techniques of impression making in complete dentures/ orthodontics courses online

Impression techniques in complete dentures.INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.comwww.indiandentalacademy.com

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Table of contentsIntroduction DefinitionshistoryReview of literaturePrinciples of impression makingTheories of impression making



Impression techniques.-muco compressive technique .-muco static technique.-Selective pressure technique.Preliminary impressions.Fabrication of custom tray.Border molding.Secondary impressions. www.indiandentalacademy.com


Specialized impression techniques.Summary ConclusionsReferences



Introduction.The impression appointment is the most important to the dentist and the patient for several reasons. It is usually the first prolonged appointment following the examination and consultation with the patient. Good impressions are basic to the needs of the contended denture wearer.www.indiandentalacademy.com


The impression problem would not be a problem if we take the impressions of the casts. The problem is due to the fact that the mouth is lined by the displaceable tissue which varies in degree of displacibility. www.indiandentalacademy.com


In view of these facts , it is reasonable to say that the ideal impression must be in the mind of the dentist before it is in his hand. He must literally make impression rather than take it. The kind of impression he will make depends on the factors which we shall presently consider. www.indiandentalacademy.com


Definitions:-

Impression:-A negative likeness or copy in reverse of an object ; an imprint of the teeth and the adjacent structures for use in dentistry.-GPT7.A complete denture impression is negetive registration of the entire denture bearing, stabilizing and border seal areas present in edentulous mouth (Heartwell)



Impression Area:-The surface recorded in an impression.-GPT7www.indiandentalacademy.com


Impression Surface:-The portion of the denture surface that has its contour determined by the impression.-GPT7Impression tray:- GPT7

1.A receptacle into which suitable impression material is placed to make the negative likeness.www.indiandentalacademy.com


2.a device used to carry , confine &control impression material while making an impression.

Preliminary impressions:-a negative likeness made for the purpose of diagnosis, treatment planning, or fabrication of the tray .GPT7



Preliminary impression is an impression made for the purpose of diagnosis or for the construction of the tray. (Heartwell).www.indiandentalacademy.com


1.the shaping of the border areas of the impression tray by functional or manual manipulation of the tissue adjacent to the borders to duplicate the contour and size of the vestibule.Border molding:-GPT7



2.determining the extension of the prosthesis by using tissue function or manual manipulation of the tissues to shape the border areas of the impression material.



Final impressions: a impression that represents the completion of the registration of the surface or the object.GPT7 A final impression is a impression for making master casts. (heartwell).



History of impressions.1600- Prior to 1600 no complete dentures were made due to lack of understanding of retention. Replacements were made only when the posterior abutments were present.1711- Mathew Gottfried Purman recorded impression using wax.



1728: Pierre Fauchard made dentures mesuring with compass and cutting bone into an appropriate shape to be filled. 1845-1899

1848: Westcott, Dwinelle, Dunning introduced guttapercha. It was used as a impression material. 1884: Plaster of paris was first used as impression material.Charles Stent introduced Impression compound



many changes became evident in this era. Till then only one impressions deemed sufficient. It advanced to a method using preliminary impressions.This was followed by secondory wash impression made of plaster within preliminary impression.www.indiandentalacademy.com


1900: Closed mouth impression procedure was introduced.1900-1929: Several basic principles of making impressions were introduced. Advances in accuracy of impression technique and increase in the method of border molding and obtaining peripheral seal were among the major advances



Green brothers introduced moco-compressive impression technique.Tyrde et al.,advocated the use of closed mouth technique.1930-1950: several impression materials were introduced such as reversible hydrocolloid ,zinc oxide and oil of cloves.www.indiandentalacademy.com


1944: Addison described mucostatic impression and attributed to Page.1950-1964: During this era there was increased emphasis on biological factors of complete dentures.Boucher proposed selective pressure technique in1951.www.indiandentalacademy.com


1965-1980: newer techniques have been developed to manage poor mandibular ridges.

Tyrde and Robert introduced sublingual flange technique .Lott and Levin introduced flange technique.www.indiandentalacademy.com


Review of literature:1. Charles H. Moses (1953): physical considerations in impression making. JPD 1953:3(4);449-62)He states that :there must be no displacement of tissues in so far as possible to avoid it.



physical considerations in impression making. JPD 1953:3(4);449-62)complete denture impressions .JPD1965:15;603-14.Posterior border seal its rationale and importance.JPD1958:8;386-97 complete denture impressions .JPD1965:15;603-14



if displacement is necessary at the peripheral borders to take advantage of atmospheric pressure, the degree of displacement must be minimized so the elastic force is not greater than the retentive force



there must be intimate contact between the denture base and the undisplaced tissues. this produces thin film of saliva.physiologic seal areas are advantageous because atmospheric pressure is an important adjunct to denture retention.ridge form is important retentive factor in denture retention.



the area covered by the denture is a factor of retention. The greator the area covered the greater will be the retention.the viscosity of saliva is the factor of retention. friction could be a factor, but it is not recommended because of the pathogenic conditions it induces.



Glen E. Tilton (1956): A minimum pressure complete denture impression technique JPD1956:6(1);6-23States that: The pressure applied in impression making must be equally balanced throught the entire area of impression.



The tissues of the mouth , or indeed any tissues of the body ,will not tolerate constant pressure without change; therefore, pressure on the tissue in function beneath a denture must be momentry.In his opinion , all denture-bearing tissue will be at rest when the mandible is in rest position.



Irving R. Hardy (1958) Posterior border seal its rationale and importance.JPD1958:8;386-97.Said that the establishment of the distal length of the basal seat and the development of the PPS is most important step in construction of the complete dentures. In addition to providing retention recording PPS has following advantages:-



it provides close contact of the denture base with the mucous membrane which prevents food getting under the tissue.it provides firm contact of the denture base with the tissue, and this diminishes or eliminates gagging



it supplies sunken distal borders which is less conspicuous to the tongue.it provides a thick borders to counteract denture warpage.



Henry A. Collett (1965); complete denture impressions .JPD1965:15;603-14.Told that the theories attempting to explain the retention of the denture seem to agree that close adaptation of the denture bases to the tissues is desirable , and the retention is proportianate to the area covered



Displaced tissues have a tendency to return to a position and form of equilibrium. Because of this , it seems to be desirable to have the patient either remove his old dentures for a day or two or to have the tissue conditioned in other manner before impressions.



Tissues that we displace while making impressions have tendency to return to their original form due to resilience and they have tendency to displace the dentures. A border seal should be created by positive pressure. This will result in retention.



