This study evaluated the relationship between the amount of cuspal deflection and linear polymerization shrinkage in resin composites and polyacid modified resin composites (compomers). Materials included were Dyract AP, Compoglass F, Z100, SureFil, Pyramid, Synergy Compact, Heliomolar and Heliomolar HB. To measure polymerization shrinkage, a custom-made linometer (R&B, Daejon) was used. Ten measurements were made for each group, and the amount of linear shrinkage that occurred in 60 seconds was statistically compared by one-way ANOVA analysis and Tukey's test. To measure the cuspal deflection of teeth, standardized MOD cavities were prepared in extracted maxillary premolars. After a self-etching adhesive was applied, the cavities were bulk filled with one of the filling materials. Fifteen teeth were used for each material. Cuspal deflection was measured by a custom-made cuspal-deflection measuring device. One-way ANOVA analysis and Tukey's test were used to determine differences between the materials. The correlation of polymerization shrinkage vs cuspal deflection was analyzed by regression analysis. The amount of polymerization shrinkage from least to greatest was Heliomolar, SureFil < Heliomolar HB < Z100, Synergy Compact < Dyract AP < Pyramid, Compoglass F (p<0.05). The amount of cuspal deflection from least to greatest was Z100, Heliomolar, Heliomolar HB, Synergy Compact, SureFil, < Compoglass F < Pyramid, Dyract AP (p<0.05). Both the amount of polymerization shrinkage and cuspal deflection were highly correlated (p<0.001).
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