CUSTOM IMPRESSION TRAYS .1. MECHANICAL-PROPERTIES

Dimensional stability of custom impression trays is an important facto r in determining the degree of accuracy achieved in forming a master c ast. Such trays must remain stable over time and must not exhibit perm anent deformation when a completed impression is removed from the oral cavity. Measurement of the mechanical properties allows comparison be tween various tray materials and is useful in interpreting data on str esses incurred during removal of the completed impression. In Part I o f this three-part series, the various mechanical properties of five tr ay resins: one autopolymerizing polymethyl methacrylate, one light-pol ymerizing, and three brands of thermoplastic resins were recorded and compared. The thermoplastic resins studied in this investigation exhib ited lower measured values for the strength and elastic modulus proper ties than the light-polymerizing resin and the autopolymerizing polyme thyl methacrylate resin studied.