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COMPLETE DENTURE IMPRESSIONS
CONTENTS• INTRODUCTION• DEFINITIONS• LITERATURE REVIEW• MUCOUS MEMBRANE• BIOLOGIC CONSIDERATIONS FOR MAXILLARY IMPRESSIONS• BIOLOGIC CONSIDERATIONS FOR MANDIBULAR IMPRESSIONS• PRINCIPLES OF IMPRESSION MAKING• CLASSIFICATION OF IMPRESSIONS• IMPRESSION TECHNIQUES• IMPRESSION PROCEDURES• IMPRESSION TECHNIQUES IN COMPROMISED SITUATIONS• SUMMARY• BIBLIOGRAPHY.
INTRODUCTION
• Complete denture impression procedures are perhaps one phase on which much has been spoken about. The literature on the subject shows a persistent disagreement ever since 1850.
• Much of this confusion results from the fact that many impression procedures have been developed on empirical basis.
• Many have used the available knowledge of functional and histological anatomy for the development of their procedures, but the variation in these techniques indicate a wide difference in interpretation of the foundation of dentures.
• Whatever the method used it is generally agreed that good impressions are basic for the construction of a good denture.
“Ideal impression must be in the mind of the dentist before it is in his hand. He must literally make the impression rather than take it”
- M.M. Devan
DEFINITIONS
IMPRESSION A negative likeness or copy in reverse of the surface
of an object . – gpt 8
• An impression can also be defined as an imprint of the teeth and adjacent structures for use in dentistry. - gpt 4
• COMPLETE DENTURE IMPRESSION A complete denture impression is a negative registration of
the entire denture bearing, stabilizing and border seal areas present in the edentulous mouth
• PRELIMINARY IMPRESSION A preliminary impression is an impression made for the
purpose of diagnosis or for the construction of a tray
FINAL IMPRESSION: A final impression is an impression for making the
master cast .
IMPRESSION MATERIAL: Any substance or combination of substances used for
making an impression or negative reproduction. -gpt 8
LITERATURE REVIEW
• Before the middle of the 18th century, no method was available for producing an impression of the alveolar ridge. A widely used method at that time was the painting of the ridge with a dye , and the pressing of a block of ivory or bone against the dyed surfaces.
• Areas of contacts were scraped away from the block until the best fit for the prosthesis was achieved
• 1756 – beeswax was apparently first used in making impressions in the mouth.
Philip Pfaff(Berlin) made a sectional wax impression of half of an arch at a time.
• 1782 -William Rae said that “he got the measurement of the jaws in a piece of wax pushed into the gum, afterwards making a cast of it with plaster of paris”
• 1840 - Charles De loude (london) made one of the earliest refrences to impression trays . He wrote
“for impressions, I use wax in tin cups or shapes, the whole size of the upper and lower jaws, right or left, half jaws and fronts.”
• 1842- Montgomery discovered gutta percha. It was obtained from various sapotaceous trees in Malaysia. It was introduced as an impression material in 1848 by Colburn.
Colburn said it should be thoroughly soaked in boiling water,
kneaded and moulded in the same way as wax and …. immediately place in the mouth, and firmly pressed to the jaws.
• 1844- Plaster of paris• Wescott, Dwinelle and Dunning have been credited
with this discovery.
• 1847 - Desirabode referred to an impression tray as“ we place wax in a box, a kind of semi elliptical gutter
of tin or silver, upon the anterior part of which is a shaft which forms a handle. The walls of this receptacle offering some resistance, opposite the deformation of the wax”.
• 1862 Franklin described the first correct impression . He used
wax for the preliminary impression followed by a plaster wash.
• 1870 Wescott described a similar technique using oversized
wax trays made by scooping out primary impressions
• 1874 - Use of impression compounds dates from contributions of J.W.Greene, P.T.Greene and of Rubert Hall.
• The Greene brothers (about 1900) introduced a modeling plastic , a method to manipulate it , and a technique that is said to have been the first to utilize all the surfaces of a mouth to advantage for denture retention. They were probably the first to describe the closed mouth all modeling plastic technique in detail.
Furthermore, they were the first to use the word “ post dam” in describing posterior palatal seal.
• 1915 - Rupert hall , perfected the first moderate heat modeling plastic for making individual trays and introduced the correctable modeling plastic-plaster technique that became a standard method for making an impression.
• Hall used a specially prepared hard black modeling plastic for making a custom tray in which a very thin mix of impression plaster was placed for correction.
• 1922- Everett described an early wax technique around this time. He used fluid wax compound of three consistencies: hard, medium and soft.
He said “ in every way possible represents the three general tissues of the mouth on the bone”
• 1925- Alphous Poller (Vienna) described his elastic material for “molding articles of all kinds, more particularly, parts of a living body.
• He was most likely the first to suggest the use of agar for dental impressions.
• Booth, however, described complete denture impression technique using agar but found it necessary to build custom water cooled trays and to pre-medicate the patient with a drug to reduce salivation.
• During late 1920’s the idea became widely held that uniform tissue support may be of value. It was believed that this would be attained by controlled placement of soft tissues.
• During this period, the first true functional impression wax was developed. The waxes before this (beeswax and parafinn wax) were far from ideal because they were hard, flowed too slowly, or were crumbly.
• 1930 - According to Applegate a series of true physiologic waxes was developed by the cooperative effort of G.C.Bowles , S.G.Applegate and himself and was made availbale in 1935.
• Early 1930’sFirst real impetus in use of zinc oxide eugenol for
impression materials came From A.W.Ward and E.B.Kelly.
Ward’s preparation was intended more so for a surgical pack , but he also said that it could also be used as lining for dentures as an impression material .
Kelly’s preparation was primarily intended as an impression material
1938Harry.L.Page introduced the mucostatic concept.
The advocates of this concept such as Page, Albinson, Dykin and Addison thought the universally accepted concept involving compression of soft tissues and relief of the hard areas was in error because hydrostatics proved that human tissues was not amenable to either of this condition.
