ELASTOMERIC IMPRESSION MATERIALS [Autosaved].pptx

elastomers, polysulfide, addition silicone, condensation silicone, polyether

1. ELASTOMERIC IMPRESSION MATERIALS

2. INTRODUCTION Impression materials are used to produce a detailed replica of the teeth and the tissues of the oral cavity. From the replica or impression a model can be made which is used in construction of complete dentures, partial dentures, crowns, bridges etc.

3. DEFINITIONS 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. GPT 8

4. IDEAL REQUIREMENTS OF AN IMPRESSION MATERIAL They should be fluid enough to adapt to oral tissues. They should be viscous enough to be contained in the tray that is seated in the mouth. While in mouth, they should transform(set) into a rubbery or rigid solid in a reasonable amount of time. Ideally the total setting time should be less than 7 min. The set impression should not distort or tear when removed from the mouth.

5. The impressions made from these materials should remain dimensionally stable at least until the cast can be poured. The impression should maintain its dimensional stability after removal of a cast so that a second or third cast can be made from the same impression. The materials should be biocompatible. The materials, associated processing equipment, and processing time should be cost-effective.

6. CLASSIFICATION

7. ELASTOMERIC IMPRESSION MATERIALS DEFINITION A group of flexible chemical polymers that are either chemically or physically cross-linked; generally, they can be easily stretched and rapidly recover their original dimensions when applied stresses are relieved. GPT 9

8. CLASSIFICATION BASED ON CHEMICAL STRUCTURE

9. ACCORDING TO THE TYPE OF POLYMERIZATION Addition polymerization materials, e.g. Polyether , addition silicones. Condensation polymerization materials , e.g. condensation silicones and poly sulfides. ACCORDING TO VISCOSITY Very high viscosity Heavy body Medium body Light body

10. 1 st dental elastomer Also known as Mercaptan or Thiokol . Supplied as Collapsible tubes. Consists of base paste and catalyst paste. POLYSULFIDE

11. COMPOSITION BASE Polysulfide polymer 80-85% it has terminal mercaptan SH group Filler 44% (lithopone or titanium oxide) it provides strength Plasticizer 5% (dibutyl/dioctyl phthalate) viscosity to the paste Acclerator - sulphur CATALYST/ACCLERATOR Lead dioxide- 60-68% catalyst Plasticizers Oleic or stearic acid to control the rate of reaction.

12. SETTING REACTION

13. It is an exothermic reaction with3-4 rise in temperature. Moisture and temperature have a significant effect on the course of the reaction . Hot and humid conditions will accelerate the setting of polysulfide impression material. Mercaptan + Lead dioxide Polysulfide rubber + Lead oxide + Water

14. PROPERTIES Working time – 4-7 mins Setting time – 7-10 mins Excellent reproduction of details Dimensional stability – Percentage contraction at 24hrs – 0.4%-0.45% Shrinkage is due to loss of polymerization byproduct such as water

15. Deformation on removal – caused by rocking the impression while removal; it should be removed with a single swift pull High tear strength –2500-7000 N/m Biocompatibility – lowest cell death count Moderately hydrophilic Unpleasant odor and taste due to lead dioxide. Can be electroplated with copper sulphate

16. ADVANTAGES Low cost compared to silicones and polyether. Low working time. High tear strength. Good detail reproduction. DISADVANTAGES Messy, bad odour and may stain clothing. Requires use of custom tray. Stretching leads to distortion. Poor dimensional stability. Should be poured within 1hr. Long setting time.

17. CONDENSATION SILICONE Condensation reaction – a polymerization reaction in which the polymer chains all grow simultaneously and a reaction byproduct is formed. First type of silicone impression material. Also known as conventional silicone. The setting occurs in room temperature. Hence called as Room temperature vulcanization silicones (RTV).

18. Supplied as: 2 paste system in collapsible tubes Putty in jars. 3 viscosities Light body Medium body Putty CONDENSATION SILICONE

19. COMPOSITION

20. SETTING REACTION Hydroxy- terminated dimethyl siloxane Silicone rubber Ethyl alcohol Tetraethyl orthosilicate Stannous octoate Material sets by cross linking between terminal groups of the silicone polymers and the alkyl silicate to form a three dimensional network. Ethyl alcohol – the byproduct of the reaction. Its subsequent evaporation accounts for much of the contraction .

21. PROPERTIES Working time – 2.5-4mins Setting time – 6-8 mins Tear strength – 2300-2600N/m %contraction at 24hrs – 0.38-0.6% Contraction occurs due to evaporation of the alcohol Hydrophobic Can be electroplated with silver and copper

22. ADVANTAGES Good working time Clean Easily seen margins DISADVANTAGES High polymerization shrinkage Volatile alcohol byproduct Low tear strength Hydrophobic Pour immediately

23. ADDITION SILICONE Also known as Polyvinyl siloxane or Vinyl polysiloxane. Mode of supply : Collapsible tubes Consists of base paste and an accelerator paste Putty is supplied in jars Supplied in 4 viscosities Light body Medium body Heavy body Putty

24. COMPOSITION COMPONENTS FUNCTION BASE Polymethyl hydrogen siloxane and other siloxane prepolymers Undergoes crosslinking to form rubber Colloidal silica Filler CATALYST Divinyl polysiloxane Colloidal silica Filler Platinium Catalyst Palladium H2 absorber

25. SETTING REACTION The addition silicone is based on addition polymerization between divinyl polysiloxane and polymethylhydrosiloxane Platinum salt is the catalyst Vinyl Siloxane Silane Siloxane Silicone Rubber Platinum salt

26. PROPERTIES Working time- 2-4 mins Setting time – 4-6.5mins Tear strength – 1500-4300N/m Percentile contraction at 24hrs – 0.14-0.17% Pseudoplastic Exhibits lowest permanent distortion

27. ADVANTAGES Excellent detail reproduction Highly accurate High dimensional stability Can be poured up to 1 week Stock or custom trays Multiple casts Pleasant odor DISADVANTAGES Expensive Hydrophobic Low tear strength Possible hydrogen gas release Sulfer contamination by latex gloves.

28. POLYETHER First elastomer to be developed primarily to function as an impression material. Mode of supply : Collapsible tubes Available as base paste and accelerator paste Third tube containing thinner maybe supplied. Available in 3 viscosities Light body Medium body Heavy body

29. COMPOSITION COMPONENTS FUNCTION BASE Polyether prepolymer Becomes cross linked to form rubber Silica Filler, to control viscosity Glycol ether or phthalate plasticizer ACCLERATOR Alkyl aromatic sulfonate ester Initiates cross linking Silica Filler Phthalate plasticizer

30. PROPERTIES Working time – 3mins Setting time- 6mins Polyethers show a clearly defined working time with a sharp transition into the setting phase. This behavior is called Snap-set Tear strength – 1800-4800 N/m Percentile contraction at 24hrs – 0.19-0.24% Pseudo plastic Biocompatibility – may cause contact dermatitis.

31. ADVANTAGES Highly accurate Good dimensional stability Least hydrophobic Good surface details Multiple casts Good shelf life DISADVANTAGES Expensive Short working time Rigid difficult to remove from undercuts Bitter taste Absorbs water - changes dimension - Leaches components

32. CONCLUSION Elastomers since their introduction have revolutionized the art of impression making hence allowing the operator to provide accurate fitting restorations. Addition silicone and polyethers accounts for major portion of current practice. Condensation silicones and polysulfides are more sensitive with respect to handling considerations, mix and pour techniques, which may affect accuracy. “No impression material fulfills all the requirements” the selection of the material best suited for a particular clinical situation and technique rests with the dentist.