The optimal activation of plastic aligner for canine distal movement: a three-dimensional finite element analysis

Effects of aligner activation and power arm length and material on canine displacement and periodontal ligament stress: a finite element analysis

BACKGROUND

This study aimed to assess the impact of aligner activation and power arm length and material on canine and aligner displacement, von Mises stress in the power arm, and principal stress in the periodontal ligament (PDL) during canine tooth distalization using finite element analysis (FEA). The effects of aligner activation and power arm length were primary outcomes, while the effect of the power arm material was a secondary outcome.

METHODS

Aligner activation (0.1 mm or 0.2 mm) was applied without using a power arm in two models. The effects of aligner activation, power arm length (12, 13, or 14 mm) and power arm material (stainless steel [SS] or fiber-reinforced composite [FRC]) on canine distalization were investigated in 12 models by evaluating displacement and stress via ALTAIR OptiStruct analysis.

RESULTS

Greater canine displacement was observed in all models with 0.2 mm than 0.1 mm of aligner activation. When models with the same aligner activation were compared, reduced mesiodistal tipping, increased palatal tipping, and increased extrusion of the canine cusp were observed with increasing power arm length. Moreover, the von Mises stress increased as the power arm length increased. Increasing the aligner activation and power arm length increased the maximum principal stress in the PDL. Power arms of the same length in both materials showed the same results in terms of canine displacement, clear aligner displacement, and maximum principal stress in the PDL. However, under conditions of equal length and aligner activation, the von Mises stress of the SS power arm was higher than that of the FRC power arm.

CONCLUSION

Using a power arm in canine distalization reduced mesiodistal tipping but increased palatal tipping and extrusion of the canine cusp. Aligner activation and additional force increased tooth movement and principal stress in the canine PDL. FRC power arms exhibited less von Mises stress than SS power arms.

Stress and movement trend of lower incisors with different IMPA intruded by clear aligner: a three-dimensional finite element analysis

BACKGROUND

During the intrusion of lower incisors with clear aligners (CAs), root disengagement from the alveolar bone often occurs, resulting in serious complications. This study aimed to determine the potential force mechanism of the mandibular anterior teeth under the pressure of CA, providing theoretical data for clinical practice.

METHODS

In this study, a 3D finite element model was established, including the CA, periodontal ligament, and mandibular dentition. Incisor mandibular plane angles were set as 5 groups: 90°, 95°, 100°, 105°, and 110°. The 4 mandibular incisors were intruded by 0.2 mm, while the canines were the anchorage teeth. The stress, force systems, and potential movement trends of mandibular anterior teeth were obtained.

RESULTS

The compressive stress of the incisors was concentrated in the lingual fossa, incisal ridge, and apex. With the increase in IMPA, the moment of central incisors changed from lingual crown moment to labial crown moment, with the turning point between 100° and 105°, but the center of resistance (CR) was always subjected to the force toward the lingual and intrusive direction. The force and moment toward the labial side of the lateral incisors were greater than those toward the central incisors. The canines always tipped distally and received extrusive force with no relationship with IMPA.

CONCLUSIONS

With the increase in the initial IMPA, the direction of labiolingual force on the mandibular incisors was reversed. However, the root of the lower incisors always tipped labially, which indicated fenestration and dehiscence.

Biomechanics of clear aligners: hidden truths & first principles

Over the past two decades clear aligner-based treatment has received remarkableattention from the orthodontic profession and more so from general practitioners.Different companies have emerged using vigorous advertisement to promote theirproducts mainly to patients and clinicians through social media. A variety of concepts,methods, and adjuncts have been introduced to enhance the efficacy andeffectiveness of clear aligners. However, the accuracy of tooth movement (vspredicted) with aligners still hovers around 50%. Fixed appliances fare much better onaccuracy and predictability of treatment. Why is there a discrepancy betweenexpected and actual outcomes? This paper utilizes 'first principles' and the existingevidence to unravel some of the key drawbacks of aligner-based therapy. Severalshortcomings in the biomechanical properties of aligner material (thermoplastics) thataffect clinical performance are discussed. Based on the first principles of alignerbiomechanics, this paper provides clinical insights for improving predictability and effectiveness of aligner therapy.