They believed that the impression should be an absolute accurate negative of the ridge tissues at rest.
• 1939 Dirksen reported the findings of his research in IOWA
which resulted in the development of still another physiologic impression wax. Over the years functional waxes have grown steadily in popularity and many clinicians have suggested methods for their use.– Applegate for immediate dentures– Mc. Cracken, borkin, and faber for mandibular
complete dentures – Hardy , ostrem and schultz for complete denture
reline procedures
• 1939 Trapozzano described one of the early techniques
using Zinc oxide eugenol paste. Compound preliminary impressions were made in stock trays and plaster of paris casts were poured. Vulcanite or shellac bases were constructed, on which occlusion rims of wax or compound were placed. After a tentative vertical and centric relation was established , the final corrective impression was made using closed mouth technique.
• 1942- Pendleton suggested a fluid wax technique using asiatic or indian paraffin fro the final mandibular impression
• Wright and Denen suggested using alginate in a border molded perforated customized acrylic tray.
• Collett described an alginate technique for the maxillary impression using the material as a wash in a modeling paste preliminary impression .
Middle 1950’sElastomeric impression materials were introduced.
They were of two chemical types.– Polysulfides– Silicone base
• Pierson in 1955 reported on a new elastic material of a polysulfide base (thiokol).
Shortly there after silicone base materials were introduced
elastomeric impression materials were intended primarily for making impressions for
• inlays • Crown • And for fixed partial dentures
• Chase in 1961 first described the moldable acrylic material used for tissue conditioning and for functional(dynamic) impression for complete dentures.
According to Emmett Beckley in 1973 , the first moldable acrylic material consisting of an ethyl methacrylate and an ethinol liquid was developed by Clark Smith and he (Beckley) performed the first practical research with this material in complete denture construction.
BIOLOGIC CONSIDERATIONS FOR MAXILLARY IMPRESSIONS
If dentures and their supporting tissues are to co-exist for reasonable length of time, the anatomy of the supporting and limiting structures must be understood for these are the foundations of the denture bearing areas, as their role determines :
1. the selective placement of forces by denture bases on supporting tissues
2. the form of the denture borders that will be harmonious with normal function of limiting structures around them.
The anatomical landmarks in the maxilla are:
• Limiting structures:
Labial frenumLabial vestibuleBuccal frenumBuccal vestibuleHamular notchPosterior palatal seal area
• Supporting Structures:
PRIMARY STRESS BEARING AREAS:-
• Hard palate• Postero- lateral slopes of residual alveolar
ridge.
SECONDARY STRESS BEARING AREAS:-
• Rugae• Maxillary tuberosity
• Alveolar tubercle.
Relief areas:
• Incisive papilla• Cuspid eminence• Mid- palatine raphe• Fovea palatina.
• SUPPORT FOR THE MAXILLARY DENTURE:
The ultimate support for
the maxillary denture is
the bone of the two
maxillae and the palatine
bone. The palatine
processes of the maxillae
are joined together at the
midline in the median
suture.
• RESIDUAL RIDGE:
The shape and size of the alveolar ridges change
when the natural teeth are removed. The alveoli
become mere holes in the jawbone and begin to fill
up with new bone, but at the same time the bone
around the margins of the tooth sockets begin to
shrink away. This shrinkage, or resorption, is rapid at
first, but it continues at a resorbed rate throughout
life.
Labial frenum The maxillary labial frenum
is a fold of mucous membrane at the median line.
No muscle attachment. This band of tissue starts
superiorly in a fan shape and converges as it descends to its terminal attachment on the labial side of ridge.
• Labial Vestibule: This anterior region of maxillary basal seat extends from one
buccal frenum to the other on the labial side. The major muscle in this area is orbicularis oris.
Three objectives are apparent:1. The impression must supply sufficient support to the upper lip
to restore the relaxed contour.2. The labial flange of the impression must have sufficient height
to reach the reflecting mucous membrane of the labial vestibular space.
3. There must be no interference of the labial flange with the action of lip in function.
• Buccal Frenum:
The buccal frenum is sometimes a single fold of
mucous membrane, sometimes double, and in some
mouths, broad and fan shaped.
Associated muscles are:
Buccinator
Orbicularis oris
Levator anguli oris
• Buccal Vestibule:
The buccal vestibule extends from the buccal frenum
to the hamular notch.
It is influenced by the buccinator and the modiolus.
And distally by the coronoid process.
• Hamular Notch: The hamular notch is a displaceable area about 2mm
wide , between the tuberosity of the maxilla and the hamulus of the pterygoid plate.
• Vibrating Line Of The Palate: This is an area at or distal to the junction of hard and
soft palate where movement occurs when patient says “ah”.
This generally is not a line and should be described rather as an area.
The area may also be identified by “Valsalva maneuver ” by asking the patient to close his nose using his fingers and asking him to blow gently through the nose .
• Posterior vibrating line that is 4-12mm or on an average is 8.2 mm dorsally to the hard and soft palate junction. In most instances the denture should end 1 or 2mm posterior to the vibratory line .
• Maxillary Tuberosity: The maxillary
tuberosities are the distal aspects of the posterior ridges.
BIOLOGIC CONSIDERATIONS FOR MANDIBULAR
IMPRESSIONS
The considerations for the mandibular impressions are generally similar to that for those of maxillary impressions and yet there are many differences owing to the following facts:– The basal seat of mandible is different in size and
form from the maxillary counterpart.– The submucosa in some parts of mandibular basal
seat contains anatomic structures different from those in the upper jaw.
– The nature of the supporting bone on the crest of residual ridge usually differs between the two jaws.
– The presence of the tongue complicates the impression procedures for the lower denture.
– The available area of support from an edentulous
mandible is 14 cm2 while the same for the
edentulous maxilla is 24cm2 .
– The supporting and the peripheral sealing areas
will be in contact with the dentures fitting or
impression areas. The support for the mandibular
denture is derived from the body of mandible.
