The Effect of Bonding Surface Design on Shear Bond Strength of 3D-Printed Orthodontic Attachments

Abstract

Introduction. This study compared the shear bond strength (SBS) of four innovative designs of the bonding surface of 3D-printed orthodontic attachments with conventional mesh design. Methods. In this in vitro study, the bonding surface design in different groups was as follows: Group 1, flat surface without any feature as a negative control; Group 2, concentric circles with no cuts; Group 3, concentric circles with 16 radial cuts; Group 4, concentric circles with 32 radial cuts; Group 5, small cones with a flat end and rounded edges; Group 6, mesh-based commercially available metal brackets of the maxillary central incisor (standard edgewise, Dentaurum®) as a positive control (n = 20). In Groups 1–5, attachments were designed with SolidWorks® Software and printed with a 2K DLP-LCD printer with hard tough resin (eSun®). All the samples were bonded to the restorative composite resin (Solafil®) surfaces with orthodontic composite resin (CuRAY-ECLIPSE®). The samples were examined for SBS with a universal testing machine after thermocycling (1,000 cycles of 5‒55°C). Data were analyzed with Shapiro–Wilk, one-way ANOVA, and Bonferroni tests. The statistical significance level was set at 0.05. Results. The mean SBS was significantly different between all the groups ($P<0.001$) except for Groups 2 and 5 ($P=1.00$) and Groups 2 and 6 ($P=1.00$). Group 4 had the highest mean of SBS. Conclusion. The bonding surface design significantly influenced the SBS of orthodontic attachments. The concentric circles with 32 cuts had higher bond strength than other designs and can be suggested as a new bonding surface design for orthodontic attachments.