Biomechanical analysis of the maxillary molar intrusion: A finite element study.

INTRODUCTION: The purpose of this study was to analyze and clarify tooth movement when intruding the maxillary molars using intrusive forces between the maxillary first and second molars. METHODS: A finite element method was used to simulate the long-term orthodontic movement of the maxillary dentition by accumulating the initial displacement of teeth produced by elastic deformation of the periodontal ligament. Intrusive forces of 2 N were applied buccally to the archwire between the maxillary first and second molars. Two different sized transpalatal arches (TPAs) (0.036-in and 0.06-in) and a gradually increased constriction bend and torque toward the posterior teeth were applied to prevent buccal tipping of the posterior teeth when intruding the maxillary posterior teeth. RESULTS: The whole maxillary dentition rotated clockwise as the intrusive force passed posteriorly to the center of resistance. Buccal crown tipping of the maxillary posterior teeth and lingual tipping of the maxillary incisors occurred. Their tipping decreased with a constriction bend and lingual crown torque and when a TPA was applied. CONCLUSIONS: Supplemental procedures such as a constriction bend and lingual crown torque and a TPA could effectively prevent the buccal crown tipping of the maxillary posterior teeth when intruding on them.

Biomechanical analysis for total distalization of the maxillary dentition: A finite element study.

INTRODUCTION: This study aimed to identify the tooth movement patterns relative to various force angulations (FAs) when distalizing the total maxillary dentition. METHODS: Long-term orthodontic movement of the maxillary dentition was simulated by accumulating the initial displacement of teeth produced by elastic deflection of the periodontal ligament using a finite element analysis. Distalization forces of 3 N were applied to the archwire between the maxillary canine and first premolar at 5 different FAs (-30°, -15°, 0°, 15°, and 30°) to the occlusal plane. RESULTS: Maxillary incisors and molars showed lingual and distal tipping at all FAs, respectively. At a force angulation of 30°, almost bodily distalization of the total maxillary dentition occurred, but incisors showed considerable lingual tipping because of the effect of clearance gap (0.003-in, 0.022 × 0.025-in bracket slot, 0.019 × 0.025-in archwire) and elastic deflection of the archwire. Medial displacement of the maxillary anterior teeth occurred because of lingual tipping during distalization. The occlusal plane rotated clockwise at all FAs because of extrusion of the maxillary incisors and intrusion of the maxillary second molars, and the amounts decreased as FA increased. CONCLUSIONS: Tooth movement patterns during distalization of the total maxillary dentition were recognized. With an understanding of the mechanics, a proper treatment plan can be established.

Biomechanical analysis for total mesialization of the maxillary dentition: A finite element study.

INTRODUCTION: The purpose of this study was to analyze and clarify tooth movement during mesialization of the whole maxillary dentition with various force angulations (FAs). METHODS: A finite element method was used to simulate the long-term orthodontic movement of the maxillary dentition by accumulating the initial displacement of teeth produced by elastic deformation of the periodontal ligament. A mesial force of 3 N was applied to the maxillary second molar at 5 different FAs (-30°, -15°, 0°, 15°, and 30°) to the occlusal plane. RESULTS: At an FA of 28°, the line of action of the force passed through the center of resistance of the maxillary whole dentition. With all FAs, the central incisors and molars tipped labially and mesially, respectively. The tipping angles gradually decreased as the FAs shifted from -30° to 30°. The molars tipped lingually with FAs of -30° and -15°, whereas they tipped buccally with FAs of 0°, 15°, and 30°. The molars tended to rotate mesiolingually more as the angle of force increased toward an FA of 30°. The occlusal plane rotated counterclockwise with FAs of -30°, -15°, and 0°, whereas it rotated clockwise with FAs of 15° and 30°. With an FA of 30°, buccal tipping and mesiolingual rotation of the molars, and the change in the occlusal plane angle decreased when the transpalatal arch (TPA) was fixed to the first molars and decreased, even more when the TPA was fixed to the second molars rather than the first molars, when a thicker TPA was used, and when the TPA was fixed to both molars rather than a single molar. CONCLUSIONS: There was a correlation between tooth movement during mesialization of the whole maxillary dentition and the angle at which the force was applied.

Tooth Movement Efficacy of Retraction Spring Made of a New Low Elastic Modulus Material, Gum Metal, Evaluated by the Finite Element Method.

The aim of this study was to evaluate the tooth movement efficacy of retraction springs made of a new ß-titanium alloy, "gum metal", which has a low Young's modulus and nonlinear super elasticity. Using double loop springs incorporated into an archwire made of gum metal (GUM) and titanium molybdenum alloy (TMA), the maxillary anterior teeth were moved distally to close an extraction space. The long-term movements were simulated by the finite element method. Its procedure was constructed of two steps, with the first step being the calculation of the initial tooth movement produced by elastic deformation of the periodontal ligament, and in the second step, the alveolar socket was moved by the initial tooth movement. By repeating these steps, the tooth moved by accumulating the initial tooth movement. The number of repeating calculations was equivalent to an elapsed time. In the GUM and TMA springs, the anterior teeth firstly tipped lingually, and then became upright. As a result of these movements, the canine could move bodily. The amount of space closure in GUM spring was 1.5 times that in TMA spring. The initial tipping angle of the canine in the GUM spring was larger than that in the TMA spring. The number of repeating calculations required for the bodily movement in the GUM spring was about two times that in the TMA spring. It was predicted that the speed of space closure in the GUM spring was smaller than that in the TMA spring.

A finite element analysis of the effects of archwire size on orthodontic tooth movement in extraction space closure with miniscrew sliding mechanics.

BACKGROUND: Sliding mechanics with miniscrews is recently used for extraction space closure. The purpose of this study was to elucidate how and why the archwire size affects long-term tooth movement in miniscrew sliding mechanics. METHODS: Long-term orthodontic tooth movements were simulated based on a remodeling law of the alveolar bone by using a finite element method, in which the bracket rotated freely within a clearance gap (a play) of the archwire-bracket slot. The archwire size was changed to 0.021, 0.018, and 0.016 in. for the 0.022-in. bracket. RESULT: Lingual crown tipping and extrusion of the incisors increased with decreasing the archwire size. Movements of the posterior teeth were approximately the same irrespective of archwire size. CONCLUSIONS: When decreasing the archwire size, a play of the archwire-bracket slot, as well as the elastic deformation of the archwire, resulted in lingual tipping of the incisors. This tipping led to extrusion of the incisors.