• The landmarks can be broadly grouped into:Limiting structures:
• Labial frenum • Labial vestibule• Buccal frenum• Buccal vestibule• Lingual frenum• Alveololingual sulcus• Retromolar pads• Pterygomandibular raphe.
Supporting structures:
• Buccal shelf area• Residual alveolar ridge
Relief areas:
• Crest of the residual alveolar ridge• Mental foramen• Genial tubercles• Torus mandibularis.
Buccal shelf area• The area between the
mandibular buccal frenum and
the anterior edge of the
masseter is known as the buccal
shelf.
• It is bounded medially by the
crest of the residual ridge ,
anteriorly by the buccal
frenum , laterally by the
external oblique line and
distally by retromolar pad.
• The buccal shelf forms the primary support for the mandibular denture as it is made primarily of cortical type of bone.
• The buccal shelf area can range from 4-6 mm wide on an average mandible to 2-3 mm or less in narrow mandible.
• The buccal shelf is very wide and is at right angles to the vertical forces of occlusion. For this reason it
offers excellent resistance to such forces.
Crest Of The Mandibular Ridge• The crest is covered by the fibrous connective tissue,
but in many mouths the underlying bone is of cancellous type without a cortical bony plate covering .
• The fibrous connective tissue is favorable for resisting the externally applied forces,such as the denture. However, with the underlying cancellous bone this advantage is lost .
Labial Frenum:
• This is single narrow band but may consist of 2 or
more bands.
• The activity of this area tends to be vertical so the
labial notch on the denture should be narrow.
Buccal Frenum:
• This is usually in the area of 1st pre molar. The oral
activities in these area are horizontal as well as
vertical (ex. Grinning and puckering) thus needing
wider clearance.
• The contour of the denture will be little narrower in
this area due to the activity of depressor anguli oris
muscle.
Labial Vestibule:
• It is the sulcus between the buccal frenums.
• The major muscle in this area is orbicularis oris
whose fibers are mainly horizontal thus
overextension in this area should be avoided.
Buccal Vestibule:
• The buccal vestibule extends from the buccal frenum
posteriorly to the outside back corner of the
retromolar pad and from the crest of the residual
alveolar ridge to the cheek.
Pear Shaped Pad:
• The retromolar pad as
described by Sicher is
described as the soft elevation
of mucosa that lies distal to
the third molar.
• It contains loose connective
tissue with an aggregation of
mucous glands and is bounded
posteriorly by the temporalis
tendon , laterally by the
buccinator, and medially by
the pterygomandibular raphe
and the superior constrictor.
Lingual Vestibule:
• It can be divided into three areas
anterior vestibule/sublingual crescent area/ anterior
sublingual fold
the middle vestibule/ mylohyoid area
the distolingual vestibule/ lateral throat form/
retromylohyoid fossa
Anterior lingual vestibule
• This extends from the lingual frenum to where the
mylohyoid ridge curves down below the level of
sulcus. Here a depression the premylohyoid fossa can
be palpated.
• This is mainly influenced by the genioglossus muscle,
lingual frenum and some part by anterior portion of
sublingual glands .
Middle vestibule:
• This is the largest area and is mainly influenced by mylohyoid muscles and somewhat by sublingual glands.
• The mylohyoid muscle is the largest muscle in the floor of the mouth whose principal function occurs during swallowing. Its intra oral appearance is misleading because the membranous attachment makes the muscle appear to be horizontal when contracting.
• Nagel and sears have shown that at maximum contraction the fibers are still in a downward and forward direction so that a denture can be extended below the muscle attachment along the mylohyioid ridge.
• The lingual borders in the mylohyoid areas are formed by contact with the mylohyoid muscle in functional, but not extreme, contracted or elevated positions.
• The average mylohyoid border is 4-6 mm beyond the mylohyoid ridge in fair to good ridge it is about 2-3 mm . If the ridge is flat it is often advantageous to make mylohyoid border thicker (4-5mm or more).
Distolingual vestibule:
• The lateral throat form is bounded anteriorly by mylohyoid muscle, laterally by pear shaped pad, posterolaterally by superior constrictor, posteromedially by palatoglossus and medially by tongue.
• The so called “s” curve of the lingual flange of the mandibular denture results from stronger intrinsic and extrinsic tongue muscles, which usually place the retromylohyoid borders more laterally and towards the retromylohyoid fossa, as the oppose weaker superior constrictor muscle.
• The posterior limit of the mandibular denture is determined mainly by the palatoglossus muscle and somewhat by weaker superior constrictor muscle this is area is called posterior/ retromylohyoid curtain.
• Neil described this area and noted that the denture
could have three possible lengths, depending on the
tonicity, activity, and anatomic attachments of the
adjacent structures-
Class III lateral throat form has minimum length and
thickness. The border usually ends 2-3 mm below the
mylohyoid ridge or sometimes just at the ridge.
Class I throat form: The horizontal border is usually 2-3 mm thick, but a thicker border of 4-5 mm should be used for better seal if the ridge is flat. The retromylohyoid curtain area should be thinner, about 2-3 mm, and very rounded and smooth.
Class II throat form is about half as long and narrow as class I and about twice as long as class III.
BASIC REQUIREMENTS FOR IMPRESSION MAKING
• Knowledge of Basic anatomy• Knowledge of basic reliable technique• Knowledge and understanding of impression
materials • Skill• Patient management
72
OBJECTIVES OF IMPRESSION MAKING
1) RETENTION2) STABILITY3) SUPPORT4) ESTHETICS5) PRESERVATION OF REMAINING
STRUCTURES
RETENTION Retention is defined as that state of a denture wherein
functional forces are unable to destroy the attachment existing between the denture and the mucoperiosteum.
Retention resists the adhesiveness of food, the force of gravity, & the forces associated with the opening of jaws.
Retention begins with the impression. It depends upon factors that produce attachment of the denture to the mucosa.
74
Factors affecting Retention
Anatomical factors Physiological factors Physical factors Mechanical factors Muscular factors
75
Anatomical factors
Size of the denture bearing area
Quality of the denture bearing area.
