An objective system for appraising clear aligner treatment difficulty: clear aligner treatment complexity assessment tool (CAT-CAT)

Evaluation of the effects of semipontic design on tooth movements during mesialization of mandibular second molar performed with clear aligner treatment by finite element analysis

INTRODUCTION

Loss of the mandibular first molar is common in orthodontic patients. One treatment option is the mesialization of the second and third molars. This study aimed to investigate the displacement and type of movement in the second molar during mandibular second molar mesialization with clear aligner treatment using finite element analysis in configurations with or without pontic, semipontic, and anatomic pontic for the edentulous space.

METHODS

Mesialization of the mandibular second molar with clear aligner treatment was simulated using the AlGOR Fempro program (ALGOR, Inc, Pa) with 3 different configurations.

RESULTS

In the transverse direction, the highest rotation occurred in the anatomic pontic model, whereas the lowest rotation was in the semipontic model. In the sagittal axis, although tooth movement was realized by tipping in all scenarios, the semipontic model showed the closest movement to translation because of a higher rate of crown-root movement. In the vertical axis, although extrusion occurred in all configurations, the semipontic model showed the least extrusion forces, whereas the anatomic pontic model showed the most.

CONCLUSIONS

Mesiobuccal rotation, mesial tipping, and extrusion were observed in all models. However, the semipontic design had the closest movement to translational. Further randomized, controlled clinical trials are needed to evaluate the effects of different pontic designs on tooth movements.

Uprighting and protraction of two unilateral mandibular molars using a cantilever arm through a sophisticated biomechanical system with clear aligner: A case report

Although clear aligner can be efficient and predictable in some tooth movements, mandibular molar protraction is the least predictable owing to biological and biomechanical limitations. This case report presents a 20-year-old female with poor prognosed left mandibular first molar (#36), deviated dental midline and mild crowding. After extraction of #36, clear aligners and an Albert cantilever were used for treatment. Through carefully designed dual mechanical system, we achieved uprighting and protraction of #37 within 27 months, with crown and root movements of 9.9mm and 12.1mm, respectively. The predictability of the crown and root movement was 107.6% and 84.6%. Coincident dental and facial midline, class I molar and canine relationship and good root parallelism were also achieved. Large-distance mandibular molar protraction can be achieved effectively with a combination of Albert cantilever arm and clear aligner.

A Bibliometric Analysis of Clear Aligner Treatment (CAT) From 2003 to 2023

Clear aligner treatment (CAT) has been evolving over the past two decades. This study aims to conduct a comprehensive and up-to-date bibliometric analysis of publications related to CAT, presenting the research trends, landscapes, and hot spots in this field. All publications were retrieved from the Web of Science Core Collection from 2003 to 2023. In addition to a general analysis of research landscapes, the following items were analyzed, i.e., countries, institutions, authors, journals, publications, and keywords. A total of 1031 relevant publications were included in this study. From 2003 to the present, the number of publications and citations in this field showed an increasing trend. Italy led in terms of publication counts, and Sichuan University in China had the highest publication counts among institutions. In total, 33 scholars had published a minimum of 10 articles, and the collaborations among them were mostly within each country. The American Journal of Orthodontics and Dentofacial Orthopedics published the most relevant publications. "Predictability of tooth movements," "influencing factors for clinical efficacy," "biomechanics," and "patients' perception and periodontal health" stood out as the core research focus on CAT. Our study identified the most influential countries, institutions and authors, and their cooperative relationships, and detected hot research topics on CAT, calling for more high-quality international collaborative research in the future.

Orthodontic Practitioners' Knowledge and Education Demand on Clear Aligner Therapy

OBJECTIVES

Clear aligner therapy (CAT) has been gaining popularity amongst the orthodontic community. No systematic course on CAT has been reported to date. The objectives of this study were to determine practitioners' knowledge and to offer insights for future tailored courses on CAT.

METHODS

An online questionnaire was distributed. The questionnaire comprised personal background information, predictability of tooth movement through CAT, and CAT knowledge that practitioners demanded to learn. Four senior expert orthodontists' answers to the predictability of tooth movement through CAT were averaged to be a standard reference. Descriptive statistics, 1-way analysis of variance (ANOVA), principal component analysis, Student t test, and multivariate logistics regression analysis were performed with significance set at P < .05.

