INTRODUCTION TO IMPRESSION MATERIALS

INTRO

1. INTRODUCTION TO IMPRESSION MATERIALS BY Dr.V.NAGARAJAN Ragas dental college

2. IMPRESSION: A negative likeness or copy in reverse of the surface of an object, an imprint of the teeth and adjacent structures for use in dentistry [GPT8] Impression of edentulous mouth Impression of dentulous mouth

3. IMPRESSION TRAY: A receptacle or device used to carry the impression material to the mouth ,confine the material in apposition to the surface to be recorded, and control the impression material while it sets to form the impression.

4. Perforated metal stock impression tray Non perforated metal stock impression tray Special tray

5. IMPRESSION MATERIALS: Any substance or combination of substances used for making an impression or negative reproduction .

6. DESIRABLE PROPERTIES OF IMPRESSION MATERIALS It should : Have pleasant taste , odor and esthetic color . Not contain any toxic or irritating ingredients . Be economical Have adequate shelf life for storage and distribution . Be easy to use with minimum equipments . Exhibit dimensional stability . Have adequate strength so that it will not break or tear while removing from the mouth

7. Posses elastic properties with freedom from permanent deformation after strain . Be able to be electroplated . Be compatible with die and cast materials .

8. CLASSIFICATION OF IMPRESSION MATERIALS Based on mode of setting Based on elasticity Based on tissue displacement Based on their usage

9. BASED ON MODE OF SETTING

10. Impression material Elastic Nonelastic Zinc oxide Eugenol Impression Compound Impression Plaster Non-aqueous elastomers Polyethers Addition silicone Condensation silicone Polysulfides Impression waxes Hydrocolloids Agar Alginate BASED ON ELASTICITY:

11. BASED ON TISSUE DISPLACEMENT

12. BASED ON THEIR USAGE:

13. NON ELASTIC (RIGID) IMPRESSION MATERIALS

14. Nonelastic Zinc oxide eugenol Impression Compound Impression Plaster Type I

15. Impression plaster ADA type I gypsum product

16. IMPRESSION COMPOUND: Classification : Type 1: Low fusing material Type 2: Higher fusing material / Tray compound Supplied as : Sticks ,Cakes, Sheets in variety of colors

17. ZINC OXIDE EUGENOL IMPRESSION PASTE ZOE impression pastes are dispensed as two separate pastes Base paste Catalyst paste

18. ELASTIC IMPRESSION MATERIALS

19. Elastic Hydrocolloids Agar Alginate

20. Non-aqueous elastomers Polyethers Addition silicone Condensation silicone Polysulfides Elastic

21. Each of these are further divided into 4 classes depending on viscosities. 1.light body 2.medium or regular body. 3.heavy body. 4.putty.

22. Most materials are supplied in paste forms in two components.Base paste and Accelerator or Reactor paste which on mixing produces a setting reaction through a combination of chain lengthening polymerization or cross linking or both by either condensation or addition reactions.

23. CLASSIFICATION OF IMPRESSIONS : Depending on purpose of impression making Depending on theories of impression making Depending on impression technique

24. DEPENDING ON PURPOSE OF IMPESSION MAKING Diagnostic impression : This impression is made for the purpose of diagnosis, treatment planning , and fabricating diagnostic casts . Materials used : Irreversible hydrocolloids . Primary impression: This is made for the purpose of making a preliminary cast on which special tray is constructed . Materials used: Impression compound , Irreversible hydrocolloids , putty and heavy body elastomeric impression materials . Final/Secondary impression : This is made for the purpose of fabricating a master cast on which the prosthesis is fabricated . Materials used : Zinc oxide eugenol paste , medium and light body elastomeric impression materials .

25. DEPENDING ON THEORIES OF IMPRESSION MAKING Mucostatic /Passive /Minimal pressure impression technique : In this technique oral mucosa is recorded in a resting state . Impression material of choice is Impression plaster . Mucocompressive /pressure impression technique : This technique compresses the denture bearing tissues during impression making . By recording the tissues in a compressed state , they would withstand functional forces , which compresses the tissues better . Impression materials of choice is Impression compound , irreversible hydrocolloids , putty and heavy body elastomeric impression materials . Selective pressure technique : It combines the principles of both pressure and minimal pressure techniques . Pressure is applied selectively on areas capable of resisting stress [stress bearing area s] and reduced from areas incapable of tolerating stress[relief areas ]. This is achieved through the design of the custom tray Example is zinc oxide eugenol impression with custom tray

26. DEPENDING ON IMPRESSION TECHNIQUE : Open mouth : This records the oral tissues in a static state with displacement . Closed mouth : In this technique oral mucosa is recorded in functional , compressed form .

27. PRINCIPLES OF IMPRESSION MAKING Retention Stability Support Preservation of residual structures Esthetics

28. RETENTION : The quality inherent in the dental prosthesis acting to resist the forces of dislodgement along the path of placement [GPT8] . STABILITY : The quality of a removable dental prosthesis to be firm ,steady , or constant , to resist displacement by functional horizontal or rotational stresses [GPT8] . SUPPORT : The resistance to the vertical forces of mastication , occlusal forces and other forces applied in a direction towards basal seat tissues . PRESERVATION OF RESIDUAL STRUCTURES : Accurate impression with selective pressure technique that places pressure only on stress bearing areas is important for this preservation of residual structures because it is important for long term success of the denture . ESTHETICS : For esthetics there should be proper thickness in denture border and denture flange .Border moulding ensures adequate thickness of this region .

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