Effects of offset design on the accuracy of bracket placement with a guided bonding device

Background This study aimed to evaluate the effects of offset design on the accuracy of bracket placement for computer-aided design and computer-aided manufacturing (CAD/CAM)-guided bonding devices (GBDs) in vitro. Methods Eight dental models were selected. Seven types of GBDs were designed and three-dimensionally (3D) printed for each model, including one without any offset and the other six with translation offsets (TF) and expansion offsets (EF) of 0.05, 0.10, and 0.15 mm, respectively. After the brackets were bonded on the models using the different GBDs in vitro, linear and angular deviations of the bracket positions were evaluated. Results In total, 56 GBDs were printed, and 784 brackets were bonded using the GBDs. No misfit between the dentitions and the devices was found during the bonding process. With increasing offset, more brackets were gingivally positioned with the frequencies ranging from 61.61 to 76.79% for the TF groups and from 58.93 to 78.57% for the EF groups. The vertical deviations of the brackets increased from 0.100 to 0.168 mm and from 0.117 to 0.150 mm in the TF and the EF group, respectively, as offset increased. No statistically significant difference was found in the vertical deviation between most of the TF and EF groups with the same offset value (p > 0.05). With respect to angulation, the mean absolute deviations were 0.881, 1.083, and 1.029 degrees in the 0.05-mm, 0.10-mm, and 0.15-mm EF groups, respectively, which were greater than those in the corresponding TF groups (0.799, 0.847, and 0.806 degrees). Similarly, with increasing offset, the mean absolute deviations for rotation in the EF groups (0.847, 0.998, and 1.138 degrees) were greater than those in the TF groups (0.853, 0.946, and 0.896 degrees). Compared with the 0.15-mm TF group, greater angulations (p < 0.05) and rotations (p < 0.01) were found in the 0.15-mm EF group. Conclusions Offset designs influenced the precision of vertical bracket placement with GBDs. Due to the smaller deviations in angulation and rotation of bracket placement, TF is preferred over EF for GBDs. Moreover, the differences between TF and EF also need to be considered in the design of other dental CAD/CAM devices.