadvantage of only examining surface stress, whilst having
the added problem of usually being supported by poor validation systems, as judged
by current standards. In the last decade the application of the finite element method
(FEM) has revolutionized dental biomechanical research.24
The finite element method (FEM) is a highly precise technique used to analyse
structural stress. Used in engineering field for years, this method uses the computer to
solve large numbers of equations to calculate stress on the basis of the physical
properties of structures being analyzed. FEM has plenty of advantages over other
methods (such as the photoelastic method), highlighted by the ability to include
heterogeneity of tooth material. The irregularity of the tooth contour can also be
formed in the model design and it has a relative ease with which loads can be applied
at different directions and magnitudes for a more complete analysis.
Finite element analysis has been used in dentistry to investigate a wide range of
topics, such as the structure of teeth, biomaterials and restorations, dental implants and
root canals. 24
FE analysis has provided a visual image of the effects of an orthodontic
force on the tooth and its supporting structures. Furthermore, it serves as a useful tool
DISCUSSION
58
to simulate different loading systems and evaluate the initial effects in the
dentoalveolar structures to better understand biomechanics.
14
The object to be studied is graphically simulated in a computer in the form of a mesh,
which defines the geometry of the body being studied. This mesh is divided, by a
process known as discretization, into a number of sub-units termed elements. These
are connected at a finite number of points called nodes, which are, in turn, defined by
their global co-ordinates. The constituent elements are prescribed the appropriate
material properties of the structure they represent. 24
By using this, the function and the actual geometry of the element, the equilibrium
equations between the external forces acting on the element and the displacements
occurring on its nodes can be determined. The information required for the software
used in the computer is as follows.
1. Co-ordinates of the nodal points
2. The number of nodes present for each element
3. Young’s modulus and poisson’s ratio of the material modelled by different
elements: Young's modulus (MPa), also known as the tensile modulus, is a quantity
used to characterize materials and also determines the stiffness of an elastic material.
Young’s modulus is also called the elastic modulus or modulus ofelasticity, because
Young's modulus is the most commonly used elastic modulus. When an object is
stretched, Poisson’s ratio is the ratio of the contraction or transverse strain
(perpendicular to the applied load), to the extension or axial strain (in the direction of
the applied load). When a sample material is compressed in 1 direction, it tends to
expand in the other 2 directions perpendicular to the direction of compression. This
DISCUSSION
59
phenomenon is called the Poisson effect. Poisson's ratio is a measure of the Poisson
effect.18
4. The boundary conditions: A boundary condition is the application of force and
constraint.
5. The forces applied on the structure.
In structural analysis, boundary conditions are applied to those regions of the model
where the displacements and/or rotations are known. Such regions may be constrained
to remain fixed (have zero displacement and/or rotation) during the simulation or may
have specified, non-zero displacements and/or rotations. 18
In the present study two finite element models of the right mandibular quadrant were
created with teeth present from the canine to the second molar. The brackets, molar
tubes and wires were modelled along with the periodontal ligament and the alveolar
bone. A study by Hohman kober et al showed that for intrusive tooth movements a
robust construction of PDL is important.31
The PDL plays a major role in orthodontic
tooth movement, and its thickness and viscoelasticity varies along the root surface.
Clinically, these variations may have an influence over the intensity of the biologic
events that take place during orthodontic tooth movement. 11, 34
In our study, the PDL
was modelled with 0.20-mm uniform linear thickness and elasticity was maintained
the same along the roots of all teeth.
In the first model a cantilever made up of 0.017x 0.025 inch TMA wire placed from
the auxiliary tube to the canine was used for intrusion of the canine. The cantilever
was tested with four different toe-in bends i.e. 0,4,6,8 degrees each applying a force of
0.10N, 0.052N, 0.082N and 0.12N respectively (table-2).
11 These bends were
DISCUSSION
60
incorporated to assess the amount of labial tipping that occurred while intruding the
canine tooth.
In the second model two mini implants were placed in the interdental area on either
sides of the canine root at a level of 8 mm from the alveolar crest (fig. 5b, 5c).55
Intrusive force of 0.12N was applied to the canine using an elastomeric chain from the
mini-implants. The amount of intrusion along with the labial tipping that occurred in
both the models was evaluated and compared using the finite element analysis.
