DR.AJAY SRINIVASDept of

orthodonticspg student

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Introduction Prenatal Dental Development The mouth of neonate – Pre-dentate period Eruption of teeth The Primary teeth and occlusion

Development of teeth Development of occlusion

The mixed Dentition period First transitional period Inter-transitional period Second transitional period

Permanent teeth and occlusion Assessment of dental age

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Dentitional and occlusal development in Young Adult Occlusion and mandibular movements Factors affecting occlusal development Role of genetics in occlusal development Conclusion References

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Mosby’s dental dictionary (Zwemer;1998) defines occlusion as ”a static morphological tooth contact relationship”

Acc. to Ash and Ramfjord , occlusion may be defined as ”the contact relationship of the teeth in function or para function”.

Acc. to Angle, occlusion is “the normal relation of the occlusal inclined planes of the teeth when the jaws are closed”.

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The term occlusion , however, refers not only to contact at an occlusal interface but also to “ all those factors concerned with the development and stability of the masticatory system and with the use of the teeth in oral motor behaviour ”

In most instances , malocclusion and dentofacial deformity are not caused by some pathological process , but by moderate distortions of normal development.

Therefore , knowledge of the process of occlusal development is necessary.

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Humans are having two sets of teeth

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Deciduous dentition Permanent dentition

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First sign of tooth development - third embryonic week – thickening of epithelial lining

At sixth week - Epithelial thickenings coalesce - dental lamina

8Dental lamina

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Bud stage Cap stage Bell stage Advanced bell stage

Initiation Proliferation Histo-differentiation Morpho-differentiation

Spatial pattern The prenatal dental arch progressively changes shape At 6-8 week- Flat antero-posteriorly 4th month - Elongation of Ant. Segment occurs - Catenary

curve Spacing

Inter-dental spacing is relatively constant during this period.

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Tooth Fields Tooth germ together with the space

mesial and distal to it within the dental arch is called tooth field

Greatest level of occupancy of a tooth field by a tooth germ is about 80 % for the first deciduous molar and lateral incisor.

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Predentate period

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Gum pads They Cover the alveolar process at birthThey are Pink, firm, covered by dense

fibrous periosteumSegmented to indicate sites of developing

teethTransverse groove divides it into ten

partsDental groove demarcates the labio-

buccal and the lingual portionsLateral sulcus seen between the canine

and the first molar is used to estimate the inter-arch width

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Size of the gum pads at birth may be determined by : State of maturity of infant at birth Size at birth as expressed by birth weight Size of developing primary teeth Purely genetic factors

Maxillary arch Horse shoe shaped Complete overjet labially and bucally is seen.

Mandibular arch Lies posterior to the maxillary arch when the gum pads

contact

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It is a developmental process that moves a tooth from it’s crypt position through

the alveolar process into the oral cavity and to occlusion with it’s antagonist

Physiologic tooth movements leading to tooth eruption can be divided into 3

phases

1. Pre - eruptive phase

2. Eruptive phase

3. Post - eruptive phase

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PRE - ERUPTIVE PHASE Consists of the movements of the developing tooth germs within the alveolar process before root formation. During this phase, the growing teeth move in various directions to maintain their position in the expanding jaws.

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POST - ERUPTIVE PHASE

Consists of tooth movements which

Maintain the position of the erupted teeth while the jaws continue to

grow

Compensate for occlusal and proximal wear

Root elongation theory Suggests that proliferating root impinges on a fixed base, the

cushion-hammock ligament, thus converting an apically directed force into occlusal movement.

Evidence against - A series of experiments where rootless teeth have erupted into functional occlusion.

Pulp constriction theory Suggests that a propulsive force is generated by extrusion of

pulp through three mechanisms : firstly growth of dentin, secondly interstitial pulp growth and thirdly, hydraulic effects within the vasculature

Evidence against - The work of Merzberg and Schour, who removed the pulp of rodent incisors and found that the eruption rates were unaffected.

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Hydrostatic pressure theory Teeth move in their sockets in synchrony with arterial

pulse, thus local volume changes may produce limited tooth movement.

Evidence against - Surgical excision of a growing root and associated tissue eliminates the periapical vasculature without stopping eruption.

Bone remodeling theory Suggests that selective deposition and resorption of bone

brings about eruption of tooth.  Evidence supporting - In experiments where tooth germ is

removed but the follicle is left in position, the eruptive pathway still forms in bone thus proving the dental follicle and not bone as the major determinant in tooth eruption.

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Periodontal ligament traction theory States that the periodontal membrane plays an important

role in the tooth eruption. Two causative agents with in the periodontal ligament which can generate eruptive force are- Collagen contraction Fibroblast traction

Evidence supporting – Changes are induced in the shape and orientation of PDL fibroblasts by a transition from impeded to unimpeded eruption.

