COMPLETE DENTURE IMPRESSIONS Guided by Dr. A.S.Kaul Professor and H.O.D dept. of prosthodontics K.D.D.C Presented by: NitiMalik 14/10/09
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 likenessor 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- Montgomerydiscovered guttapercha. 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 Dunninghave been credited with this discovery. 1847 - Desirabodereferred 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- AlphousPoller (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 availbalein 1935.
Early 1930’s First 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
1938 Harry.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 Trapozzanodescribed 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 Denensuggested using alginate in a border molded perforated customized acrylic tray. Collettdescribed an alginate technique for the maxillary impression using the material as a wash in a modeling paste preliminary impression .
Middle 1950’s Elastomeric 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.
MUCOUS MEMBRANE The bones of the upper and lower edentulous jaws are covered with soft tissue, and the oral cavity is lined with soft tissue known as mucous membrane. The denture bases rest on the mucous membrane, which serves as a cushion between the bases and the supporting bone.
The mucous membrane is composed of two layers Mucosa Submucosa The mucosa is formed by the stratified squamous epithelium and a subjacent layer of connective tissue known as the lamina propria.
The thickness and consistency of submucosa are largely responsible for the support that the soft tissue affords the denture, since in most instances the submucosa makes up the bulk of the mucous membrane.
In a healthy mouth the submucosa is firmly attached to the periosteum of the underlying bone of the residual ridge and will usually successfully withstand the pressure of the denture.
HISTOLOGY OF THE MUCOUS MEMBRANE COVERING CREST OF THE RESIDUAL RIDGE BONE PERIOSTEUM SUBMUCOSA MUCOSA
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.
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.
The impression must supply sufficient support to the upper lip to restore the relaxed contour. The labial flange of the impression must have sufficient height to reach the reflecting mucous membrane of the labial vestibular space. There must be no interference of the labial flange with the action of lip in function.
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.
Crest of the residual alveolar ridge Mental foramen Genial tubercles Torus mandibularis.
Buccal shelf area The area between the mandibularbuccalfrenum 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 buccalfrenum , 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.
BuccalFrenum: 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 angulioris muscle.
Labial Vestibule: It is the sulcus between the buccalfrenums. The major muscle in this area is orbicularisoris whose fibers are mainly horizontal thus overextension in this area should be avoided.
Buccal Vestibule: The buccal vestibule extends from the buccalfrenumposteriorly 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 pterygomandibularraphe and the superior constrictor.
Lingual Vestibule: It can be divided into three areas
the distolingual vestibule/ lateral throat form/ retromylohyoidfossa
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 premylohyoidfossa 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 retromylohyoidfossa, 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
79 OBJECTIVES OF IMPRESSION MAKING RETENTION STABILITY SUPPORT ESTHETICS PRESERVATION OF REMAINING STRUCTURES
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 :-
The most adhesive saliva is thin serous but contains some mucous components. Thick & ropy salivais 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.
101 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.
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 coverageof all usable ridge bearing areas.
Primary support area:- area of edentulous ridge that are at right angle to occlusal forces & usually do not resorb easily .
a)posterior ridge b) flat areas of the palate
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
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.
109 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.
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.
115 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.
116 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.
117 Depending on the technique
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.
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.
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.
125 Depending on the purpose of the impression
Impression techniques may be classified depending on: Amount of pressure used 1. Pressure technique 2. Minimal pressure technique 3. Selective pressure technique Based on the position of the mouth while making impression 1. Open mouth 2. Close mouth Based on the method of manipulation for border molding. 1. Hand manipulation 2. 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 Excess pressure could lead to increase alveolar bone resorption. Excess pressure was often applied to the peripheral tissues and the palate. Dentures which fit well during mastication tend to rebound when the tissue resume their normal resting state. 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 patient Seating the patient Selection of the tray Selection of the material Making 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 patient Position 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.
Second technique:- one- step border- molded tray: A material that will allow simultaneous molding of all borders has two general advantages: The number of insertions of the tray for maxillary and mandibular border molding is reduced. 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: Have sufficient body to allow it to remain in position on the borders during loading of the tray. Allow some preshaping of the form of the borders without adhering to the fingers. Have a setting time of 3 to 5 min Retain adequate flow while the tray is seated in the mouth 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. Place adhesive for polyether impressions on the borders of tray. 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. 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: Reduce the borders on the tray that protrude through the polyether. Remove any material that extends internally within the tray more than 6mm. Remove the relief wax. Reduce the thickness of labial flange to approximately 2.5 to 3mm from one buccalfrenum to another. Make the final impression in silicone, metallic oxide paste, or rubber base.
Third technique:- custom tray design based on previously worn denture: The denture is treated like a standard impression, and a stone cast is poured. An acrylic resin tray is made on the cast over a wax spacer that is outlined just short of the borders of the impression. The tray is tried in the mouth and checked for overextensions. The spacer is removed, relief holes prepared, an adhesive is applied and an impression is made in the preferred material.
SPECIAL IMPRESSION TECHNIQUES IMPRESSIONS OF UNSUPPORTED MOVABLE TISSUES IMPRESSION PROCEDURE FOR THE SEVERELY ATROPHIED MANDIBLE WAX BASE DEVELOPMENT FOR COMPLETE DENTURE IMPRESSIONS
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
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 occlusalrim.
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.
Appelbaum and Rivetti : WAX BASE DEVELOPMENT FOR COMPLETE DENTURE IMPRESSIONS; JPD; may 1985; 53(5); 663-666
The objective of the denture base development is the retention and stability. The retention enhancing potential of the border seal and the effect of properly contoured and polished surfaces against a functioning musculature must be recognised.
Denture base retention is maintained by a constantly changing interplay between the physical and physiologic forces during speech, mastication, and deglutition. The physiologic forces are mainly muscular and are exerted by the lips, cheeks, and tongue. And the physical forces include cohesion, adhesion, and interfacial surface tension, which operate in the film of saliva between the denture and the tissues.
Three objectives of base development to secure optimum retention and stability must be attained : 1) The impression procedure and material of choice should permit the detailed reproduction of healthy mucosa and ridge bearing tissue at rest to secure optimum retention by interfacial surface tension acting on the base through the medium of saliva.
2) The base should be extended to, but not encroach on, functional muscle attachments to permit greater distribution of masticatory stresses and a greater surface for the development of interfacial surface tension, which leads to the production of the border seal.
3) The base should be adapted to the musculature of the oral cavity to secure active and passive muscular fixation of denture base, because the importance of muscle activity may transcend all other factors responsible for denture retention. The most important muscle in this regard are the buccinator, orbicularis oris, and intrinsic and extrinsic muscles of the tongue.
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.
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.
BIBLIOGRAPHY Impressions for complete dentures- Bernard Levin Boucher’s prosthodontic treatment for edentulous patients- 10th edition. Appelbaumand 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