impression techniques of complete denture

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2. CONTENTS INTRODUCTION DEFINITIONS PRINCIPLES OF IMPRESSION MAKING CLASSIFICATION OF IMPRESSIONS IMPRESSION TECHNIQUES IMPRESSION PROCEDURES IMPRESSION TECHNIQUES IN COMPROMISEDSITUATIONS SUMMARY BIBLIOGRAPHY. 3. INTRODUCTIONIMPRESSIONA negative replica or copy in reverse of the surface ofan object . gpt 8 An impression can also be defined as an imprint ofthe teeth and adjacent structures for use in dentistry.- gpt 4 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 5. BASIC REQUIREMENTS FOR IMPRESSION MAKING Knowledge of Basic anatomy Knowledge of basic reliable technique Knowledge and understanding of impressionmaterials Skill Patient management 6. OBJECTIVES OF IMPRESSION MAKING1) RETENTION2) STABILITY3) SUPPORT4) ESTHETICS5) PRESERVATION OF REMAINING STRUCTURES 6 7. RETENTIONRetention is defined as the ability of denture to resist the displacement against vertical forcesRetention 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. 8. Factors affecting RetentionAnatomical factors Physiological factors Physical factors Mechanical factors Muscular factors8 9. Factors affecting RetentionAnatomical factors Size of the denture bearing area Quality of the denture bearing area. 9 10. Factors affecting RetentionPhysiological factors Saliva and its quality10 11. Factors affecting RetentionPhysical factors Adhesion Cohesion Interfacial surface tension Capallarity and capillary attraction Atmospheric pressure and peripheral seal 11 12. 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 . 13. Adhesion is achievied by ionic forces betweencharged salivary glycoproteins & surface epitheliumor acrylic resin. Quality of adhesion depends on :- Close adaption Size of ofdenture Type of denture bearingsaliva area 14. The most adhesive saliva is thin serous but containssome mucous components. Thick & ropy saliva is very adhesive but tends to buildup so that it is too thick in palatal area & interfereswith oral adaptation . In this situation patient should rinse out the ropysaliva every two to three hours 15. The amount of retention provided by adhesion isdirectly proportional to the area covered by denture. Mandibular dentures cover less surface area thanmaxillary prosthesis & therefore are subject to alower magnitude of adhesive retentive forces. Similarly patients with small jaws or very flat alveolarridges cannot expect retention to be as great as canpatients with large jaws or prominent alveoli. 16. Cohesion:-it is the physical attraction of like molecules for each other . it occurs within the layer of fluid (usually saliva ) thatis present between the denture base & the mucosa. 17. Normal saliva is not very cohesive , therefore most ofthe retentive forces of denture mucosa interfacecomes from adhesive & interfacial surface tensionfactors. 18. 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 wetthe rigid surrounding material . 19. If the surrounding material has low surface tension ,as oral mucosa does ,fluid will maximize its contactwith the material, thereby wetting it readily &spreading out in a thin film. If the material has high surface tension ,fluid willminimize its contact with the material , resulting information of beads on the material surface. 20. All denture base material have higher surface tensionthan oral mucosa ,but once coated by salivary pellicle,their surface tension is reduced ,which promotesmaximizing the surface area between liquid & base. Role of surface tension is through capillary attractionor capillarity. When the adaptation of denture base to mucosa issufficiently close ,the space filled with a thin film ofsaliva act like a capillary tube in that the liquid seeksto increase its contact with both denture & mucosalsurface. 21. It plays a major role in retention of maxillary denture.It is totally dependent on presence of air at themargin of liquid & solid contact (liquid air interface). As there is excess saliva along the lower border ofmandibular denture, Surface tension is lost inmandibular denture due to loss of liquid air interfaceat denture border . 22. Mucostatics dismiss adhesion and cohesion asfactors in retention, the entire phenomenon beingattributed to interfacial surface tension. But an analysis has proved that if it was not for theforces of adhesion and cohesion, the forces ofinterfacial surface tension wont exist. Attachment of adenture is possible because both tissue and denturebase material can become wet which means itsmolecule will adhere to water molecules. 