Objective To investigate the biomechanical characteristics of the mandibular anterior teeth intrusion assisted by buccal mini-implants,so as to provide theoretical guidance for the clinical treatment of deep overbite and other conditions requiring intrusion of the mandibular anterior teeth.Methods A finite element model of implant screws,clear aligners(CAs)and mandibular complex including the mandibular dentition,periodontal ligament(PDL)and alveolar bone was constructed.The model was designed with 0.2 mm intrusion in the mandibular anterior teeth.Seven groups were set:without traction,30 g,50 g,100 g,150 g,200 g,and 250 g force groups.The stress and displacement of the teeth as well as the related stress distributions of PDL and CAs in each group after loading were analyzed.Results Without traction and under different traction forces,the mandibular anterior teeth tended to be tipped and intruded.With the increase of traction force,the increasing trend was manifested in the vertical displacement and labial displacement of the mandibular anterior teeth.When the traction force reached 200 g,the vertical displacement showed a significant increase,the subsequent increase then showed a tendency to flatten.The ratio of the labial tipping displacement to the intrusive displacement of the mandibular anterior teeth showed a decreasing trend with the increase of traction force.Within a reasonable force range,increasing traction force led to greater bodily intrusion of the anterior teeth.When the traction force was less than 150 g,the mandibular posterior teeth exhibited a tendency of extrusion.When the traction force of more than 150 g was applied,it showed a tendency of intrusion.The PDL stress was concentrated on the labial and cervical surface of the anterior teeth.Conclusions Intrusion efficiency of the mandibular anterior teeth has been effectively improved with CAs assisted by buccal mini-implants.Moreover,the traction force of the mini-implants has a significant impact on the movement of the mandibular anterior teeth.Based on a comprehensive analysis of factors such as the displacement trend of the mandibular dentition and the PDL stress,the optimal force value for buccal traction of the mini-implants to intrude the mandibular anterior teeth can be selected as 150-200 g force.

Objective To investigate the biomechanical characteristics of the mandibular anterior teeth intrusion assisted by buccal mini-implants,so as to provide theoretical guidance for the clinical treatment of deep overbite and other conditions requiring intrusion of the mandibular anterior teeth.Methods A finite element model of implant screws,clear aligners(CAs)and mandibular complex including the mandibular dentition,periodontal ligament(PDL)and alveolar bone was constructed.The model was designed with 0.2 mm intrusion in the mandibular anterior teeth.Seven groups were set:without traction,30 g,50 g,100 g,150 g,200 g,and 250 g force groups.The stress and displacement of the teeth as well as the related stress distributions of PDL and CAs in each group after loading were analyzed.Results Without traction and under different traction forces,the mandibular anterior teeth tended to be tipped and intruded.With the increase of traction force,the increasing trend was manifested in the vertical displacement and labial displacement of the mandibular anterior teeth.When the traction force reached 200 g,the vertical displacement showed a significant increase,the subsequent increase then showed a tendency to flatten.The ratio of the labial tipping displacement to the intrusive displacement of the mandibular anterior teeth showed a decreasing trend with the increase of traction force.Within a reasonable force range,increasing traction force led to greater bodily intrusion of the anterior teeth.When the traction force was less than 150 g,the mandibular posterior teeth exhibited a tendency of extrusion.When the traction force of more than 150 g was applied,it showed a tendency of intrusion.The PDL stress was concentrated on the labial and cervical surface of the anterior teeth.Conclusions Intrusion efficiency of the mandibular anterior teeth has been effectively improved with CAs assisted by buccal mini-implants.Moreover,the traction force of the mini-implants has a significant impact on the movement of the mandibular anterior teeth.Based on a comprehensive analysis of factors such as the displacement trend of the mandibular dentition and the PDL stress,the optimal force value for buccal traction of the mini-implants to intrude the mandibular anterior teeth can be selected as 150-200 g force.