Factors affecting Retention
76
Physiological factors
Saliva and its quality
Factors affecting Retention
77
Physical factors
Adhesion Cohesion Interfacial surface tension Capallarity and capillary attraction Atmospheric pressure and peripheral seal
Factors affecting Retention
Adhesion :- It is the physical attraction of unlike molecules • It acts when saliva sticks to the denture base & to
the mucous membrane of basal seat .
• Adhesion is achievied by ionic forces between charged salivary glycoproteins & surface epithelium or acrylic resin.
• Quality of adhesion depends on :-
Close adaption of denture
Size of denture bearing area Type of saliva
• The most adhesive saliva is thin serous but contains some mucous components.
• Thick & ropy saliva is very adhesive but tends to build up so that it is too thick in palatal area & interferes with oral adaptation .
• In this situation patient should rinse out the ropy saliva every two to three hours
• The amount of retention provided by adhesion is directly proportional to the area covered by denture.
• Mandibular dentures cover less surface area than maxillary prosthesis & therefore are subject to a lower magnitude of adhesive retentive forces.
• Similarly patients with small jaws or very flat alveolar ridges cannot expect retention to be as great as can patients with large jaws or prominent alveoli.
Cohesion:-it is the physical attraction of like molecules for each other .
• it occurs within the layer of fluid (usually saliva ) that is present between the denture base & the mucosa.
• Normal saliva is not very cohesive , therefore most of the retentive forces of denture –mucosa interface comes from adhesive & interfacial surface tension factors.
Interfacial surface tension :-it is the resistance to separation of two parallel surfaces that is imparted by a film of liquid between them .
• It is dependent on the ability of the fluid to wet the rigid surrounding material .
• If the surrounding material has low surface tension ,
as oral mucosa does ,fluid will maximize its contact
with the material, thereby wetting it readily &
spreading out in a thin film.
• If the material has high surface tension ,fluid will
minimize its contact with the material , resulting in
formation of beads on the material surface.
• All denture base material have higher surface tension than oral mucosa ,but once coated by salivary pellicle ,their surface tension is reduced ,which promotes maximizing the surface area between liquid & base.
• Role of surface tension is through capillary attraction or capillarity.
• When the adaptation of denture base to mucosa is sufficiently close ,the space filled with a thin film of saliva act like a capillary tube in that the liquid seeks to increase its contact with both denture & mucosal surface.
• It plays a major role in retention of maxillary denture. It is totally dependent on presence of air at the margin of liquid & solid contact (liquid air interface).
• As there is excess saliva along the lower border of mandibular denture, Surface tension is lost in mandibular denture due to loss of liquid air interface at denture border .
Mucostatics dismiss adhesion and cohesion as factors in retention, the entire phenomenon being attributed to interfacial surface tension.
But an analysis has proved that if it was not for the forces of adhesion and cohesion, the forces of interfacial surface tension wont exist. Attachment of a denture is possible because both tissue and denture base material can become wet which means its molecule will adhere to water molecules.
Oral & facial musculature :-supplement retentive forces , provided :-
a)Teeth are positioned in “neutral zone “between the cheeks & tongue
b)The polished surface of the denture are properly shaped.
• If the buccal flange of maxillary denture slope up & out of occlusal surface of teeth & the buccal flange of mandibular denture slope down & out from the occlusal plane, the contraction of buccinator will tend to retain both denture on basal seat.
Atmospheric pressure:-
• Act to resist dislodging forces applied to the denture ,if the denture have an effective seal around their borders.
• Retention due to atmospheric pressure is directly proportional to the area covered by the denture base.
In function, atmospheric pressure is superior to interfacial surface tension as a retentive force, for forces horizontal as well as parallel to the mean of mucosal plane are resisted.
Interfacial surface tension will resist only forces perpendicular to the axis of surface tension forces.
92
Factors affecting Retention
Mechanical factors
Undercuts Retentive springs Magnetic forces Denture adhesive Suction chambers and
suction discs
93
Muscular factors
The muscles apply supplementary retentive
forces on the denture.
It is most effective in the neutral zone.
Factors affecting Retention
94
STABILITY
The quality of a denture to be firm, steady, or constant, to resist displacement by functional stresses and not to be subject to change of position when force is applied. It is the ability of the denture to withstand horizontal forces.
95
Vertical height of the residual ridge.
Quality of soft tissue covering the ridge.
Occlusal plane
Quality of the impression.
Teeth arrangement.
Contour of the polished surfaces.
Factors Affecting Stability
SUPPORT
• It is the resistance to vertical forces of mastication & to occlusal or other forces applied in a direction toward the basal seat .
• When the natural teeth are missing ,the alveolar ridge & their covering of mucosal tissue become the supporting elements.
• Unfortunately , they were never meant to endure the forces of mastication & other constant occlusal pressure that result from swallowing , clenching ,or bruxing.
• To make the best of bad situation , it is necessary to enhance the available support by utilizing maximum coverage of all usable ridge bearing areas.
Areas of support are divided into:-
slight
pimary
secondary
Primary support area:- area of edentulous ridge that are at right angle to occlusal forces & usually do not resorb easily .
• Maxillary:- a)posterior ridge b)
flat areas of the palate
• Mandibular:- a)buccal shelf area b)Posterior ridge c)pear shaped pad
Secondary supporting area:- area of edentulous ridge that are greater than at right angle to occlusal forces ; also the area of dentulous ridge that are at right angle to occlusal forces but tend to resorb under load.
• Maxillary :- anterior ridge ,rugae & all ridge slopes
• Mandibular:- anterior ridge & all ridge slopes
101
ESTHETICS
The thickness of the denture flanges is one of the important factors that govern esthetics.
Thicker denture flanges are preferred in long-term edentulous patients to give required labial fullness.
Impression should perfectly reproduce the width and height of the entire sulcus for the proper fabrication of the flanges.
102
PRESERVATION OF REMAINING STRUCTURES
De Van (1952) stated that, “the preservation of that which remains is of utmost importance and not the meticulous replacement of that which has been lost.
