Stress and movement trend of lower incisors with different IMPA intruded by clear aligner: a three-dimensional finite element analysis

Abstract

Background During the intrusion of lower incisors with clear aligners (CAs), root disengagement from the alveolar bone often occurs, resulting in serious complications. This study aimed to determine the potential force mechanism of the mandibular anterior teeth under the pressure of CA, providing theoretical data for clinical practice. Methods In this study, a 3D finite element model was established, including the CA, periodontal ligament, and mandibular dentition. Incisor mandibular plane angles were set as 5 groups: 90°, 95°, 100°, 105°, and 110°. The 4 mandibular incisors were intruded by 0.2 mm, while the canines were the anchorage teeth. The stress, force systems, and potential movement trends of mandibular anterior teeth were obtained. Results The compressive stress of the incisors was concentrated in the lingual fossa, incisal ridge, and apex. With the increase in IMPA, the moment of central incisors changed from lingual crown moment to labial crown moment, with the turning point between 100° and 105°, but the center of resistance (CR) was always subjected to the force toward the lingual and intrusive direction. The force and moment toward the labial side of the lateral incisors were greater than those toward the central incisors. The canines always tipped distally and received extrusive force with no relationship with IMPA. Conclusions With the increase in the initial IMPA, the direction of labiolingual force on the mandibular incisors was reversed. However, the root of the lower incisors always tipped labially, which indicated fenestration and dehiscence.

The displacement of teeth and stress distribution on periodontal ligament under different upper incisors proclination with clear aligner in cases of extraction: a finite element study

“…The appropriate direction for intrusion, which maintained the vertical position of incisors, was consistently 10° labial to the long axis of incisors. Likewise, another FEA analysis [32] revealed that as the IMPA increased from 90° to 110°, the moment of mandibular central incisors changed from a lingual crown moment to a labial crown moment. Additionally, an intrusion force of approximately 50-100 g per side have been proved effective and safe [33,34].…”

Effectiveness of different intrusion modes of maxillary anterior teeth with mini-implants in clear aligner treatment: a three-dimensional finite element analysis

“…In clear aligner treatment, when the anterior teeth are intruded with the aligner, the posterior teeth will be extruded as anchorages [ 14 , 30 ]. In order to improve the intrusion efficiency and prevent the CA from off-tracking, it is necessary to design retention attachments on the posterior teeth [ 14 , 30 ].…”

“…In clear aligner treatment, when the anterior teeth are intruded with the aligner, the posterior teeth will be extruded as anchorages [ 14 , 30 ]. In order to improve the intrusion efficiency and prevent the CA from off-tracking, it is necessary to design retention attachments on the posterior teeth [ 14 , 30 ]. This study found that, when mini-implant anchorage was used, there still existed off-tracking tendencies of the CA at the posterior teeth, which should be paid attention to in clinical practice and more retention attachments should be designed if necessary.…”

“…The periodontal ligaments (PDLs) were modeled on root shape with uniform thickness of 0.25 mm [ 8 ]. Based on Masterforce (Angelalign Technology Inc., Shanghai, China), a more realistic CA model with nonuniform thickness was established by simulating the thermoforming process in Abaqus (version 2016; Simula, USA) [ 14 ]. Then, all components were assembled to generate the final model.…”

Three-dimensional finite element analysis of the optimal mechanical design for maximum inward movement of the anterior teeth with clear aligners

“…In the finite element (FE) model, the periapical bone was established as a fixed constraint, the interfaces between the dentition and periodontium, periodontium and alveolar bone, and attachment and dentition were set as fixed contacts. Additionally, the relationships between the clear aligner and dentition, as well as between adjacent teeth, were configured as sliding frictional contacts, with a friction coefficient of 0.2 based on prior research 14 , 15 .…”