Orthodontic brackets shear bond strength: comparison between different trays

Objectives: Transfer trays allow a much more accurate bracket placement. The purpose of this study was to compare the shear bond strength (SBS) of orthodontic brackets bonded to buccal vs lingual surfaces with either a direct or an indirect bonding technique using different transfer trays. Methods: Brackets were bonded to buccal and lingual aspects of sixty extracted bovine incisors, which were divided into 4 groups (GR1-GR4): GR1 - direct bonding technique. GR2 indirect bonding with silicone transfer tray. GR3 and GR4 a combination of silicone and plastic tray was used. GR3 light-cure was applied through both materials and in GR4 first curing through both materials, followed by a second step only through silicone after removal the plastic part. Shear force was applied a week later via a loading machine and the maximal force during debonding was measured. SBS was calculated as the maximal force divided by the brackets' base area. Then, resin remnants on teeth were determined (ARI). Differences between groups were analyzed by ANOVA with repeated measures, Tukey and Wilcoxon tests. Results: SBS was 15.8±5.3 MPa for GR1 (direct bonding) and 13.7±3.7,9.8±2.4,11.9±2.3 MPa for GR2,3,4 respectively (indirect bonding) for buccal surfaces and 13.9±3 MPa for GR1 and 11.8±3,12.1±3.3,12.5±2.2 MPa for GR2,3,4 respectively for lingual surfaces. No significant difference in SBS between buccal and lingual surfaces (P=0.52) and between different transfer trays (p>0.05) were observed. However, shear bond strength for direct bonding was significantly higher than indirect bonding (p<0.05). Resin remnants index showed no significant difference between groups (P=0.9). Conclusion: Direct bonding provides higher bonding strength than indirect method. Clinically transfer trays are adequate for use in indirect brackets bonding to the buccal or lingual sides.