Accuracy of indirect bracket bonding via virtual setup and 3D printing

Abstract

Accurate bracket positioning is an essential factor to determine success in orthodontic treatment. The indirect bracket bonding technique using setup models helps placing the bracket in a more precise position. Recently, three-dimensional (3D) imaging and printing techniques have enabled us to make a virtual setup and customized bracket system. The objective of this study is to perform a comparative evaluation between the accuracy of indirect bracket bonding technique utilizing virtual setup and 3D printing and manual indirect bracket bonding technique. The study involved initial diagnostic models of 10 patients who were treated in non-extraction scheme and presented with permanent dentition, no missing teeth, and mild to moderate crowding. The initial diagnostic models were duplicated, and brackets were indirectly bonded. Three groups were divided by the methods of setup and indirect bonding, as follows. Group 1: Following the manual setup, vacuum-formed clear trays were fabricated. Group 2: After virtual bracket positioning on the digitally scanned manual setup models, transfer jigs were manufactured by computer-aided design and manufacture (CAD/CAM) and 3D printer. Group 3: virtual setup was performed followed by scanning of the initial models. Then, transfer jigs were manufactured by CAD/CAM and 3D printer. These bracket-placed models were digitally scanned and superimposed for measuring the position and angular differences of the brackets between the groups.

1. The vertical, mesio-distal, and bucco-lingual positional differences of brackets between the three groups were generally within 0.5 mm of range. For the mandibular central incisor, unlike group 1 and 2, brackets of group 3 were more occlusally positioned for more than 0.5 mm in the vertical direction. The brackets of group 2 and 3 were positioned more closly to the tooth surface in bucco-lingual direction than group 1.

2. For the tip (mesio-distal angulation), brackets in the group 2 and 3 were more distally tipped than group 1, but the differences were smaller than 3°.

3. The discrepancy in the rotation was generally smaller than 3°, except for the maxillary and mandibular second molars.

4. For the torque, brackets of the group 2 and 3 presented more buccal-torque than group 1 regardless of the type of tooth, and they exhibited the largest discrepancy. Discrepancy in torque was larger at the posterior teeth than anterior teeth, but they were still within the slot-wire torque play.

5. The linear and angular differences between the group 2 and 3 were generally within 0.5 mm and 3°.

6. The average linear and angular differences of the group 1 and 3 were similar to that of group 1 and 2, but more widely distributed.

The results indicated that the accuracy of bracket indirect bonding technique via virtual setup and 3D printing is generally within the clinically acceptable limit when comparing the manual setup and manual indirect bonding. However, the possibility of collision of bracket slot and wire resulted in considerable discrepancy in the torque. Therefore, delicate adjustments in virtual bracket positioning are essential.