COMPLETE DENTURE IMPRESSIONS

COMPLETE DENTURE IMPRESSIONSGuided byDr. A.S.KaulProfessor and H.O.D dept. of prosthodonticsK.D.D.C

Presented by:Niti Malik14/10/09

CONTENTSINTRODUCTIONDEFINITIONSLITERATURE REVIEWMUCOUS MEMBRANEBIOLOGIC CONSIDERATIONS FOR MAXILLARY IMPRESSIONSBIOLOGIC CONSIDERATIONS FOR MANDIBULAR IMPRESSIONSPRINCIPLES OF IMPRESSION MAKINGCLASSIFICATION OF IMPRESSIONSIMPRESSION TECHNIQUESIMPRESSION PROCEDURESIMPRESSION TECHNIQUES IN COMPROMISED SITUATIONSSUMMARYBIBLIOGRAPHY.

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 parisWescott, 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 1920s 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 1930sFirst real impetus in use of zinc oxide eugenol for impression materials came From A.W.Ward and E.B.Kelly.

Wards 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 .Kellys 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 denturesMc. 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 1950sElastomeric impression materials were introduced. They were of two chemical types.PolysulfidesSilicone 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 forinlays 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

MUCOUS MEMBRANEThe 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 submucosa is formed by connective tissue. It may contain glandular , fat , or muscle cells and transmits the blood and nerve supply to mucosa.

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

BONEPERIOSTEUM

SUBMUCOSA

MUCOSA

The masticatory mucosa covers the crest of the ridge the residual attached gingiva firmly adherent to the supporting bonehard palate. It is characterized by a well defined keratinized layer on its outermost surface subject to changes in thickness.

The specialized mucosa covers the dorsal surface of the tongue. This mucosal covering is keratinized.

The lining mucosa is generally devoid of the keratinized layer. It is found to cover the :mucous membrane of lips, cheekvestibular spaces alveolingual sulcussoft palate ventral surface of the tongue and,the unattached gingiva found on slopes of residual ridge.

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 palatePostero- lateral slopes of residual alveolar ridge.SECONDARY STRESS BEARING AREAS:-RugaeMaxillary tuberosityAlveolar tubercle.

Relief areas:

Incisive papillaCuspid eminenceMid- palatine rapheFovea 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 frenumThe 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: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.

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 vestibuleBuccal frenumBuccal vestibuleLingual frenumAlveololingual sulcusRetromolar padsPterygomandibular raphe.

Supporting structures:

Buccal shelf areaResidual alveolar ridge

Relief areas:

Crest of the residual alveolar ridgeMental foramenGenial tuberclesTorus mandibularis.

Buccal shelf areaThe 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 RidgeThe 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 foldthe middle vestibule/ mylohyoid areathe 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 MAKINGKnowledge of Basic anatomyKnowledge of basic reliable techniqueKnowledge and understanding of impression materials SkillPatient management

79OBJECTIVES OF IMPRESSION MAKINGRETENTIONSTABILITYSUPPORTESTHETICSPRESERVATION 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.

81Factors affecting RetentionAnatomical factors Physiological factors Physical factors Mechanical factors Muscular factors

82Anatomical factors

Size of the denture bearing area

Quality of the denture bearing area.Factors affecting Retention

83Physiological factors

Saliva and its qualityFactors affecting Retention

84Physical factors

AdhesionCohesionInterfacial surface tensionCapallarity and capillary attractionAtmospheric 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 :-

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 & tongueb)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.

96

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.

Factors affecting RetentionMechanical factors

UndercutsRetentive springsMagnetic forcesDenture adhesiveSuction chambers and suction discs99

100Muscular factorsThe muscles apply supplementary retentive forces on the denture.It is most effective in the neutral zone. Factors affecting Retention

101STABILITYThe 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.

102Vertical height of the residual ridge.Quality of soft tissue covering the ridge.Occlusal planeQuality 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.

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Areas of support are divided into:-

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

108ESTHETICSThe 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.

109PRESERVATION OF REMAINING STRUCTURESDe 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

112Depending on theories of impression makingMucostatic

Mucocompressive

Selective pressure

113Mucostatic or Passive ImpressionFirst 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.

115Mucocompressive 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.

116Selective 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.

117Depending 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.

121Depending on the tray type

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

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.

125Depending on the purpose of the impression

126Diagnostic ImpressionThe 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.

127Primary 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

128Secondary Impression(WASH IMPRESSION)Involve:

Fabriction of custom tray.

Border molding.

Developing the posterior palatal seal.

Making the wash impression.

129Depending on the material used

IMPRESSION TECHNIQUES

Impression techniques may be classified depending on:

Amount of pressure used1. Pressure technique2. Minimal pressure technique3. Selective pressure techniqueBased on the position of the mouth while making impression1. Open mouth 2. Close mouth 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 theoryExcess 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 Pascals law.

TechniqueA 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.

DemeritsThe 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 theoryAdvocated 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 techniqueMade with tray held by dentist and mouth open

Muscle movements may be emphasized and can be seen by the operator

Closed mouth techniqueThe 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 manipulationDentist uses hand manipulation for movements of lips and cheeksFunctional movementsPatient makes functional movements such as sucking, swallowing, licking or grinning

STEPS IN MAKING AN IMPRESSIONPreliminary examination of the patientSeating the patientSelection of the tray Selection of the materialMaking impression-primary border molding secondary

Preliminary examination of the patientA 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.

IMPRESSION PROCEDURESFirst 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 makingWith 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 manufacturers 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:

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 minRetain 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 buccal frenum 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

IMPRESSION PROCEDURE FOR THE SEVERELY ATROPHIED MANDIBLE

WAX BASE DEVELOPMENT FOR COMPLETE DENTURE IMPRESSIONSIMPRESSIONS OF UNSUPPORTED MOVABLE TISSUES

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.

PROCEDUREA 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

PROCEDUREA 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.

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 waxA 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 manufacturers 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.

SUMMARYMost of the difficulties encountered when making impressions can be traced to the operators 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.

BIBLIOGRAPHYImpressions for complete dentures- Bernard Levin

Bouchers 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