Silicone based impression materials

Condensation silicones

1. SILICONE BASED IMPRESSION MATERIALS CONDENSATION SILICONE AAMIR GODIL FIRST YEAR P.G. DEPARTMENT OF PROSTHODONTICS M.A.R.D.C.

2. OUTLINE 2 CONDENSATION SILICONE IMPRESSION MATERIAL Introduction Chemistry of Condensation Silicone Impression Material Review of Physical and Chemical Properties Advantages and Disadvantages Conclusion

3. INTRODUCTION 3 CONDENSATION SILICONE IMPRESSION MATERIAL

4. Elastic impression materials were developed from synthetic rubber by S.L. Pearson at the University of Liverpool in 1955 .   The introduction of rubber-based, polysulfide impression materials was followed by silicone-based materials, both of which are still in use. Following these, elastic polyether impression materials were introduced, followed in recent times by polyvinylsiloxane impression materials. Hoffman- Axthelm , W. History of Dentistry. Chicago, Quintessence Put. CO., Inc., 1981. p. 284 4

5. Condensation silicone was the first type of silicone impression material. Also known as conventional silicones. Setting occurs at room temperature , and so are also called RTV silicones. CONDENSATION SILICONE IMPRESSION MATERIAL 5

6. CHEMISTRY OF CONDENSATION SILICONE IMPRESSION MATERIAL (C- Silicone) 6 CONDENSATION SILICONE IMPRESSION MATERIAL

7. 7 CONDENSATION SILICONE IMPRESSION MATERIAL

8. COMPOSITION Supplied as two paste system: Base paste : • Hydroxyterminated polysiloxane polymer • Filler ( cristobalite , talc, starch ) Catalyst: Liquid catalyst: Cross-linking agent ( e.g tetraethoxy silane ) + Activator ( dibutyl -tin dilaurate ) Paste catalyst: Cross-linking agent, activator, inert oil Filler 8 CONDENSATION SILICONE IMPRESSION MATERIAL

9. Institute of Medical Biochemistry, 1st Fac. Med., Charles University, and Institute of Dental Research in Prague 9

10. The instability of condensation-type silicone materials is attributed to the production of an alcohol byproduct during polymerization A two-step putty/wash technique was developed in which the use of a thin layer of wash material minimizes the amount of alcohol byproduct and thereby retains the dimensional stability within acceptable limits. (Craig RG. A review of properties of rubber impression materials. J Mich Dent Assoc 1977;59:254-61.) To further overcome some of the problem associated with condensation silicones, another silicone material was introduced that polymerizes by an addition reaction in which no byproduct is produced. CONDENSATION SILICONE IMPRESSION MATERIAL 10

11. REVIEW OF PHYSICAL AND CHEMICAL PROPERTIES 11 CONDENSATION SILICONE IMPRESSION MATERIAL

12. OVERVIEW CONDENSATION SILICONE IMPRESSION MATERIAL 12

13. The proposed definition of the working time of an elastomeric impression material suggested by ISO (1988) is "the period of time between the start of mixing and the commencement of the development of elasticity and the loss of plasticity" This would seem to be a very sensible definition, but most techniques used for the evaluation of working time simply monitor a change in viscosity or rigidity (Wilson, 1966; McCabe and Bowman, 1981; ISO, 1988) CONDENSATION SILICONE IMPRESSION MATERIAL 13 WORKING AND SETTING TIME

14. MEAN WORKING TIME MEAN SETTING TIME Usually, working time is measured at room temperature and setting time at mouth temperature 14 CONDENSATION SILICONE IMPRESSION MATERIAL

15. HOW ARE THE WORKING AND SETTING TIME ASSESSED? Penetrometer tests are used End of working time: The time when a blunt needle of specified dimension fails to penetrate the volume of given material at a specified depth End of setting time: The time when a blunt needle of specified dimension fails to permanently indent the set material In British Standards Test, reciprocating rheometer is used. The property recorded is more close to viscosity and shear thinning properties compared to elasticity 15 CONDENSATION SILICONE IMPRESSION MATERIAL

16. WHAT ARE THE FACTORS INFLUENCING WORKING AND SETTING TIME? 16 CONDENSATION SILICONE IMPRESSION MATERIAL

17. DIMENSIONAL STABILITY WHAT ARE THE FACTORS AFFECTING DIMENSIONAL STABILITY? 17 CONDENSATION SILICONE IMPRESSION MATERIAL

