Effectiveness of an anterior mini-screw in achieving incisor intrusion and palatal root torque for anterior retraction with clear aligners

Evaluation of the effect of attachments on torque control of palatally positioned maxillary lateral teeth with clear aligners: Finite element analysis

Objective

The effect of different attachment positions on torque control during the labialization of maxillary lateral incisors with clear aligners was evaluated using finite element analysis.

Methods

Anatomical data acquired through cone-beam computed tomography, combined with the design of 0.625-mm-thick aligners and horizontal attachments, were integrated into the software. Six distinct simulations were generated: (1) attachment-free, (2) labial attachment placed gingivally, (3) labial attachment placed mid-crown, (4) labial attachment placed incisally, (5) palatal attachment, and (6) attachment placed labially and palatally. The evaluation was performed using a default aligner activation of 0.25 mm.

Results

The crown of the lateral incisor demonstrated labial movement, while the root exhibited palatal movement in all models. Group 6 showed the lowest crown and root displacements on both axes, whereas the attachment-free group exhibited the greatest crown movement. The aligner experienced maximum deformation at the incisal edge, with deformation progressively decreasing towards the gingival region. Group 6 demonstrated the least deformation of all groups. The Von Mises stresses in the periodontal ligament (PDL) were most pronounced at the gingival level, with higher values on the palatal side than on the labial side.

Conclusions

The use of attachments, particularly the combination of labial and palatal attachments, enables a more precise labialization process, helping to reduce tipping. Increasing crown movement of the lateral incisor elevates stress within the PDL, with the highest stress observed in the palatal region at the gingival level.

Three-dimensional finite element analysis of maxillary molar distalization treated with clear aligners combined with different traction methods

BACKGROUND

This study aimed to analyze the effects of maxillary molar distalization using clear aligners with different intramaxillary and intermaxillary traction via the three-dimensional (3D) finite element method.

METHODS

A 3D finite element model consisting of the maxilla, mandible, dentitions, periodontal ligaments (PDLs), attachments, and clear aligners was constructed. Five groups were established based on different traction modalities: group 1 (control group); group 2 (orthodontic mini-implants (OMIs) were implanted between the maxillary first molars and the second premolars on the buccal side); group 3 (OMIs were implanted in the infrazygomatic crest area between the maxillary first and second molars on the buccal side); group 4 (OMIs were implanted between the maxillary first molars and the second premolars on the palatal side); and group 5 (class II elastics were utilized between the maxillary canines and the mandibular first molars). OMIs were implanted 4 mm away from the alveolar crest in each experimental group. A force of 1.5 N was applied to each experimental group. The 3D displacement of the target teeth and stress distribution around the PDLs were analyzed.

RESULTS

Group 4 exhibited the least amount of torque change in the upper anterior teeth and the highest displacement of the maxillary second molars. Group 3 showed smaller changes in anterior teeth torque and higher molar distalization efficiency compared to group 2. Group 5 showed adverse effects such as anterior teeth extrusion and mandibular anchorage loss.

CONCLUSION

OMIs implanted on the palatal side have advantages in preserving anterior teeth anchorage and improving the efficiency of molar distalization compared to those positioned on the buccal side. OMIs implanted in the infrazygomatic crest area between the first and second molars on the buccal side demonstrate benefits in the aforementioned aspects when compared to OMIs implanted between the first molars and the second premolars on the buccal side.

Cantilever-aided bodily protraction of a mandibular molar with clear aligner: A finite element analysis

OBJECTIVE

To analyse the biomechanics of molar protraction through clear aligner therapy (CAT) with and without a buccal cantilever.

METHODS

Models were composed of mandible, lower dentition, periodontal ligaments, attachments, a buccal cantilever, and clear aligner. Four groups were designed: (1) control (aligner only), (2) aligner+buccal cantilever with buccal class II traction, (3) aligner+buccal cantilever with buccal class II and lingual class II tractions, (4) aligner+buccal cantilever with buccal horizontal traction named buccal class I, buccal class II, and lingual class II tractions.

RESULTS

CAT alone caused mesial tipping, lingual tipping, and intrusion of mandibular second molar. Adding the buccal cantilever on the mandibular second molar with 100-g buccal class II traction was effective in preventing the mesial tipping of mandibular second molar, but resulted in a greater lingual tipping tendency. Further addition of lingual class II traction prevented aforementioned lingual tipping and bodily protraction was achieved in sagittal dimension, while buccal tipping was present. Bodily protraction without buccolingual tipping was achieved through clear aligner, buccal class II, lingual class II, and buccal class I tractions, and the stress concentrated on the alveolar bone was reduced.

