Three-Dimensional Digital Superimposition of Orthodontic Bracket Position by Using a Computer-Aided Transfer Jig System: An Accuracy Analysis

Abstract

Accurate bracket placement is essential for successful orthodontic treatment. An indirect bracket bonding system (IDBS) has been developed to ensure proper bracket positioning with three-dimensional computer-aided transfer jigs. The purpose of this study was to investigate the accuracy of bracket positioning by a one-body transfer jig according to the tooth type and presence/absence of a resin base. In total, 506 teeth from 20 orthodontic patients were included in this study. After initial dental models were scanned, virtual setup and bracket positioning procedures were performed with 3D software. Transfer jigs and RP models were fabricated with a 3D printer, and brackets were bonded to the RP model with or without resin base fabrication. The best-fit method of 3D digital superimposition was used to evaluate the lineal and angular accuracy of the actual bracket position compared to a virtual bracket position. Although all the measurements showed significant differences in position, they were clinically acceptable. Regarding the tooth types, premolars and molars showed higher accuracy than anterior teeth. The presence or absence of a resin base did not consistently affect the accuracy. In conclusion, the proper application of IDBS should be performed considering the errors, and resin base fabrication might not be essential in ensuring high-accuracy IDBS.

Keywords: 3D printing; best-fit method; indirect bonding; intraoral scanner; model scanner; one-body transfer jig.

Figure 1

One-body transfer jig system based on CAD/CAM technology for indirect bonding. (A) An example of a transfer jig design for a premolar. (B) Manufactured transfer jig by three-dimensional printing technology. (C) Virtual design of transfer jig for a molar. (D) Bracket transfer jig precisely implemented with three-dimensional printing technology. (E) A customized resin base was formed through additional laboratory procedures.

Figure 2

Examples of one-body jig system. (A) For maxillary dentition, (B) For whole dentition.

Figure 3

On the digital interface, Bioquick brackets were positioned virtually to the individual tooth surface using 3Txer software (CENOS co, Indeokwon, Gyeonggido, Korea). (A) Noncrowded case, (B) Crowded case.

Figure 4

One-body transfer jig fabricated by CAD/CAM technology with rapid prototyping (RP) models. (A) Brackets transferred to the noncrowded model by indirect bonding procedure using the jig system, (B) Brackets transferred to the crowded model by indirect bonding procedure using the jig system.

Figure 5

Schematic diagram of the experimental group. All subjects were classified into two groups depending on the presence or absence of a resin base (Group A: with resin base, Group B: without resin base). In addition, sub-groups were organized by tooth type. Sub-group 1 had six anterior teeth, a total of 226 subjects. Sub-groups 2 and 3 were the premolar and molar teeth, respectively, with a total of 112 and 158 subjects.

Figure 6

Three-dimensional digital superimposition (best-fit method) data. Combination between virtual model data with reverse engineering technique (yellow color) and intraoral scan data of post-transfer model (green color) using Rapidform software 2006 (INUS technology, Seoul, Korea).

Figure 7

Three-dimensional coordinate system. The origin of the coordinate system was set to coincide with the center point of the bracket base. (A) The mesiodistal axis (x-axis) was to be parallel to the bracket slot (red color). The buccolingual direction (y-axis) was formed by drawing a normal line based on the lingual surface of the bracket slot (green color). The z-axis (occlusogingival direction) was determined to be perpendicular to the plane of the other two axes (blue color). (B) Measurement of linear bracket displacements. Positive values in each direction indicate mesial in the x-axis, occlusal in the y-axis, and buccal in the z-axis. (C) The values of angular discrepancy can be calculated between the coordinate vectors of the control group (virtual bracket position) and the experimental group (post-transfer bracket position) formed according to the preceding description. The rotation of the bracket with respect to the x-axis represents torque, the y-axis represents angulation, and the z-axis represents rotation. Positive values represent crown buccal torque, mesial root tip, and mesiobuccal rotation.

Figure 8

Histogram of frequencies for six measurements with one-tailed equivalence test in group A. (A–C) linear measurements, (D–F) angular measurements.

Figure 9

Histogram of frequencies for six measurements with one-tailed equivalence test in group B. (A–C) linear measurements, (D–F) angular measurements.

Figure 10

Profile plot for estimated marginal means of (A) M-D, (B) B-L, (C) O-G, (D) torque, (E) angulation, and (F) rotation. Tooth type 1, 2, and 3 represent six anterior teeth, premolars, and molars, respectively. The blue line represents the experimental group with resin base formed in advance, and the red line represents the group without resin base.