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Factors regulating and affecting eruption

Heredity Socioeconomic status Racial differences Nutritional influence Mechanical disturbance Localised pathosis

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Begins at around 6 months of age with the

eruption of lower central incisors.

Completed after all the 2nd molars have attained

occlusion i.e. usually around 2.5 years of age.

Little changes take place in the deciduous

dentition between 2.5 to 5 years of age.

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Calcification Central incisor- 14 week 1st molar- 15 week Lateral incisor- 16 week Canine- 17 week 2nd molar- 18 week

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Eruption

Sexual differences Males - early eruption till 15 month Females - surpass after 15 months

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Developmental anomalies less frequent fewer than 1% incidence of congenitally missing teeth.

Primary tooth resorption Plays an important role in permanent tooth eruption Mainly occurs due to pressure from the erupting permanent

successor though it may occur even in its absence Its Hastened by inflammation and occlusal trauma Its Delayed by splinting and absence of permanent successor

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Ankylosis Primary teeth are more likely to be involved as

compared to permanent teeth. In ankylosis, Teeth are fused to alveolar bone and

their eruption is prevented MOST COMMONLY SEEN IN- molars Often seen bilaterally Trauma or excessive pressure is said to be the cause Posterior open bite seen due to involved tooth being

“submerged ”.

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Neuromuscular considerations

Sequential inter-dentation begins in the front as the incisors erupt

Teeth are guided into occlusal position by muscular functional matrix during active growth of the facial skeleton.

Low cusp ht. and ease of wear of occlusal surfaces also contribute to this adaptability

Muscle behaviour is adaptive to skeletal morphology

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Arch form In maxilla

• Ovoid in shape

• Increased intercanine width by 6 mm is seen between 3-13 yrs

• Increased Intermolar width of 2 mm is seen between 3-5 yr

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Arch form In mandible

Ovoid shape

Increased intercanine width by 3.7 mm seen between 3-13 yrs

Increased Intermolar width of 1.5 mm seen between 3-5 yr

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Arch length and circumference minute amount of decrease is seen. This is mainly due to mesial

migration of second primary molars during eruption.

can be affected by proximal caries

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SpacingUsually generalised inter-dental spacing is

seen

• Primate spaces• In 87% of maxillary arches its seen between

lateral incisor and canine• In 78% of mandibular arches its seen between

canines and first primary molars

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Flush terminal plane

Here the distal surfaces of upper and the lower second molars are in one plane

This makes it favorable for the

eruption of the first permanent molars into a normal relation

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Occlusal relations

Mesial step

Distal surface of lower molar is more mesial to upper molar

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Distal step Distal surface of lower

molar is more distal to upper molar

Prognostically unfavourable

Can arise due to habits like thumb sucking

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Acc. to a study by Bishara et al , the distribution of terminal plane relationships was found to be:

Distal step - 10% Flush terminal plane - 29% Mesial step of 1 mm -42% Mesial step > 1-0 mm -19%

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Over bite It’s the Vertical Incisor overlap

Average - 1- 2mm

It Decreases steadily ; which is a reflection of skeletal maturation

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Overjet Horizontal overlap of incisors Normal :- 0-4 mm in primary dentition

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Spaced anteriors Primate spaces Shallow overbite and overjet Straight terminal plane Class - I molar and cuspid relationship Almost vertical inclination of anterior teeth Ovoid arch form

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Anterior deep bite Cause – Incisors are

more upright

Correction occurs by

• Forward and downward growth of mandible

• Attrition of incisal edges

• Eruption of permanent molars

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Primate spaces Correction by Early mesial shift

Flush terminal plane Early mesial shift Late mesial shift

Physiologic spaces Helps in accomodation of Permanent

incisors

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Period of both primary and permanent dentition

Those permanent teeth that follow into place in the arch once held by a primary teeth are called SUCCESSIONAL TEETH - Incisors, cuspids and bicuspids)

Those teeth that erupt posteriorly to the primary teeth are termed as ACCESSIONAL TEETH

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Clinical importance

Utilization of arch perimeter is done for: Alignment of permanent incisors. Eruptive Space for cuspids and premolars. Adjustment of the molar occlusion.

Adaptive changes occur in occlusion during the transition from deciduous dentition to permanent dentition.

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SequenceMaxillary

6-1-2-4-3-5-7 or 6-1-2-4-5-3-7Mandibular

6-1-2-4-3-5-7 or 6-1-2-3-4-5-7

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IN First transitional period :- there is Emergence of first

permanent molars. Replacement of

deciduous incisors with permanent incisors.

Followed by Establishment of occlusion

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1st molar eruption Mandible

• Guided into its occlusal position by distal surface of 2nd primary molar• Mesial and lingual path of eruption is seen.

