Abstract
Background. Repairing aged composite resin is a challenging process. Many surface treatment options have been proposed to this end. This study evaluated the effect of different surface treatments on the shear bond strength (SBS) of nano-filled composite resin repairs.Methods. Seventy-five cylindrical specimens of a Filtek Z350XT composite resin were fabricated and stored in 37°C distilled water for 24 hours. After thermocycling, the specimens were divided into 5 groups according to the following surface treatments: no treatment (group 1); air abrasion with 50-μm aluminum oxide particles (group 2); irradiation with Er:YAG laser beams (group 3); roughening with coarse-grit diamond bur + 35% phosphoric acid (group 4); and etching with 9% hydrofluoric acid for 120 s (group 5). Another group of Filtek Z350XT composite resin samples (4×6 mm) was fabricated for the measurement of cohesive strength (group 6). A silane coupling agent and an adhesive system were applied after each surface treatment. The specimens were restored with the same composite resin and thermocycled again. A shearing force was applied to the interface in a universal testing machine. Data were analyzed using one-way ANOVA and post hoc Tukey tests (P < 0.05).Results. One-way ANOVA indicated significant differences between the groups (P < 0.05). SBS of controls was significantly lower than the other groups; differences between groups 2, 3, 4, 5 and 6 were not significant. Surface treatment with diamond bur + 35% phosphoric acid resulted in the highest bond strength. Conclusion. All the surface treatments used in this study improved the shear bond strength of nanofilled composite resin used.
Highlights
This study evaluated the effect of different surface treatments on the shear bond strength (SBS) of nanofilled composite resin repairs
The specimens were divided into 5 groups according to the following surface treatments: no treatment; air abrasion with 50-μm aluminum oxide particles; irradiation with Er:YAG laser beams; roughening with coarse-grit diamond bur + 35% phosphoric acid; and etching with 9% hydrofluoric acid for 120 s
The highest shear bond strength was found in group 4 and the
Summary
Composite resins have significantly improved over the last decades; failures may occur as a result of discoloration, secondary caries, margin ditching or fractures.[1,2,3,4] Treatment choices are repairing or replacing the whole restoration.[1,5,6,7,8,9] Replacing a deficient restoration completely results in overextension of the preparation,[10] loss of sound tooth structure and increased risk of pulpal exposure.[3,7,8,9,11] According to several clinical studies, repairing the pre-existing restoration is a more conservative alternative that can increase the longevity of the restoration, preserve the sound tooth structure and reduce operative trauma.[4,5,12]In clinical practice, bonding between two composite layers is accomplished by the presence of an oxygen-enriched surface layer that remains unpolymerized.[3,5,7,13] This layer contains unreacted C=C bonds, allowing the monomers of the new composite resin to bond to it.[7,13,14] In an aged composite resin the adhesion to a new one reduces 25% to 80% of its original cohesive strength due to a diminished amount of unreacted double bonds.[1,12,15] The success of new composite-to- old composite resin adhesion depends on the chemical composition of the surface, roughness, wetting and the surface conditioning methods applied.[7,12,13] different surface treatment modalities have been used to enhance the repair bond strength of composite resins,[1,2,4,7,8,9,16] including bur roughening, etching with hydrofluoric or phosphoric acids, air abrasion, silica coating and silanization.[4,6,7,8,9,15,16] In recent years there has been more focus on the efficiency of lasers for composite repair bond strength, including Er:YAG laser.[4,8,9,17]. The specimens were divided into 5 groups according to the following surface treatments: no treatment (group 1); air abrasion with 50-μm aluminum oxide particles (group 2); irradiation with Er:YAG laser beams (group 3); roughening with coarse-grit diamond bur + 35% phosphoric acid (group 4); and etching with 9% hydrofluoric acid for 120 s (group 5). Another group of Filtek Z350XT composite resin samples (4×6 mm) was fabricated for the measurement of cohesive strength (group 6).
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