[Objectives] Recently, maxillary molar distalization with TADs is an increasingly popular option for the correction of Class II molar relationship. In the treatment utilizing TADs, it is essential to understand the biomechanical property of each force system precisely. In this study, we generated a model in which the maxillary molars were distalized by TADs, and examined the effect of different traction sites applied to the maxillary posterior segment by Electronic Speckle Pattern Interferometry (ESPI).
[Methods] An experimental model was constructed by various simulated materials, including braces (0.022-inch slot preadjusted edgewise appliance) and sectional arch wire (0.019 0.025-inch stainless steel wire). The TADs were inserted between the maxillary second premolar and the first molar at 3 mm higher than the alveolar crest. The accurate displacement of the maxillary posterior segment was analyzed by ESPI using laser. The orthodontic force applied to the maxillary posterior segment was generated by the traction between TADs and the first or second premolar.
[Results] The greater distal movement was generated by the traction from the second premolar. The greater crown buccal torque was generated by the traction from the first premolar. Therefore, it was demonstrated that more effective traction was obtained from the second premolar than the first premolar.
[Conclusions] The finding of this study provides valuable information on the effective force system in planning distal movement of the maxillary molars using TADs.