Effect of different surface treatments on shear bond strength of orthodontic brackets on microfilled and hybrid composite restorations

Abstract

Bond failure at the interface of bracket and composite restoration occurs in cases of improper surface preparation. Materials and methods: Three handred sixty composite cubes were randomly divided into 18 groups of 20 samples each, according to the type of composite (microfilled Heliomolar, or hybrid Tetric-N-Ceram), mechanical preparation (without preparation, Roughening with bur, or air abrasion) and chemical preparation (H3PO4 etching, Single Bond, Monobond-S). Samples were kept in distilled water at 37C for 14 days. Brackets were then bonded on to the prepared surfaces with a no-mix composite, and the samples were kept again in distilled water at 37C for 1 week. Universal testing machine was used to measure SBS in debonding of bracket from the samples. Mean SBS of groups were analyzed using Univariate ANOVA and Tukeys post-hoc test. Adhesive Remnant Index (ARI) and the site of debonding were also evaluated. Results: With mirofilled composite, mechanical preparation (sandblasting and bur Roughening) resulted in significant increase in SBS. With hybrid composite, only sandblasting caused an increase in SBS. Single Bond showed a significantly higher SBS compared to phosphoric acid etching and Monobond-S with microfilled composite. In hybrid composite, however, etching and Single Bond revealed a higher SBS compared to Monobond-S. In hybrid composite group, the highest SBS was seen in Single Bond with air abrasion (32.11 MPa) and the lowest SBS was seen in Monobond-S without mechanical preparation (19.88 MPa). In the mircofilled composite group, the highest SBS was observed with Single Bond with bur preparation (28.36 MPa) and the lowest SBS was observed with acid etching without mechanical preparation (11.73MPa). The absence of adhesive on the cohesive composite was the most frequently recorded ARI. Cohesive failure occurred in 72.77% and 59.44% of microfilled and hybrid composite samples, respectively. Conclusion: Hybrid composites show a higher bracket-composite SBS compared to microfilled composites. SBS is higher in cases in which a combination of a mechanical and a chemical preparation method has been used. Cohesive composite failures occur often, with a higher instance in microfilled composite.