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

Effect of archwire size and lever arm length on anterior and posterior teeth movement during en-masse retraction in personalized lingual orthodontics: A 3-dimensional finite element study

OBJECTIVE

To evaluate the biomechanical effect of anterior and posterior teeth in en-masse retraction in lingual orthodontics using varied archwire sizes and lever arm lengths.

METHODS

A finite element model of lingual orthodontics for retracting maxillary anterior teeth was established. The archwire was designed into: Archwire 1: 0.016×0.022-inch stainless steel (SS) with 15° extra torque on central incisors, Archwire 2: 0.016×0.024-inch SS with 13° extra torque on anterior teeth, Archwire 3: 0.017×0.025-inch SS with laterally 0.016×0.024-inch, and Archwire 4: 0.018×0.025-inch SS with laterally 0.016×0.0225-inch. Moreover, the lever arm was set to 0mm, 2mm, 4mm, 6mm, 8mm, and 10mm. Initial displacements were calculated after applying 1.5N force from mini-implant to lever arms.

RESULTS

In Archwire 1, increasing intrusion and labial tipping on central incisors and decreasing lingual tipping on lateral incisors and canines, as well as decreasing palatal tipping and distal inclination on posterior teeth were observed with lever arm length increase. In Archwire 2, with the lever arm length increase, incisors exhibited increasing labial tipping, while palatal inclination and intrusion of posterior teeth decreased. In Archwire 3 and 4, torque control ability of anterior teeth increased with longer lever arms, as well as decreasing extrusion was observed on central incisors. Posterior teeth moved buccally and distally.

CONCLUSIONS

Thick archwire without extra torque combined with longer lever arm are more conducive to en-masse retraction of central incisor. Moreover, extra torque on thinner archwire can also effectively control torque. Besides, additional torque and lever arm lengths affect the movement of posterior teeth.

Effect of multiple hook heights and positions during en masse maxillary distalization using infrazygomatic crest miniscrew- single and double points of force application: a finite element analysis study

BACKGROUND

This study aimed to simulate maxillary dentition distalization as one unit anchored to infrazygomatic crest (IZC) miniscrew using different hook positions and lengths.

MATERIALS AND METHODS

Eleven finite-element models (FEM) were constructed from a cone beam computed tomography scan of a patient with Class II malocclusion. Different force vectors to the IZC miniscrew were simulated using one point of force application either mesial to the canine or mesial to the first premolar, using different hook lengths (0, 2, 4, and 6 mm). In the novel approach, two point-force system was constructed using double-hook retraction in three conditions. The FEM yielded tooth displacement patterns and stress contour plots of the periodontal ligament.

RESULTS

When hooks were placed mesial to the canine, the incisor showed palatal translation with controlled palatal tipping at 0 and 2 mm, palatal bodily displacement at 4 mm, and palatal translation with torquing at 6 mm. In hooks mesial to the first premolar, the pattern showed palatal translation with torquing, except with the 0-mm hook where controlled palatal tipping occurred. Whereas, vertically, it shows extrusion at the 0- and 2-mm hooks mesial to the first premolar and intrusion with the remaining single hook simulations. The molar exhibited translation with controlled distal tipping at all hook lengths mesial to the canine and 0 mm mesial to the first premolar, while it demonstrated distal translation with torquing at 2-,4-, and 6-mm hooks mesial to the first premolar. Vertically, it showed extrusion with hooks mesial to the canine, which changed to intrusion with hooks mesial to the first premolar. In double-hook simulations, the incisor showed bodily displacement only with hooks mesial to the canine and second premolar, whereas the molar showed distal bodily movement with hooks mesial to the first and second premolars.

CONCLUSION

Hook height and position variations are crucial in the resultant displacement pattern. Accordingly, different force systems should be tailored individually based on the patient's initial malocclusion.

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.