Effect of Magnet Position on Tipping and Bodily Tooth Movement in Magnetic Force-Driven Orthodontics

Effectiveness of a low-intensity static magnetic field in accelerating upper canine retraction: a randomized controlled clinical trial

INTRODUCTION

Neodymium-iron-boron magnets have been suggested as a contemporary method for accelerating the process of orthodontic tooth movement (OTM). A limited number of clinical trials evaluated their effectiveness in accelerating OTM which is desirable for both orthodontists and patients. The present study aimed to investigate the effectiveness of a low-intensity static magnetic field (SMF) in accelerating upper canine retraction movement.

MATERIALS AND METHODS

Seventeen patients (mean age 20.76 ± 2.9 years) with their orthodontic treatment decision to extract the upper and lower first premolars due to bimaxillary protrusion malocclusion were included in this split-mouth study. Canine retraction was performed using Nickel-titanium (Ni-Ti) closed-coil springs (150 g of force on each side). The experimental side received SMF via an auxiliary wire that carried 4-neodymium iron-born magnets with an air gap of 2 mm between the magnets to produce a magnetic field density of 414 mT in the region corresponding to the lateral ligament of the upper canine. To determine the rate of upper canine retraction and upper molar drift, alginate impressions were taken once a month to create plaster casts, which were analyzed digitally via a three-dimensional method.

RESULTS

The rate of upper canine retraction was significantly greater (P < 0.05) on the SMF side than that on the control side during the first and second months, with an overall duration (19.16%) that was greater than that on the control side. The peak acceleration occurred during the second month (38.09%). No significant differences in upper molar drift were detected between the experimental and control sides (P > 0.05).

CONCLUSION

A low-intensity static magnetic field was effective at accelerating upper canine retraction. The difference between the two sides was statistically significant but may not be clinically significant. The SMF did not affect upper molar drift during the upper canine retraction phase.

TRIAL REGISTRATION

The trial was retrospectively registered at the ISRCTN registry ( ISRCTN59092624 ) (31/05/2022).

3D digital analysis of tooth movement with magnets and elastics in vitro

Objectives

Magnets have many advantages in orthodontics, and our previous studies confirmed their therapeutic potential through 3D-data analysis. The aim of this study was to compare tooth movements, including rotation, obtained via magnetic and elastic forces in crowded cases in vitro.

Methods

Typodont models mimicking a crowded case were prepared. In the magnetic force-driven orthodontics (MG) group, Nd-Fe-B magnets were attached to the labial surfaces from UR4 to UL4 for attracting force, and to UR6 and UL6 for repulsing force. For the elastic force-driven orthodontic (EL) group, brackets were placed on labial surfaces from UR2 to UL2 with power-chain elastics. A NiTi archwire was used in both groups. The models were 3D scanned before and after tooth movement and exported as STL files. The pre- and post-movement STL files were superimposed. The 3D coordinates of the measurement points of the crown and root apex were obtained, and tooth displacement, 3D movements (X, Y, and Z-axis), and rotation (yaw, pitch, and roll) were calculated. Two-tailed Student's t-test was performed for comparison of the results between MG and EL groups (n = 3).

Results

Overall, both groups indicated similar movement and rotation to achieve the planned arch form. In the crown movement and rotation, no significant differences were observed between MG and EL groups. However, in the root movement, there was a significant difference between MG and EL groups in X and Z axis for the canines.

Conclusions

Magnetic force-driven orthodontics demonstrated comparable results to elastics with less tipping movement, suggesting a potential future orthodontic modality.

Clinical significance

This in vitro study showed the potential of magnetic force for orthodontic application. The magnetic force-driven orthodontics might provide less tipping tooth movement compared to conventional methods, such as power chains, and could be a future technique for comprehensive orthodontic treatment.