18. Linear contraction of four elastomeric impression materials SIGNIFICANCE To attain maximum accuracy, polysulfide and C- silicone casts should be poured immediately. Immediately is defined as the period within the first 30 minutes, even for putty wash technique. (Phillips’) Polyether and A-silicone will yield accurate casts even after 24 hours to one week. 18 CONDENSATION SILICONE IMPRESSION MATERIAL

19. DIMENSIONAL CHANGE AFTER SETTING The unrestrained dimensional change after setting has been reported by Craig (1986b), Mansfield and Wilson (1975), Eames et al (1979), Ohsawa and Jorgensen (1983), and Bell et al (1976). The values show some variation from product to product of the same type, but the decreasing order of dimensional stability is ADDITION SILICONES POLYETHERS POLYSULFIDES CONDENSATION SILICONES (After 24 hr in air of 50% relative humidity) CONDENSATION SILICONE IMPRESSION MATERIAL 19

20. EFFECT OF HUMIDITY ON DIMENSIONAL STABILITY Bell et al (1976) The effect of low, medium, and high humidity on the dimensional changes of stored rubber impressions of polysulfides , condensation silicones, and polyethers The dimensional change of all three types was affected. The standard polysulfide was affected the least, followed by the condensation silicone and polyether The optimum storage condition for polysulfides was high humidity; for condensation silicone, medium humidity; and for polyether, low humidity CONDENSATION SILICONE IMPRESSION MATERIAL 20 BELL, J.W.; DAVIES, E.H.; and VON FRAUNHOFER, J.A. (1976): The Dimensional Changes of Elastomeric Impression Materials under Various Conditions of Humidity, / Dent 4:73-82.

21. REPRODUCTION OF ORAL DETAIL ACCURACY OF STONE MODELS A variety of laboratory models has been used to evaluate the accuracy of rubber impression materials. 21 CONDENSATION SILICONE IMPRESSION MATERIAL ( Reisbick and Matyas , 1975; Stackhouse, 1975; Stauffer et al., 1976; Marcinak et al., 1980; Lacy et al., 1981a, b; Augsburger et al., 1981; Marcinak and Draughn , 1982; Finger and Ohsawa , 1983; Johnson and Craig, 1985)

22. RECOVERY FROM UNDERCUTS Johnson and Craig (1985) The addition and condensation silicones demonstrated the best recovery as a result of being removed from undercuts and the least change between models from an initial and a second pour CONDENSATION SILICONE IMPRESSION MATERIAL 22

23. Tjan et al. (1986) and Linke et al. (1985) Standard gold castings were used to evaluate the accuracy of dies from the impressions of crowns, MOD's, and occlusal inlays. Agar was less accurate than were silicones and the polyether for making impressions of occlusal or MOD inlays. A delay in pouring condensation silicone impressions of MOD's and crowns resulted in a decrease in accuracy which was not observed for occlusal inlays. CONDENSATION SILICONE IMPRESSION MATERIAL 23 TJAN, A.H.L.; WHANG, S.B.; TJAN, A.H.; and SARKISSIAN, R. (1986): Clinically Oriented Evaluation of the Accuracy of Commonly Used Impression Materials, / Prosthet Dent 56:4-8. LINKE, B.A.; NICHOLLS, J.I.; and FAUCHER, R.R. (1985): Distortion Analysis of Stone Casts Made from Impression Materials,/ Prosthet Dent 54:794-802 ACCURACY

24. WETTING AND CONTACT ANGLE CONDENSATION SILICONE IMPRESSION MATERIAL 24

25. COMPATIBILITY WITH DIE MATERIALS Lorren et al. (1976) measured the contact angles of mixes of dental stone on elastic impression materials and found values : CONDENSATION SILICONE IMPRESSION MATERIAL 25 Condensation Silicone 95° Polysulfide 70° Polyether 50° Addition Silicone ( Hydrophillic ) 40° They also found a direct relationship between the contact angle and the number of bubbles occurring on casts. LORREN, R.A.; SALTER, D.J.; and FAIRHURST, C.W. (1976): The Contact Angles of Die Stone on Impression Materials, / Prosthet Dent 36:176-180.