RESULTS

In total, 190 practitioners participated in this study. As compared to the standard reference, participants overestimated the predictability of difficult-to-be-achived tooth movements (eg, molar mesialisation; P < .0001). Strategy of managing troubleshooting cases and extraction cases ranked the highest CAT knowledge that participants requested to learn. Practice type, number of completed CAT cases, number of undergoing CAT cases, years of practice, education background, and time of using CAT were the influencing factors of the questions regarding the predictability of tooth movement through CAT and CAT knowledge that were demanded to be learned.

CONCLUSIONS

The predictability of difficult-to-be-achieved tooth movement through CAT is often overestimated by practitioners with limited clinical experience. Tailored education on CAT, especially managing troubleshooting cases and extraction cases, should be designed for all practitioners.

Coronal Repercussions of the Maxillary Central Incisor Torque in the First Set of Aligners: A Retrospective Study

Coronal torque is one of the key factors in orthodontic treatment. An adequate torque value has an impact on aesthetics and soft tissue profile. The aim of this quantitative, comparative and observational longitudinal cohort study was to analyze the efficacy of the maxillary central incisor coronal torque in the Invisalign® system and evaluate the relation between coronal torque movement and patient's facial biotype. In total, 27 patients were selected. The planned movements (TP) were obtained from the Invisalign Doctor Site® using mathematical formulas that consider the T0 measurements. Pre-treatment (T0) and after full use of the first set of aligners (T1) scanners were evaluated using Geomagic® Control X TM by superimposing T0 and T1 models using a transverse plane and the long axis of the tooth crown. IBM® SPSS® software was used for statistical purposes. We found statistically significant differences between T0 and T1 in pro-inclination and retro-inclination, as well as between achieved and planned values in pro-inclination (p = 0.011). We verified that hyperdivergent clinical cases presented higher mean values of coronal torque, and hypodivergent cases presented lower values. In pro-inclination, the differences between the planned and achieved values were greater in hypodivergent cases and smaller in hyperdivergent cases. In retro-inclination, the differences between the planned and achieved values were greater in normodivergent cases and smaller in hypodivergent cases. This study highlights that inefficacy is more accentuated in pro-inclination. Aligners are an effective tool for producing coronal repercussions of torque movement, being more effective in retro-inclination.

Accumulated biomechanical effects of mandibular molar mesialization using clear aligners with auxiliary devices: an iterative finite element analysis

BACKGROUND

The biomechanics generated by the clear aligner (CA) material changes continuously during orthodontic tooth movement, but this factor remains unknown during the computer-aid design process and the predictability of molars movement is not as expected. Therefore, the purpose of this study was to propose an iterative finite element method to simulate the long-term biomechanical effects of mandibular molar mesialization (MM) in CA therapy under dual-mechanical systems.

METHODS

Three groups including CA alone, CA with a button, and CA with a modified lever arm (MLA) were created. Material properties of CA were obtained by in vitro mechanical experiments. MM was conducted by the rebound force exerted by CA material and the mesial elastic force (2N, 30° to the occlusal plane) applied to the auxiliary devices. Stress intensity and distribution on periodontal ligament (PDL), attachment, button and MLA, and displacement of the second molar (M2) during the iterations were recorded.

RESULTS

There was a significant difference between the initial and cumulative long-term displacement. Specifically, compared to the beginning, the maximum stress of PDL decreased by 90% on average in the intermediate and final steps. The aligner was the main mechanical system at first, and then, the additional system exerted by the button and MLA dominated gradually. The stress of attachments and auxiliary devices is mainly concentrated on their interfaces with the tooth. Additionally, MLA provided a distal tipping and extrusive moment, which was the only group that manifested a total mesial displacement of the root.

CONCLUSIONS

The innovatively designed MLA was more effective in reducing undesigned mesial tipping and rotation of M2 than the traditional button and CA alone, which provided a therapeutic method for MM. The proposed iterative method simulated tooth movement by considering the mechanical characteristic of CA and its long-term mechanical force changes, which will facilitate better movement prediction and minimize the failure rate.

