Adhesive strength of metal brackets on existing composite, amalgam and restoration-enamel complex following air-abrasion protocols

Abstract

Bracket adhesion on restored tooth surfaces is occasionally necessary in clinical orthodontic practice. The objective of this study was to compare the effects of two air-abrasion methods on adhesion of metal brackets to enamel, resin composite, amalgam and composite/amalgam–enamel complexes. Cavities in standard dimensions (12.56mm2) were filled with resin composite (Anterior Shine, Cavex) and amalgam (non-gamma 2, Cavex) on bovine incisors (N=40), which were then embedded in acrylic resin. Metal brackets were bonded on the following surfaces (n=10 per group): (1) enamel, (2) enamel–composite, (3) enamel–amalgam, (4) composite, and (5) amalgam. All restorative materials were either silica (SiO2)-coated (CoJet, 30μm) and silanized (ESPE-Sil) or air-abraded with alumina (Korox, 50μm, Al2O3) and silanized (Monobond Plus). Enamel was etched with H3PO4 for 30s in Groups 1–3. Metal brackets were bonded onto the conditioned substrates. Specimens were stored in distilled water (24h, 37°C) following bonding. The brackets were then debonded using a Universal Testing Machine (1mm/min). Shear bond strength (SBS) data were recorded and failure types were categorized. Data (MPa) were analyzed using 1-way and 2-way ANOVA, Tukey׳s post hoc test and 2-parameter Weibull distribution. While substrate type significantly affected the SBS (p<0.001), surface conditioning did not show a significant effect (p=0.256). Interaction terms were not significant (p=0.159). Mean SBS was significantly higher (p<0.001) on enamel (26.72MPa), composite (29.97–31.37MPa) and enamel+silica-coated composite complex (25.89MPa) than those of other groups (10.96–20.64MPa). The presence of amalgam resulted in the lowest SBS regardless of the conditioning method (10.96–12.41). Air-abrasion with Al2O3 followed by Monobond Plus and silica-coating and silanization did not show significant difference (p>0.05). Weibull distribution presented lower shape for restoration-enamel complexes (2.20–6.31) compared to single component surfaces (10.14–12.15). SBS on composite was similar to that of enamel but it presented predominantly cohesive failures. Failure types were frequently cohesive in composite alone or composite–enamel complex.