The selection of the impression material or combination of material should be determined by the objectives of the dentist and the skill with which he manipulates the material



Gred Tryde et al (1965); dynamic impression techniques .JPD1965:15;1023-32.Described that dynamic impression methods are the means of overcoming treatment difficulties of patients with advanced mandibular ridge resorption.The advantages of dynamic impression methods are



avoidence of the dislocating effect of the muscles on improperly formed denture borders.complete utilization of the possibilities of the passive and active tissue fixation of the dentures.



These advantages are the direct result of the impression material being shaped by the functional movements of the muscles muscle attachments that border the denture base.



V . Kubalek (1966) : impressions by the use of subatmospheric pressure .JPD1966:16;213-23.Described that the denture can no better be than the impressions by which it is made. A new concept was developed to eliminate the functional limitations of the impressions.



The term vacustatics has been coined to describe accurately the concepts and the techniques.the term describes subatmospheric pressure as a significant factor in this technique. It then denotes the equilibrium of forces which results when the controlled vacuum is applied



Richard A. Smith (1973) Impression border molding with a cold cure resin.JPD1973:30;914-17.He described a technique for molding the borders of the impression tray with a cold cure resin . Advantage :eliminating the use of stick modeling compound and its tempering water bath.



Impression border molding with a cold cure resin.JPD1973:30;914-17principles involved in complete dentures.JPD1973:29;594-9 border molding of complete denture impressions using a polyether impression material.JPD1979:41;347-51 7



It is most applicable with the elastic impression materials because of the possibility of the cast fracture in undercut areas if rigid tray materials are used throught.



Theorde E. Logan(1973): principles involved in complete dentures.JPD1973:29;594-97.He said that: Inadequate mouth preparations and improper tissue control make adequate impressions and denture bases impossible.over extention of impressions and subsequently of the denture bases may be the result of choice of impression materials



Under extention of the the denture bases may be due to under extended impressions.Placement of a posterior palatal seal and perfection of the thickness and extension of the denture borders should be determined by the dentist.Denture-base extension is dependent on the border extension and fullness in the impression.



The use of tissue conditioner before the impressions is indicated for most patients who are wearing the dentures.Impressions should be varied to control tissues where surgery is contraindicated.Dentures require less maintenance when impressions are properly made



The final impressions determine the shape of the basal surface of the denture and extentions of its borders.The impressions made after mouth preparation is basic to all the steps in denture construction which follow.



Dale E. Smith (1979): one step border molding of complete denture impressions using a polyether impression material.JPD1979:41;347-51.A technique was described which uses the polyether impression material for border molding the impression.



This technique has the following advantages:There is simultaneous molding of all borders of either maxillary or mandibular impressions.Border molding can be accomplished with one insertion of the tray.



Functional movements performed by the patients are used in border molding.The technique is easily mastered



Awni Rihani (1981): pressures involved in complete denture impressions.JPD1981:46;610-14.In his study he showed that the pressure in the impression was not equally distributed



the greatest pressure during impression making was recorded by the manometer located in the centre of the palate.pressures were not able to register at the borders.the shape of the palate did not effect the distribution of the pressures



H.Hotkin et al (1987) :tongue positions in relation to mandibular impressions . JPD1987:57;458-62.Made a study to describe an impression technique that provides a mandibular denture base with the contours that encourage anterior positioning of the tongue for effective harnessing of the stabilizing and retentive forces exerted in the forward position



He concluded that this technique is indicated where advanced residual ridge resorption is present. An adjustable easily located impression tray handle was used as a device to control tongue position and muscular forces for mandibular complete denture impression making.



Mohammed Khaled Ahmed Azzam et al (1992): the sublingual crescent extensions and its relation to the stability and retention of mandibular complete dentures.JPD1992:67;205-10.He stated that the extension of the flange in the sublingual crescent region is an important factor for mandibular denture stability and retention.



the sublingual crescent extensions and its relation to the stability and retention of mandibular complete dentures.JPD1992:67;205-10 Functional metallic handles for final impressions of complete dentures.JPD1998:79;607-8



Making the impression with the minimum pressure on the floor of the mouth while the tongue is at rest allows greater mobility of the underlying tissue without denture dislodgement and without occlusion of the sublingual gland ducts.



The anatomy of the sublingual crescent region and the clinical procedure for recording the anterior lingual seal region was described. Upon completion of the impression, resistance to the dislodgement is usually achieved .



A.R. Odgen (1994): disposable trays for complete denture construction :a dimensional study of a type frequently used in UK and its suitability for the edentulous patients.BDJ1994;23:303-9.This study compares the sizes of patients edentulous arches with the shapes of disposable stock trays from one manufacturer .in many dimensions there is considerable discrepancy between the two



It is concluded that , even with the tray modification it is almost impossible to obtain an accurate impressions of the shape of the all-important sulcus regions. Such a conclusion emphesises the importance of obtaining further impressions in special trays which are modified appropriately.



Izharul Haque Ansari (1997): establishing the posterior palatal seal during the final impression stage.JPD1997:78;324-25.



A procedure for adding the posterior palatal seal at the final impression stage with green stick modeling compound is described. This procedure was suggested to be more accurate than the arbitary scraping of the master cast



The advantages of this method was :the procedure places the entire responsibility of locating and incorporating the PPS into the hands of the clinician.the practitioner will then be able to assess the retentive qualities of the finished dentures.



PPS is incorporated into the trial dentures for added retention , thus increasing the diagnostic information and accuracy of record taking procedures.overcompression of impressions is avoided



The fluid wax technique is the method of choice but it has following disadvantages.more time is required during impression appointmentsa heating unit is used to condition the wax.



difficulty may be experienced in handling the material.added care during the boxing procedure for cast formation is necessary to prevent distortion of the carefully added PPS wax.



ALEXANDRE Malachias (1998);: Functional metallic handles for final impressions of complete dentures.JPD1998:79;607-8.He stated that one of the fundamental requirement for the final impressions is the correct muscular record that can be achived with the patient or the dentist



His work presented a technical modification in the complete denture final impression by using a removable functional handle that can be reusable and can be easily attached to acrylic resin individual trays that allow muscular records to be obtained from the patients movements.



T. Paul Hyde (1999): survey of prosthodontic impression procedures for complete dentures in general practice in United Kingdom. JPD1999:81;295-9.This study identifies the materials and methods used by general practitioners for recording impressions for the provision of replacement of complete dentures.



Within the limits of this study ,the following conclusions were drawn :Irreversible hydrocolloid dominated the market for impressions materials for complete dentures.the use of special trays is normal practice for complete dentures.



Cenk Cura,(2003) Fabrication of a sectional impression tray and sectional complete denture for a patient with microstomia and trismus. (J Prosthet Dent 2003;89:540-3.)This article describes techniques used to fabricate mandibular and maxillary sectional trays and a folding maxillary complete denture for a patient with limited oral opening caused by scleroderma.



