Marginal adaptation and compressive strength of esthetic restorations

Background: Esthetic restorations in posterior teeth with composite resins are often performed in dental offices. Although composite materials have reached great development, composite shrinkage during polymerization is the main cause of failures of composite resin restorations that affects the integrity of the tooth/restoration bonding interface.

Objectives: To evaluate the compressive strength and marginal adaptation of composite onlays, using indirect and direct techniques, after thermal and mechanical cycling.

Methods: Onlay standardized cavities were prepared in fifty permanent molars and restored with Z-250 composite resin using indirect (IRT) or direct (DRT) restorative techniques. The restorations were submitted or not to thermal (500 cycles, 5 to 55º C) and mechanical cycling (50,000 cycles, 50N). The teeth were distributed into five groups (n=10): G1- IRT/cycling; G2- IRT/ no cycling; G3 – DRT/cycling; G4 – DRT/no cycling and G5 (control group) – sound teeth. All prepared teeth were stored in 100% relative humidity at 37ºC for 24 hours, followed by finishing with Soflex discs. A caries detector solution was applied on the tooth-restoration interface of all teeth for 5 seconds, followed by washing and drying. Four digital photographs were taken of each tooth surface. The extent of gaps was measured using standard software (Image-Tool 3.0). All groups were submitted to compression testing in a universal testing machine (INSTRON) at a crosshead speed of 1mm/min until failure. The compressive strength (CS) and marginal adaptation data were submitted to ANOVA and Tukey test (p<0.05).

Results: For both evaluation criteria (compressive strength and marginal adaptation), there were no statistically significant differences among the restorative techniques. Deterioration over time was observed for both types of restorations. However, the prevalence of catastrophic fractures increased among direct restorations

Conclusions: Onlay restorations prepared with both indirect and direct techniques had similar compressive strength and marginal adaptation. The application of thermal/mechanical cycling only influenced marginal adaptation.