The effects of aligner anchorage preparation on mandibular first molars during premolar-extraction space closure with clear aligners: A finite element study

INTRODUCTION

This study aimed to determine the effectiveness of different aligner anchorage preparations on mandibular first molars during premolar-extraction space closure with clear aligners and to assess the effects of different modes of Class II elastics on mandibular first molars.

METHODS

Finite element models were constructed on the basis of cone-beam computed tomography data from an orthodontic patient. The models comprised maxilla, mandible, maxillary and mandibular teeth without first premolars, periodontal ligaments, attachments and aligners. Tooth displacement tendencies were calculated using different aligner anchorage preparations and Class II elastics on the models from the same patient. Three group sets were designed on the basis of the positions of aligner cutouts and buttons (mesiobuccal, distobuccal and lingual). Four groups were established in each of the 3 group sets. Four groups were created: (1) no elastic traction + no anchorage preparation, (2) anchorage preparation only, (3) elastic traction only, and (4) elastic traction + anchorage preparation. Different aligner anchorage preparations (0°, 1°, 2°, 3°) were applied on mandibular second premolars and molars. The Class II traction force was set to 100 g.

RESULTS

With clear aligners, mandibular first molars were subject to mesial tipping, lingual tipping and intrusion. In the condition of no elastic traction, aligner anchorage preparation resulted in distal tipping, buccal tipping, and extrusion effect on mandibular first molars. Aligner anchorage preparation was more effective in the distal and lingual cutout groups than in the mesial cutout group. In the condition of Class II elastic traction, the bodily movement of mandibular first molars was achieved with a 3° anchorage preparation for the mesial cutout group and a 1.7° anchorage preparation for distal and lingual cutout groups. Absolute maximal anchorage was achieved with a 2° anchorage preparation for distal and lingual cutout groups.

CONCLUSIONS

Clear aligner therapy caused mesial tipping, lingual tipping and intrusion of mandibular first molars during premolar-extraction space closure. Aligner anchorage preparation effectively prevented mesial and lingual tipping of mandibular molars. Distal and lingual cutout modes were more effective than mesial cutout modes in aligner anchorage preparation. For each aligner stage (0.25 mm), 1.7° aligner anchorage preparation and Class II elastics with distal or lingual cutouts led to the bodily movement of mandibular first molars, whereas 2° anchorage preparation reached absolute maximal anchorage.

Clear Aligners and Smart Eye Tracking Technology as a New Communication Strategy between Ethical and Legal Issues

Smart eye-tracking technology (SEET) that determines visual attention using smartphones can be used to determine the aesthetic perception of different types of clear aligners. Its value as a communication and comprehension tool, in addition to the ethical and legal concerns which it entails, can be assessed. One hundred subjects (50 F, 50 M; age range 15-70) were equally distributed in non-orthodontic (A) and orthodontic (B) groups. A smartphone-based SEET app assessed their knowledge of and opinions on aligners. Subjects evaluated images of smiles not wearing aligners, with/without attachments and with straight/scalloped gingival margins, as a guided calibration step which formed the image control group. Subsequently, the subjects rated the same smiles, this time wearing aligners (experimental images group). Questionnaire data and average values for each group of patients, and images relating to fixation times and overall star scores, were analyzed using these tests: chi-square, t-test, Mann-Whitney U, Spearman's rho, and Wilcoxon (p < 0.05). One-way ANOVA and related post-hoc tests were also applied. Orthodontic patients were found to be better informed than non-orthodontic patients. Aesthetic perception could be swayed by several factors. Attachments scored lower in aesthetic evaluation. Lips distracted attention from attachments and improved evaluations. Attachment-free aligners were better rated overall. A more thorough understanding as to the opinions, expectations and aesthetic perception of aligners can improve communication with patients. Mobile SEET is remarkably promising, although it does require a careful medicolegal risk-benefit assessments for responsible and professional use.

The predictability of orthodontic tooth movements through clear aligner among first-premolar extraction patients: a multivariate analysis

BACKGROUND

The purpose was to determine the predictability of tooth movements through clear aligner among premolar extraction patients and to explore the effects of various factors on tooth movements.