CONCLUSION

CAT produced mesial tipping, lingual tipping, and intrusion of mandibular molar during protraction. The incorporation of the buccal cantilever into the clear aligner improves the biomechanical effect of molar protraction. Bodily molar protraction can be achieved with a judicious combination of buccal class II, lingual class II and buccal class I tractions with clear aligner and buccal cantilever.

Effects of Attachment Orientation and Designed Vertical Movement on Molar Distalisation With Clear Aligners: A Biomechanical Finite Element Study

OBJECTIVE

This study aimed to evaluate the effects of molar attachment orientation and designed molar vertical movement on molar distalisation using clear aligners. Specifically, the study focused on the impact of vertical forces during upper second molar distalisation.

MATERIALS AND METHODS

A three-dimensional finite element analysis was conducted to simulate upper molar distalisation using clear aligners. Four attachment orientations (0°, 45°, 90° and 135°) were designed. The study included three scenarios: distalisation alone; distalisation combined with intrusion; and distalisation combined with extrusion. The displacement tendencies and stress distribution on the second molar under various attachment orientations and vertical movements were analysed.

RESULTS

Molar distalisation resulted in buccal tipping, distal tipping and intrusion tendency in all models. The molar with 135° attachment orientation exhibited the most significant distal movement under intrusive force, while the one with 45° attachment showed the greatest distal movement under extrusive force. Additionally, greater distal movement was achieved with intrusive force compared to extrusive force, likely due to improved aligner grip on the attachments and teeth during intrusion.

CONCLUSION

Attachment orientation significantly affects the effectiveness of molar distalisation and vertical movement with clear aligners. The 90° attachment group achieved the most effective molar distalisation. The 135° attachment is more effective under intrusive force, while the 45° attachment is preferable under extrusive force.

Protraction of a mandibular second molar into the adjacent atrophic first-molar extraction site with ridge-split technique through clear aligners: A case report

This case report describes the successful orthodontic management of a 25-year-old female patient presenting with Class II Division 2 malocclusion, moderate maxillary anterior crowding, and a missing mandibular left first molar. Treatment plan involved extraction of two maxillary first premolars to address crowding and protraction of two mandibular left molars, combined with the strategic use of mini-implants for precise tooth movement control. Ridge-split surgery was adopted to manage alveolar ridge resorption in the edentulous area. This procedure was essential for widening the narrow alveolar ridge, thereby reducing resistance and facilitating the mesial movement of two mandibular left molars. Lingual and labial biomechanics, including linguoincisal elastics and a cantilever system, were utilized to optimize torque control and molar protraction. Clear aligners were employed throughout the treatment phases, navigating challenges such as the closure of extraction spaces and achieving stable buccal interdigitation. The treatment spanned 4 years, using a total of 175 aligners. The initial phase required 66 aligners to close maxillary extraction spaces and the mandibular edentulous space, followed by 52 aligners in the first refinement and 57 aligners in the second refinement phase. Posttreatment evaluations demonstrated successful alignment of dental arches, correction of malocclusion, and enhancement of facial aesthetics. This case highlights the efficacy of integrated orthodontic techniques in achieving comprehensive functional and aesthetic outcomes in complex orthodontic cases.

Effectiveness of palatal anchorage device (PAD) for maxillary anterior retraction with clear aligners using finite element study

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.

Anchorage loss of the posterior teeth under different extraction patterns in maxillary and mandibular arches using clear aligner: a finite element study

BACKGROUND

Extracting the premolars is an effective strategy for patients with bimaxillary dentoalveolar protrusion. Clear aligners (CAs) close the extraction spaces through shortening the length of aligners. The contraction force generated by the terminal of aligners makes the posterior teeth tip mesially, which is known as the roller coaster effect. This phenomenon is even worse in the 2nd premolar extraction cases. Posterior anchorage preparation is commonly used to protect the angulation of molars, taking the form of presetting distal tipping value. However, the distal tipping design aggravates the anchorage loss of anterior teeth simultaneously. This study aimed to explore the different anchorage loss of the posterior teeth when the 1st or 2nd premolars were extracted using CAs, respectively in maxillary and mandibular arches, further providing guidance for anchorage preparation design in clinical practice.

METHODS

Two bimaxillary finite element models with different extraction patterns were established to simulate the anterior en-masse retraction process of the CAs. In Model 1, the maxillary and mandibular 1st premolars were extracted, while in Model 2, the 2nd premolars were extracted. Finite element analysis methods were utilized to analyze the tipping angle of the anterior and posterior teeth.

