Effects of Overcorrection on Mitigating Uncontrolled Tipping During Incisor Retraction Using Clear Aligners: Finite Element Analysis and in vitro Experiment.

The palatal anchorage device (PAD) is commonly used in fixed appliance for anchorage, but the biomechanics of PAD in patients treated with clear aligners(CAs)remains poorly understood, especially in its elastic mode and force magnitude. This study aimed to assess the biomechanical effects of using PAD for retraction during clear aligner treatment (CAT) with the extraction of two maxillary first premolars. Four finite element models were created: (1) Incisors retraction (IR) with active contraction of the clear aligner only; (2) IR with PAD using different forces (50,75,100 g) or not; (3) PAD without IR (forces of 50,75,100 g), and (4) Different elastic directions (D1, D2, D3) from aligner to PAD without IR. IR caused lingual tipping and extrusion of the central incisors, as well as mesial and buccal tipping of the first molar. PAD during IR provided strong anchorage for the first molar, with elastics slightly increasing the lingual tipping and extrusion of the central incisors. Elastics applied to the U-shaped arch led to central incisor intrusion and reduced lingual retraction. The highest stress was observed on the mesial attachment of the canine. PAD effectively reinforced posterior anchorage in CAT, while anterior positioning facilitated anterior teeth intrusion. The biomechanical importance of the canine’s mesial attachments in maxillary teeth treatment planning was highlighted.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-024-77320-x.

During intrusion and retraction, the mandibular incisors tend to tip labio-lingually, which might damage the surrounding alveolar bone. This study aimed to investigate the effect of torque overcorrection on the tooth movement and the stress distribution of the periodontal tissues. Mandible and mandibular dentition were reconstructed in the digital software. Three groups were divided: first premolar non-extraction with incisor intrusion (NEI) group, first premolar extraction with incisor intrusion (EI) group, and first premolar extraction with incisor intrusion and retraction (EIR) group. The intrusion amount of 0.25mm with different torque overcorrection degrees (0°, 1°, 2°, 3°) were sequentially added on the incisors. The biomechanical responses of the teeth and periodontal tissues were calculated in the ANSYS software. With no overcorrection, the incisors were intruded with lingual tipping, while the canines and premolars were extruded with mesial tipping. The compressive stress was concentrated on the lingual cervical and labial apical areas of the periodontal ligaments (PDLs) and alveolar bone. The incisors in the EIR group showed the most lingual displacement and the highest stress level. When 1°, 1° and 3° overcorrection degrees were added in the NEI, EI and EIR groups, respectively, the lingual displacement of the incisors decreased to zero and the stress was uniformly distributed on the PDLs and alveolar bone. With the increase of the overcorrection degrees, the incisors tended to tip labially, while the canines and premolars also gradually showed distal tipping tendencies. The compressive stresses were concentrated on the labial cervical and lingual apical areas of the PDLs and alveolar bone. During mandibular incisor intrusion, the torque overcorrection design may help reduce the lingual tipping tendencies of the incisors, relieve the compressive stress on the periodontal tissues, and protect the anchorage from the canines and premolars. When the first premolar was extracted, similar overcorrection degrees are required if the incisor retraction was not designed. However, more overcorrection degrees are required if the incisor intrusion and retraction were designed synchronously.

Objectives:The objective of this study was to analyze the impact of gradient thickness of clear aligners(CAs) on incisors during retraction in extraction cases. Materials and methods: A three dimensional(3D) finite element model was constructed including maxilla, dentition, periodontal ligaments(PDLs) and CAs. The gingival-side thickness of the CAs was set as 0.8, 0.9, 1.0, 1.1, and 1.2 mm respectively. The occlusion-side thickness was adjusted to maintain the average thickness at 0.75 mm. Incisor retraction was simulated, after which, the total and segmental displacement as well as stress distribution were calculated. Results: In all groups, the incisors exhibited lingual tipping and extrusion, while the canines and premolars demonstrated mesial tipping. With the increase in the gingival-side thickness of the CAs, the maximum displacement and apical reverse movement of the incisors were reduced, accompanied by the labial and apical movement of the rotation center. Concurrently, the retraction and extrusion of incisors decreased. The stress distribution in PDLs of incisors became more uniform. Conclusions: The gradient thickness CA can reduce the extrusion and apical reverse movement, produce uniform stress distribution in PDLs, and shift the rotation center labially and apically. This proposal can be a promising strategy for torque control of incisors and prevention of root resorption.