Impressions should record the details of the basal seat and peripheral structures in an appropriate form to prevent injury to the oral tissues.
IMPRESSIONS
CLASSIFICATION
classification
Depending on the theories of impression
making.
Depending on the
technique
Depending on the tray
type
Depending on the purpose of the impression
Depending on the
material used
105
Depending on theories of impression making
Mucostatic
Mucocompressive
Selective pressure
106
Mucostatic or Passive Impression
First proposed by Richardson and later popularised by
Harry Page.
The impression is made with the oral mucous membrane
and the jaws in a normal, relaxed condition. Border
moulding is not done here.
The impression is made with an oversized tray.
Impression material of choice is impression plaster.
Retention is mainly due to interfacial surface tension.
The mucostatic technique results in a denture, which
is closely adapted to the mucosa of the denture-
bearing area but has poor peripheral seal.
108
Mucocompressive Impression (Carole Jones)
Records the oral tissues in a functional and displaced form. The materials used for this technique include impression compound, waxes and soft liners.
The oral soft tissues are resilient and thus tend to return to their anatomical position once the forces are relieved. Dentures made by this technique tend to get displaced due to the tissue rebound at rest. During function, the constant pressure exerted onto the soft tissues limit the blood circulation leading to residual ridge resorption.
109
Selective Pressure Impression (Boucher)
In this technique, the impression is made to extend over as much denture-bearing area as possible without interfering with the limiting structures at function and rest.
The selective pressure technique makes it possible to confine the forces acting on the denture to the stress-bearing areas. This is achieved through the design of the special tray in which the non stress-bearing areas are relieved and the stress-bearing areas are allowed to come in contact with the tray.
110
Depending on the technique
Open-mouth
Closed-mouth
Open mouth impressions
The open mouth impression is built in a tray which
carries the impression material of choice into the
desired contact with the supporting tissues and into an
approximate relation to the peripheral tissues when
the mouth is opened and without applied pressure.
The rationale behind this method is that the dentures
do not dislodge when subjected to biting force.
The open mouth methods provide clearance for the
tissues that are pulled over the edges of the dentures
as in function of speech.
It develops a contour of impression surface which is in
harmony with the relaxed supporting tissues, and
which may be out of perfect adaptation with these
tissues when the denture is subjected to occlusal
loading.
Closed mouth impression technique
These require wax occlusal rims to be fabricated on the preliminary cast .
The patient is made to close on these rims and a
generous clearance is made for the various frenula so that the patient can manipulate his tissues by closing, grimacing, sucking and swallowing to form peripheral borders.
114
Depending on the tray type
Stock tray
Custom tray
Type of tray
Some dentists use a stock tray and an impression
material such as alginate , impression plaster or
impression compound is used .However such
impressions are generally overextended and serve as
primary impressions.
Edentulous stock trays
TYPES OF TRAYS
CUSTOM MADESTOCK TRAYS
METTALIC NON-METTALIC
EDENTULOUS DENTULOUS1.DISPOSABLE2.REUSABLE
On casts made from these primary impressions,
special/custom trays are fabricated. The tray is tried
in the mouth and modified and the final impressions
are made using zinc oxide eugenol or other such
materials.
119
Depending on the purpose of the impression
Diagnostic
PrimarySecondary
120
Diagnostic Impression The negative replica of the oral tissues used to prepare a
diagnostic cast.
Used for study purposes like measuring the undercuts, locating
the path of insertion.
Is made as a part of treatment plan and to estimate the
amount of pre-prosthetic surgery.
Articulate the casts on tentative jaw relation and evaluate the
inter-arch space.
121
Primary Impression(PRELIMINARY IMPRESSION)
An impression made for the purpose of diagnosis or for the construction of a tray.
There should be at least 5mm clearance between the stock tray and the ridge.
The tray should extend over hamular notch and maxillary tuberosity. Mandibular tray should cover retromolar pad.
Tray can be extended using modelling wax.
Impression compound, Alginate, Impression plaster
122
Secondary Impression(WASH IMPRESSION)
Involve:
Fabriction of custom tray.
Border molding.
Developing the posterior palatal seal.
Making the wash impression.
123
Depending on the material used
Reversible hydrocolloid impression.
Irreversible hydrocolloid impression.
Modeling plastic impression.
Plaster impression.
Wax impression.
Silicone impression.
Thiokol rubber impression. (Polysulphide)
IMPRESSION TECHNIQUES
Impression techniques may be classified depending on:
a) Amount of pressure used1. Pressure technique2. Minimal pressure technique3. Selective pressure technique
b) Based on the position of the mouth while making impression
1. Open mouth 2. Close mouth
c) Based on the method of manipulation for border molding.
1. Hand manipulation2. Functional movements
Pressure theory or mucocompressive theory:
• This theory was proposed on the assumption that tissues recorded under functional pressure provided better support and retention for the denture.
• Greene in 1896 gave this concept
Primary impression made with impression compound
Special tray made using shellac base plate.
Second Impression is made in this tray using compound
Bite rims with uniform occlusal surfaces are then made.Areas to be relieved are softened and the impression is inserted in mouth and held under biting pressure for one or two minutes.
Borders are molded by asking the patient to perform functional movements.
Demerits of the theory
1. Excess pressure could lead to increase alveolar bone resorption.
2. Excess pressure was often applied to the peripheral tissues and the palate.
3. Dentures which fit well during mastication tend to rebound when the tissue resume their normal resting state.
4. Pressure on sharp bony ridges results in pain.
Applied aspects:
• The technique tells that border tissues are recorded in their functional positions and denture cannot be dislodged during functional movements of jaws.
• The pressure applied is more and directed towards the palate and peripheral tissues. So the retention will be for short time and will be lost as soon as the bone undergoes resorption.
• Usually this technique is used for preliminary impression making as it gives a positive peripheral seal and tissues are recorded in function. Amount of pressure applied is for short duration and the areas can be relieved during the final impression.
Minimal pressure or mucostatic theory –
The main advantage of this technique is its high regard for tissue health & preservation.