RESULTS

Compared between two models, the anterior teeth exhibited a greater lingual inclination tendency and the posterior teeth exhibited a slighter mesial tipping tendency in Model 1 regarding individual tooth. The closer to the extraction spaces, the greater the tip, and the distal tipping tendency of the 1st premolars was more evident than the mesial tipping tendency of the 1st molars in Model 2. Compared between the maxillary and mandibular arches, the mesial tipping tendency of individual posterior tooth was more evident in the maxilla. In addition, the highest hydrostatic stress of the periodontal ligaments was concentrated on the cervical and apical parts directly adjacent to the extraction spaces, and it exhibited relatively uniform distribution in Model 1.

CONCLUSIONS

The individual posterior tooth showed the same mesial tipping direction but to different degree when the 1st or the 2nd premolars were extracted during clear aligner treatment. Presetting anchorage preparation design for the posterior teeth is essential to alleviate the roller coaster effect, especially in the 2nd premolar extraction cases. Furthermore, larger anchorage preparation value should be proposed for the maxillary posterior teeth.

Comparison of orthodontic clear aligners and fixed appliances for anterior teeth retraction using finite element analysis

Orthodontic clear aligners are utilised in order to correct mal-positioned teeth. The comparative effectiveness of transparent aligners and fixed appliance therapy using finite analysis has not been thoroughly studied. Therefore, it is of interest to evaluate the superiority of clear aligners over fixed orthodontic therapy in anterior tooth retraction using finite element analysis (FEA). A maxillary dentition lacking 1stpremolars and with periodontal ligaments was represented by 3D digital models. A transparent aligner, brackets and archwire were produced in a 3D printed lingual retractor. Five distinct models of clear aligners for maxillary anterior internal retraction were designed and created as part of the study: Model M0-Control, Model M1-Posterior Micro-implant, Model M2-Anterior Micro-implant, Model M3-Palatal Plate, Model M4-Enhanced structure and Model A0- Fixed Appliance. The study result has shown that the crown-root of the central incisor's sagittal displacement varied least in the improved clear aligner Model M 3. Nonetheless, noticeable differences in the patterns of tooth movement were noted between the fixed appliance model and the clear aligner models. The teeth's movement pattern stayed the same in the clear aligner models. Compared to transparent aligner types, the fixed appliance shown greater anterior torque control and improved safety for the posterior anchorage teeth. It has been demonstrated that clear aligners are non-invasive, aesthetically acceptable and effective treatment modality.

Does Invisalign Outperform Fixed Appliance in Treating Vertical Discrepancies?

Aligners became popular among adult patients for their superior aesthetics and comfort in comparison to conventional fixed appliances. It has undergone numerous enhancements over time, allowing it to address more complex malocclusions. Many researchers argued that managing vertical discrepancies is more challenging than addressing anteroposterior issues. This complexity arose from the mechanical requirements for treatment and the required mechanics to prevent relapse. Studies assessing the treatment outcome of anterior open bite closure using clear aligners have yielded conflicting results regarding the mechanisms of bite closure. Proposed mechanisms included extrusion of upper or lower incisors, lingual tipping of upper or lower incisors, intrusion of upper or lower molars, counterclockwise rotation of the mandible, or various combinations of these mechanisms. The research highlighted the biomechanical challenges associated with using aligners for the treatment of deep bites as mandibular incisor intrusion and leveling the curve of Spee remain among the least predictable movements. Given the widespread use of aligners, it is imperative to rigorously assess the effectiveness of clear aligners in achieving overbite correction to ensure they deliver the desired outcome. This review aimed to assess the performance of Invisalign in the management of vertical discrepancies. It sought to identify the dentoskeletal effects of clear aligners in addressing deep bite and anterior open bite cases, understand the mechanisms behind overbite correction, and provide a comprehensive overview of the existing research on this topic.

Prognostic risk factors for apical root resorption in orthodontic patients - Are the Kjær's morphologic characteristics of clinical relevance?

BACKGROUND

Patients undergoing orthodontic treatment (OT) face an increased risk of developing external apical root resorption (EARR). A prognostic risk assessment prior to OT can potentially be conducted through anatomical features in panoramic radiography. This retrospective study aimed to assess the significance of Kjær's morphological characteristics in analyzing the risk of EARR.

METHODS

Panoramic radiographs of 1,156 patients (624 females, 532 males) were retrospectively analyzed. Anamnestic and treatment-related data were extracted from patient records. The mean age at the start of OT was 12.8 ± 2.2 years (min. 6.4 years, max. 22.3 years) and at the end of OT 15.9 years (min. 8.5 years, max. 24.1 years). The mean treatment duration was 3.1 ± 1.6 years. Panoramic radiographs with a minimum of two per patient were examined for the presence of Kjær's characteristics. The degree of EARR was registered defining resorption in four degrees of severity. Bivariate analysis and multivariate Poisson regression were performed to assess the association between Kjær's characteristics and EARR patient- and tooth- related (α = 0.05).