A few studies have been done to determine true intrusion of the canine. Caballero et al
in an FEA study used a cantilever loop with different toe in bends to intrude the
mandibular canine and showed that the 6 degree toe in bend produced pure intrusion
of the canine tooth with negligible labial tipping. The study also showed that the
amount of tipping decreased with an increase in the toe-in bend. The anchor molar
displayed tendency for extrusion and distal tipping.11
A study by Telma martin et al
used mini implants along with an elastic force to intrude a canine tooth and showed
favourable results,15
an FEA study done by Thote et al showed that pure intrusion of
mandibular canine in lingual orthodontics occurred with an optimal force of 20-
30gm.21
In our study the movement of the crest (tip of buccal cusp, node no. 12806) and the
root nodes (tip of apex of root, node no. 129160) were used to determine the amount
of intrusion and labial tipping. The amount of intrusion obtained by different toe in
bends of the cantilever was assessed. The intrusion produced by 8º toe-in bend of the
cantilever was found to be the highest among all models and the least value was
produced by the cantilever with 0º toe-in bend (table-3, graph-1). The amount of pure
intrusion increased with increase in the degree of toe-in bend, and the amount of labial
DISCUSSION
61
tipping of the canine decreased with increase in toe in upto 6 degree, but the 8 degree
toe in bend produced lingual tipping of the tooth. Both the implant model and the 6
degree toe-in model showed almost pure intrusion with least amount of labial tipping,
although the intrusion values produced by the 6 degree toe in of cantilever model were
higher. The maximum tipping was present in the cantilever with a zero degree toe- in
bend, indicating that incorporating a toe-in reduces the tendency of labial tipping of
the concerned tooth (table-4, graph-2). This is in accordance with the study by
caballero.11
In the posterior segment, the anchor molar showed tendency for extrusion and distal
tipping in all the cantilever models (fig. 10a, 10b, 10c, 10d) whereas, this was
negligible in the implant model (fig.10e) inferring that the implant model produces
intrusion of the canine with negligible effect on the posterior anchorage.
A few studies have been done to evaluate the amount of stress that occurs in the
periodontium during tooth movement. A study by jones Hickam et al showed that the
maximum strains recorded in the surrounding alveolar bone were 35 times less than
for the PDL. This FEM model validated that, the PDL is the main mediator of
orthodontic tooth movement.24
Puente et al, studied the stress difference between tipping and torque movements on a
computer model of a mandibular canine and inferred that, the dental apex and bone
crest zones are the areas that suffer the greatest stress when forces are directed bucco-
lingually. It was concluded that, a tri dimensional model is useful to investigate the
biomechanics of tooth movement, keeping in mind that it is more valid as a qualitative
study 21
. A study done by David J. Rudolph et al showed that intrusive, extrusive, and
rotational forces produce more stress at the apex. Bodily movement and tipping
DISCUSSION
62
forces concentrate forces at the alveolar crest, not at the apex.26
Geramy (2002)
reported the stress produced in the periodontal membrane by orthodontic loads in the
presence of varying loss of alveolar bone and concluded that, bone loss caused
increased stress under the same load compared with healthy bone support. Tipping
caused increased stress in the cervical margin of the periodontal membrane and in
case of intrusive movements, at the apical and subapical levels.25
Tanne et al (1987),
in a 3D FEM study, reported a cervical margin stress of 0.012 N/mm2 when, a
lingually directed tipping force of 1N was applied to the centre of a mandibular
premolar model.23
In the present study the periodontium and the alveolar bone around the canine tooth
and posterior segment was studied for stress changes. Among the models the
maximum periodontal stress was seen with the model having the cantilever with 0º toe
in bend followed by the 6º, 8º and 4º toe-in cantilever models and the least was seen
with the implant model (table-5, graph-3, fig 8a,8b,8c,8d,8e). The cantilever with a 0º
toe in bend produced labial tipping of the crest node as well as the lingual tipping of
the root node thereby producing more stress around the periodontium due to
uncontrolled tipping. The alveolar bone showed maximum stress around the mini
implants placed in the bone (table-6, graph-4). In the posterior segment negligible
stresses were noted in the periodontium as well as the alveolar bone.