For the foldable denture, the anterior teeth had to be arranged on a second base and the hinge fitted at a location higher than the denture base. These 2 factors increased the thickness of the denture and limited the volume of the tongue. Nevertheless, a single-piece denture base provided the patient with ease in placement and removal of the denture.



Carl J. Drago(2003) A Retrospective Comparison of Two Definitive Impression Techniques and Their Associated Postinsertion Adjustments in Complete Denture Prosthodontics. J Prosthodont 2003;12:192-197.



Compared the number of postinsertion adjustment visits required by edentulous patients whose dentures were made from border-molded definitive impressions using modeling plastic impression compound (traditional technique) with patients whose dentures were made from border-molded definitive impressions using heavy-body vinyl polysiloxane impression material.



They concluded Within the limitations of this clinical study, border-molding custom denture impression trays with vinyl polysiloxane impression material provided similar results in terms of postinsertion visits for one year as compared to dentures made from impressions border molded with modeling plastic impression compound.



Vicki C. Petropoulos (2004) Current Concepts and Techniques in Complete Denture Final Impression Procedures J Prosthodont 2003;12:280-287.



In 2001, a survey of U.S. dental schools was conducted to determine which concepts, techniques and materials are currently prevalent in the teaching of final impression procedures for complete dentures in the predoctoral clinical curriculum.



Conclusions: Predoctoral clinical complete denture educational programs agree on many aspects of final impression making, however, there is variability in their teachings regarding the impression philosophy and the materials used.



M. M. De Van (2005) basic principles in impression making. JPD2005:93;503-8The objective of his article was to bring to your attention the basic and fundamentals in impression making- the impressions of mouth tissues for the purpose of constructing mucosa attached complete dentures.



In conclusion he said that the importance of impression phase is over emphasized. Steps in retention have played up while the forces that lead to stability have not received the emphasis that they merit.



Principles and objectives of impression making.The principles involved in impression making are:Preservation of the residual alveolar tissue.Retention.Stability.Support.Esthetics.



Preservation of the residual alveolar tissues:

M.M De Vans dictumIt is more important to preserve what already exists than replace the missing.It is physiologically accepted that with loss of stimulation of the natural teeth the alveolar ridges will atropy and resorb.



During making impressions it should be kept in mind that the impression technique and materials may have effect on the health of the hard and soft tissues.



Pressure in the impression technique is reflected as pressure in the denture base and results in soft tissue damage and bone resorption.In making impressions this rule is followed by not using heavy pressure and covering as much as supporting areas as possible to minimize the possibility of soft tissue abuse and bone resorption.



Retention.Retention for a denture is its resistance to removal in a direction opposite to that of its insertion (Boucher).Retention is that quality of the prosthesis acting to resist the forces of dislodgement along the path of placement (GPT7).



Denture retention is the resistance of the movement of the denture from its basal seat, especially in a vertical direction. (Winkler).www.indiandentalacademy.com


It is the quality inherent in dentures to resists the force of gravity , adhesiveness of foods, and the forces associated with the opening of the jaws.



When the soft tissues over the bones are displaced under pressure , the denture bases may loose their retention because of change of adaptation of the denture to the basal seat.



Factors governing the retention1.Physical factors: adhesion. cohesion. interfacial surface tension. Capillary attraction. atmospheric pressure.2.Physiological factors: physical condition. www.indiandentalacademy.com


degree of tissue tone. condition of mucosa and submucosa. neuromuscular control. ridge characteristics. ridge relationship.3.Physcological factors: intelligence. expectation. apprehension or fear of embarrassment. gagging.www.indiandentalacademy.com


4.Mechanical factors. mechanical locking into the undercuts. Contour of denture bases. magnets Suction chambers.5.Surgical. Implant dentures. ridge extension.www.indiandentalacademy.com


Physical factors.Adhesion:Adhesion is a physical attraction of unlike molecules to each other.It acts when saliva wets and sticks to the basal surface of the dentures and at the same time , to the mucous membrane of the basal seat.



The effectiveness of adhesion depends on the close adaptation of the dentures to the supporting tissues and fluidity of the saliva.



Saliva that is thick and ropy adheres well to both the denture base and the mucosa; but since much of it is produced by the palatal glands under the maxillary basal seat , it builds up and literally pushes the denture out of position. The forces of adhesion still acts on both surfaces , but the hydraulic pressure produced may overpower them.



In xerostomia adhesion is not effective for retaining dentures.Adhesion is best effective in patients having mixed type of saliva.



Patients with small jaws (basal seats) cannot expect retention by adhesion to be as effective as patients with large jaws can.Thus dentures (and hence the impressions ) must extend to the limits of the oral tissues if they are to have maximum retention by adhesion.



Cohesion:

Cohesion is attraction of the like molecules to each other.It is retentive because it occurs in the layer of saliva between the denture base and the mucosa. Since saliva is a liquid, the layer of saliva should be thin to aid in retention.Therefore the adaptation of the denture base to the mucosa should be as close as possible.



Cohesive failure means the seperation of molecules within the body against inter-or intramolecular forces.The bubbles caused in the saliva film would certainly cause loss of retention.www.indiandentalacademy.com


Interfacial surface tensionInterfacial surface tension is the resistance to the separation possessed by the thin film of liquid between two well adapted surfaces.



Page refers interfacial surface tension as a phenomenon which refer to the forces involved in maintaining the attraction of two opposed ground solid plates with an intervening fluid film that resists displacing forces applied at right angles to the fluid film surface.



On assuumption that the denture base is wetted by the saliva, an attempt to withdraw denture generates along its periphery a narrow highly negetively curved saliva surface.There is therefore a lowered pressure in the liquid filled space and a retentive force is experienced.www.indiandentalacademy.com


It is effective in direct proportion to the size of the basal surface of the dentures.One of its requirements is minimal distortion or displacement of the soft tissues by the impressions and of course the denture.A perfect fit is essential.



Capillary attraction:Capillary action or capillarity is a force that causes surface of the fluid to elevate or depressed when it is in contact with a solid.



When the adaptation of the denture base to the mucosa on which it rests is sufficiently close, the space filled with a thin film of saliva acts like a capillary tube and helps to retain the denture.This force is directly proportionate to the area of the basal seat covered by the denture base.



Atmospheric pressure:

Atmospheric pressure can act to resist dislodging forces applied to the dentures.It has been called as suction because it is a resistance to the removal of the forces from their basal seat



For atmospheric force to be effective the denture should have a perfect seal around the entire border.Sydner et al., in 1945 demonstrated the effect of reduced atmospheric pressure on the retention of maxillary complete dentures.