RESULTS

In total, 72.8% of the patients showed EARR at the end of OT with lateral maxillary incisors most frequently affected. Short roots (p < 0.001) were significantly associated with EARR in patients. Tooth-related microdontia (#12, #22, lower second premolars), narrow crowns (#11, #21, lower incisors), short roots (upper incisors, lower first molars) and ectopia (#11, #21, #13), such as shorter distal roots of the mandibular first molar showed a significant association with EARR depending on severity degree. The type of orthodontic appliance (fixed: p < 0.001, fixed and removeable: p = 0.008), as well as treatment duration (p < 0.001) were also identified as risk factors for EARR.

CONCLUSIONS

Although the risk assessment for EARR development through panoramic radiography analysis is limited, predisposition appears to be present in specific dental characteristics and treatment-related factors.

Effectiveness of different intrusion modes of maxillary anterior teeth with mini-implants in clear aligner treatment: a three-dimensional finite element analysis

BACKGROUND

The intrusion of maxillary anterior teeth is often required and there are various intrusion modes with mini-implants in clear aligner treatment. The objective of this study was to evaluate the effectiveness of maxillary anterior teeth intrusion with different intrusion modes, aiming to provide references for precise and safe intrusion movements in clinical practice.

METHODS

Cone-beam computed tomography and intraoral optical scanning data of a patient were collected. Finite element models of the maxilla, maxillary dentition, periodontal ligaments (PDLs), clear aligner (CA), attachments, and mini-implants were established. Different intrusion modes of the maxillary anterior teeth were simulated by changing the mini-implant site (between central incisors, between central and lateral incisor, between lateral incisor and canine), loading site (between central incisors, on central incisor, between central and lateral incisor, between lateral incisor and canine), and loading mode (labial loading and labiolingual loading). Ten conditions were generated and intrusive forces of 100 g were applied totally. Then displacement tendency of the maxillary anterior teeth and CA, and stress of the PDLs were analyzed.

RESULTS

For the central incisor under condition L14 and for the canine under conditions L11, L13, L23, and L33, the intrusion amount was negative. Under other conditions, the intrusion amount was positive. The labiolingual angulation of maxillary anterior teeth exhibited positive changes under all conditions, with greater changes under linguoincisal loading. The mesiodistal angulation of canine exhibited positive changes under labial loading, while negative changes under linguoincisal loading except for condition L14.

CONCLUSIONS

The intrusion amount, labiolingual and mesiodistal angulations of the maxillary anterior teeth were affected by the mini-implant site, loading site, and loading mode. Labial and linguoincisal loading may have opposite effects on the intrusion amount of maxillary anterior teeth and the mesiodistal angulation of canine. The labiolingual angulation of the maxillary incisors would increase under all intrusion modes, with greater increases under linguoincisal loading.

Effect of varying auxiliaries on maxillary incisor torque control with clear aligners: A finite element analysis

INTRODUCTION

This study aimed to evaluate the effects of varying auxiliaries on tooth movement and stress distribution when maxillary central incisors were torqued 1° with a clear aligner through finite element analysis.

METHODS

Three-dimensional finite element models, including maxillary alveolar bone, periodontal ligament, dentition, and clear aligner, were constructed. According to the auxiliaries designed on the maxillary central incisor, 5 models were created: (1) without auxiliaries (control model), (2) with the power ridge, (3) with the semi-ellipsoid attachment, (4) with the horizontal rectangular attachment, and (5) with the horizontal cylinder attachment. The tooth movement and periodontal ligament stress distribution after a palatal root torque of 1° were analyzed for each of the 5 models.

RESULTS

With 1° torque predicted, the maxillary central incisor without auxiliaries showed a tendency of labial tipping, mesial tipping, and intrusion. The rotation center moved occlusally in the power ridge model. The labiolingual inclination variation increased in the semi-ellipsoid attachment model but decreased in the power ridge model. The maxillary central incisor is twisted in the distal direction in the power ridge model. The maxillary central incisor of the horizontal rectangular attachment and the horizontal cylinder attachment model behaved similarly to the control model. Periodontal stresses were concentrated in the cervical and apical areas. The maximum von Mises stresses were 11.6, 12.4, 3.81, 1.14, and 11.0 kPa in the 5 models. The semi-ellipsoid attachment model exhibited a more uniform stress distribution than the other models.

CONCLUSIONS

Semi-ellipsoid attachment performed better efficacy on labiolingual inclination, and power ridge performed better efficacy on root control. However, a distal twist of maxillary incisors could be generated by the power ridge.

