OBJECTIVE: The purpose of the present study was to analyze the influence of debonding force location in shear bond strength testing of orthodontic brackets in vitro. METHODS: Ninety extracted permanent bovine mandibular incisors were randomly divided into 3 groups of 30 specimens each. Teeth were bonded with stainless steel orthodontic brackets. Enamel surfaces were etched with 37% phosphoric acid for 30s and bonded with a composite adhesive. Debonding force measurements were performed with a universal testing machine. Location of the debonding force was: bracket base (group A), ligature groove (group B), occlusal bracket wings (group C). RESULTS: Mean shear bond strength measurements were as follows: 22.70(4.23)MPa (group A), 11.52(2.74)MPa (group B), 9.44(2.96)MPa (group C). Analysis of variance indicated that there were significant differences in shear bond strength. Post-hoc Tukey tests showed that bond strength measurements of group A were significantly different from those of groups B and C. The adhesive remnant index also showed significant differences and ranged from a mean of 1.53 in group A to a mean of 2.10 in group C. SIGNIFICANCE: Debonding force location had a significant influence on shear bond strength measurements and bond failure pattern, indicating that this parameter needs to be taken into consideration for interstudy comparison of in vitro results.
