CUSP MOVEMENT IN PREMOLARS RESULTING FROM COMPOSITE POLYMERIZATION SHRINKAGE

This study examined the effect of cavity size, hydration conditions an d type of composite on cusp movement following placement of MOD compos ite restorations in vitro. A microscope with a micrometer stage was us ed to measure deflection of cusps for 14 days after initiation of curi ng. The intercuspal width decreased for the first few minutes after th e composites were placed, then increased toward the original dimension s. Teeth with small cavities contracted less than those with large cav ities, and recovery was complete or nearly complete only in teeth with small cavities. Hydrated teeth and restorations recovered more rapidl y and more completely than those that were dry. Differences in deflect ion of the cusps were observed with two different restorative material s.