Biomechanical analysis of retracting maxillary incisors using clear aligners with palatal mini-implants in extraction cases: a finite-element analysis

Background At present, the clinical orthodontic effects associated with the application of clear aligners to extraction cases featuring retraction of the anterior teeth remain a cause for concern. Here, we analyzed the biomechanical effects of this strategy on the maxillary dentition, periodontal ligament, and clear aligners when using palatal micro-implants in combination with different traction methods. Methods Several models, including the maxillary dentition (without first premolars), maxilla, periodontal ligaments (PDLs), and aligners, were constructed and imported to finite element software. Four model groups were created: (1) G1 (pure aligner retraction force), (2) G2 (the combination of aligner retraction force with elastic force applied between the palatal mini-implant and the Angel button), (3) G3 (the combination of aligner retraction force with elastic force applied between the palatal mini-implant and the precision cutting), and (4) G4 (the combination of aligner retraction force with passive ligation). The magnitude of the elastic traction force was increased from 100 g to 250 g, with a gradient increment of 50 g. Subsequently, finite element analysis was performed to simulate the biomechanical effects. Results Compared with G1, the incisors in G2 exhibited a larger incisor retraction distance and better vertical control. Although incisor retraction in G3 was slightly lower than that in G2, this method demonstrated better control of anterior tooth torque and anchorage of the posterior tooth. In G4, there was a tendency for a slight reduction in incisor retraction compared to G1, while vertical extrusion and lingual tipping of the incisors were the most severe. In G2 and G3, the magnitude of the palatal elastic retraction force within the range of 100 to 150 g was conducive for the retraction of incisors, torque and vertical control of anterior teeth. Conclusions The combination of aligner retraction force with an appropriate retraction force applied to palatal micro-implants was beneficial for improving the efficiency of incisor retraction, as well as enhancing both vertical control and torque control. However, appropriate overtreatment should be designed to ensure bodily retraction and reduce tipping movement. Clinical Trial number: Not applicable.