Accessories in clear aligner therapy: Laypeople's expectations for comfort and satisfaction

Background

This study explored the layperson's perception of comfort, satisfaction, and willingness to use various accessories in clear aligner therapy.

Methods

A total of 267 people analyzed standardized intraoral photographs of a female model in orthodontic treatment using: 1) only clear aligner (CA), the control group; 2) clear aligner+attachments (AT); 3) clear aligners+Cl II elastics (EL); 4) clear aligner+hybrid treatment with esthetic braces (HEB); 5) Clear aligner+hybrid treatment with metallic braces (HMB); 6) clear aligner+mini-implants (MI); 7) clear aligner+mini-implants and elastics for intrusion (MIE). In addition, a social media questionnaire was distributed to assess the willingness to undergo orthodontic treatment with various accessories.

Results

There was a significant difference between CA and all the other groups (P<0.001), with CA being considered more comfortable and providing greater satisfaction compared to other accessories. Moreover, AT showed a significant difference in reducing treatment time compared to other groups.

Conclusion

The CA was the most comfortable, exhibiting a higher satisfaction rate and a greater willingness to use it. The AT therapy was perceived as more comfortable and was associated with higher satisfaction and a greater likelihood of use, especially if it resulted in reduced treatment time. On the other hand, the participants reported that the HMB, MI, and MIE accessories were less comfortable.

Three-dimensional finite element analysis of the optimal mechanical design for maximum inward movement of the anterior teeth with clear aligners

This study aims to refine clinical designs within clear aligner therapy, exploring the appropriate ratio of anterior tooth retraction to intrusion under maximum anchorage. Using a three-dimensional finite element model and evaluating 19 load scenarios with first premolar extraction, the research identifies the optimal force angle for anterior tooth retraction as 45 to 55°. For clinical planning, it is recommended to design a retraction of 0.19 mm combined with an intrusion of 0.16 mm to achieve anterior tooth retraction. This investigation is crucial for enhancing understanding of biomechanical principles in clear aligner orthodontics, offering significant insights for effective treatments.

Effects of different intrusion patterns during anterior teeth retraction using clear aligners in extraction cases: an iterative finite element analysis

Background

Overtreatment design of clear aligner treatment (CAT) in extraction cases is currently primarily based on the clinical experience of orthodontists and is not supported by robust evidence on the underlying biomechanics. This study aimed to investigate the biomechanical effects of overtreatment strategies involving different maxillary anterior teeth intrusion patterns during anterior teeth retraction by CAT in extraction cases.

Materials and methods

A finite element model of the maxillary dentition with the first premolar extracted was constructed. A loading method of clear aligners (CAs) based on the initial state field was proposed. The iterative method was used to simulate the long-term orthodontic tooth movement under the mechanical load exerted by the CAs. Three groups of CAs were utilized for anterior teeth retraction (G0: control group; G1: incisors intrusion group; G2: anterior teeth intrusion group). Tooth displacement and occlusal plane rotation tendency were analyzed.

Results

In G0, CAT caused lingual tipping and extrusion of the incisors, distal tipping and extrusion of the canines, mesial tipping, and intrusion of the posterior teeth. In G1, the incisors showed minimal extrusion, whereas the canines showed increased extrusion and distal tipping tendency. G2 showed the smallest degree of posterior occlusal plane angle rotation, while the inclination tendency of the canines and second premolars decreased.

Conclusion

1. In CAT, tooth displacement tendency may change with increased wear time. 2. During anterior teeth retraction, the incisor intrusion pattern can provide effective vertical control for the lateral incisors but has little effect on the central incisors. Anterior teeth intrusion patterns can alleviate the inclination of canines and second premolars, resulting in partial relief of the roller-coaster effect.

How well does Invisalign ClinCheck predict actual results: A prospective study

INTRODUCTION

This study aimed to compare achieved movements with predicted movements after 28-week use of Invisalign Lite aligners.

SETTINGS AND SAMPLE POPULATION

The digital impressions of 21 subjects treated with Invisalign Lite at a private practice and in the dental clinic (Milan, Italy) were taken and analysed. Subjects were Caucasian with a mean age of 20.1 years.

METHODS

Patients were analysed at two time points: at T0, before starting therapy, and at T1, after 28 weeks of treatment with Invisalign clear aligners, with a 2-week change interval. The changes that occurred between T0 and T1 were compared to the predicted changes between T0 and Ts (setup/ClinCheck). Tooth movement performance was estimated through variables calculated as the difference between obtained and planned movements.

RESULTS

In both maxillary and mandibular arches, the teeth that exhibited the least accurate expression of torque were the central incisors. Tip was not accurate on maxillary central incisors and canines, mandibular central incisors, lateral incisors, first premolars, second premolars and first molars. Rotations were under-expressed on maxillary lateral incisors, canines and second premolars and on mandibular central incisors, canines, first premolars, second premolars and first molars. The overall angular changes showed a tendency to underperformance. Transverse linear changes were accurate with a significant overperformance on maxillary and mandibular first molars.