METHODS

A total of 31 extraction patients (10 males and 20 females; age 14-44) receiving clear aligner treatment (Invisalign) were enrolled in this study. The actual post-treatment models and pre-treatment models were superimposed using the palatal area as a reference and registered with virtual post-treatment models. A paired t test was used to compare the differences between actual and designed tooth movements of maxillary first molars, canines, and central incisors. A multivariate linear mixed model was performed to examine the influence of variables on actual tooth movements.

RESULTS

Compared to the designed tooth movements, the following undesirable tooth movements occurred: mesial movement (2.2 mm), mesial tipping (5.4°), and intrusion (0.45 mm) of first molars; distal tipping (11.0°), lingual tipping (4.4°), and distal rotation of canines (4.9°); lingual tipping (10.6°) and extrusion (1.5 mm) of incisors. Age, crowding, mini-implant, overbite, and attachments have differential effects on actual tooth movements. Moreover, vertical rectangular attachments on canines are beneficial in achieving more predictable canine and incisor tooth movements over optimized attachments. Lingual tipping and extrusion of incisors were significantly influenced by the interaction effects between incisor power ridge and different canine attachments (p < 0.05).

CONCLUSIONS

Incisors, canines, and first molars are subject to unwanted tooth movements with clear aligners among premolar extraction patients. Age, crowding, mini-implant, overbite, and attachments influence actual tooth movements. Moreover, vertical rectangular attachments on canines are beneficial in achieving more predictable incisor tooth movements over optimized canine attachments.

Biomechanical Characteristics of Maxillary Molar Distalization Using Different Attachments with Clear Aligners: A 3-Dimensional Finite Element Analysis

This study aimed to compare the biomechanical characteristics of maxillary teeth in molar distalization with different orthodontic attachments. A 3-dimensional finite model of maxillary molar distalization with clear aligners was generated by computed tomography and contained different components. Four models—non-attachment (model A), horizontal rectangular attachment (model B), vertical rectangular attachment (model C), and combined attachment (model D)—were set up. The modalities of molar distalization were simulated using a finite element analysis. The results showed that the minimum displacement (rotation center) of the second molar in models A and B was located at the root furcation. In model C, the minimum displacement was located in the middle third of the palatal root. In model D, the minimum displacement was located at the apical third of the root. The anchorage teeth in all the four groups tended to have mesial tipping movement. Models B and D had more uniform stress distribution of the periodontal ligament than models A and C. Models with attachment had a larger tooth displacement pattern than that without attachment. Collectively, if molar distalization is planned before treatment, the appropriate application of attachments can help achieve the desired tooth movements more efficiently.

Biomechanical analysis of effective mandibular en-masse retraction using Class II elastics with a clear aligner: a finite element study

Background

This study aimed to evaluate the displacement and stress distribution of mandibular dentition by various positions of the Class II elastics during en-masse retraction in clear aligner therapy.

Methods

Models including a mandibular dentition (without first premolars), periodontal ligament (PDL), mandible, as well as attachments, aligners and buttons were constructed and imported into Ansys Workbench 2019 (ANSYS, USA) to generate the three-dimensional (3D) finite element model. Six combinations were created: (1) aligner alone (control), (2)-(5) Class II elastics with buttons placed on the mesiobuccal (MB), distobuccal (DB), mesiolingual (ML) and distolingual (DL) surface of the mandibular first molar, and (6) Class II elastics with a button on the aligner corresponding to the mesiobuccal surface of the mandibular first molar (AMB). The elastic force was set to 2 N for simulations.

Results

The central incisors appeared lingual tipping in the six models. The lingual crown movement of the central incisors was 0.039 mm, 0.034 mm, 0.034 mm, 0.042 mm, 0.041 mm, and 0.034 mm for control model, MB model, DB model, ML model, DL model, and AMB model, respectively. The first molars showed mesial tipping in the six models. The mesial movement of the mesiobuccal cusps of the first molars was 0.045 mm, 0.060 mm, 0.063 mm, 0.048 mm, 0.051 mm, and 0.055 mm for control model, MB model, DB model, ML model, DL model, and AMB model, respectively.

Conclusions

Class II elastics reduced lingual tipping of anterior teeth but aggravated mesial tipping of posterior teeth. Mesiolingual elastics developed minimum mesial tipping of the posterior teeth. When Class II elastics are required, attaching elastics on the mesiolingual surface of the mandibular first molar is recommended to prevent mandibular anchorage loss.