Different Composite Veneer Surface Preparations for Metal Orthodontic Bracket Bonding: An In Vitro Study

Objective: This research aimed to assess the shear bond strength (SBS) of metal brackets bonded to composite veneers using different surface preparations. Methods: One-hundred composite disks were divided into 10 different groups whereby each group combines a surface preparation (roughening or no roughening), etching agent (37% phosphoric or 9.5% hydrofluoric acid), adhesive protocol (self-etch or total-etch), and bonding agent (with or without G-Premio Bond). Orthodontic metal brackets were bonded to prepared composite surfaces by Transbond XT resin and light-cured. The prepared samples were incubated at 37˚C for 24 h and underwent thermocycling. A universal testing machine was loaded until the failure moment to assess SBS. Adhesive remnant index (ARI) was used to classify the failure sites between the composite surface and bracket base. Tukey, Fisher's exact, and chi-square tests were used for statistical analyses. Statistical significance level was 0.05. Results: Surface roughening and the type of material used for surface preparation significantly affected bond strength (p  < 0.0001). There was no significant difference in bond strength between phosphoric acid and hydrofluoric acid (p  > 0.05). The highest bond strength was observed in the group with roughening + total-etch with phosphoric acid + G-Premio Bond (10.24 ± 2.99 MPa). The lowest bond strength was found in the group without roughening, etched with phosphoric acid (1.47 ± 1.06 MPa). In the groups without roughening, ARI scores of 0 and 1 were found, while in the groups with roughening, ARI scores of 0, 1, and 4 were observed. Conclusions: The SBS with G-Premio Bond is high with ARI score 4 which may pose a risk of damage to the veneers during debonding. Therefore, surface preparation of the veneers that result in lesser bond strength should be used unless in patients with frequent bracket breakages.