CONCLUSIONS

Torque correction of maxillary central incisors, as well as rotational correction of most of the teeth, showed significant differences between what was planned and what was obtained.

Effect of clear aligner type on maxillary full-arch intrusion: 3D analysis using finite element method

BACKGROUND

Vertical maxillary excess (VME) is one of the most common reasons for seeking orthodontic treatment. Total intrusion with aligners is a promising alternative to surgery in some cases. Considering the elastic deformation of aligners, this study aimed to evaluate the possible desirable and undesirable teeth displacements during full maxillary arch intrusion using clear aligners and temporary anchorage devices (TADs).

METHODS

The maxillary arch and clear aligners were modeled in SolidWorks. Four aligner brands including Leon, Duran, Duran Plus, and Essix Plus were selected based on their material properties. Anterior and posterior intrusion forces of 80 and 300 g were applied from attachments between the canines and first premolars and between the first and second molars, respectively. Vertical and anteroposterior tooth displacements were determined.

RESULTS

The greatest intrusion was recorded at the buccal of the second molar, followed by the first molar. The lowest value was measured at the palatal of the molars with all aligners except Duran, which indicated minimal intrusion in the central incisor. All teeth were mesially displaced at the incisal/occlusal except incisors that moved distally. All apices showed distal movement.

CONCLUSIONS

Total intrusion using clear aligners may be accompanied by other tooth movements, including buccal tipping and mesial-in rotation of the molars, retrusion of incisors, and mesial movement of other teeth.

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.

Orthodontic considerations in hypodivergent craniofacial patterns

This article examines the characteristics of hypodivergent craniofacial patterns and explores treatment modalities in response to these features. It discusses the impact of robust masticatory muscles, which produce heavy occlusal forces. In addition, it examines the use of Botox or splints to reduce gonial angles in individuals with a square face. A nonextraction treatment approach supported by temporary skeletal anchorage devices is recommended; however, if anatomical limitations persist, extraction may be necessary when arch expansion, molar distalization, incisor proclination, or interproximal reduction cannot create the necessary space. In hypodivergent cases where a nonextraction approach is impractical, a single-arch extraction strategy may be considered to prevent a reduction in the vertical dimension. Emphasizing esthetics, particularly maxillary incisor display, a protocol of total arch extrusion of the maxillary dentition assisted with temporary skeletal anchorage device, bite raisers, and interarch elastics is suggested.

The effect of enhanced structure in the posterior segment of clear aligners during anterior retraction: a three-dimensional finite element and experimental model analysis

BACKGROUND

Mesial tipping of posterior teeth occurs frequently during space closure with clear aligners (CAs). In this study, we proposed a new modification of CA by localized thickening of the aligner to form the enhanced structure and investigate its biomechanical effect during anterior retraction.

METHODS

Two methods were employed in this study. First, a finite element (FE) model was constructed, which included alveolar bone, the first premolars extracted maxillary dentition, periodontal ligaments (PDL), attachments and aligners. The second method involved an experimental model-a measuring device using multi-axis transducers and vacuum thermoforming aligners. Two groups were formed: (1) The control group used common CAs and (2) the enhanced structure group used partially thickened CAs.

RESULTS

FE model revealed that the enhanced structure improved the biomechanics during anterior retraction. Specifically, the second premolar, which had a smaller PDL area, experienced a smaller protraction force and moment, making it less likely to tip mesially. In the same vein, the molars could resist movement due to their larger PDL area even though they were applied larger forces. The resultant force of the posterior tooth was closer to the center of resistance, reducing the tipping moment. The canine was applied a larger retraction force and moment, resulting in sufficient retraction of anterior teeth. The experimental model demonstrated a similar trend in force variation as the FE model.

CONCLUSIONS

Enhanced structure allowed force distribution more in accordance with optimal principles of biomechanics during the extraction space closure while permitting less mesial tipping and anchorage loss of posterior teeth and better retraction of anterior teeth. Thus, enhanced structure alleviated the roller coaster effect associated with extraction cases and offered a new possibility for anchorage reinforcement in clear aligner therapy.

Comparative assessment of orthodontic clear aligner versus fixed appliance for anterior retraction: a finite element study

BACKGROUND

The aim of this study is to conduct a comparative evaluation of different designs of clear aligners and examine the disparities between clear aligners and fixed appliances.

