Shear bond strength of repaired composite-resin using different repair protocols

Objective: Resin-based composite restorations, in common with all restorations, suffer deterioration and degradation in clinical service. In some circumstances it is preferable to repair, rather than replace, existing composite restorations. Although various methods have been suggested to establish adequate bond strength between aged and new composite, there is currently no consensus regarding which repair protocol is most successful. The objective of this study was to evaluate the effect of number of bonding agent coatings and bonding agent application time on shear bond strength between artificially aged and new composite and surface topography of the composite surfaces.

Method: Cylindrical composite-resin (Spectrum, Dentsply, Germany) specimens (n=200) were prepared using a custom-made PTFE mold. Specimens were aged by storage in artificial saliva for 21 days followed by thermal cycling (55, 5°C) for 1000 cycles, and randomly divided into 10 groups of 20 specimens. Specimens were roughened using silicon carbide paper and subjected to different repair protocols based on a factorial study design, using 0, 1, 2 or 3 coatings of bonding agent (XP Bond, Dentsply, Germany) with an application time of 15, 30 or 45 s. Subsequently, increments of new composite (Ceram X Mono, Dentsply, Germany) were applied to the aged, treated composite, and light cured. Shear bond strength was measured using a Universal mechanical testing machine.

Results: Application of 3 coats of bonding agent for 15 s each resulted in statistically significantly enhanced shear bond strengths [24MPa (p < 0.0001)] when compared to the control group (18.9MPa). Failure was predominantly adhesive, and there were no clear morphological differences between the differently treated composite surfaces.

Conclusions: All protocols resulted in reasonable shear bond strengths, but applying 3 coats of bonding agent for 15 s each to the “aged” composite surface resulted in the highest bond strength compared to no bonding agent.