BackgroundDespite the popularity of clear aligner treatment, the effect of the thickness of these aligners has not been fully investigated. The objective of this study was to assess the effects of incisor torque compensation with different thicknesses of clear aligner on the three-dimensional displacement tendency of teeth in cases of extraction.MethodsThree-dimensional finite element models of the maxillary dentition with extracted first premolars, maxilla, periodontal ligaments, attachments, and aligners were constructed and subject to Finite Element Analysis (FEA). Two groups of models were created: (1) with 0.75 mm-thick aligners and (2) with 0.5 mm-thick aligners. A loading method was developed to simulate the action of clear aligners for the en masse retraction of the incisors. Power ridges of different heights were applied to both groups to mimic torque control, and the power ridges favoring the translation of the central incisors were selected. Then, we used ANSYS software to analyze the initial displacement of teeth and the principle stress on the PDL.ResultsDistal tipping, lingual tipping and extrusion of the incisors, distal tipping and extrusion of the canines, and mesial tipping and intrusion of the posterior teeth were all generated by clear aligner therapy. With the 0.5 mm-thick aligner, a power ridge of 0.7 mm could cause bodily retraction of the central incisors. With the 0.75 mm-thick aligner, a power ridge of 0.25 mm could cause translation of the central incisors. Aligner torque compensation created by the power ridges generated palatal root torque and intrusion of the incisors, intrusion of the canines, mesial tipping and the intrusion of the second premolar; these effects were more significant with a 0.75 mm-thick aligner. After torque compensation, the stress placed on the periodontal ligament of the incisors was distributed more evenly with the 0.75 mm-thick aligner.ConclusionsThe torque compensation caused by power ridges can achieve incisor intrusion and palatal root torque. Appropriate torque compensation with thicker aligners should be designed to ensure bodily retraction of anterior teeth and minimize root resorption, although more attention should be paid to the anchorage control of posterior teeth in cases of extraction.

Finite element analysis of the biomechanical effect of clear aligners in extraction space closure under different anchorage controls

Biomechanical effects of different initial posterior inclinations during extraction space closure with clear aligners: A finite element analysis.

Clear aligner treatment (CAT) provides orthodontic patients with a comfortable treatment alternative; however, this device has limited capacity to facilitate tooth movements. Although composite attachment has been proposed to facilitate tooth displacement, some of its aspects, such as aligner thickness, can influence CAT's precision. This work aimed to compare the stress distribution patterns produced by clear aligners with different thicknesses and composite attachment shapes during anterior retraction. Maxillary models consisting of clear aligners, maxillary teeth, and various attachments to the upper central incisor's labial surface were generated. Three models were built to mimic the retraction of the upper central incisors. Each had a distinct attachment design (rectangular attachment, ellipsoid attachment, and pyramidal attachment) and various aligner thicknesses (0.75, 0.85, 0.95, 1.05, and 1.15 mm). Upper central incisor retraction was accomplished using clear aligners. Finite element analysis was used to examine the built models. Stress distribution pattern was examined. The greater the thickness of the aligner, the higher the stress experienced by the teeth. The 0.75 mm-thick aligner induces the lightest stress with a minimum of 0.0037623 MPa and a maximum of 0.32859 MPa. Meanwhile, the 1.5 mm-thick aligner has the highest stress with a minimum of 0.004679 MPa and a maximum of 0.43858 MPa. The force distribution on rectangular attachments appears evenly distributed. The maximum pressure force on rectangular attachments has a minimum of 0.38828 MPa, which is smaller than the maximum on ellipsoid and pyramidal attachments at 0.40933 and 0.45099 MPa, respectively. The best aligner thickness is 0.75 to 0.85 mm for anterior retraction. An aligner with 0.95 mm thickness can still be used when a remarkable amount of tooth movement force is needed; however, this exception is only applicable to a limited number of clear aligner trays. The ellipsoid attachment is the best type of attachment because the resulting force is substantial and evenly distributed.

