Effect of acid etching, adhesive type and composite resin aging on the bond strength of orthodontic brackets to resin composite

In many cases, it is necessary to bond orthodontic attachments to composite resin restorations. The aim of this study was to evaluate the effect of different surface treatments and duration, aging and the adhesive type on shear bond strength of orthodontic brackets to composite resin surfaces. In this experimental study, 204 discs of two composite resins (Z100 and Point 4) were prepared and mounted in acrylic blocks. Half of the specimens in each group (52) were stored in distilled water at 37ºC for 3 months before bonding to evaluate the effect of aging. Each of the 4 groups were subdivided into 4 subgroups of 13 specimens each according to the surface treatment (application of diamond bur followed by phosphoric acid etching and phosphoric acid etching alone) and adhesive system used (self-curing and light-cured). Shear bond strengths were measured with Dartec testing machine after bracket bonding. Statistical analysis was carried out by four-way ANOVA (α=0.05). There were no statistically significant differences in mean shear bond strengths between the two restorative composite resins (p value = 0.529). Other variables under study (duration, surface treatment type and adhesive type) had statistically significant effects on the shear bond strength of orthodontic brackets to composite resin surfaces (p value < 0.05). Surface treatment, adhesive type and time elapsed after composite setting had significant effects on bond strength of orthodontic brackets to composite resin surfaces. Application of light-cured adhesives after surface roughening by bur and acid-etching can increase bond strength dramatically.