Evaluation of Biomechanical Systems Associated with Orthodontic Clear Aligners

Objectives: The in vitro pilot study was conducted to evaluate the three-dimensional force systems generated on teeth around a simulated maxillary arch for incisor, canine, premolar, and molar lingual displacements when using clear orthodontic aligners.
Methods: An electro-mechanical Orthodontic SIMulator (OSIM) was configured with stainless steel anatomical teeth and positioned to mimic a typical maxillary archform. Using a three-dimensional scan of the archform and subsequent dental stone cast, 0.75mm thick aligners were formed from three materials: Zendura (polyurethane-based), Invisocryl A (polyethylene-based) and Essix A+ (polyethylene-based). Before each experiment, OSIM teeth were positioned such that force levels were below 0.1N. The first left molar, second right premolar, first left premolar, right canine, and left central incisors were individually displaced lingually 0.20mm and the force system on each tooth was measured. This process was repeated ten times per tooth for all materials.
Results: At maximum lingual displacement, the largest buccally-directed forces occurred on the canine (5.4 +0.35N), first premolar (4.45 +0.39N), and canine (3.09 +0.29N) for Zendura, Invisocryl A, and Essix A+, respectively. Overall trends showed that material affected the magnitude of applied forces with lingual displacement. Differences in measured forces on the displaced tooth for the same material were noted around the arch, where forces acting on displaced incisors and molars were up to 3.71 N less than those acting in the premolar-canine region.
Conclusions: Force systems generated by clear orthodontic aligners for lingually-displaced teeth around a simulated arch were measured in vitro. It was found that both selected material base and the tooth being displaced for a given aligner affected the generated force system. Outcomes from this pilot work will be instrumental in designing future biomechanical studies to investigate fundamental research questions surrounding the use of clear aligners in orthodontic treatment.