Different biomechanical effects of clear aligners in closing maxillary and mandibular extraction spaces: Finite element analysis

In clear aligner therapy, tooth movement can be designed individually by computer software. However, the deformation of the aligner created by the virtual movement of one tooth may affect the actual movement of other teeth. This study aimed to evaluate the impact of the amount of canine movement on the responses of incisors and posterior teeth during maxillary anterior en-masse retraction with clear aligner. A three-dimensional finite element model of maxillary dentition was constructed for first premolar extraction. The incisors were retracted by 0.15mm with an intrusion of 0.10mm. The canine was bodily retracted in six groups with different amount of 0 mm, 0.10mm, 0.15mm, 0.20mm, 0.25mm, and 0.30mm. The groups were named after the amount of canine movement. Separate canine retraction of 0.25mm was set in an additional group. ANSYS® software was used to calculate the initial displacements and forces on the dentition in each group. In incisor retraction with no canine movement (group 0), the incisors underwent uncontrolled lingual tipping and the canine exhibited mesial tipping. As the amount of canine movement increased, the lingual retraction force and clockwise moment on the incisors gradually weakened. The incisors exhibited less lingual inclination with more extrusion, while the canine displayed more distal inclination and less extrusion. The central and lateral incisors showed controlled lingual tipping and lingual root movement respectively in group 0.25, and both the incisors inclined labially in group 0.30. During separate canine retraction, the canine experienced distal tipping and the incisors showed labial tipping. Posterior teeth exhibited mesial tipping in all groups, the amount of which was in positive correlation with the amount of canine movement. During en-masse retraction with clear aligner, the uncontrolled lingual tipping of incisors can be eliminated by increasing the amount of canine retraction. Practitioners need to pay attention to the reciprocal effects of the designed tooth movements during clear aligner therapy.

Periodontal disease is a common disease and leads to the loss of supporting structures and pathologic tooth migration. In order to achieve a functionally sound and aesthetically satisfactory treatment outcome, combined orthodontic-periodontal therapy may be necessary. In this study, we focus on the anterior tooth movement when designing different thickness of power ridge for patients with periodontal disease and investigate its biomechanical effects during anterior retraction using clear aligners (CAs). Two models of maxillary with different heights of alveolar bone were constructed, and three models of CAs were created with different power ridge designs. This study includes a total of six finite element models, which included alveolar bone, the first premolars extracted maxillary dentition, periodontal ligaments (PDL), attachments, and CAs. And the biomechanical effects were analyzed and compared in each model during anterior retraction using CAs. Compared to the models with normal height of alveolar bone, the patients with alveolar bone loss had more tooth displacement when the retraction distance was the same. And the center of the rotation of the anterior tooth moved towards the root direction. The total displacement of the central incisor increased in models with power ridges, and 0.5mm power ridges caused the maximum displacement in both normal alveolar bone and reduced alveolar bone height models. In normal alveolar bone models, the crown and root moved in the same direction in 0.7mm power ridges, but in reduced alveolar bone models, it was 0.5mm. The von Mises stress values and maximum principal stress values for PDL increased as the depth of power ridges increased, and 0.7mm power ridges caused concentration of stress in both models with normal alveolar bone or reduced alveolar bone. In patients with periodontal disease, the displacement of the entire maxillary dentition increased in comparison to those with normal alveolar bone. And an appropriate thickness of power ridge is beneficial to achieve torque control of anterior teeth. However, excessive thickness of power ridges is not suitable for anterior tooth retraction because of the stress concentration on the PDL.

