Biomechanical Effects of Different Auxiliary-Aligner Designs for the Extrusion of an Upper Central Incisor: A Finite Element Analysis

Aim

To evaluate the biomechanical effects of four different auxiliary-aligner combinations for the extrusion of a maxillary central incisor and to define the most effective design through finite element analysis (FEA).

Materials and Methods

A full maxillary arch (14 teeth) was modelled by combining two different imaging techniques: cone beam computed tomography and surface-structured light scan. The appliance and auxiliary element geometries were created by exploiting computer-aided design (CAD) procedures. The reconstructed digital models were imported within the finite element solver (Ansys® 17). For the extrusion movement, the authors compared the aligner without an attachment with three auxiliary-aligner designs: a rectangular palatal attachment, a rectangular buccal attachment, and an ellipsoid buccal attachment. The resulting force-moment (MF) system delivered by the aligner to the target tooth and the tooth displacement were calculated for each scenario.

Results

The maximum tooth displacement along the z-axis (0.07 mm) was obtained with the rectangular palatal attachment, while the minimum (0.02 mm) was obtained without any attachments. With the ellipsoid attachment, the highest undesired moments M_x and M_y were found. The rectangular palatal attachment showed the highest F_z (2.0 N) with the lowest undesired forces (F_x = 0.4 N; F_y = −0.2 N).

Conclusions

FEA demonstrated that the rectangular palatal attachment can improve the effectiveness of the appliance for the extrusion of an upper central incisor.

A three-dimensional finite element analysis of the effect of archwire characteristics on the self-ligating orthodontic tooth movement of the canine

BACKGROUND:

In orthodontics, the tooth movement is a biologic reaction to applied force systems, brackets, archwires, and periodontium tissue.

OBJECTIVE:

To investigate the effects of the various archwire characteristics like the friction coebetween bracket and archwire, the cross-section shape, and the cross-section dimension, on the displacement and the periodontal ligament (PDL) stresses of canine’s movement in a self-ligating treatment using the finite element (FE) analysis method.

METHODS:

Models of teeth and their supporting tissues, brackets and archwires were constructed. Ten kinds of archwires were used for the simulation.

RESULTS:

Considering the translation movement, the maximum displacement, highest stress, and Rc⁢r increased with an increase in the cross-section area. The maximum displacement and highest stress increased with an increase in the friction coefficient. The Rc⁢r values increased with an increase in the friction coefficient in the round archwires, while decreased with an increase in the rectangular archwires. However, these change tends were different in rotation and inclination movement.

CONCLUSION:

The archwire characteristics (round archwire, rectangular archwire, cross-section area, and friction coefficient) exhibited different effects on the tooth translation, rotation, and inclination. Our results can assist in the improvement of the self-ligating orthodontic treatment.

Finite element method analysis of the periodontal ligament in mandibular canine movement with transparent tooth correction treatment

Background

This study used the 3D finite element method to investigate canine’s displacements and stresses in the canine’s periodontal ligament (PDL) during canine’s translation, inclination, and rotation with transparent tooth correction treatment.

Methods

Finite element models were developed to simulate dynamic orthodontic treatments of the translation, inclination, and rotation of the left mandibular canine with transparent tooth correction system. Piecewise static simulations were performed to replicate the dynamic process of orthodontic treatments. The distribution and change trends of canine’s displacements and stresses in the canine’s PDL during the three types of tooth movements were obtained.

Results

Maximum displacements were observed at the crown and middle part in the translation case, at the crown in the inclination case, and at the crown and root part in the rotation case. The relative maximum von Mises and principal stresses were mainly found at the cervix of the PDL in the translation and inclination cases. In the translation case, tensile stress was mainly observed on the mesial and distal surfaces near the lingual side and compressive stress was located at the bottom of the labial surface. In the inclination case, tensile stress was mainly observed at the labial cervix and lingual apex and compressive stress was located at the lingual cervix and labial apex. In the rotation case, von Mises stress was mainly located at the cervix and inside the lingual surface, tensile stress was located on the distal surface, and compressive stress was detected on the mesial surface. The stress and displacement value rapidly decreased in the first few steps and then reached a plateau.

Conclusions

Canine’s movement type significantly influences the distribution of canine’s displacement and stresses in the canine’s PDL. Changes in canine’s displacement and stresses in the canine’s PDL were exponential in transparent tooth correction treatment.