Primer on the base of polycarbonate brackets: should we apply it or not?

OBJECTIVE: The purpose of this study was to evaluate shear bond strength of polycarbonate brackets bonded with or without the previous application of primer on their bases. MATERIALS AND METHODS: Forty-six extracted bovine permanent mandibular incisors were obtained and randomly divided into two groups of 23 each: group 1 (control), 37% phosphoric acid and direct bonding with Orthoprimer (Morelli Orthodontic Products, São Paulo, Brazil) and Orthobond (Morelli Orthodontic Products); and group 2, Orthoprimer application on bracket base prior to conventional bonding. Polycarbonate maxillary central incisor brackets (Composite, Morelli Orthodontic Products) were used in this study. All products were used according to the manufacturer's instructions. An Universal Testing Machine was used to apply an occlusal shear force directly onto the enamel-bracket interface at a speed of 0.5mm/min. The groups were compared using Student's t-test. RESULTS: Mean results and standard deviation (in MPa) for the groups were: group 1 - 5,81 (1,90); and group 2 - 6,09 (1,28). Significant difference was not observed in the bond strengths of the two groups evaluated (p=0.5601). The adhesive remnant index (ARI) did not indicate significant difference (p=0.617) between the two groups. CONCLUSIONS: These results indicated that primer application on polycarbonate bracket base did not result in increased bond strength.