Measurements made in a pressure chamber at4.7psi simulating a 30,000-foot ascent from the earth demonstrated a decrease in retention.With a 70% decrease in atm pressure , 50% decrease of retention was noted.



For atmospheric pressure to be effective the seal around the denture is crucial.It acts by the way of pressure difference. Beneath the denture there must be a lower pressure and the full effect will be felt only if there is vacumm .



Oral and facial musculature:

The oral and facial musculature can provide retentive forces provided 1. the teeth are positioned in the neutral zone between the cheeks and the tongue. 2. the polished surfaces of the tongue are perfectly shaped.



The buccal and the lingual flanges must be shaped so that it makes it possible for the musculature to fit automatically against the denture and reinforce the border seal.The buccal flanges of the maxillary denture slope up and out from the occlusal surfaces of the teeth and the buccal flanges of the mandibular dentures slope down and out.



The lingual surfaces of the lingual flanges slope towards the center of the mouth so the tongue can best fit against them and perfect the border seal on the lingual side of the denture.



Physiological factors:www.indiandentalacademy.com


Ridgecharecteristics: ridge forms influence the retention of dentures;Classified by Charles H Moses in mandibleclass1A -inverted u shaped ridge-very retentiveclass1B-flat inverted ushape.



Class1 C u shaped: presents little retention in comparision to class1A but resists displacement in upper direction.Class2 vshaped ridge: is the least retentive of all.



Class 3A parallel walled thin ridge: there is no much retention as the area at the crest of ridge is very small.Class 3B parallel walled ,broad crested ridge: it is the most retentive of all. www.indiandentalacademy.com


Degree of tissue tone:the swelling which is the charecteristic of inflammation changes the gross form of the tissues to be recorded in the impression.Inflammation should be reduced by keeping the old dentures out of the mouth until the tissues are healthy. If the patient does not agree tissue conditioning materials should be used.



How ever the old dentures should be kept out of the mouth atleast 24hrs before the impressions are made.If excessive amounts of the hyperplastic tissue is present a finger massage is done on daily basis or surgical removal of the hyperplastic tissue.www.indiandentalacademy.com


Neuromuscular control: Good neuromuscular is essential for the effective use of complete dentures.When tongue movements are used for border molding the lingual flanges of the mandibular impression,the timing ,the direction and amount of are critical to the success of molding.



Mechanical factors: Undercuts, Rotational insertion paths and Parallel walls:The resiliency of the mucosa and the submucosa overlying the basal bone allows existance of the modest undercuts that can enhance retention.www.indiandentalacademy.com


Less severe undercuts of lateral tuberosities , maxillary premolar area distolingual areas and lingual mandibular mid bone area are extreamly helpful in retention.Some under cuts are only undercuts in relationship to a linear path of insertion.



If the undercut is seated first in a direction that deviates from the vertical and the remainder of the denture base can be brought into proximity on rotation of the prosthesis around the undercut that is already seated. This rotational path provide resistance to the vertical displacement.



For example : this is found in the area inferior to the retromolar pad into which the distolingual extension of the mandibular denture is introduced from the posterior and the superior before rotating the anterior segment of the denture down over the alveolar process.



Prominent alveolar ridges with parallel buccal and lingual walls provide significant retention.Very flat ridges resists displacement perpendicular to basal seat ,but does not resist movement parallel to basal seat.



Contour of denture bases: Craddock described to maximise the role of denture bases in retention ,proper contour and design of the polished surfaces should harmonise the function of the lips ,cheeks and tongue to effect seating of the dentures. www.indiandentalacademy.com


Magnets: Magnetic retention offers many advantages as it serves to dissipate lateral functional forces .Small magnets are embedded beneath the molar and the premolar teeth and arranged to similar poles to each other. In theory repulsion keeps both the dentures in place.



In practice it will be found that , owing to magnetic force being inversely proportional to the square of the distance and also small size of the magnets which is possible to fit, the repulsive effect is undetectable when the dentures are seperated by more then 1-2mm.



Suction chambers:

They resemble relief areas in shape but differ by having a clearly defined outline instead of merging into the surrounding surfaces.When the denture is inserted in the mouth the patient creates partial vaccum in this chamber by sucking, this small area of reduced pressure keeps the denture in place.www.indiandentalacademy.com


Rubber suction discs: they consists of rubber disc which is fixed to a stud on the fitting surface of the denture.Partial vaccum is created within the disc which holds the upper denture suspended from hard palate.



Surgical factors:The retention of the dentures can be increased by the use of implants.Ridge corrections:The sharp and spiny residual ridges ,bony tuberosity interferences is surgically corrected to enhance retention. www.indiandentalacademy.com


The size of the ridges by surgical procedures such as bone grafts,inserts of biomechanical materials and vestibuloplasties .



Stability:

Stability is quality of prosthesis to be firm, steady, or constant to resist displacement by functional horizontal or rotational stresses(GPT7).It refers resistance against horizontal movement and forces that tend to alter the relationship between the denture base and its supporting foundation in horizontal or rotatory direction.



The factors that contribute to stability of dentures are:1.Ridge anatomy.2.Base adaptation.3.Residual ridge relationships.4.Occlusal harmony.5.Neuromuscular control.www.indiandentalacademy.com


Ridge anatomy: Large,square, broad ridges offer greater resistance to lateral forces than do small, narrow, tapered ridges.Small rounded irregularities of the residual ridges also contribute favorable to stability.www.indiandentalacademy.com


Another factor to be considered in stability is the arch form.Square and tapered arches tend to resists rotation of the prosthesis better than oviod arches.www.indiandentalacademy.com


The shape of the palatal vault also contributes to stability.A steep palatal vault may enhance stability by providing greater surface area of contact and long inclines approaching a right angle to the direction of force.



Impression techniques in complete dentures.