The aim of this work was to determine advanced the oxidative protein products (AOPPs), total antioxidant capacity (TAC), and myeloperoxidase activity (MPO) in the saliva of patients undergoing orthodontic treatment with clear removable aligners in comparison with another group in treatment with fixed passive self-ligating brackets applying light forces, before treatment, after 30 days, and after 90 days of treatment. This non-randomized clinical trial recruited patients consecutively, all of which were over 18 years of age and due to undergo orthodontic treatment. They were divided into two groups according to treatment type: Group A, 48 patients treated with clear aligners (Invisalign®); and Group B, 19 patients treated with Damon System® 0.22″ self-ligating brackets applying light forces. Saliva samples were collected by a single clinician following the same protocol and underwent three analyses—AOPPs, TAC, and MPO levels–at baseline before placing the apparatus, after 30 days, and after 90 days treatment. Orthodontic treatment, whether with clear aligners or fixed self-ligating brackets and light forces, increased AOPPs after the first 30 days of treatment. During the initial phases of orthodontic treatment, neither clear aligners nor fixed self-ligating brackets applying light forces showed changes in TAC and MPO. Orthodontic treatment with both clear aligners and fixed apparatus self-ligating brackets applying light forces increases oxidative stress (AOPPs) after the first 30 days of treatment. There are no differences in AOPP levels between treatment with clear aligners and self-ligating brackets during the first 90 days of treatment. The antioxidative capacity of saliva during the initial phases of orthodontic treatment, whether with self-ligating brackets or clear aligners, does not undergo significant changes. With either orthodontic technique, the patients’ salivary antioxidant capacity is similar.

Objective: To compare the effects of expansion screw with maxillary protractor and clear aligners combined with maxillary protractor on the maxilla and maxillary dentition of mixed dentition patients with class Ⅲ skeletal malocclusion using finite element analysis, further providing clinical guidance for clear aligner treatment. Methods: A finite element model was established based on maxillofacial cone-beam CT data of a 10-year-old boy with mixed dentition, class Ⅲ skeletal malocclusion, who visited Department of Orthodontics, School of Stomatology, The Fourth Military Medical University in January, 2024. The expander with protractor group (group A) and the clear aligners with protractor group (group B) were divided. The arch was extended by 0.25 mm in both groups, and the forward pull force was 2.94 N (working condition 1) and 4.90 N (working condition 2), respectively. The initial displacement trend of maxilla and maxillary dentition in two groups under two working conditions were evaluated. Results: Under two working conditions, the maxilla of both groups showed clockwise rotation and labial inclination. The labial inclination of maxilla was more significant in clear aligners with protractor group, about 2.2-3.0 times that of expander with protractor group under the same working condition. Maxillary dentition showed mesial and buccal displacement, with anterior teeth extrusion and posterior teeth intrusion in two groups under two working conditions. Under the working condition 1 and 2, the labial displacement of central incisor of clear aligners with protractor group (-0.065, -0.089 mm) were greater than that in expander with protractor group (-0.024, -0.024 mm). Under two working conditions, the posterior teeth of expander with protractor group moved close to the buccal bodily direction, while those of clear aligners with protractor group moved tilted towards the buccal direction in the horizontal direction. The forward displacement trend of maxilla and maxillary dentition in clear aligners with protractor group was more obvious than expander with protractor group with the increase of the forward pull force. Under two working conditions, the anterior teeth' s hydrostatic stress of periodontal membrane and the equivalent stress of alveolar bone in clear aligners with protractor group were higher than those in expander with protractor group, mainly concentrated on the labial cervical region of the incisor. Conclusions: Clear aligners combined with maxillary protractor can produce forward force on the maxilla, but labial inclination occurs in the anterior teeth. It can be an effective orthopedic treatment strategy for mixed dentition patients with class Ⅲ skeletal malocclusion.