• 1946 Page gave the concept of mucostatic based on Pascal’s law.
Technique
• A compound impression is made.
• A baseplate wax space is adapted.
• A special tray is adapted over the wax spacer.
• Spacer is removed and an impression is made with a free flowing material with little pressure.
• Escape holes are made for relief.
Demerits
• The short denture borders are readily accessible to the tongue which might provoke irritation.
• The lack of border molding reduces effective peripheral seal.
• The short flanges may reduce support for the face.
• The shorter flanges prevent the wider distribution of masticatory stresses.
• The shorter flange would mean less lateral stability.
Applied aspect:
• The technique holds good in the sense it helps in preservation of tissue health.
• In practice with short flanges the oral musculature is non supported and stresses are not widely distributed.
• Food can slip beneath the denture and tongue can readily access the denture borders.
• This technique is useful in impressions of flabby and sharp or thin ridges.
Selective pressure theory
• Advocated by Boucher in 1950 it combines the principles of both pressure and minimal pressure technique.
• In this technique idea of tissue preservation is combined with mechanical factor of achieving retention, through minimum pressure which is within physiologic limits of tissue tolerance.
• This theory is based on a thorough understanding of the anatomy and physiology of basal seat and surrounding areas.
Demerits
• Some feel that It is impossible to record areas with varying pressure.
• Some areas still recorded under functional load, the dentures still faces the potential danger of rebounding and loosing retention.
Applied aspect:
• Inspite of some of its apparent drawbacks all the impression techniques based on the selective pressure technique are still popular.
• Final impressions using this technique are made where relief areas are provided and pressure is distributed on the stress bearing areas.
Open mouth technique
Made with tray held by dentist and mouth open
Muscle movements may be emphasized and can be seen by the operator
Closed mouth technique
The rationale behind this technique is that the supporting tissues are recorded in a functional relationship.
Requires occlusal rims to be made
Border molding done and final impressions made
Hand manipulation
Dentist uses hand manipulation for movements of lips and cheeks
Functional movements
Patient makes functional movements such as sucking, swallowing, licking or grinning
STEPS IN MAKING AN IMPRESSION
Preliminary examination of the patientSeating the patientSelection of the tray Selection of the materialMaking impression-primary border molding secondary
Preliminary examination of the patient
• A complete case history and thorough clinical examination is done.
• Factors that can complicate impression making are identified.
• Patient education.
Seating of the patientPosition of the operator for maxillary impression
Position of the operator for mandibular impression
Selection of tray:
• The beginning of good impression starts with the selection of the correct stock tray.
• Tray is a device that is used to carry, confine and control impression material while making an impression.
• The space available in the mouth for upper impression is studied carefully by observation of the width and height of the vestibular spaces with mouth partly open.
• And in the lower the general form and size of basal seat is studied.
IMPRESSION PROCEDURES• First technique:- border- molded special tray:
Preliminary impression:
An edentulous stock metal tray that is approximately 6mm larger than the outside surface of the residual ridge is selected.
The borders of the stock tray are lined with a strip of soft boxing wax so a rim is created to help confine the alginate material.
The objective is to obtain a preliminary impression that is slightly overextended around the borders.
The tissue surface and borders of the tray, including the rim of wax, are painted with an adhesive material.
The loaded tray is positioned in the mouth.
The tray is left in the mouth for 1 minute after the initial set. The impression is removed and inspected to ensure all basal seat is included.
The impression is poured in artificial stone.
Primary impression making
• With alginate (Maxillary)
(Mandibular impression with alginate)
A wax spacer is placed within the outlined border to provide space in the tray for final impression material.
A custom tray made using self- curing acrylic resin.
• Preparing the final impression tray: Border molding is the process by which the shape of
the borders of the tray is made to conform accurately to the contours of the buccal and labial vestibules.
It begins with manipulation of the border tissues against a moldable impression material that is properly supported and controlled by tray.
Border molding
Mandibular border molding
Stick modeling compound is added in sections to the shortened borders of the resin tray and molded to a form that will be in harmony with the physiologic action of the limiting anatomic structures.
The final impression material is mixed according to manufacturer’s directions and uniformly distributed within the tray.
Secondary impression
Mandibular secondary impression
• Second technique:- one- step border- molded tray:
• A material that will allow simultaneous molding of all borders has two general advantages:
1. The number of insertions of the tray for maxillary and mandibular border molding is reduced.
2. Developing all borders simultaneously avoids propagation of errors caused by a mistake in one section affecting the border contours in another.
• The requirements of such a material are that it should:
1. Have sufficient body to allow it to remain in position on the borders during loading of the tray.
2. Allow some preshaping of the form of the borders without adhering to the fingers.
3. Have a setting time of 3 to 5 min4. Retain adequate flow while the tray is seated in the
mouth 5. Allow finger placement of the material into
deficient parts after the tray is seated
• Not cause excessive displacement of the tissues of the vestibule.
• Be readily trimmed & shaped so excess material can be carved & the borders shaped before the final impression is made.
• The following procedure utilizes polyether impression materials for border molding.
1. Place adhesive for polyether impressions on the borders of tray.
2. Express a 3- inch strip of polyether material from large tube onto a mixing pad. Next express 2.5 inches of catalyst to provide sufficient working time to complete border molding.
3. Thoroughly mix material for 30 to 45 seconds using a metal spatula.
4. Position the polyether material on the borders, making certain that a minimum width of 6 mm exists on inner portion.
5. Quickly preshape material to proper contours with fingers moistened in cold water
6. Place the impression tray in the mouth .
7. Inspect all borders to be sure that impression material is present in the vestibule
8. Border molding is done
9. Remove tray when impression material is set.
10. Examine border molding to determine that it is adequate.
• Preparing the tray to secure the final impression:
1. Reduce the borders on the tray that protrude through the polyether.
2. Remove any material that extends internally within the tray more than 6mm.
3. Remove the relief wax.4. Reduce the thickness of labial flange to
approximately 2.5 to 3mm from one buccal frenum to another.