Maxilla• Forward direction of maxillary growth is seen

• Thereby Space is created posteriorly leading to distal and buccal path of eruption of teeth

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Factors affecting first molar eruption

• Congenital absence of tooth itself• Congenital absence of premolars• Distal caries of deciduous 2nd molar• Early loss of deciduous 2nd molar• Developmental disturbances

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Molar adjustment occurs by- Early mesial shift

• Facilitated by Closure of primate spaces and other inter-dental spaces from the rear

Late mesial shift- Occurs by Mesial migration of first

permanent molar after loss of second deciduous molar using leeway space.

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5 Yr

7 Yr

Leeway space Its the difference between the mesio-distal width of the

primary canine,1st molar,2nd molar and their permanent successors.

In Maxillary arch 1.5 mm per side

In Mandibular arch2.5 mm per side

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Occlusal changesFlush terminal plane of primary dentition leads to class l

molar relation of permanent molars Achieved by

• Late mesial shift• Greater forward growth of mandible • Combination of both

A distal step in primary dentition results most likely in class II occlusion in permanent dentition

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Incisor eruption Mandible

• Central incisors usually follow mandibular first molars

• They erupt labially to their normal balanced position between tongue and lip and the facial musculature

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Incisor eruption Maxilla

• Usually follow mandibular centrals or erupt concurrently with mandibular laterals

• More labial eruption than primary incisors is seen• Lateral incisors- Erupt more labially than centrals

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Incisor liability

Its the difference between the amount of space needed for the incisors to erupt and the amount available for them

6-7 mm: Avg value

It causes a transitory stage of mandibular incisor crowding at age 8 – 9

It’s a Normal developmental feature

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Second transitional period

Characterised by- Emergence of

Bicuspids, cuspids, 2nd molars

Establishment of occlusion

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Mandible Most favorable and the most common

eruption sequence 6-1-2-3-4-5-7

Eruption of cuspids first helps in Maintenance of arch perimeter Prevention of lingual tipping of incisors

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If tooth size-space available ratio is poor , the cuspid may be stopped in its eruption by the first molar or the primary molar may be hastened in its exfoliation

1st Bicuspids Rarely any difficulty in eruption is

encountered Sometimes show rotation due to

uneven resorption of primary molar roots

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2nd bicuspids Last lower succedaneous teeth to erupt Extreme variation in calcification and development schedule Often congenitally missing Eruption complication seen due to

• Mesial migration of 1st molar• Poor tooth size - space available ratio• Premature exfoliation of 2nd primary molar

First molar must not be allowed to move mesially untill the second bicuspid has attained its proper position in the arch

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MaxillaSequence of eruption

6-1-2-4-5-3-7 or 6-1-2-4-3-5-7

1st bicuspid Minimal difficulty in eruption is seen Nearly the same size as its

predecessor

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Maxilla2nd bicuspid

Easy eruption is seen

Larger mesio-distal width of primary predecessor permits easy eruption in its place in the arch

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Cuspid More difficult and tortuous path of eruption

than any other tooth Uses leeway space for acomodation Favourable sequence

• Cuspid eruption before 2nd molar

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2nd molarsLast teeth to erupt before 3rd molarMandible

If eruption precede 2nd bicuspid, the 1st molar may tip mesially

Erupts typically before maxillary second molarMaxilla

Eruption of maxillary second molar ahead of the mandibular second molar is said to be symtomatic of a developing class ll malocclusion

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Ugly Duckling stage\ Midline diastema 8-9 years(Broadbent phenomenon)

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Mandibular anterior crowdingCorrection by

Increased inter-canine width Tongue pressure

• Labial movement and change in inclination of incisors

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End on molar relationCorrection by

Late mesial shift• Utilisation of Leeway space

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Mesial drift

strong inherent tendency of the teeth to move mesially even before they appear in the oral cavity

Anterior component of force Axial inclination of permanent teeth are such

that some of the forces of chewing produce a mesial resultant through the contact points of the teeth

Result of muscle forces acting through the inter-cuspation of the occlusal surface.

Counteracted by proximal contacts of the teeth and by the musculature of the lips and cheeks.

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Arch WidthWidth increase involves alveolar process growthMaxillary alveolar processes diverge while the

mandibular processes are more parallel

MaxillaMaxillary width increases are much greater and

they can be more easily altered in treatment Mid-palatal suture can be reopened with RME

Mandible There is Widening of the basal bony width – by

deposition on lateral borders of corpus mandibularis

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Mandibular inter-canine arch width completed Girls – 9 years Boys – 10 years

Maxillary inter-canine arch width completed Girls – 12 years Boys – upto 18 years

Maxillary inter-canine arch width increase serves as a ‘safety valve’ for the dominant horizontal basal mandibular growth during growth spurts.