23. Oral & facial musculature :-supplement retentive forces, provided :-a)Teeth are positioned in neutral zone between thecheeks & tongueb)The polished surface of the denture are properlyshaped. If the buccal flange of maxillary denture slope up &out of occlusal surface of teeth & the buccal flange ofmandibular denture slope down & out from theocclusal plane, the contraction of buccinator willtend to retain both denture on basal seat. 24. Atmospheric pressure:- Act to resist dislodging forces applied to the denture,if the denture have an effective seal around theirborders. Retention due to atmospheric pressure is directlyproportional to the area covered by the denturebase. 25. 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. 26. Factors affecting RetentionMechanical factors Undercuts Retentive springs Magnetic forces Denture adhesive Suction chambers andsuction discs26 27. Factors affecting RetentionMuscular factorsThe muscles apply supplementary retentiveforces on the denture.It is most effective in the neutral zone. 27 28. STABILITYThe quality of a denture to be firm, steady, orconstant, to resist displacement by functionalstresses and not to be subject to change of positionwhen force is applied. It is the ability of the dentureto withstand horizontal forces.28 29. Factors Affecting Stability Vertical height of the residual ridge. Quality of soft tissue covering the ridge. Occlusal plane Quality of the impression. Teeth arrangement. Contour of the polished surfaces. 29 30. SUPPORT It is the resistance to vertical forces of mastication &to occlusal or other forces applied in a directiontoward the basal seat . When the natural teeth are missing ,the alveolarridge & their covering of mucosal tissue become thesupporting elements. 31. Unfortunately , they were never meant to endure theforces of mastication & other constant occlusalpressure that result from swallowing , clenching ,orbruxing. To make the best of bad situation , it is necessary toenhance the available support by utilizing maximumcoverage of all usable ridge bearing areas. 32. Areas of support are divided into:-secondary pimaryslight 33. Primary support area:- area of edentulous ridge that are at right angle to occlusal forces & usually do not resorb easily . Maxillary:-a)posterior ridgeb) flat areas of the palate Mandibular:- a)buccal shelf area b)Posterior ridge c)pear shaped pad 34. Secondary supporting area:- area of edentulous ridgethat are greater than at right angle to occlusal forces; also the area of dentulous ridge that are at rightangle to occlusal forces but tend to resorb underload. Maxillary :- anterior ridge ,rugae & all ridge slopes Mandibular:- anterior ridge & all ridge slopes 35. ESTHETICS The thickness of the denture flanges is one of theimportant factors that govern esthetics. Thicker denture flanges are preferred in long-termedentulous patients to give required labial fullness. Impression should perfectly reproduce the width andheight of the entire sulcus for the proper fabrication ofthe flanges. 35 36. PRESERVATION OF REMAINING STRUCTURES De Van (1952) stated that, the preservation of thatwhich remains is of utmost importance and not themeticulous replacement of that which has been lost. Impressions should record the details of the basalseat and peripheral structures in an appropriate formto prevent injury to the oral tissues. 36 37. IMPRESSIONS 38. CLASSIFICATION Depending on the theories of impressionmaking. DependingDepending on the on thematerial used technique classificationDependingon the Dependingpurpose of on the tray thetypeimpression 39. Depending on theories of impression makingMucostatic Mucocompressive Selective pressure39 40. Mucostatic or Passive Impression First proposed by Richardson and later popularised byHarry Page. The impression is made with the oral mucousmembrane and the jaws in a normal, relaxed condition.Border moulding is not done here. The impression is made with an oversized tray.40 41. Impression material of choice is impression plaster. Retention is mainly due to interfacial surface tension.The mucostatic technique results in a denture, whichis closely adapted to the mucosa of the denture-bearing area but has poor peripheral seal. 42. Mucocompressive Impression (Carole Jones) Records the oral tissues in a functional and displaced form.The materials used for this technique include impressioncompound, waxes and soft liners. The o