Scanning Accuracy of Bracket Features and Slot Base Angle in Different Bracket Materials by Four Intraoral Scanners

Abstract

Through the dental model acquired at the time of re-diagnosis of patients undergoing orthodontic treatment, not only the relationship between the entire dentition and the arch, but also the position of the bracket is reevaluated. To evaluate whether the bracket prescription is accurately expressed by checking the height, position, and angle of the bracket slot can help to produce a good treatment result. Orthodontic tooth movement can also be easily evaluated using IOS. The purpose of this study was to evaluate the accuracy of digital scan images of brackets produced by 4 IOSs when scanning the surface of dental model attached with different bracket materials (metal, ceramic, resin, resin bracket with metal slot). The images scanned with a laboratory scanner and images taken with a scanning electron microscope were used as references. Each bracket axis was set in the reference image, and the axis was set identically by superimposing with the IOS image, and then only the brackets were divided to perform quantitative and qualitative analysis. By quantitative analysis, precision and trueness were analyzed as RMS values and calculated maximum discrepancy. By qualitative analysis, the bracket wing was divided into 4 parts; upper-mesial, upper-distal, lower-mesial, and lower-distal to confirm the frequency of error more than 20 ㎛. For the bracket slot, the slot base angle and the parallelism of the slot wall were measured. The results of this study are as follows. 1. There were significant differences in the scanning accuracy of the bracket according to the type of scanner. In quantitative analysis, precision RMS was the smallest in Trios 3, followed by Primescan, CS3600, and i500 (P <0.001). Trueness RMS was smallest in Trios 3, followed by Primescan, i500, and CS3600 (P <0.001). The maximum discrepancy was the smallest in Trios 3, followed by Primescan, CS3600, and i500 (P <0.001). 2. There were significant differences in the scanning accuracy of the bracket according to the type of brackets. In the qualitative analysis, the scan accuracy of the bracket wing was the smallest in Trios 3, followed by Primescan, CS3600, and i500 (P <0.001). The parallelism measured by the difference between the upper and lower angles of the slot wall was 0.48 in SEM, 7.00 in Primescan, 5.52 in Trios 3, 6.34 in CS3600, and 23.74 in i500 (P <0.001). The difference between the manufacturer's torque and the bracket slot base angle was 0.39 in SEM, 1.96 in Primescan, 2.04 in Trios, and 5.21 in CS3600 (P <0.001). 3. The maximum discrepancy according to the bracket materials was the lowest in ceramic, followed by metal, resin and resin bracket with metal slot (P <0.05). In the qualitative analysis, the scan accuracy of the bracket wing was lower in resin and resin metal brackets than in ceramic and metal (P <0.05). Brackets that are more translucent and transmit light, such as resin or resin brackets with metal slots, tended to show greater errors than metal or polycrystalline ceramic brackets. This study evaluated the accuracy of the bracket only. According to the results of this study, it was possible to confirm the bracket slot base angle, which is difficult to obtain by the conventional impression method according to the scanner type. However, it must be admitted that there is some error in recognizing slots through scanning in general. Considering only the scan of the bracket in this study, Primescan and Trios 3 were more accurate among the 4 types of IOSs, Primescan, Trios 3, CS3600, and i500. Among the brackets, it should be noted that the polycrystalline ceramic bracket, which has less reflection or absorption of light when using the scan, has high accuracy, and there is more error when using other types of brackets.