Objective: To investigate the effects of two-step retraction and en-masse retraction on tooth movement pattern of anterior teeth and posterior anchorage with clear aligners using three-dimensional finite element analysis. Methods: A finite element model of maxillary first premolar extraction case undergoing clear aligner treatment was established based on maxillofacial cone-beam CT data of a 24-year-old adult male with individual normal occlusion, who visited Department of Oral Surgery, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine for impacted mandibular third molar in June, 2022. The initial tooth displacements of five anterior retraction protocols (canine retraction of two-step retraction, incisor bodily retraction of two-step retraction, incisor overtreatment retraction of two-step retraction, en-masse bodily retraction, and en-masse retraction with incisor overtreatment) were evaluated. Results: Canine retraction of two-step retraction caused distal tipping of the canine and labial tipping of the incisors (0.18° for central incisor and 0.13° for lateral incisor). Incisor retraction of two-step retraction caused mesial tipping of the canine. In incisor bodily retraction of two-step retraction protocol, uncontrolled lingual tipping was found in central incisor (0.29°) and lateral incisor (0.32°). In incisor overtreatment retraction of two-step retraction protocol, the movement pattern of the incisors didn't change, but the inclinations reduced to 0.21° and 0.18°. En-masse retraction caused distal tipping of the canine. In en-masse bodily retraction protocol, uncontrolled lingual tipping was also found in central incisor (0.19°) and lateral incisor (0.27°). In en-masse retraction with incisor overtreatment protocol, the central incisor showed controlled lingual tipping (0.02°) and the lateral incisor showed palatal root movement (0.03° labial inclination). Posterior teeth exhibited mesial tipping in all five protocols. Conclusion: En-masse retraction with incisor overtreatment was beneficial to incisor torque control in clear aligner treatment.

The orthodontic treatment of patients with a history of severe periodontitis helps to improve periodontal health, functional occlusion, and esthetics. The use of aligners in patients with a history of severe periodontitis, with a single protocol of periodontal treatment, and the report of periodontal parameters throughout the orthodontic treatment has not yet been evidenced. Therefore, this manuscript aimed to describe the treatment with a clear orthodontic aligner system in two patients with reduced periodontium associated with a history of severe periodontitis. Two male participants (43-year-old and 62-year-old, respectively) were diagnosed with generalized, stage III, grade B periodontitis and treated with the same periodontal treatment protocol. After a 12-month follow-up of periodontal maintenance, the subjects were referred for tooth migration and Class II malocclusion orthodontic treatment. The subjects received orthodontic treatment with clear aligners. After starting orthodontic therapy, the patient received periodontal maintenance and clinical monitoring at 3, 6, 9, and 12 months. The periodontal parameters remained stable throughout the aligner treatment. At 12 months of orthodontic treatment, an improvement in angulations, inclinations, and dental positioning was observed, obtaining a stable occlusion, and reaching the proposed objectives for the treatment stage. A significant improvement in the occlusal relationship could be achieved with the clear orthodontic aligner system in adult patients with reduced periodontium by a history of severe periodontitis. Orthodontic therapy with clear aligners was shown to be safe in maintaining good periodontal health with the protocol of periodontal treatment used in the clinical cases presented. This case presentation is a contemporary and innovative approach to orthodontic and periodontic treatment of patients with a history of severe periodontitis that in the recent past would not be referred to an interdisciplinary treatment because of the lengthy orthodontic treatment time and the difficulty of hygiene that fixed appliance brings, putting at risk the permanence of these teeth in the oral cavity even with adequate periodontal treatment. The keys to the success of this partnership intervention are a precise diagnosis and careful treatment planning of orthodontic treatment and a correct periodontal intervention to keep teeth and periodontium in good health. The primary limitation is without a doubt, the patient's collaboration both in the correct use of the aligners and in the adherence to periodontal treatment.

The optimal anchorage strategy for controlling anterior teeth en-masse retraction and persistent posterior teeth using clear aligner on extraction orthodontic treatment: An in vitro study of 3D element analysis.