The simulations of this finite element study showed that a significant amount of labial
crown tipping occurs when intrusive forces are applied to a canine tooth without any
labio-lingual control. In such cases, the control of tipping movements of a tooth is
extremely important as it can lead to a variety of unwanted problems. Increased
DISCUSSION
63
tipping of the tooth can lead to an increased risk of gingival recession, periodontal
problems, alveolar bone loss and also abfractions of the tooth. Also, uncontrolled
canine intrusion may lead to buccal crown tipping and may contribute to an increased
mandibular intercanine width, which eventually could increase the chances of
orthodontic treatment relapse.19
A study by bernhardt et al evaluated the multifactorial
causes that lead to abfractions and concluded that gingival recessions are associated
with the genesis of abfractions and must be seen as co-factors.41
More recently
cervical tooth loss has been linked with cuspal flexure. It has been suggested that
occlusal loads cause the tooth to flex, particularly during lateral excursion. As the
tooth flexes, tensile and shear stresses are generated in the cervical region of the tooth
that cause disruption of the bonds between the hydroxyapatite crystals, leading to
crack formation and eventual loss of enamel and the underlying dentine. 48
This
increased risk can be explained as a result of increased proclination of the tooth which
leads to alteration of force vectors that act on the teeth during masticatory and lateral
excursive movements. The above factors reinforce the importance of the results of
this study.
In the present FEM study, a cantilever loop with different toe-in bends and mini-
implants with an elastic force module were tested for their efficacy in producing pure
intrusion of mandibular canine tooth. The results showed that the amount of labial
tipping tendency of the tooth decreased when a toe-in bend was added to the
cantilever. The 6º toe-in bend of cantilever was sufficient to produce almost pure
intrusion of canine with very less amount of tipping tendency. This is in accordance
with the results seen with the study by caballero. The forces applied from the mini-
implants also produced pure intrusion of the canine with negligible tipping, but the
DISCUSSION
64
amount of intrusion produced was less compared to the cantilever model. Although
the forces applied from different toe in bends had major influence on the canine tooth
but the posterior teeth were not much affected. The posterior segment was
consolidated and served as a rigid anchorage system in cantilever models and hence
only a slight tendency for extrusion and distal tipping was noted in the molar 11
.The
molar had negligible counter-effects in the mini-implant model as the main forces
were applied only from the mini-implant, while the rest of the posterior segment
served as an anchorage unit. The periodontal stresses were observed to be
concentrated majorly around the canine periodontium and alveolar bone. Maximum
amount of stress was noted in the model with 0º toe-in bend, and the least periodontal
stress was seen in mini implant model (graph-3). Although the stresses seen with the
6º toe in model were slightly on the higher side, it produced good amount of pure
intrusion with almost negligible labio-lingual tipping making it the appliance of
choice when true intrusion of a canine is desired.
In the present FEM study, idealized tooth models were used to simulate the conditions
and the results obtained from this study were based on a one time simulated tooth
movement. In day to day practice when dealing with patients having different tooth
morphologies, differences in periodontal health, alveolar bone conditions and
biological reactions the resultant effects may vary. The results obtained in this study
may serve as a future reference guide for further customization of different
compensatory bends with cantilever and also influence the mechanics with mini-
implants. Further clinical studies over a period of time are needed to confirm the
results of this study.
CONCLUSION
65
CONCLUSION
This study was conducted to assess the effects of mandibular canine intrusion by using
a cantilever with different compensatory toe-in bends and with mini-implants using 3-
dimensional finite element method.
The following conclusions can be made within the limits of this study.
As assessed by finite element analysis
1. This FEM study showed that among all the models, the cantilever model with
a 6º toe-in produced a good amount of intrusion with minimal labial tipping.
2. The present FEM study proved that, incorporation of compensatory toe-in
bends in a cantilever is necessary to prevent undesirable labial or lingual
crown tipping, of the mandibular canines on application of intrusive forces.