26. Norling and Reisbick (1979) measured the contact angles of saturated calcium sulfate dihydrate solutions to be: Polysulfide impressions = 80° Condensation silicone impressions = 97° polyether impressions = 15° When they incorporated non-ionic surfactants into polysulfide and silicone impression materials, the wettability of gypsum mixes increased and the number of surface bubbles decreased. The working time of the silicone was increased; however, the working time of the polysulfide was unchanged, as was the permanent deformation or dimensional change. CONDENSATION SILICONE IMPRESSION MATERIAL 26 NORLING, B.K. and REISBICK, M.H. (1979): The Effect of Nonionic Surfactants on Bubble Entrapment in Elastomeric Impression Materials, / Prosthet Dent 42:342-347

27. DISINFECTION Recommended material for elastomeric impression materials: Glutaraldehydes Chlorine compounds Iodophores Phenolics Method: Immersion Disinfectant requiring more than 30 minutes exposure time are not recommended. 27 CONDENSATION SILICONE IMPRESSION MATERIAL

28. 28 CONDENSATION SILICONE IMPRESSION MATERIAL COMMERCIALLY AVAILABLE DISINFECTANTS

29. An evaluation of polysulfides , poly ethers, and condensation and addition silicones with a variety of disinfectants was conducted. They found in some cases that some disinfectants adversely affected impression materials, and therefore care should be used in selection of a satisfactory combination. The smallest dimensional changes were observed for addition silicones with: CONDENSATION SILICONE IMPRESSION MATERIAL 29 BERGMAN, M.; OLSSON, S.; and BERGMAN, B. (1980): Elastomeric Impression Materials. Dimensional Stability and Surface Detail Sharpness Following Treatment with Disinfection Solutions, Siued Dent J 4:161-167. STORER, R. and McCABE , J.F. (1981): An Investigation of Methods Available for Sterilising Impressions, Br Dent J 151:217-219. Bergman et al (1980) Storer and McCabe (1981) Cidex 2.4% activated glutaraldehyde Techno- sept Propanolol Hibitane 8g/L chlorhexidine gluconate K-644 Potassium bromide Benzalkon Benzalkonium chloride

30. RHEOLOGICAL PROPERTIES The data for condensation silicones could be fitted to kinetic equations, but the kinetics was not consistent with the stoichiometry . However, the dependence of reaction rate on catalyst-base ratio was qualitatively consistent with kinetic and network considerations. 30 CONDENSATION SILICONE IMPRESSION MATERIAL COOK, W.D. (1982a): Rheological Studies of the Polymerization of Elastomeric Impression Materials. I. Network Structure of the Set State, / Biomed Mater Res 16:315-330. COOK, W.D. (1982b): Rheological Studies of the Polymerization of Elastomeric Impression Materials. II. Viscosity Measurements, / Biomed Mater Res 16:331-344. COOK, W.D. (1982c): Rheological Studies of the Polymerization of Elastomeric Impression Materials. III. Dynamic Stress Relaxation Modulus, / Biomed Mater Res 16:345-357.

31. Polysulfide C-Silicone A- Silicone Polyether 31 CONDENSATION SILICONE IMPRESSION MATERIAL Creep Compliance The rate at which strain increases for a constant applied stress

32. ELASTICITY The material should be adequately elastic such that it does not undergo permanent deformation on retrieval Setting time as mentioned by the manufacturer may not be adequate to provide sufficient elasticity under clinical conditions Amount of permanent deformation following strain in compression 32 CONDENSATION SILICONE IMPRESSION MATERIAL

33. CONDENSATION SILICONE IMPRESSION MATERIAL 33

34. Refers to the resistance to fracture of an elastomeric material subjected to a tensile force acting perpendicular to surface flaw. Tear strength (N/m) (lb/m) = Maximum force needed to pull the specimen apart (N) Thickness of the specimen (m) TEAR STRENGTH 34 CONDENSATION SILICONE IMPRESSION MATERIAL

35. WHAT IS THE SIGNIFICANCE OF TEAR STRENGTH? Material can tear while recording impression of subgingival or interproximal areas If a material tears in such areas, a portion may remain embedded in the gingival sulcus or the interproximal area, which may be difficult to locate due to lack of radiopacity of these materials (except polysulfides ) Tear Strength 35 CONDENSATION SILICONE IMPRESSION MATERIAL

36. BIOCOMPATIBILITY Cell Cytotoxicity Analysis: +++ Significance: If evidence of tearing is detected during careful inspection of gingival sulcus , immediate retrieval of the remnant should be done 36 CONDENSATION SILICONE IMPRESSION MATERIAL

37. ADVANTAGES AND DISADVANTAGES 37 CONDENSATION SILICONE IMPRESSION MATERIAL

38. 38 CONDENSATION SILICONE IMPRESSION MATERIAL

39. CONCLUSION 39 CONDENSATION SILICONE IMPRESSION MATERIAL

40. Thank You 40 CONDENSATION SILICONE IMPRESSION MATERIAL