2.Relationship of the denture base to tissues:Friedman describes contacting the buccal and lingual flanges with the buccal and lingual slopes of the ridge is the contributing factor for stability .www.indiandentalacademy.com


Adequate extention of the denture base as limited by the movable tissues not only allows the establishment of the border seal and coverage of maximum supporting area but also provides maximum contact of the denture base with the facial and lingual slope ridges.www.indiandentalacademy.com


Optimal denture stability requires that those tissues that provide resistance to the horizontal forces be properly recorded and related to denture base.www.indiandentalacademy.com


Boucher notes that stability is obtained by incorporating the surfaces of the maxillary and mandibular ridges which are at right angle to the occlusal plane. He further states that stability requires maximum use of all bony foundations where the tissues are firmly attached to bone



Residual ridge relationships:A problem of stability is seen in prognathic and retrognathic patients.Normal dental relationships of the artificial teeth set on ridges that are in severe posterior crossbite can adversely affect stability.www.indiandentalacademy.com


In complete dentures the normal tooth tooth position may be altered to enhance retention and stability.Weinberg recognizes the need to set the artificial teeth in cross bite when the ridges are in severe crossbite.www.indiandentalacademy.com


In class III patients they frequently display a lower arch anterior to in centric relation.This causes the maxillary denture to tip anteriosuperiorly , traumatizing the maxillary anterior ridge and loosening the maxillary denture.www.indiandentalacademy.com


Occlusal harmony: to minimize the dislodging forces the occlusion should be balanced throughout the functional range of movement of the patient.www.indiandentalacademy.com


Tooth position and occlusal plane:A mandibular occlusal plane that is too high can reduce the denture stability because:1.Lateral tilting forces directed against the teeth are magnified as the plane is raised.2.An elevated plane prevents the tongue from reaching the over the food table in the buccal vestibule.www.indiandentalacademy.com


This compromises stability and makes control of the food bolus and denture more difficult.www.indiandentalacademy.com


Occlusal plane: the best stability is obtained when the occlusal plane is parallel to and anatomically oriented to the ridges.If the occlusal plane is tipped there is shunting effect and a loss of stability.www.indiandentalacademy.com


Relationship of the external surface and periphery to surrounding orofacial musculature:Actions of the muscles on the denture base generally result in the lateral and the vertical dislodging forces.www.indiandentalacademy.com


The relationship of external surface with the denture base



The denture borders should be extended to contact the movable tissues. This enhances stability.The actions of the canninus, incisivus, triangularis, mylohyoid, mentalis and genioglossus muscles can lead to dislodging forces if the denture bases does not provide freedom for these muscles to action. www.indiandentalacademy.com


The basic geometric design of the denture bases should be triangular.In frontal cross section , both the dentures should appear as two triangles whose apex correspond to the occlusal surface.www.indiandentalacademy.com


The buccal and labial flanges of the maxillary and the mandibular dentures should be concave to permit positive seating of the lips and cheeks. the proper contour of the flanges permits the horizontally directed forces that occurs during the contraction of buccinator and orbicularis oris muscles to be transmitted as vertical forces tending to seat the prosthesis.



Support:

Support is the resistance of a denture to the vertical components of mastication and to occlusal forces or other forces applied in direction towards the basal seat. (boucher)

Support is the resistance to vertical movement of the denture base towards the ridge. (Jacobson and Krol)www.indiandentalacademy.com


Support can be considered from two points of view:1.Maxillary and mandibular dentures should conform to the underlying tissues so that the occlusal surfaces can correctly oppose one another at the time of insertion.2.The denture bases should maintain this relationship for a period of time.www.indiandentalacademy.com


Initial denture support is achieved by using impression procedures that provide optimal extension and functional loading of supporting tissues, which vary in their resiliency.www.indiandentalacademy.com


Long-term support is obtained by directing the forces of occlusal loading toward the tissues most resistant to remodelling and resorptive changes.www.indiandentalacademy.com


Effective support is realized when The denture is extended to cover a maximal surface area without impinging on movable tissues .The tissues most capable of resisting resorption are loaded during function.The tissues most capable of resisting vertical displacement are allowed to make firm contact with the denture base during function



Compensation is made for the varying tissue resiliency to provide for uniform denture base movement under function and maintain a harmonious occlusal relationship.



Nature of supporting tissues:

Ideally ,the soft tissues should be -firmly bound to underlying cortical bone-contain resilient layer of submucosa , and be covered by keratinised mucosa.www.indiandentalacademy.com


The underlying bone should be :-resistant to pressure induced remodeling.-cortical bone is more resistant to resorption than cancellous bone.www.indiandentalacademy.com


The areas of support :Primary areas of support: Areas of the edentulous ridge that are at right angles to the occlusal forces and donot resorb easily.Maxillary- residual ridge, horizontal portion of hard palate.Mandible-buccal shelf area .www.indiandentalacademy.com


Secendory:Maxilla:rugea areas

Mandible: slopes of the residual ridge.www.indiandentalacademy.com


Importance of covering the buccal shelf:It is the area of support because:It has a cortical bone.It is at right angle to the occlusal plane.When the ridge is flat the buccinator is almost attached to the centre of the ridge. The denture can cover this area as this muscle is flaccid and inactive as its fibers function in horizontal direction.www.indiandentalacademy.com


In the maxilla horizontal portion of the hard palate lateral to mid palatine raphe should provide primary support to complete dentures because the submucosa contains fatty tissue anterolaterally and glandular tissue posteriolaterally. This resilient layer acts as a cushion to the functional stresses.www.indiandentalacademy.com


It is enhanced by selective placement of the pressures that are in harmony with the resiliency of the tissues that make up the basal seat.



Esthetics:

The role of esthetics in impression making refers to the development of the labial and buccal borders so that they are not only retentive but also support the lips and the cheeks.These structures should not be over supported with borders that are too thick.



Hence it is ideal to complete the impressions with the peripheral width that will be utilized in the polished dentures.



Theories of impression making:Mucostatic theory/minimal pressure impressions.Mucocompressive theory/definitive pressure impressions.Selective pressure.



Mucocompressive theory:

Because denture retention is tested most severly during mastication, many dentists formerly considered it is essential for the tissue to remain in contact with the denture during chewing.It appeared logical to them to make impressions that would press the tissues in the same manner as the chewing forces.



However the dentures did not fit well at rest , because tissues distorted tend to rebound.There was a question weather tissues so abused will long maintain the shape that they assumed during the day of impression.



Advocates of this technique closed-mouth procedures (Tryde et al.,) this technique presumes that the occlusal loading during the impression will be same as the occlusal loading during function.



Critics of this procedure point out that the dentures are in actual occlusal contact only for a short period of time and the constant pressure will over-stress the tissues



This theory of impression making was not always able to obtain the desired pressure but tended to create excessive pressure.This often resulted in good initial retention but eventual bone resorption and loose dentures.



Mucostatic impression theory:

Addison in 1944 described the mucostatic impressions and attributed them to Page.The main point of the mucostatic principle concerned Pascals law which states that the pressure on the confined liquid will be transmitted throught the liquid in all directions.



According to this concept. mucosa being more than 80% of water will react like liquid in a closed vessel and thus cannot be compressed.This is not true, insofar the fluids escape from the border of the denture.The mucosa is not a closed vessel.



According to this principle the impression material should record, without distortion, every detail of the mucosa so that the completed denture will fit in the elevations and depressions . For this reason separating medium was not used at any point of the procedure.