3. Intrusion of the mandibular canine with less labial tipping can also be achieved
using two mini-implants. The labial tipping is reduced with the use of a 0.019x
0.025inch stainless steel wire placed just below the bracket of the tooth
4. In the posterior anchorage segment, the first molar displayed a tendency for
extrusion and distal crown tipping in all the cantilever models whereas the
effects were negligible in the mini-implant model
5. Most of the registered periodontal stresses were around the canine root. The
stress was the highest with a cantilever that was devoid of any compensatory
toe in bend.
6. Further clinical studies are needed to validate the results of this study over a
period of time to determine the long term effects and stability.
SUMMARY
66
SUMMARY
A finite element analysis was conducted to study the effects of mandibular canine
intrusion produced by segmented arch technique, using a cantilever versus mini-
implants. A geometric model of the mandibular base and teeth from canine to second
molar of the right quadrant was created through CT scan and converted to a three
dimensional step file format through reverse engineering technique. Further, it was
converted into finite element format through the meshing software, ANSYS. Three
dimensional geometry of periodontal ligament (PDL), alveolar bone, bracket, molar
tubes, arch wire, cantilever and mini-implants were separately constructed using the
modelling and meshing softwares. All brackets were sited on the facial-axis points.
The posterior teeth from the second molar to the first premolar were levelled, and the
canine with its surrounding alveolar bone (elastic modulus 345 MPa; poisson’s ratio 0.3)
was extruded by 1.5 mm. Two 3- dimensional solid models were constructed and
periodontal ligament (elastic modulus 0.71 MPa; poisson’s ratio of 0.4) modified with
0.20-mm linear thickness uniformly.
A finite element analysis was done using two 3-dimensional solid models, one having
a cantilever with different compensatory toe-in bends placed from molar auxiliary
tube and tied to the canine bracket and other having two mini-implants placed on
either side of the canine tooth interdentally on the labial side. Based on these 3-
dimensional solid models, a finite-element mesh was created to make a node-to-node
connection between the tooth, PDL, and alveolar bone. The amount of pure intrusion
of the canine produced by both the cantilever with different toe-in bends and with
mini-implant was assessed.
SUMMARY
67
The undesirable labial/lingual tipping and effects on the posterior anchorage that
occurred as a result of intrusion were evaluated. The periodontal and alveolar bone
stresses occurring in all the models were also assessed. In the mini implant model, an
elastic chain was used to apply intrusive forces on the canine from the mini-implants.
Also a 0.019×0.02inch stainless steel rigid wire was fabricated and placed alongside
the buccal surface of the canine tooth to prevent tipping.
CONCLUSION:
Two nodes, the tip of the buccal cusp (crest node- no. 128046), and the apex of the
root (root node- no. 129160) were selected for evaluating the movement of the canine
along the Y-axis indicating intrusion and the Z-axis indicating tipping of the tooth in
the labial or lingual direction.
In the first model with 0º toe-in bend of cantilever, the amount of crown movement
was 0.9μmm apically, and the root movement was 0.18μmm apically, the 4º toe-in
bend showed 3.0μmm apical movement of crown and 2.4μmm apical root movement,
the 6º toe-in showed crown movement of 5.4μmm apically and root movement of
5.0μmm, the 8º toe-in showed apical crown movement of 7.3μmm and apical root
movement of 7.37μmm. In the second model the amount of crown and root
displacement along the y axis produced as a result of forces from the mini-implant
were 1.9μmm and 1.6μmm towards apex respectively.
The amount of labial displacement of the crest node that occurred with the 0º toe-in of
the cantilever was 3.7μmm while the root node moved lingually by 3.2μmm, 4º toe-in
bend produced 3.59μmm labial displacement of the crest node and the root node
moved lingually by 1.5μmm, 6º toe-in bend produced 0.6μmm labial movement of
SUMMARY
68
crest node and 0.65μmm movement of root node lingually. The opposite effect was
seen with the 8º toe-in bend of cantilever which produced a lingual displacement of
both the crest node and the root node by 3.01μmm and 2.4μmm respectively. The
amount of labial displacement of crest node produced by the forces from mini implant
was 0.048μmm while the root node moved lingually by 0.03μmm.
