Torque value accuracy of preadjusted metal brackets for upper and lower incisors

The more accurate the adjustments built into the brackets, the less the need of additional bends in orthodontic archwires during treatment.

The aim of this study was to investigate the torque value accuracy of Roth prescription brackets from several commercially available brands. A total of 360 upper and lower incisor brackets from six different commercial brands (i.e. 3M Abzil, KiriumLine; Dentsply GAC, Ovation; Morelli, Roth Light; Ormco, Synthesis; Rocky Mountain Orthodontics, Integra; and 3M Unitek, Miniature Twin) were selected and divided into 18 experimental groups (N.=20).

The brackets were submitted to SEM examination to acquire clear photomicrographs of all edges. The angles formed by the slot's walls and bracket's base were measured to calculate the torque values. The measured torque values were submitted to Student's t-test or Mann-Whitney test (global α=0.05) for comparing the experimental groups to Roth prescription values, depending on the bracket indication: +12°, +8° or -1°. A tolerance of ±1° (ISO 27020:2010) was considered. Only experimental groups using upper central incisor brackets from Rocky Mountain Orthodontics (P=0.037) and 3M Unitek (P=0.001) were statistically different compared to the Roth prescription ones (+12°). However, all the groups presented great variability (standard deviation) regarding the same brand and indication, showing that there is no accuracy in the fabrication process.

It is evident that the manufacturing methods of orthodontic brackets need to reach higher degrees of precision and homogeneity.