5. Make the final impression in silicone, metallic oxide paste, or rubber base.
• Third technique:- custom tray design based on previously worn denture:
1. The denture is treated like a standard impression, and a stone cast is poured.
2. An acrylic resin tray is made on the cast over a wax spacer that is outlined just short of the borders of the impression.
3. The tray is tried in the mouth and checked for overextensions.
4. The spacer is removed, relief holes prepared, an adhesive is applied and an impression is made in the preferred material.
Impression techniques in compromised/special situations
• Techniques are modified in compromised situations to achieve as much retention and stability as possible within limits. 1. Hyper active gag reflex2. Restricted mouth opening3. Severely resorbed mandibular ridge4. Hypermobile / hyperplastic ridges
5. Reline impressions 6. Fibrous mandibular ridge that has not been
employed for support
• 7. Flat lower ridge with atrophic mucosa• 8. Functional ,e.g. denture space(neutral zone)
and functional reline impression• 9. Replica/Template impression technique
Hyperactive gag reflex
• Patients problems should be identified before impression is made.a) Prosthodontic management
- Avoid thick or over extended trays.- Avoid excess loading of material- Use a fast setting material- Singer’s marble technique can be followed
b) Distraction maneuvers- Engage the patient in conversation of some special interest.- ask the patient to concentrate on one foot or to raise it.
c) Pharmacologic measures- Local anaesthetics - Antihistamines, Sedatives, CNS depressants
d) Psychological intervention - Hypnosis helpful in certain cases
Restricted mouth opening
• Patient’s may exhibit limited opening of the mouth following radical surgery or a sequel facial burns, or due to other pathological conditions.
• Impressions with the use of sectional trays are made.
Severely resorbed mandibular ridge
• Lack of ideal amount of supporting structures decreases support and
encroachment of the surrounding mobile tissues onto the denture
border reduces both stability and retention. The main is to gain
maximum area of coverage.
• Flange technique by Lott & Levin involves making impressions of the
soft structures of the mouth adjacent to the buccal, lingual and
palatal surfaces and incorporating the resulting extension or flange
into the denture.
• Tryde used the dynamic impression method.
• McCord and Tyson in 1997 gave the admixed technique.
Admixed material is used to make the impression of a highly resorbed mandibular ridge
Hypermobile or hyperplastic ridges
• These ridges should be recorded without distortion.
Selective displacive technique. Window technique
SELECTIVE DISPLACIVE TECHNIQUE
• This techniques aims to displace but not distort the flabby ridge as if in function. A primary impression is taken in a mucostatic impression material (e.g. impression plaster or alginate) and cast in stone. A spaced special tray for an impression compound impression is then constructed on this model. The tray is loaded with compound and an impression taken of the model of the patient's mouth. This reduces the risk of displacing the flabby ridge. The tray is then warmed and placed in the patient's mouth. It is adapted and border moulded to the tissues, and should be quite retentive. The impression is removed and warmed all over apart from the flabby ridge area. The impression is retaken, the flabby ridge is compressed but not distorted as the other portions of the impression compound sink into the tissues. The impression is removed inspected and re-tried in the mouth to check that it is stable. If any instability occurs then the impression should be reheated and re-taken. A wash impression may be taken in impression paste to obtain maximum detail and retention and stability.
WINDOW TECHNIQUE
• A primary impression is taken in alginate loaded in a stock tray. The impression is then poured and a special tray is constructed on the model. The special tray is close fitting and has a hole or "window" over the area corresponding to the flabby ridge. An impression is taken in impression paste (mucodisplacive). Once this has set it is left in place and impression plaster (mucostatic) is painted over the flabby ridge and allowed to set and removed as one impression. The impression is removed as one, cast and the denture constructed on the resulting model
• After cutting the window the light bodied elastomeric impression material can be injected thru the window onto the flabby tissues and let it set ,once set it can be taken off as one single impression.
Fibrous (unemployed) posterior mandibular ridge
• Jaggers, Shay and Khan : Impressions of unsupported movable tissues; JADA october 1981, 103; 590-592
• In conditions where patients have worn maxillary complete denture opposed only by mandibular anterior teeth.
COMBINATION SYNDROME
• KELLY (1972) introduced the term
“Combination Syndrome”
• The remaining soft tissues in the anterior maxillary region are easily distorted by routine impression procedures, resulting in an unstable denture base.
• Surgical reduction of the pliable tissues often results in the loss of the anterior mucobuccal fold area.
this may cause retention problems
• To avoid these problems, a technique that minimises distortion when impressions of edentulous arches with unsupported, moveable tissues are made is used.
PROCEDURE
• A primary impression is made and a cast is poured.
• An indelible pencil is used to outline the unsupported movable tissue.
• A single custom tray is made, and an opening is cut in the tray as indicated by the transfer of indelible pencil line.
• Modelling plastic is adapted bilaterally on the posterior aspect of the tray to act as handles.
• The tray is adjusted in the mouth, and a routine border molding is formed.
• The tray is painted with an adhesive and a regular body impression is made.
• The excess material is trimmed to the outline of the aperture
• The completed base impression is returned to the mouth.
• This impression does not touch the unsupported tissues.
• Then a highly mucostatic impression material, impression plaster is brushed on the unsupported movable tissue.
• The initial layer precludes entrapment of air and enables visualisation of the unsupported tissue.
• A separating media is applied to the impression plaster and the master cast is made
AN IMPRESSION PROCEDURE FOR THE SEVERELY ATROPHIED MANDIBLE : JPD 1995 ; 73(6); 574-577
• The objective is to maximize the supportive aspect of the available denture foundation by two approaches
- Functional
- Anatomic
• Peripheral borders are developed functionally with the mouth closed
• The final phase of impression is made with the mouth open to satisfy the anatomic approach
PROCEDURE
• A maxillary final impression is made and cast is poured
• Construct a record base for the maxillary cast and develop a flat wax occlusal rim.
• Make a preliminary impression of the mandible and make a lower tray to be used initially as a record base with a flat wax occlusion rim.
