Alignermodifikationen zur verbesserten Drehmomentübertragung für die palatinale Translationsbewegung eines oberen mittleren Schneidezahns

Abstract

Introduction The majority of biomechanical studies indicated the limitation of aligners regarding bodily or a root torque movement of incisors in vestibulo-oral direction. For a palatal bodily movement, a palatally-directed force and a high moment eliminating the tipping effect of this force are required. The purpose of this thesis was to investigate the potential of aligners for inducing a palatal bodily movement by in-vitro measurements of the three-dimensional force-moment (3D F/M) systems exerted to a maxillary central incisor by aligners with and without pressure points.

Methods In the experimental series, the 3D F/M system exerted to tooth 11 separated from a maxillary Frasaco® model was analyzed with tooth 11 in neutral position and during its bodily movement in palatal direction. Aligners with three different modification geometries (crescent, cylindrical and spherical forms) with different modification depths (0.5, 1.0, 1.5 and 2.0 mm) incorporated in the aligner at the labial cervical region of tooth 11 were evaluated in combination with PET-G aligners (Duran®, Scheu Dental, Germany) of different thicknesses (0.4 – 1 mm). Aligners without any modification served as control. An effective movement range is present, if the aligner could generate the combination of negative Fy and negative Mx values.

Results Aligners with modifications were able to achieve an effective movement range with a palatally directed force (-Fy) and a sufficiently high palatal torqueing moment required for palatal translation or root torque. The cylindrical 1.5 mm deep modification form implemented the largest effective range inducing a palatal tooth displacement determined at the center-of-resistance of only 0.1 mm. Shallower modifications showed shorter effective ranges (Kruskal-Wallis-Test, p > 0.01) with values of 0.02 and 0.19 mm for the 0.5-mm- and 1.0-mm depths, respectively. Even the thinner aligners (thickness 0.4 mm) could generate an effective movement range.

Conclusion The experimental series indicate that the palatal bodily movement of maxillary central incisors should be achievable with modified aligners. Some tested aligners even produced sufficient moment values for palatal root torque. Further studies are required to examine the effect of long-term loading on the presented F/M values and effective ranges.