RESUMO
OBJECTIVE: To evaluate the effects of ultrasonic instrumentation with different scaler-tip angulations on the shear bond strength (SBS) and bond failure mode of metallic orthodontic brackets. METHODS: Adhesive pre-coated metallic brackets were bonded to 72 extracted human premolars embedded in autopolymerizing acrylic resin. The teeth were randomly divided into 3 groups (n = 24 each) to undergo no treatment (control group) or ultrasonic instrumentation with a scaler-tip angulation of 45degrees (45degrees-angulation group) or 0degrees (0degrees-angulation group). SBS was tested in a universal testing machine, and adhesive remnant index (ARI) scores were recorded. The Kruskal-Wallis test and Mann-Whitney U-test were used for statistical analysis. RESULTS: The control group had a significantly higher mean SBS value than the treated groups, which showed no significant differences in their mean SBS values. The ARI scores were not significantly different among the groups. CONCLUSIONS: Ultrasonic instrumentation around the bracket base reduces the SBS of metallic orthodontic brackets, emphasizing the need for caution during professional oral hygiene procedures in orthodontic patients. The scaler-tip angulation does not influence the SBS reduction and bond failure mode of such brackets.