![]() The latter have been introduced relatively recently and are also called polyvinylsiloxanes ( Lacy et al., 1981a, Lacy et al., 1981b). Four basic types of elastomer impression materials are currently in use in the dental profession: (1) silicone rubbers which polymerize by a condensation reaction, (2) polysulfide (mercaptan) rubbers, (3) polyethers, and (4) silicones which polymerize an addition reaction. ![]() In the last decade, several investigators have recommended using newer elastomeric materials such as polyvinylsiloxane and polyether for final impressions to replace the older and more traditional materials ( Chee and Donovan, 1992, McCord et al., 2005, Petrie et al., 2005). The manner in which the impression was made may be more important than the material ( Firtell and Koumjian, 1992, Ivanhoe et al., 2002). More important than selection of material is the dentist’s complete understanding of the concepts and principles in impression making ( Zarb et al., 1985, Lang, 1994, Boucher, 2004, Petropoulos and Rashedi, 2005, Al-Ahmad et al., 2006). Selection of material is left to the discretion of the dentist, who makes choices based on personal preference and experience. The materials available for impression tray construction are as varied as are the materials for border molding and the final impression. Some impression materials have been developed to accomplish specific goals and, at the time at least, were considered desirable for the purpose ( Starcke, 1975, Zinner and Sherman, 1981, Zarb et al., 1985). The history of complete denture impression procedures has been influenced largely by the development of impression materials from which new ideas and techniques arose. In the case of an edentulous arch, this requires a unique combination of managing movable soft tissue commensurate with integrating different materials and a technique for accurate reproduction. An impression is a record, a facsimile of mouth tissues taken at an unstrained rest position or in various positions of displacement ( Devan, 2005).
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