But the draw back was the impression materials and the casts exhibited sufficient dimensional change to render worthless the care taken to record all the minute details.Mucostatics further demand the use of metal base than the dimensionally unstable acrylics.



But Stephen in 1946 told that the mucosal topography is not static over 24hr period. There is difference between the mucosal contour just after rising in the morning , and that which exists after 12hrs in upright position.So it would appear that the achieved impression would be altered by the time the denture is finished.



This principle considered interfacial surface tension as the only important retentive mechanism in the complete dentures. Therefore they did not use conventional flanges because they could not resists the vertical displacement ,with was only the movement interrupting the surface tension.



Dykins in 1947 recommended short lingual flange that resists lateral movements.The mucostatic principle ignores the value of dissipating the masticatory forces over largest possible basal seat area.The mucostatic denture minimized the retentive role of muscles, as described by Fish in1948.



Selective pressure theory:

This theory combines pressure over certain areas and little pressure over others.The principle behind this theory is based on the belief that the mucosa over the ridge is best able to withstand pressure, whereas that covering the midline is thin and contains very little submucosal tissue (Boucher, 1951).



How ever this technique demands firm, healthy mucosal covering over the ridge.If flabby ridges exists, it is preferable to use a minimal pressure impression.



Impression techniques.Classification:Amount of pressure used -minimal pressure technique. -mucocompressive technique. -selective pressure technique.2.Open or closed mouth technique.3.Hand manipulations or functional movements.4.Type of tray.www.indiandentalacademy.com


The position of the operator and patient.The dental chair is set in an upright position ,this being specially important during impressions since on of the fears existing among the patients is that of being choked by the material used.



The head rest should be adjusted so that the head and the neck line are in line with the trunk.If the head is allowed to bend backwards the suprahyoid and the infrahyoid muscles will tense and cause difficulty in swallowing.



If the impression material fragment breaks it can easily fall in the throat and cause airway obstruction.



Position of the operator and the patient:



Mucocompressive impression technique.



The following technique is designed to take an impression of the tissues under pressure so that ,under the stresses of mastication , the pressure transmitted through the entire mucosa to the underlying bone is approximately equal over its whole surface.www.indiandentalacademy.com


Material used : a impression compound should be selected which softens at temperature around 65deg C ,flows readily when softened ,can be flamed without burning and blistering and which sets hard at room temperature.



Primary impressions:The primary impressions are obtained with a low viscosity alginate or plaster to obtain casts with good surface detail.The trays are made in self cure resin with a spacer between the cast and the tray of 3mm.www.indiandentalacademy.com


The periphery of the trays should be well short of the mucobuccal fold.The maxillary tray extends about 5mm on the soft palate and straight across one hamular notch to other.The mandibular tray finishes a few mm on the pear-shaped pad.www.indiandentalacademy.com


Cover the impression tray with the compound with even thickness.Apply petroleum jelly on the compound and make the impression of the cast making sure the material flows into the mucobuccal fold.Remove the excess material before it sets and chill in cold water.www.indiandentalacademy.com


The impression:Bowls of hot and cold water, a small pin-point flame will be required.Soften the impression compound lining the tray by immersing in hot water.As soon as it becomes soft , it is seated in the mouth with gentle pressure.www.indiandentalacademy.com


The impression should be kept in the mouth until it has hardened.The impression is placed in the bowl of cold water .The impression is now dried ,the whole surface is rapidly heated with a low flame until glossy, dipped in hot water ,seated in the patients mouth and pressure is applied.www.indiandentalacademy.com


The pressure In the maxilla must be directed upwards ,and more evenly balance is obtained by pressing the finger in center of the palate than one finger of each hand on either side.Remove the impression after it sets and place once in cold water.www.indiandentalacademy.com


The impression obtained is under an upward and backward load of unknown quantity which is somewhat overextended and do not have peripheral seal.The peripheral borders are now trimmed 3mm short of the functional position of sulci and frena.



The width is also reduced to about 3mm by removing part of rolled out border in contact with the cheeks and the lips.Once trimming of the impression compound is completed the periphery is rebuilt using low fusing compound in stick form.www.indiandentalacademy.com


Begin with the distal end of the buccal border ,dry, add 2-3mm of low fusing compound, flame , temper, insert and mould in functional position.Repeat the procedure until the whole periphery from tuberosity to tuberosity has been readapted.



The vibrating line of the soft palate is first located and then it is recorded.Finally the hamular notches are recorded by seating the impression firmly and asking the patient to swallow several times which will trim the soft tissues in this region.www.indiandentalacademy.com


The impression should be completed and it should be impossible for the patient to dislodge it by any normal movements of lips and cheeks.www.indiandentalacademy.com


Minimum pressure techniquesIra E Klein and Alan S Broner(1985)Thy described a impression for complete denture to minimize distortion of the ridge and border tissues.www.indiandentalacademy.com


Technique:The primary impression is made in modelling compound and wax for the borders.www.indiandentalacademy.com


Preparation of secondary impression trays:Maxillary tray:Tray is fabricated on a artificial stone cast.The tray is processed in clear acrylic resin and is fully extended in height and width of the cast borders.www.indiandentalacademy.com


A handle is formed on the tray.The tray is placed in the mouth and checked for retention ,stability and muscle interferences.Check is made for tissue blanching clearly visible through the tray.Regions of tissue blanching indicate the regions where displacement has occurred in primary impressions.www.indiandentalacademy.com


The regions of blanching are marked and these areas are relieved.The procedure is repeated until all tissue blanching has been eliminated.Using a no6 bur holes are drilled in ant palatal region.www.indiandentalacademy.com


Six holes are drilled 5mm apart in the anterior flange from canine to canine.4 holes are made in both buccal flanges from first premolar to second molar 5mm apart.www.indiandentalacademy.com


Mandibular tray:The tray is fabricated in clear acrylic resin.It is checked for stability, retention and muscle interferences.Tissue blanching regions are observed and relieved.www.indiandentalacademy.com


4 holes are drilled 5mm apart on each posterior lingual flange.Platforms of modeling compound are placed bilaterally in premolar and molar region to serve as finger rests.www.indiandentalacademy.com


Secendory impressions:Maxillary:The material of choice is zinc-oxide eugenol paste.The material is mixed as per manufacturers direction and loaded into a thoroughly dry tray.www.indiandentalacademy.com


The maxillary tray is supported by single finger in the mid palatal region after the tray is seated fully upward and slight posteriorly.Proper functional movements are made by the patient.www.indiandentalacademy.com


Movements include opening and closing of the mouth, moving mandible from side to side, pursing the lips and smiling.The impression is removed after final set of impression paste.www.indiandentalacademy.com


Mandibular:

The loaded mandibular impression tray is seated posteriorly first and then in downward and anterior direction.The tray is fully seated and finger supported bilaterally on compound impression platforms.www.indiandentalacademy.com


The patient is asked to activate the lips and cheeks in the same manner as for maxillary impressions.Lingual trimming is done by protruding the tongue, move the tongue into the cheeks, and protrude the tongue toward the commisure of the lips.