• Make a jaw registration at a selected vertical dimension of occlusion.
• Develop the border extensions with tissue conditioning material.
• Develop the lingual borders with the mouth open and have the patient make essential tongue movements.
• Also instruct the patient to border mold the material physiologically by producing “ooo” and “eee” sounds while biting on the occlusal rim.
• Repeat the step as often as necessary to develop proper extension.
• Relieve the tray wherever it shows through the conditioning material before each subsequent addition.
• Remove overextensions with a hot knife blade.
• Leave each application of conditioning material in the mouth approx. 10 minutes to allow it to stabilize.
• After the desired extensions are formed with the conditioning material, make the final second impression with a polysulfide rubber impression material with the mouth open and use standard border molding procedures.
• Pour the cast immediately to avoid distortion of the material.
• This procedure will provide the patient with a denture that has function with maximum support and stability.
• The greatest disadvantage of this procedure is the amount of the time necessary to develop the final impression. The average appointment time needed is 45-60 mins.
Developing the base with mouth temperature wax
• A preliminary functional impression tray with wax occlusion rims is made with an opposing occlusion rim or denture.
• The tray trimmed to relieve functioning muscle impingements.
• A closed mouth impression with mouth temperature wax is made to establish maximum coverage within tissue tolerance.
• The IOWA wax is prepared in a container in a hot water bath and is applied to the tray with a soft brush. (firm contact produces glossy surface)
• After full ridge tissue contact is made, wax is applied to the borders and is adapted to the functioning musculature to develop the border and flanges of impression tray.
• Essential actions :
- Protrusion and retrusion of the lips for the facial musculature (“proo-wiss”)
- Moving the mandible laterally and protrusively to record coronoid process of mandible
- Placing the tongue alternatively into the cheeks and by wiping the lips by the tongue to develop lingual and retromylohyoid flange of mandibular tray
• The impression is allowed to remain in the mouth and allowed to remain for 8 to 12 minutes to permit as close adaptation of the wax to all surfaces as possible.
• During this period, the patient periodically performs the approppriate muscle functions. And then ice-cold water is poured into the mouth to chill the wax, and the impression is carefully removed.
• Impression is boxed by plaster and pumice and cast is poured.
• Separating media is applied on the cast and after the separating media has dried, an autopolymerising soft resilient liner is applied to the undercuts.
• Spacer is applied and a resin tray is fabricated
• When the tray resin has set, the bottom side of the cast is reduced on a cast trimmer just short of contact with the tray material.
• The cast with tray is placed in hot water to soften the wax shim and the cast is fractured with a hammer to permit recovery of the tray without damage
• Wax spacer is removed, and excess resin is removed from the tray.
• The final impression material, metallic oxide paste is mixed according to manufacturer’s directions and loaded into the tray.
• Impression material is wiped along all the flanges of the impression tray in contact with functioning musculature.
• The patient is instructed to perform the previously described muscular movements while the impression material is developing its body.
• The tray is removed from the mouth after the material has set and the impression is inspected.
• This technique permits the harnessing and stabilizing effects of an active musculature to operate on the ultimate denture base.
• The musculature imparts properties of retention and stability to the base that will tend to provide the greatest longevity for the residual alveolar ridge.
SUMMARY
• Most of the difficulties encountered when making impressions can be traced to the operator’s lack of attention to details of technique, and especially the acceptance of a poor stock tray impression.
• It is of extreme importance that the preliminary impression records the entire possible denture-bearing surface but, at the same time, does not encroach on movable muscular tissues.
CONCLUSION
• PRESERVATION OF WHAT REMAINS RATHER THAN METICULOUS REPLACEMENT OF WHAT IS MISSING
………………………the journey of a thousand miles begins with one step
BIBLIOGRAPHY• Impressions for complete dentures- Bernard Levin
• Boucher’s prosthodontic treatment for edentulous patients- 10th edition.
• Appelbaum and Rivetti : Wax base development for complete denture impressions; JPD; may 1985; 53(5); 663-666
• Richard P Frank: Controlling pressures during complete denture impressions.; Dental Clinics of North America- Vol 14, No.3 (July, 1970)
• Evaluation of factors necessary to develop stability in mandibular dentures: J Pros. Dent May- June, 1966.
• DeFranco and Sallustio : An impression procedure for the severely atrophied mandible; JPD; june 1995; 73(6); 574-577
• Jaggers, Shay and Khan : Impressions of unsupported movable tissues; JADA october 1981, 103; 590-592
• M.M. Devan – Basic principles of impression making. JPD 1952, Vol-2.
• Chastain and Porter – “Mucostatics” – Panacea or Propoganda – JPD, 1953; Vol-3.
• George A. Buckley – Diagnostic factors in the choice of impression material and methods. JPD, 1955 Vol-5.
• Henry A. Collett – Complete denture impressions. JPD 1965; Vol-15.
• Iwao Hayakawa, Ikki Watanabe - Impressions for complete denture using new silicone impression materials Quintessence Int. 2003;34.
• A.M Sofou,Mordohai,Pissoti – Fabrication of a custom made impression tray for making preliminary impression of edentulous mandible. Quintessence Int.1998;VOL-29
• Tryde,Kaisa olsson,A.A Jensen – Dynamic impression methods.JPD 1965;VOL-16
• Jacobson TE, Kroll. A contemporary review of the factors involved in CD retention,stability and support.JPD 1983;49:5-15;165-172
• Basker RM,Ogden Complete denture prescription—BrDent J 1993;174:278-84
• Treatment of edentulous patients—J.F.McCord,Philip,Nicholas Grey
• Impression making –BDJ 2000 MAY 13,188(9):484-491• I.H.Ansari duplicating an existing complete denture to
make a replica.JPD oct 1994;72(4):445-47• Manoli SG Duplicate denture technique JPD 1969;21:104-
107• McCord JF,Tyson K.W. A conservative prosthodontic option
for the treatment of edentulous patients with atrophic mandibular ridges. BDJ 1997; 182:469-72
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“Good Impressions Last Forever”
