Comparision of bracket transfer accuracy of indirect bonding methods

Objective To compare bracket transfer accuracy of indirect bonding method using two different transfer trays with different dental crowding conditions. Methods Casts of 30 patients were collected. Each casts was impressed twice and the casts were grouped into A and B. According to crowding degrees, casts were grouped into A1, A2, B1 and B2 (n=15). A1 and B1 were mild crowding groups, while A2 and B2 were moderate crowding groups. Casts with brackets were scanned using CBCT and 3D reconstructed using Mimics software. Indirect bonding transfer trays for group A and B were made with one-layer film and bilayer films, separately. Transfer trays were put on to initial casts to complete bonding. Casts were scanned and 3D reconstructed again using CBCT and Mimics, and images were imported into Geomagic Studio software for superimposition and analysis to compare the change of brackets position during transfer. Results The maximum distance and average distance of brackets movement before and after transfer have no statistical significance among different groups(P>0.05). The standard deviation of average distance of group B is greater than group A, with statistically significant differences (P<0.05). The standard deviation of average distance of group B2 is greater than group A1, A2 and B1, with statistically significant differences (P<0.05). Conclusions The braceket transfer accuracy of indirect bonding methods difference between using one-layer film and bilayer films has no statistical difference, while the stability is better by using one-layer film. Increased degree of crowding may reduce the stability of brackets transfer. Key words: Transfer accuracy; Transfer tray; Digital model