Bond strength analysis of custom base variables in indirect bonding techniques

Introduction: Various methods are used to prepare the cured composite-adhesive interface for orthodontic indirect bonding. The intent of this study was to determine the effect on the shear bond strength of the following variables: use of a filled flowable composite resin as an adhesive, light air-abrasion of the cured composite bracket pad, and wetting the cured composite bracket pad with an unfilled resin. Methods: The sample of 240 brackets was divided into 2 groups of 120 each. The first group was further divided into 4 groups of 30 each. Brackets were bonded to bovine incisors with a filled flowable composite resin (Filtek, 3M ESPE, St Paul Minn), but the bracket pads were prepared differently in the 4 groups: unfilled resin was applied (Orthosolo, Ormco, Glendora, Calif), the surface was air abraded, the surface was air abraded followed by application of an unfilled resin (Orthosolo), and a control group. A matching sample of 120 brackets was bonded without the flowable composite as an adhesive. The different bracket pad preparations were chosen to represent the various techniques clinicians use in indirect bonding. The shear bond strength was measured on a universal testing machine. Results: Two-way ANOVA analysis showed significant differences in the shear bond strength among the different surface preparations, but not between the use and nonuse of flowable composite. The Scheffé test showed that the mean shear bond strength of the air-abraded surface was significantly higher than all other surface preparations. Conclusions: Air abrading orthodontic bracket-pad composite surfaces in indirect bonding increased the shear bond strength, whereas the use of flowable composite did not affect bond strengths.