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Arch Circumference or perimeter In Maxilla

increases slightly Angulation of incisors and greater

increase in width – helps in Preservation of circumference

Mandible Reduction is seen due to

Late mesial shift Lingual positioning of incisors due to

differential mandibulo-maxillary growth Original tipped position of incisors and molars

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Overjet and overbiteMixed to permanent dentition

Overbite• Increases followed by a decrease• Great variability is seen and is Correlated with a

number of facial dimensions ( eg . Ramus height ) Overjet

• It’s a reflection of antero-posterior skeletal relationship• Sensitive to abnormal lip and tongue function

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DENTAL AGE - 6

Near simultaneous eruption of permanent mandibular central incisors, maxillary 1st molars and mandibular 1st molars is seen.

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DENTAL AGE - 7

Eruption of maxillary central incisors

followed by mandibular lateral incisors.

Root formation of maxillary lateral incisor

advanced.

Premolars and canines in stage of crown

completion.

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DENTAL AGE - 8

Eruption of maxillary lateral incisors

Delay of 2-3 years before any more permanent teeth erupt.

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DENTAL AGE - 9 Primary canines,1st and 2nd

deciduous molars present

Root development of maxillary canines and all second premolars is just beginning

One third of the root of the mandibular canines and all of the first premolars have been completed.

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DENTAL AGE - 10

Completion of one half of the root development of mandibular canine, mandibular 1st premolar and maxillary 1st premolar

Completion of roots of mandibular incisor teeth

Near completion of roots of maxillary laterals.

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DENTAL AGE - 11

Near simultaneous eruption of mandibular canine , mandibular 1st premolar and maxillary 1st premolar.

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Eruption of maxillary canine, maxillary and mandibular 2nd premolar.

Second permanent molars in both the arches are nearing eruption.

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DENTAL AGE – 13 , 14 , 15

Progressive completion of roots of permanent teeth.

If 3rd molar is present crown formation is complete.

Dimensional changes Decrease in arch perimeter during the late adolescent and

young adult period

Occlusal changes Decrease in overjet and overbite in 2nd decade

Changes in Sagittal relationships due to• Mesial drifting tendency• Inter-proximal wear• Continuing growth of mandible 3rd molar eruption

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Curve of spee• First described by Von Spee in

1928• Seen in Inclination of teeth in

lateral view• Antero-posterior curvature of the

occlusal plane • The average value 2.5 – 3 mm

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Curve of Wilson• Seen in frontal view

• Maxillary arch - Slight buccal inclination • Mandibular arch - Lingual inclination

• Medio-lateral or transverse curvature of the occlusal plane

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General factors Heredity Skeletal factors Muscle factor

Local factors Aberrant

developmental position of teeth

Supernumerary teeth

Hypodontia Oral habits Localized soft tissue

anomalies

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Occlusal characteristics could be inherited in two major ways An inherited disproportion between the size of the teeth

and the size of the jaws, which would produce crowding or spacing

An inherited disproportion between size or shape of the upper and lower jaws, which would cause improper occlusal relationships.

The more independently these characteristics are determined, the more likely that disproportions could be inherited.

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Normal versus ideal occlusion

Normal occlusion implies more than a range of anatomically acceptable values.

It also indicates physiological adaptability and the absence of recognizable pathological manifestations.

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Ideal occlusion is a state in which no neuromuscular adaptation is needed because no occlusal interferences are present

• The concept of an ideal occlusion refers both to an esthetic and physiological ideal

• It is a hypothetical formula which does not and cannot exist in man

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Occlusion , good or bad, is the result of an intricate and complicated synthesis of genetic and environmental relationships at work throughout the early developmental stages of childhood and young adulthood.

Understanding the concepts has thus got far reaching implications in diagnosis, treatment planning and prognosis of malocclusion.

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Robert Meyers. Handbook of orthodontics Samir E. Bishara . Textbook of Orthodontics William R. Profitt .Contemporary orthodontics: fourth

edition Wheelers dental anatomy Woelfel , Scheid .Dental anatomy A.R. Ten Cate . Oral histology – development, structure

and function Berkovitz ,Holland and Moxham .Oral anatomy,histology,

embryology Ramfjord SP. Occlusion McLaughlin , Bennett and Trevisi – Systemized

orthodontic treatment mechanics

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Andrew L.F. The six keys to normal occlusion . Am J Orthod. Vol. 62; 1972: 296-302.

Samir E. Bishara .Changes in molar relationship between deciduous and permanent dentition – a longitudinal study. Am J Orthod. 1988; 93:19-28.

Lo RT , Moyers Re : Studies in the etiology and prevention of malocclusion . I. The sequence of eruption of the permanent dentition . Am J Orthod 1953 39 : 460-467

Fleming HB .An investigation of the vertical overbite during the eruption of the permanent dentition . Angle Orthod 1961;31:53-62

Functional occlusion for orthodontist . JCO 1981;jan 32-51

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Thank you