Finite Element Analysis of Stress in Maxillary Dentition during En-masse Retraction with Implant Anchorage

Abstract

The goal of this study was to investigate how the height of the archwire hook and implant anchor affect tooth movement, stress in the teeth and alveolar bone, and the center of resistance during retraction of the entire maxillary dentition using a multibracket system. Computed tomography was used to scan a dried adult human skull with normal occlusion. Three-dimensional models of the maxillary bone, teeth, brackets, archwire, hook, and implant anchor were created and used for finite element analysis. The heights of the hook and the implant anchor were set at 0, 5, or 10 mm from the archwire. Orthodontic force of 4.9 N was systematically applied between the hook and the implant anchor and differential stress distributions and tooth movements observed for each traction condition. With horizontal traction, the archwire showed deformation in the superior direction anterior to the hook and in the inferior direction posterior to the hook. Differences in traction height and direction resulted in different degrees of deformation, with biphasic movement clearly evident both in front of and behind the hook. With horizontal traction of the hook at a height of 0 mm, all the teeth moved distally, but not with any other type of traction. At a height of 5 mm or 10 mm, deformation showed an increase. The central incisor showed extrusion under all traction conditions, with the amount showing a reduction as the height of horizontal or posterosuperior traction increased. The center of resistance was located at the root of the 6 anterior teeth and entire maxillary dentition. The present results suggest that it is necessary to consider deformation of the wire and the center of resistance during en-masse retraction with implant anchorage.

The Effect of Varied Positioning of Mini-screw, Anterior Retraction Hook, and Resultant Force Vector on Efficient En-Masse Retraction Using Finite Element Method: A Systematic Review

“…However, before writing this systematic review, several in-vitro FEM studies were published which have addressed various aspects of en-masse retraction as stated. Studies such as Zhang et al, 13 Sung et al, 14 Chetan et al, 17 Parashar et al, 18 Namburi et al, 20 Jain et al, 22 Shreevats et al, 21 and Suzuki et al 24 have not concluded either optimum position of mini-screw, size of ARH, reference plane to be considered, or the exact position of CR in their respective published articles. To elucidate the above aspects, it was imperative that a systematic review be conducted for discernment.…”

“…Zhang et al, 13 Sung et al, 14 Kojima et al, 15 Ashekar et al, 16 Chetan et al, 17 Hedayati et al, 19 Namburi et al, 20 Bohara et al, 23 and Suzuki et al 24 used ANSYS software for simulation, whereas Jain et al have not mentioned the software used for the study. Kojima et al, 15 Suzuki et al, 24 and Parashar et al 18 designed an FEM model based on the CT scan and converted it into a 3D model, while other studies such as Ashekar et al, 16 Chetan et al, 17 and Hedayati et al 19 designed a model based on Wheeler's dental anatomy textbook. Jain et al 22 and Bohara et al 23 did not quote the model design.…”

“…The method of retraction and force used for retraction varied in the studies. The force of 150 gm was used in studies conducted by Zhang et al, 13 Ashekar et al, 16 Chetan et al, 17 Hedayati et al, 19 Shreevats et al, 21 Jain et al, 22 Bohara et al, 23 and Suzuki et al 24 Sung et al 14 and Parashar et al 18 used 200 gm of force and Namburi et al 20 used 120 g for retraction and 60 gm for the intrusion. Jain et al 22 showed the method of en-masse retraction using NiTi spring in comparison with the power chain.…”

“…The positioning of ARH in between lateral incisors and canine was common, and this was specifically mentioned in the 12 studies. Zhang et al 13 considered a molar hook for deciding the dimensions of ARH, whereas an arch wire was reported as the reference plane in studies by Sung et al, 14 Kojima et al, 15 Ashekar et al, 16 Chetan et al, 17 Parashar et al, 18 Hedayati et al, 19 Namburi et al, 20 Shreevats et al, 21 and Suzuki et al 24 Biomechanical effects of different positions of mini-screw were compared with the fixed dimension of ARH by Chetan et al 17 (2-mm ARH), Namburi et al 20 (9 mm), and Bohara et al 23 (6-mm ARH for gingival model and 2-mm ARH for incisal model), respectively, whereas other studies such as those by Zhang et al, 13 Sung et al, 14 Kojima et al, 15 Ashekar et al, 16 Parashar et al, 18 Hedayati et al, 19 and Suzuki et al 24 evaluated different dimensions of ARH with fixed position of mini-screw. Sung et al 14 and Hedayati et al 19 varied the ARH for four different heights.…”

“…Park et al 25 took the bracket slot as a reference plane for placement of mini-screw. Studies such as Sung et al, 14 Kojima et al, 15 Ashekar et al, 16 Chetan et al, 17 Parashar et al, 18 Hedayati et al, 19 Namburi et al, 20 Bohara et al, 23 and Suzuki et al 24 had taken arch-wire level as reference. Zhang et al 13 and Shreevats et al 21 placed the mini-implant at a fixed height from the respective reference planes and varied the ARH height.…”