METHODS

3D digital models were created, consisting of a maxillary dentition without first premolars, maxilla, periodontal ligaments, attachments, micro-implant, 3D printed lingual retractor, brackets, archwire and clear aligner. The study involved the creation of five design models for clear aligner maxillary anterior internal retraction and one design model for fixed appliance maxillary anterior internal retraction, which were subsequently subjected to finite element analysis. These design models included: (1) Model C0 Control, (2) Model C1 Posterior Micro-implant, (3) Model C2 Anterior Micro-implant, (4) Model C3 Palatal Plate, (5) Model C4 Lingual Retractor, and (6) Model F0 Fixed Appliance.

RESULTS

In the clear aligner models, a consistent pattern of tooth movement was observed. Notably, among all tested models, the modified clear aligner Model C3 exhibited the smallest differences in sagittal displacement of the crown-root of the central incisor, vertical displacement of the central incisor, sagittal displacement of the second premolar and second molar, as well as vertical displacement of posterior teeth. However, distinct variations in tooth movement trends were observed between the clear aligner models and the fixed appliance model. Furthermore, compared to the fixed appliance model, significant increases in tooth displacement were achieved with the use of clear aligner models.

CONCLUSIONS

In the clear aligner models, the movement trend of the teeth remained consistent, but there were variations in the amount of tooth displacement. Overall, the Model C3 exhibited better torque control and provided greater protection for posterior anchorage teeth compared to the other four clear aligner models. On the other hand, the fixed appliance model provides superior anterior torque control and better protection of the posterior anchorage teeth compared to clear aligner models. The clear aligner approach and the fixed appliance approach still exhibit a disparity; nevertheless, this study offers a developmental direction and establishes a theoretical foundation for future non-invasive, aesthetically pleasing, comfortable, and efficient modalities of clear aligner treatment.

Biomechanical analysis of miniscrew-assisted molar distalization with clear aligners: a three-dimensional finite element study

BACKGROUND/OBJECTIVES

To compare the biomechanical characteristics of maxillary molar distalization with clear aligners in conjunction with three types of miniscrew anchorage.

MATERIALS/METHODS

Three-dimensional (3D) finite element models of maxillary molar distalization with clear aligners and three types of miniscrew anchorage were established, including (A) control group, (B) direct buccal miniscrew anchorage group, (C) direct palatal miniscrew anchorage group, and (D) indirect buccal miniscrew anchorage group. The 3D displacement of maxillary teeth and the principal stress (maximum tensile and compressive stress) on the root and periodontal ligament (PDL) during molar distalization were recorded.

RESULTS

The tooth displacement pattern during maxillary molar distalization in the four groups showed similarities, including labial tipping of anterior teeth, mesial and buccal tipping of premolars, and distal and buccal tipping of molars, but with varying magnitudes. Group C exhibited the greatest molar distalization, with the first molar achieving 0.1334 mm of crown distalization. Group D demonstrated a notable buccal crown movement (0.0682 mm) and intrusion (0.0316 mm) of the first premolar. Compared to Groups A and B, Groups C and D showed less labial crown tipping of the central incisor. Group B showed the greatest amount of maxillary incisor intrusion (central incisor: 0.0145 mm, lateral incisor: 0.0094 mm). Moreover, Groups C and D displayed significantly lower levels of compressive and tensile stress in the roots and PDL of the maxillary central and lateral incisors.

LIMITATION

Molar distalization is a dynamic process involving sequential tooth movement stages; however, our research primarily examined the tooth movement patterns in the initial aligner.

CONCLUSIONS/IMPLICATIONS

The use of miniscrew anchorage, especially direct palatal miniscrew anchorage, may enhance the treatment efficacy of maxillary molar distalization with clear aligners, leading to increased molar distalization, reduced mesial movement of premolars, and minimized labial tipping of anterior teeth.

Biomechanical analysis for different mandibular total distalization methods with clear aligners: A finite element study

Objective

: The purpose of this finite element method (FEM) study was to analyze the biomechanical differences and tooth displacement patterns according to the traction direction, methods, and sites for total distalization of the mandibular dentition using clear aligner treatment (CAT).

Methods

: A finite element analysis was performed on four FEM models using different traction methods (via a precision cut hook or button) and traction sites (mandibular canine or first premolar). A distalization force of 1.5 N was applied to the traction site by changing the direction from -30 to +30° to the occlusal plane. The initial tooth displacement and von Mises stress on the clear aligners were analyzed.

Results

: All CAT-based total distalization groups showed an overall trend of clockwise or counterclockwise rotation of the occlusal plane as the force direction varied. Mesiodistal tipping of individual teeth was more prominent than that of bodily movements. The initial displacement pattern of the mandibular teeth was more predominant based on the traction site than on the traction method. The elastic deformation of clear aligners is attributed to unintentional lingual tipping or extrusion of the mandibular anterior teeth.

