Investigating the effect of different composite restorations surface preparation methods on the shear bond strength of orthodontic brackets.

Abstract

Background: Bond failure at the interface of bracket and composite restoration occurs in cases of improper surface preparation. Aim: The aim of this study is Investigating the effect of different composite restorations surface preparation methods on the shear bond strength of orthodontic brackets. Materials and methods: 180 composite cubes were mounted in acrylic blocks. The samples were first stored in normal saline at 37°C for 14 days. Then the samples were randomly divided into 12 groups of 15. Diamond burs were used for mechanical preparation of groups 1, 2, 3, and 4; sandblasting was used for groups 5, 6, 7, and 8; and groups 9, 10, 11, and 12 were left without mechanical preparation. For bracket bonding to the samples, GC Ortho Connect composite was used in half of the groups (groups 1, 2, 5, 6, 9, and 10) and Transbond XT 3M composite was used in the other half (groups 3, 4, 7, 8, 11, and 12). G-Premio bonding was used in half of the groups that used GC Ortho Connect composite (groups 1, 5, and 9) and no bonding was used in the other half (groups 2, 6, and 10). Also, in half of the groups that used composite Transbond XT 3M was used. G-Premio bonding was used (groups 3, 7, and 11) and in the other half, Transbond XT 3M was used (groups 4, 8, and 12). After connecting the American Central Dental bracket to the composite samples with the aforementioned methods, the samples were stored in 37°C normal saline for another week. A universal testing machine was used to measure the shear strength of the bond when separating the bracket from the surface of the composite restorations. The adhesive residue index (ARI or adhesive residue index) was also examined. To compare the failure and shear bond strength based on the type of preparation and type of composite, a two-way ANOVA test (if normal) and a Kruskal-Wallis test (if abnormal) were used. For significant cases of ANOVA test, Tukey's post hoc test will be used for pairwise comparison of groups. A multifactor ANOVA test was used to compare means. The significance level in all tests was considered less than 5%. Results: The shear bond strength in the sandblasting method was significantly lower than without mechanical preparation. However, it was similar to the milling method. There was also no significant difference between the milling method and without mechanical preparation. The shear bond strength in the application of G-Premio bonding was significantly higher than that of Transbond XT 3M and no bonding. Also, the strength in Transbond XT 3M bonding was significantly higher than that of no bonding. The type of composite did not have a significant effect on the shear bond strength. In summary, the results showed that mechanical preparation (p = 0.019) and bonding (p < 0.001) had significant effects on the shear bond strength, while composite did not (p = 0.347). The interaction effects were not significant, indicating that the effect of each factor on the shear bond strength was independent of the others. The remaining adhesive index study showed that the highest frequency of adhesive index 3 (all adhesive remaining on the initial composite) was in group 3 (Transbond XT 3M composite, milling, G-Premio bonding) with a frequency of 66.7%, group 4 (Transbond XT 3M composite, milling, Transbond XT 3M bonding) with a frequency of 46.7%, and group 1 (GC ORTHO CONNECT composite, milling, G-Premio bonding) with a frequency of 40%. The highest frequency of adhesive index zero (no adhesive remaining on the initial composite) was in group 6 (GC ORTHO CONNECT composite, sandblasting, no bonding) with a frequency of 93.3%. Conclusion: Mechanical preparation has significant effects on shear bond strength. The method without mechanical preparation along with the use of G-Premio bonding has the highest shear bond strength. The type of bonding has significant effects on shear bond strength. The shear bond strength was significantly higher in the use of G-Premio bonding. The type of composite has no significant effects on shear bond strength. The interaction effects (mechanical preparation, bonding type, and composite type) are not significant, indicating that the effect of each factor on shear bond strength is independent of the others.