Effect of Light-unit And Aging Process on Bonding of Composite-restorations

Objectives: To evaluate the effect of light-curing-units (LCU) and aging process on bond-strength and marginal integrity of composite-resin restorations. Methods: Proximal cavities (4.5x6.0x1.5mm) with cervical margin in dentin were prepared in 200 bovine incisors. The adhesive system Single Bond/3M ESPE and the composite-resin Filtek Z250/3M ESPE were used for the restorations. The LCU used were: HAL–Halogen–Optilux501/Demetron; LED–Blue LED–EliparFreeLight2/3M ESPE; LAS–Argon Laser–AccCure3000/LaserMed and PAC–Xenon Plasma Arc–Apollo95E Elite/DMD. After 24h, restorations were polished and submitted to the following aging process (n=10): TC: thermal aging(1,000cycles: 5±2^oC/55±2^oC); CM: mechanical aging (200,000cycles: 75N/2Hz); CM/TC: association between mechanical and thermal aging; 1A: one year storage in Hank solution and CM/TC/1A: association of all aging process. Epoxy resin replicas for marginal gap evaluation at SEM (500-1,000x) in terms of length (μm) and incidence (%) were obtained before and after each aging process. Then, teeth were cut in slabs that were trimmed to an hourglass shape at the bond interface (1mm²) for microtensile test (v=0.5mm/min). Results: There were no difference among LCU related to bond-strength values; however significant difference could be seen among aging process (ANOVA/Tukey;alpha=5%). Specimens submitted to CM/TC/1A and 1A showed significantly inferior bond-strength than CM, TC and CM/TC groups; however no difference could be seen between TC and 1A. Prior to aging, there was no difference among LCU related to gaps length and incidence. Following aging, there was significant increase on gaps length and incidence (Wilcoxon signed rank; Student's t). PAC and LAS showed gap percentage higher than HAL; also, PAC presented gap length greater than HAL and LED(ANOVA/Tukey;alpha=5%). Conclusion: The association of all types of aging process significantly damaged the bond strength of composite-resin to proximal dentin; moreover, none of the LCU was able to maintain the quality of marginal sealing after aging(FAPESP03/12592-8).