Effect of occlusal loading and mechanical properties of resin composite on stress generated in posterior restorations.

PURPOSE: To investigate the effect of the occlusal load condition in association with the mechanical properties of resin composite, expressed by elastic modulus and post-gel shrinkage, on stresses in a premolar restored with various composites. METHODS: Five resin composites (4 Seasons, Beautifil II, Filtek LS, Filtek Z250, and Z100) indicated for restoring posterior teeth were tested. Elastic modulus was measured using Knoop indentation tests (n=5). Post-gel shrinkage was measured with strain gauges (n = 10). Finite element analysis was used to calculate the stresses in a two-dimensional pre-molar model under four conditions: (We, without occlusal contact, representing stresses due to composite shrinkage only; Ct: contact generated between enamel of restored tooth and antagonist tooth; Cm: contact on tooth/composite restoration margin; Cc: stable centric contact on the composite restoration). RESULTS: Elastic modulus varied between 12.6 (Filtek LS) and 21.5 (Z100) GPa; post-gel shrinkage varied between 0.11 (Filtek LS) and 0.96 (Z100) vol%. Composites with higher elastic modulus and post-gel shrinkage increased stress in the restored tooth. Occlusal contact on the tooth/composite restoration margin increased the stresses around the margin of the restoration. Stable centric contact on the restoration resulted in better stress distribution.