This study showed that the amount of intrusion obtained by the 8º toe-in bend of the
cantilever was found to be the highest followed closely by the 6º, 4º and mini-implant.
The least value was produced by the cantilever with 0º toe-in bend. Also, it was noted
that a 0º toe-in bend produced the highest amount of labial tipping of the canine tooth.
As the toe-in bend increased from 0º to 6º, the amount of labial tipping of the canine
decreased whereas with an 8º toe-in bend the tooth tipped lingually. The molar
displayed a slight tendency for extrusion and distal tipping in all the cantilever models
but these counter-effects were negligible in the mini-implant model. The periodontal
stress was seen to be the maximum with 0º toe-in cantilever model and least with mini
implant.
This FEM study concluded that when pure intrusion of a canine is desired, the use of a
cantilever with a 6º toe-in proved to be the appliance of choice as it produced a good
amount of intrusion with minimal tipping. As this study, was a one-time FEM study,
further clinical studies are needed to evaluate the effects on a long term basis and also
to determine the stability of these mechanics.
Key words: FEM; arch wire; brackets; buccal tube; cantilever; mini-implants.
SUMMARY
69
LIMITATIONS OF THE STUDY:
1. In this study the results were tabulated on the basis of a one-time finite element
study. The stability of intrusion produced must be determined. Also, the effects
of these appliances on the tooth and alveolar bone needs to be evaluated with
long term clinical studies
2. Idealised models were used in this FEM study, the effects may differ when
used on individuals with various tooth morphologies. The presence of
periodontal diseases and bone loss may also influence the intrusion mechanics.
3. In FEM analysis, certain assumptions are made to simulate the physical
environment which can result in errors of stress or displacements.
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53. Vollmer D. Determination of the center of resistance in an upper human canine
and idealized tooth model. European journal of orthodontics 21(1999) 633-648
54. Ira J. Heller, Nanda R. Effect of metabolism & alteration of periodontal fibers
on orthodontic tooth Movement An experimental study. Am J Orthod Volume
75, Number 3 March, 1979
55. Lee J.S et al. Applications of orthodontic mini-implants
CONSENT FORM
77
CONSENT FORM
DEPARTMENT OF ORTHODONTICS AND DENTOFACIAL
ORTHOPAEDICS
GOVERNMENT DENTAL COLLEGE AND REASEARCH INSTITUTE
BANGALORE
This is an in-silico study (finite element analysis) and hence no consent form is
required.
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PROFORMA PROTOTYPE
78
TABLE 1: MATERIAL PROPERTIES OF THE MEMBERS:
Member Elastic modulus Poissons ratio
Tooth
Periodontal ligament
Bone
Stainless steel wire
Titanium molybdenum alloy
Implant
TABLE 2: AMOUNT OF FORCE ON THE X-AXIS PRODUCED WITH THE
TOE-INS TESTED
Toe-in Force in the Y-axis (N)
0º
4º
6º
8º
TABLE 3: AMOUNT OF INTRUSION OF CREST NODE AND ROOT NODE
DISPLACEMENT ALONG Y AXIS
0 degree 4 degree 6 degree 8 degree Mini-
implant
Crest node
Root node
TABLE 4: LABIAL/LINGUAL MOVEMENTS OF CREST AND ROOT NODE
DISPLACEMENT ALONG Z AXIS
0 degree 4 degree 6 degree 8 degree Mini-
implant
Crest node
Root node
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TABLE 5: STRESSES IN CANINE PERIODONTIUM:
0 degree 4 degree 6 degree 8 degree Mini-
implant
Stress
(MPa)
TABLE 6: ALVEOLAR BONE STRESS AROUND CANINE:
0 degree 4 degree 6 degree 8 degree Mini-
implant
Stress
(MPa)
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FIGURES:
FIG 1 : CT MODEL OF THE MANDIBULAR ARCH
FIG 2a: CUT MODEL OF THE BONE FROM CANINE TO THE SECOND MOLAR
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FIG 2b: MESH FORM OF THE TEETH
FIG (2c): TEETH WITH 1.5MM OFFSET OF THE CANINE
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FIG 3a: CANINE TOOTH AND ITS PERIODONTIUM
FIG 3b: PERIODONTIUM OF THE DENTITION
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FIG 3c: ALVEOLAR BONE WITH SOCKETS
FIG 4a: TEETH WITH BRACKET AND WIRE
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FIG 4b:WITH 4 DIFFERENT TOE-IN BENDS OF CANTILEVER i.e 0,4,6,8
DEGREES (ZERO FROM LEFT SIDE) ASSEMBLY WITH CANTILEVER
ARRANGEMENT
FIG 4c: MODEL IN ANSYS SOFTWARE
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FIG 5a: MINI-IMPLANT MODEL WITH 1.2 MM DIAMETER AND 6MM LENGTH
FIG 5b: MODEL WITH ELASTIC CHAIN PLACED FROM MINI-IMPLANTS TO
CANINE
FIG 5c: MODEL WITH MINI-IMPLANT
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Boundary Conditions :
Both the ends of the bone structure is constrained in all the directions.
