Dual-section versus conventional archwire for en-masse retraction of anterior teeth with direct skeletal anchorage: a finite element analysis

Biomechanical effect of dual-dimensional archwire on controlled movement of anterior teeth compared with rectangular archwire: A finite element study

INTRODUCTION

This study aimed to determine and compare the effectiveness of the use of the dual-dimensional archwire and conventional rectangular archwire on tooth movement patterns when combined with various lengths of power arms.

METHODS

Displacements of the maxillary central incisor and the deformation of the wire section were calculated when applying retraction forces from different lengths of power arms using the finite element method.

RESULTS

Torque control of the incisor could be carried out more effectively when using the dual-dimensional archwire combined with long power arms than with the rectangular archwire. The use of the dual-dimensional archwire produced bodily movement of the central incisor at height levels of the power arm between 8 and 10 mm and lingual root tipping at the level of 10 mm.

CONCLUSIONS

The use of the dual-dimensional archwire provided better-controlled movement of the incisor, including bodily movement or root movement, than the rectangular archwire.

Anchorage effects of ligation and direct occlusion in orthodontics: A finite element analysis

BACKGROUND AND OBJECTIVE

During orthodontic treatment, the figure-of-eight ligature and the physiological occlusion play an important role in providing anchorage effects. However, their effects on reaction forces of tooth and stress state in periodontal ligament (PDL) have not been quantitatively evaluated yet. In this study, we presented a finite element analysis process for simulating posterior molar ligature and direct occlusion during orthodontics in order to quantitatively assess their anchorage effects.

METHODS

A high precision 3D biomechanical model containing upper and lower teeth, PDL, brackets and archwire was generated from the images of computed tomographic scan and sophisticated modelling procedures. The orthodontic treatment of closing the extraction gap was simulated via the finite element method to evaluate the biomechanical response of the molars under the conditions with or without ligation. The simulations were divided into experimental and control groups. In the experimental group, orthodontic force of 1 N was first applied, then direct occlusal forces of 3 and 10 N were applied on each opposite tooth. While in the control group, occlusal forces were applied without orthodontic treatment. The tooth displacement, the stress state in the PDL and the directions of the resultant forces on each tooth were evaluated.

RESULTS

In the case of molars ligated, the maximum hydrostatic stress in the molars' PDL decreases by 60%. When an initial tooth displacement of several microns occurs in response to an orthodontic force, the direction of the occlusal force changes simultaneously. Even a moderate occlusal force (3 N per tooth) can almost completely offset the mesial forces on the maxillary teeth, thus to provide effective anchorage effect for the orthodontics.

CONCLUSIONS

The proposed method is effective for simulating ligation and direct occlusion. Figure-of-eight ligature can effectively disperse orthodontic forces on the posterior teeth, while a good original occlusal relationship provides considerable anchorage effects in orthodontics.