The advantage of this technique is :Reduction of time because border molding is unnecessary.Elimination of potential pressure spots before impression material is inserted.Close aproximation of physiologic and anatomic ideals.Preservation of residual ridge.www.indiandentalacademy.com


Disadvantages:Failure to register the tissues that are important for retention and stability.Metal bases should be fabricated.Increased cost.www.indiandentalacademy.com


Impression techniques in complete dentures



Selective pressure impression technique.This technique is based on the theory proposed by Boucher in1951.



This theory combines pressure over certain areas and little pressure over others.The principle behind this theory is based on the belief that the mucosa over the ridge is best able to withstand pressure, whereas that covering the midline is thin and contains very little submucosal tissue (Boucher, 1951).



The physiology of selective pressure technique is that certain areas of mandible and maxilla are better adapting in nature to withstand extra loads from the forces of mastication.The tissues are recorded under shifted placement of pressure while other tissues must be recorded at rest or relieved with minimal pressure with least possible interferences to the tissues.



COMBINATION OF MUCOSTATIC AND MUCOCOMPRESSIVE PRINCIPLE INCLUDES SITES OF MINIMAL PRESSURESITES WITH PRESSUREPERIPHERAL SEAL



The areas where the pressure can be applied is selected for making the impressions.The areas where the pressure is applied are the stress bearing areas.The areas which are relieved are the relief areas.www.indiandentalacademy.com


Nature of tissues:

Ideally ,the soft tissues should be -firmly bound to underlying cortical bone-contain resilient layer of submucosa , and be covered by keratinised mucosa.www.indiandentalacademy.com


The underlying bone should be :-resistant to pressure induced remodeling.-cortical bone is more resistant to resorption than cancellous bone.www.indiandentalacademy.com


Primary stress bearing areas: Areas of the edentulous ridge that are at right angles to the occlusal forces and donot resorb easily.Maxillary- residual ridge, horizontal portion of hard palate.Mandible-buccal shelf area .www.indiandentalacademy.com


Residual ridge is the primary stress bearing area because:The mucous membrane covering the crest of the ridge is firmly attached to the underlying bone.The crest of the residual ridge is covered with the fibrous connective tissue .



But the bone is subjected to resorption which limits the potential for support, unlike the palate , which is resistant to resorption.www.indiandentalacademy.com


In the maxilla horizontal portion of the hard palate lateral to mid palatine raphe should provide primary support to complete dentures because the submucosa contains fatty tissue anterolaterally and glandular tissue posteriolaterally. This resilient layer acts as a cushion to the functional stresses.www.indiandentalacademy.com


Buccal shelf:It is the primary stress bearing area because:It has a cortical bone.It is at right angle to the occlusal plane.When the ridge is flat the buccinator is almost attached to the centre of the ridge. The denture can cover this area as this muscle is flaccid and inactive as its fibers function in horizontal direction.www.indiandentalacademy.com


Secendory:Maxilla: rugea areas: they are irregular shaped rolls of soft tissues. they should not be distorted in the impression technique.Since it is placed at an angle to the occlusal plane it can be a secondary stress bearing area. www.indiandentalacademy.com


Mandible: slopes of the residual alveolar ridges



The areas which provide peripheral seal are:The mucosa of the labiobuccal vestibule between the residual alveolar ridge and the cheeks and the lips.In the posterior border of the hard palate at its junction with the hard palate.



According to Van Scotter and Boucher (the nature of supporting of supporting tissues for complete dentures JPD 1965;15)The tissues of the oral vestibule and the soft palate are ideally situated to provide peripheral seal.The tissues are delicate and adapt themselves to the denture borders.www.indiandentalacademy.com


They say that the peripheral tissues (valve producing area) can become secendory stress bearing area in conditions where the adipose and glandular tissue of the palate are abnormally reduced in volume.The musculature in this area can adequately withstand stresses of mastication.



Relief areas:Maxilla: incisive papilla

It covers the incisive foramen .Relief should be provided in denture to avoidAny possible interferences to blood supply and nerve supply www.indiandentalacademy.com


Mid palatine raphe:The mucosa covering it is thin .This area acts as a fulcrum and the denture exhibits tendency to rock.



Mandible: crest of the residual alveolar ridge:The under lying bone is cancellous.



Preliminary impressions.For the preliminary impressions the stock trays are used which are either metal or plastic trays. They may be perforated or non-perforated.www.indiandentalacademy.com


The different types of stock trays are:Caulks rimlock trays.Mc Gowen winkler trays.STO-K trays.



Charles .M. Heartwell etal.,Comparison of impressions made in perforated and non-perforated rimlock trays (JPD 1972;27,3)In there study they showed that there was no significance difference in accuracy of impressions made in perforated and non perforated rim lock trays using alginate. www.indiandentalacademy.com


Even correctly selected stock tray will not fit the denture bearing area perfectly. Therefore when the impressions are made , it is advisable to select an impression material that has relatively high viscosity, therefore allowing the material to compensate more easily for the deficiency of the tray. www.indiandentalacademy.com


The most suitable materials are silicon putty alginate impression compound.



Silicon putty: -it has high viscosity.

-it will flow beyond the tray to compensate for underextension of the tray.-exhibits some degree of elasticity ,so records the undercuts with reasonable accuracy.www.indiandentalacademy.com


Disadvantage: due to its high viscosity it records it records the surface details poorly.

-it cannot be added if any part of the impression is deficient.www.indiandentalacademy.com


Irreversible hydrocolloids:

They record the surface details accurately if they are properly controlled.They exhibit defects in the palatal part of the impression as they donot absorb the mucous secretions.Thy loose the moisture rapidly hence they distort.www.indiandentalacademy.com


The weight of the artificial stone distorts the impression if they are not supported by the borders of the tray.



Impression compound:It is used for compressing the soft tissues.It can be used for any technique requiring close peripheral seal.It can be used in combimation with other materials.www.indiandentalacademy.com


It distorts easily where excessive undercut is present.It does not provide fine surface detail.



