Influence Of Photoactivation Method On Bond Strength And Microhardness Composites

Objective: The aim in this study was to evaluate the influence of photoactivation method on bond strength and Knoop microhardness of resin composites stored for 6 months.

Method: Resin composites Filtek Z350 and Filtek LS were bonded in cavities made on 80 human premolars and photoactivated with QTH device using two photoactivation methods: continuous light (600 mW/cm²) or soft-start (150 mW/cm² + 600 mW/cm²). Twenty samples of each resin composite were evaluated for microhardness and push-out bond strength after 24h and the others twenty were stored for 6 months in distilled water. Both the microhardness and bond strength tests were made on the same specimen (n=10). The data were submitted to three-way ANOVA and Tukey’s test (α=0.05).

Result: Filtek Z350 (80.5 KHN) showed Knoop microhardness significantly higher than Filtek LS (56.9 KHN). There was no significant difference between continuous light (68.3 KHN) and soft-start (69.1 KHN), neither nor 24 h (69.6 KHN) and 6 months (67.8 KHN) storage time in distilled water. Push-out bond strength test showed no significant difference between Filtek LS (16.5 MPa) and Filtek Z350 (16.4 MPa). Soft-start (17.6 MPa) was significantly higher than continuous light (13.8 MPa) in 6 months, but not for 24 h (16.1 MPa and 18.1 MPa, respectively). The storage for 24 h showed higher push-out bond strength than 6 months for continuous light, but not for soft-start method.

Conclusion: Soft-start method showed ability to preserve the bond strength after 6 months, while did not showed decrease on Knoop microhardness. Filtek Z350 was superior to Filtek LS in mechanical properties while had no influence on bond strength results.