Anex vivoinvestigation to compare orthodontic bonding using a 4-META-based adhesive or a composite adhesive to acid-etched and sandblasted enamel

OBJECTIVE: This study investigates the shear-peel orthodontic bond strengths of brackets bonded with an unfilled acrylic resin containing 4-META (MCP Bond or a no-mix composite adhesive (Right On) to acid-etched or sandblasted enamel. DESIGN: Ex vivo. MATERIALS AND METHODS: Eighty human pre-molar teeth were separated into four equal groups, according to the adhesive used and method of enamel pre-treatment. Group I-Right On with enamel etched using phosphoric acid for 30 seconds. Group II-Right On with enamel sandblasted using 50- microm alumina particles at 80 psi for 3 seconds. Group III-MCP Bond with enamel etched using phosphoric acid for 30 seconds. Group IV-MCP Bond with enamel sandblasted using 50- microm alumina particles at 80 psi for 3 seconds. Subsequently, the specimens were stored in distilled water for 24 hours prior to bond strength testing using an Instron universal testing machine. Each debonded tooth was scored using the adhesive remnant index (ARI) to determine the site of bond failure. RESULTS: The mean bond strength (1 SD) were Group I: 10.7 (2.7) MPa, Group II: 5.3 (1.3) MPa, Group III: 15.9 (3.4) MPa, Group IV: 15.0 (2.2) MPa. Statistical analysis using one-way analysis of variance and Tukey test found no statistical difference between Group III and Group IV (P > 0.05), but the other groups were statistically different from each other (P < 0.05). The data were found to fit the Weibull distribution and Weibull analysis showed stress required for a 5 per cent probability of failure was: Group I: 5.77 MPa; Group II: 3.32 MPa; Group III: 10.31 MPa; Group IV: 10.58 MPa. Chi-square test showed a statistically significant difference existed between the ARI scores (P < 0.001), principally through less adhesive remnants being observed on the sandblasted specimens. CONCLUSION: The adhesive containing 4-META achieved significantly higher bond strengths than the composite adhesive, particularly in the case of sandblasted enamel.