Cuspal flexure of composite-restored typodont teeth and correlation with polymerization shrinkage values

The relationship between post-gel shrinkage, total shrinkage, and cuspal flexure was examined. Cuspal flexure was measured on restored typodont teeth, which offered a standardized tooth shape for comparison of shrinkage stress effects among restorative composites.

Six restorative composites were compared (Filtek LS, Venus Flowable, Tetric EvoCeram, Filtek Flowable, Esthet-X, and Filtek Supreme). Total shrinkage was determined from changes in projected surface area before and after polymerization (n=10). Post-gel shrinkage was determined with a biaxial strain gauge that measured strain development during polymerization (n=10). Cuspal flexure was determined using typodont maxillary second premolars with standard MOD slot preparation (n=10). Flexure was determined by comparing the three-dimensionally scanned cuspal surfaces before and after restoration. Restoration bonding to the typodont cavity was achieved by sandblasting and adhesive application. Bond integrity was verified by measuring dye penetration. Results were analyzed using ANOVA and Student-Newman-Keuls post hoc test (significance level 0.05). Pearson was used for correlations.

Total and post-gel shrinkage were significant different for all composites (t-test; P<0.001). Depending on the composite, only 9-41% of the total shrinkage was recorded as post-gel shrinkage. Bond integrity of restored typodont teeth was 96-99%. Cuspal flexure correlated strongly with post-gel shrinkage, but there was no correlation with total shrinkage.

Cuspal flexure of restored typodont teeth showed the effect of shrinkage stress caused by polymerizing composite restorations, ensuring standardization while maintaining the effects of tooth/cavity geometry. Post-gel shrinkage gave a good indication to screen composites for the stress they may generate; total shrinkage had no direct correlation with stress.