Effective contribution ratio of the molar during sequential distalization using clear aligners and micro-implant anchorage: a finite element study

Abstract

Introduction This study aims to investigate the biomechanical effects of anchorage reinforcement using clear aligners (CAs) with microimplants during molar distalization. And also explores potential clinical strategies for enhancing anchorage in the sequential distalization process. Methods Finite element models were established to simulate the CAs, microimplants, upper dentition, periodontal ligament (PDL), and alveolar bone. In group set I, the 2nd molars underwent a distal movement of 0.25 mm in group set II, the 1st molars were distalized by 0.25 mm after the 2nd molars had been placed to a target position. Each group set consisted of three models: Model A served as the control model, Model B simulated the use of microimplants attached to the aligner through precision cuts, and Model C simulated the use of microimplants attached by buttons. Models B and C were subjected to a series of traction forces. We analyzed the effective contribution ratios of molar distalization, PDL hydrostatic stress, and von Mises stress of alveolar bone. Results The distalization of the 2nd molars accounted for a mere 52.86% of the 0.25-mm step distance without any reinforcement of anchorage. The remaining percentage was attributed to the mesial movement of anchorage teeth and other undesired movements. Models B and C exhibited an increased effective contribution ratio of molar distalization and a decreased loss of anchorage. However, there was a slight increase in the undesired movement of molar tipping and rotation. In group set II, the 2nd molar displayed a phenomenon of mesial relapse due to the reciprocal force produced by the 1st molar distalization. Moreover, the efficacy of molar distalization in terms of contribution ratio was found to be positively correlated with the magnitude of force applied. In cases where stronger anchorage reinforcement is required, precision cuts is the superior method. Conclusions The utilization of microimplants in conjunction with CAs can facilitate the effective contribution ratio of molar distalization. However, it is important to note that complete elimination of anchorage loss is not achievable. To mitigate undesired movement, careful planning of anchorage preparation and overcorrection is recommended.

Biomechanical analysis of the effect of aligner overtreatment on molar distalization with clear aligners: a finite-element study

“…Similarly, the reciprocal force acted on the central incisor passed occlusally to the center of resistance, resulting in labial tipping and intrusion of the central incisor. Previous biomechanical analysis and clinical research have con rmed the results of this study [11,13,34].…”

“…Moreover, since the Class II elastic traction was directly applied onto the canine, the canine exhibited more lingual tipping, distal tipping and extrusion in the button group. Other biomechanical studies had con rmed this result [13,37]. Thus, we suggest that Class II elastic traction is able to enhance molar distalization and to prevent anchorage loss (proclination) of the anterior teeth.…”

“…Clear aligner is advantageous in offering "pushing" force rather than "pulling" force [10,11]. Thus, upper molar distalization, achieved by "pushing" force exerted on molars, is one of the most predictable tooth movements with clear aligner [12,13]. However, labial movement of anterior teeth occurs during molar distalization due to its reciprocal force, posing periodontal threats to those with inadequate periodontal support [14,15].…”

Effects of different tooth movement patterns and aligner thicknesses on maxillary arch expansion with clear aligners: a three-dimensional finite element study

“…Studies have shown that when using clear aligners to distalize molars and intrude anterior teeth, sequential molar distalization ( Liu et al, 2023 ) and distributed anterior teeth intrusion ( Liu and Hu, 2018 ) are more sensible than overall movement. Therefore, different distributed movement patterns were designed in this study to investigate the influence of tooth movement patterns on expansion with clear aligners.…”