Evaluation of the effect of aging on the shear bond strength between old composite resin restoration and the repair composite resin: an in-vitro study.

Background: The current study aimed to evaluate the effect of aging on the repair bond strength between old composite resin and repaired composite resin and to evaluate which type of repair composite material provides better bond strength in different time durations.

Methods: Eighty nano-hybrid composite specimens were randomly divided into four groups (N.=20) and exposed to accelerated aging from 0 to 2 years. Each group was further divided into two subgroups, A and B, repaired with packable and flowable composite respectively, after micro-abrasion treatment. Shear bond strength was assessed and statistically analyzed.

Results: It was observed that with an increase in aging time, the bond strength of both the composite materials used for repair decreased. The flowable composite's mean bond strength (22.09±0.65, 18.74±2.36, and 17.74±2.38 MPa) was more than the packable composite (21.97±0.84, 17.97±3.85, and 15.97±2.45 MPa) used for repair on aged specimens. In contrast, the bond strength of the packable was more than the flowable composite in control group specimens that were not aged (23.25±0.89 vs. 22.40±1.26).

Conclusions: As restored composites age, their bond strength decreases. Flowable composite displays better repair shear strength than packable composite as aging progresses. Micro abrasion followed by flowable composite bonding can repair aged composite restorations effectively.