Effects of customized resin base on bonding strength of spherical self-ligating brackets.

PURPOSE: Fabricating resin bases has become an easy and economical method to achieve the customization of brackets. This study aimed to assess the effect of the resin base on bonding strength of spherical self-ligating brackets. METHODS: A defined amount of adhesive was bonded to the bracket base and constituted the new resin base. The thickness of the adhesive was measured and controlled at 0.5, 1.0, 1.5 and 2.0 mm, and a group without a resin base was used as a control. Sixty extracted human premolars were randomly divided into five groups. The brackets in each group were bonded to the specimen, and debonding tests were conducted. The shear bond strength (SBS) was calculated according to the measured debonding force in relation to the base area. The adhesive remnant index (ARI) score and the residual location of the fractured resin base were recorded. Enamel damage was also analyzed by scanning electron microscopy. After assessing for data normality and homogeneity, statistical comparisons between the groups and correlations among parameters were determined. P < 0.05 was regarded as significant. RESULTS: The correlation analysis revealed an inverse correlation between the resin base thickness and the SBS (Coeff = -0.719, P < 0.01). The highest SBS was 9.33 MPa, in the control group, which was significantly greater than the lowest SBS (6.03 MPa), in the 2.0-mm group (P < 0.05). Multiple comparisons analysis revealed no differences in SBS between the 1.0-, 1.5- and 2.0-mm groups. Nonparametric analysis found that only the ARI score in the 0.5-mm group (2.92) was significantly different (P < 0.05) from that in the control group (1.25). As the thickness of the resin base increased, the fractured resin base tended to remain at the bracket base, and the risk of enamel damage decreased. CONCLUSIONS: As the thickness of the resin base increased, the bonding strength of the spherical bracket decreased. However, the required clinical bonding strength was still satisfied when the thickness was less than 2.0 mm. The existence of a resin base could protect the enamel surface from damage caused by debonding. The customization of spherical brackets by tailoring a resin base can be applied in clinical practice because of the clinically acceptable bonding strength.