Relationship between bond strength and marginal and internal adaptation of composite restorations photocured by different methods

Abstract

Objective. This study evaluated the relationship between bond strength and marginal and internal adaptation of composite restorations photocured using different methods with a quartz-tungsten-halogen light. Material and Methods. A push-out test was performed to evaluate bond strength of conical restorations in 50 bovine incisors. To evaluate marginal (external) and internal restoration adaptation, 50 circular all-enamel margin preparations were done in bovine incisors. For both tests, the preparations were filled with Esthet•X resin composite. Specimens were distributed into 5 groups (n=10) depending on photoactivation method: G1: continuous light 700; G2: continuous light 150; G3: soft-start; G4: intermittent light; and G5: pulse-delay. The energy density for each method was standardized: 14 J/cm2. Caries Detector® (Kuraray) was placed in restoration margins for detection of marginal adaptation. The percentage of interfaces present as gaps was determined using digital images. Specimens were then sectioned, stained, and the internal adaptation was recorded in a similar manner. Data were submitted to ANOVA and the Tukey HSD test, pre-set α = 0.05. Results. Bond strength G5 (7.2 MPa±1.3) was significantly greater (p=0.00280) than G1 (4.6 MPa±1.5). G2, G3, and G4 showed equivalent, intermediate strength values. No significant difference was found in marginal adaptation of any of the groups (p=0.16911). Internal adaptation results were the inverse of strength results: G5 (2.8%±4.9) showed significantly less (p=0.00979) gap formation compared to G1 (10.1%±6.2). Conclusion. Some modulated photocuring methods can increase bond strength while decreasing internal gap formation. An inverse relationship was found between push-out bond strength and internal adaptation. Marginal adaptation was not affected by any photoactivation method.