Tray selection.The space available in the mouth for the upper impression is studied carefully by observing the width and height of the vestibular spaces with the mouth partway open and the lip held slightly outward and downward.An edentulous stock tray that is approx 5mm larger than the outside surface of the ridge is selected



This is done by initially positioning the tray by centering the labial notch of the tray over labial frenum.The posterior extent is relative to the posterior palatal seal area is maintained, and the handle is dropped downward to permit visual inspection .Posteriorly the tray should include both the hamular notches and the vibrating line.



For the mandibular tray :

A tray that provides approx 5mm of the impression material over the entire basal seat area is selected.Posteriorly, the retro molar pads should be covered by the tray.www.indiandentalacademy.com


The tray is raised anteriorly for observation of the relationship of the between the lingual flanges and the lingual slopes of the ridge.www.indiandentalacademy.com


Preliminary impressions:Maxilla:An edentulous stock tray that is approx 5mm larger than the out-side surface of the upper residual ridge is selected.The borders of the stock tray are lined with the soft boxing wax so a rim is created to help confine the alginate impression material.www.indiandentalacademy.com


The objective is to obtain a preliminary impression that is slightly overextended around the borders.The tissue surface of the borders of the tray, including the rim of wax , are painted with an adhesive material.



Alginate is mixed according to the manufacturers instruction and is placed in the tray and evenly distributed to fill the tray to the level of its borders.www.indiandentalacademy.com


A small amount of the material is placed in the rugae of the hard palate to prevent the air entrapment.The loaded tray is positioned in the mouth.www.indiandentalacademy.com


The tray is left in the mouth for 1min after initial set of the irreversible hydrocolloid. The impression is removed from the mouth in one motion and inspected to ensure that all the basal seat is included.www.indiandentalacademy.com


Now the borders of the custom tray are determined.Two choices are available:The periphery is outlined at chairside with a indelible marker.The outline can be approximated on the poured cast in the lab.www.indiandentalacademy.com


The impression is outlined as follows:1.The posterior border, about 2mm pas the estimated final border, using the hamular notches and vibrating lines as guides.2.The mucolabial and mucobuccal reflections, about 1mm from deepest portion of the periphery.www.indiandentalacademy.com


3.Extra clearance is allowed for labial and buccal frenums.www.indiandentalacademy.com


Mandible:An edentulous impression tray that will provide for 5mm bulk of impression material over the entire basal seat area is selected .The borders of the tray is lined with the soft boxing wax and the tray is again tried in the mouth.www.indiandentalacademy.com


The tissue surface and the borders of the tray is painted with the adhesive material.The impression material is loaded with the alginate from lingual surface and evenly distributed to fill the tray to the level of the borders.www.indiandentalacademy.com


The tray is centered on the residual alveolar ridge, with the tongue raised slightly so that it will be in the tongue space.The tray is seated gently by applying alternative pressure with the index pressure on either side in the first molar region, the patient is asked to relax his tongue.www.indiandentalacademy.com


The tray is held steadily for 1min in mouth .It is removed In one motion and inspected.www.indiandentalacademy.com


Mandibular outline is marked as follows:The base and outline of pear shaped pad.The edge of external oblique line.3.The mucolabial and mucobuccal reflections, about 1mm from deepest portion of the periphery.www.indiandentalacademy.com


4.Extra clearance is allowed to the labial and buccal frenums.5. The lingual border, about 1mm from the mucolingual reflection allowing the clearance for lingual frenum.www.indiandentalacademy.com


Fabrication of custom tray.Trimming of the casts:The casts are trimmed so that there is 12mm of stone in the thinnest part.The maxillary cast is trimmed within 4-5mm of the posterior border.The land areas should be 3mm wide and no higher than 1mm high as high land areas interfere with the fabrication of the tray.www.indiandentalacademy.com


Placing the relief areas.

According to the selective pressure theory the pressures should be placed only in the areas which can bear the stresses.The areas which cannot bear the stresses should be relieved.



Relief can be done by using Wax spacersScrapping the impression made in compound.



Richard P. Frank (1956)

He analysed the pressures produced during maxillary edentulous impressions.he showed that:www.indiandentalacademy.com


Awani Rihani(1981)Made a study on pressures involved in ebentulous impressionsHe found that

1.The pressures were not equally distributed.2.The greatest pressures were located in the center of the palate.www.indiandentalacademy.com


Pressures were not able to record at the borders.Shape of the palate did not affect distribution of pressures.



Osamu Komiyama etal(2004)In their study they showed that use of 1.40mm 0f spacer made be used to selectively reduce the pressure in the palatal region when making an impression.www.indiandentalacademy.com


Spacer designs.www.indiandentalacademy.com


Boucher: the spacer design proposed wasIn maxilla: full coverage.In mandible: except the buccal shelf 2mm short of the vestibule.www.indiandentalacademy.com


1mm of wax spacer is placed on the cast within the outlined border to provide space for the final impression material in the tray.The posterior palatal border is not covered .www.indiandentalacademy.com


The tray contacts here and the additional stresses are placed here to achieve PPS.This part also acts as a guiding stop to position the tray.www.indiandentalacademy.com


Mandible: 1mm thick wax spacer is placed over the crest and slopes of the ridges.The buccal self area is left uncovered so that the tray contacts this area.



Winkler & Heartwell.Maxilla: rugea ,mid-palatine region,incisive papilla are relieved by scraping the impression compound.www.indiandentalacademy.com


Sharry : full spacer with 4 stops.www.indiandentalacademy.com


Halperin etal., 1mm thick baseplate wax over the peripheral extention and buccal slope region of the tray.www.indiandentalacademy.com


JACQUELINE P. DUNCAN JPD 2004,92: 299-301www.indiandentalacademy.com


W . Smith etal (1999): he gave variable design features of spacer thickness according to different materials and clinical situations.Non-undercut regions:Plaster -2mm spacing,tissue stops.ZOE 0.5mmwww.indiandentalacademy.com


Non-undercut &undercut ridges:Alginate- 3mm spacing ,tissue stops.Elastomers- 1.5mm spacing, tissue stopsDisplaceble tissue :there should be provision for material to escape.(BDJ 1999;187,423-6)www.indiandentalacademy.com


Fabrication of custom trays:Materials used to fabricate custom trays are:Shellac base plateSelf cure acrylic resinLight cure resins.www.indiandentalacademy.com


Fabrication with self cure resin.After blocking out the under cuts and providing the additional relief the resin is mixed and placed in a rollete board and the material is rolled in desired form.Oblong for lower & squarish for upper.www.indiandentalacademy.com


The material is adapted over the cast. Preparation of handles:Small amount of resin is mixed .The handle is formed about 3mm thick and made to extend vertically from the crest of the anterior ridge.www.indiandentalacademy.com


A right angle bend is made so the handle will extend forward about 10-15mm.The tray should measure 25mm f

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