FIG 6a: (VECTOR PLOT FOR BEAM ELEMENT)ANALYSIS RESULTS FOR 0
DEGREE :
FIG 6b: (VECTOR PLOT FOR BEAM ELEMENT)ANALYSIS RESULTS FOR 4
DEGREE
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FIG 6c: (VECTOR PLOT FOR BEAM ELEMENT )ANALYSIS RESULTS FOR 6
DEGREE
FIG 6d: (VECTOR PLOT FOR BEAM ELEMENT)ANALYSIS RESULTS FOR 8
DEGREE
FIG 6e: (VECTOR PLOT FOR BEAM ELEMENT ) ANALYSIS RESULTS FOR MINI-
IMPLANT )
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FIG 7a: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH 0º TOE-IN)
FIG 7b: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH 4º TOE-IN)
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FIG 7c: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH 6º TOE-IN)
FIG 7d: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH 8º TOE-IN)
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FIG 7e: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH MINI-IMPLANTS)
FIG 8a: STRESS IN THE CANINE PERIDONTIUM (0º TOE-IN)
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FIG 8b: STRESS IN THE CANINE PERIDONTIUM (4º TOE-IN)
FIG 8c: STRESS IN THE CANINE PERIDONTIUM (6º TOE-IN)
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FIG 8d: STRESS IN THE CANINE PERIDONTIUM (8º TOE-IN)
FIG 8e: STRESS IN THE CANINE PERIDONTIUM (MINI-IMPLANT)
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FIG 9a: STRESS IN THE ALVEOLAR BONE (0º TOE-IN)
FIG 9b: STRESS IN THE ALVEOLAR BONE (4º TOE-IN)
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FIG 9c: STRESS IN THE ALVEOLAR BONE (6º TOE-IN)
FIG 9d: STRESS IN THE ALVEOLAR BONE (8º TOE-IN)
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FIG 9e: STRESS IN THE ALVEOLAR BONE (MINI-IMPLANT)
FIG 10a: EFFECTS ON THE MOLAR (0º TOE-IN)
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FIG 10b: EFFECTS ON THE MOLAR (4º TOE-IN)
FIG 10c: EFFECTS ON THE MOLAR (6º TOE-IN)
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FIG 10d: EFFECTS ON THE MOLAR (8º TOE-IN)
FIG 10e: EFFECTS ON THE MOLAR (MINI-IMPLANT)
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FIG 11a: STRESS CHANGES IN POSTERIOR SEGMENT (0º TOE-IN)
FIG 11b: STRESS CHANGES IN POSTERIOR SEGMENT (4º TOE-IN)
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FIG 11c: STRESS CHANGES IN POSTERIOR SEGMENT (6º TOE-IN)
FIG 11d: STRESS CHANGES IN POSTERIOR SEGMENT (8º TOE-IN)
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FIG. 11e: STRESS CHANGES IN POSTERIOR SEGMENT (MINI-IMPLANT)