3D ssessment of bracket position accuracy for lingual appliances using CAD/CAM technology: a pilot study

Introduction: While lingual orthodontics have evolved and matured to deliver excellent treatment outcomes comparable to labial appliances, one problem has yet to be completely resolved for any bonded appliance. Despite the meticulous digital setup and transfer of lingual appliances, bond failure of individual brackets is inevitable throughout the course of treatment. An average of 2-3 bond failures within the first year of orthodontic treatment can be expected (Ziebura et al, 2014). ❧ Objectives: The overall goal of this investigation was to determine the accuracy of and to compare three different single-tooth rebond methods for a CAD/CAM lingual orthodontic appliance. The three rebond methods to be assessed and compared were direct bond, flexible tray indirect bond, and 3D-printed rigid jig indirect bond. The specific goals of this pilot study were: (1) To quantify and compare the accuracy for rebonding brackets with a flexible tray, 3D printed rigid jig, and direct bonding, (2) to compare the accuracy of the three methods for different tooth morphologies (molar vs. premolar vs. anterior tooth), and (3) to compare the accuracy of each rebond method in each translational dimension. The null hypotheses were that there would be no significant difference in the precision of bracket position for each of the rebond methods; no difference between incisor, premolar, and molar bracket position accuracies for any of the rebond methods; and no difference in the position accuracy between the translational dimensions. The significance level was set at α = 0.05, and the clinically acceptable limit was set at 0.5mm. ❧ Materials & Methods: 30 identical malocclusion models were 3D-printed with the MoonRay 3D printer (SprintRay, Inc., Los Angeles, CA). 10 were assigned to each of the 3 rebond methods. After brackets were bonded, they were scanned with an iTero scanner (Align Technologies, San Jose, CA) for a superimposition study of the deviations which were evaluated by a proprietary imaging software (Swift Health Systems, Irvine, CA). Statistical analysis was with descriptives and a two-way ANOVA using SPSS (Armonk, NY). ❧ Results: The largest deviations in bracket placement were observed for the direct bond and rigid jig methods, between which there was no significant difference, but the flexible tray method had significantly less error than either. There was a tendency for lingual displacement using the rigid jig. The tendency for gingival deviation was observed when using the direct bond method for all teeth and the flexible tray method for the incisor and premolar. ❧ Conclusions: The overall most consistently accurate rebond method was the flexible tray. Placement onto the molar was the most accurate across all rebond methods, compared to bracket placement onto the premolar or incisor. Brackets were positioned most accurately in the mesiodistal translational dimension for all rebond methods. The flexible tray method resulted in the overall most accurate bracket placement in each of the translational planes. Brackets were positioned most accurately in the mesiodistal translational dimension for all rebond methods.