Conclusions

: The initial tooth displacement can vary according to different distalization strategies for CAT-based total distalization. Discreet application and biomechanical understanding of traction sites and directions are necessary for appropriate mandibular total distalization.

The displacement of teeth and stress distribution on periodontal ligament under different upper incisors proclination with clear aligner in cases of extraction: a finite element study

OBJECTIVES

To investigate the displacement of dentition and stress distribution on periodontal ligament (PDL) during retraction and intrusion of anterior teeth under different proclination of incisors using clear aligner (CA) in cases involving extraction of the first premolars.

METHODS

Models were constructed, consisting of the maxilla, PDLs, CA and maxillary dentition without first premolars. These models were then imported to finite element analysis (FEA) software. The incisor proclination determined the division of the models into three groups: Small torque (ST) with U1-SN = 100°, Middle torque (MT) with U1-SN = 110°, and High torque (HT) with U1-SN = 120°. Following space closure, a 200 g intrusion force was applied at angles of 60°, 70°, 80°, and 90° to the occlusal plane, respectively.

RESULTS

CA therapy caused lingual tipping and extrusion of incisors, mesial tipping and intrusion of canines, and mesial tipping of posterior teeth in each group. As the proclination of incisors increased, the incisors presented more extrusion and minor retraction, and the teeth from the canine to the second molar displayed an increased tendency of intrusion. The peak Von Mises equivalent stress (VMES) value successively decreased from the central incisor to the canine and from the second premolar to the second molar, and the VMES of the second molar was the lowest among the three groups. When the angle between the intrusion force and occlusal plane got larger, the incisors exhibited greater intrusion but minor retraction.

CONCLUSIONS

The "roller coaster effect" usually occurred in cases involving premolar extraction with CA, especially in patients with protruded incisors. The force closer to the vertical direction were more effective in achieving incisor intrusion. The stress on PDLs mainly concentrated on the cervix and apex of incisors during the retraction process, indicating a possibility of root resorption.

Evaluation of the Clinical Variables Affecting Attachment Reproduction Accuracy during Clear Aligner Therapy

BACKGROUND

The purpose of this study was to evaluate some of the clinical variables that influence the accuracy of reproducing the planned attachment shape. The following clinical variables were considered: the template material, type of composite, and pressure application on the template during attachment curing.

METHODS

In this study, the evaluated materials for the thermoplastic transfer template construction are Erkolen 0.8 (polyethylene: PE) and Erkodur 0.8 (polyethylene terephthalate glycol-PET-G), and two types of composite resins: Enaflow (light-curing low-viscosity composite resin) and Enamel plus dentina HRI (light-curing high-viscosity composite resin). Two different light-curing lamps were used: Valo cordless color with no pressure and push light pressure (SCS). The 26 models included in the study were imported into the 3 Shape Ortho System 2022 (ver. 85.0.20 3 Shape, Denmark), and attachments were virtually placed on the dental elements of the first premolar and on both sides of the first upper molars. The accuracy of the attachment reproduction was evaluated through linear and angular evaluations against the reference model (MCAD). Three physical models were obtained: model A (MA), which was printed with attachments; model B (MB) with attachments made with a PE template; and model C (MC) with attachments made with a PET-G template.

RESULTS

The results showed statistically significant differences (p < 0.05) between the PE and PET-G templates with greater precision using the PET-G template. Statistically significant differences (p < 0.05) were found among the high-viscosity composite and low-viscosity composite with pressure curing.

CONCLUSIONS

In light of the obtained data, using a PET-G template is recommended. The pressure application during composite curing reduces the reproduction accuracy with a low-viscosity composite.

Effects of overtreatment with different attachment positions on maxillary anchorage enhancement with clear aligners: a finite element analysis study

BACKGROUND

The effect of attachment positions on anchorage has not been fully explored. The aim of the present study is to analyze the effect of overtreatment with different anchorage positions on maxillary anchorage enhancement with clear aligners in extraction cases.

METHODS

Models of the maxilla and maxillary dentition were constructed and imported into SOLIDWORKS software to create periodontal ligament (PDL), clear aligners, and attachments. Attachment positions on second premolars included: without attachment (WOA), buccal attachment (BA), and bucco-palatal attachment (BPA). Overtreatment degrees were divided into five groups (0°, 1°, 2°, 3°, 4°) and added on the second premolars. The calculation and analysis of the displacement trends and stress were performed using ANSYS software.

RESULTS

Distal tipping and extrusion of the canines, and mesial tipping and intrusion of the posterior teeth occurred during retraction. A strong anchorage was achieved in cases of overtreatment of 2.8° with BA and 2.4° with BPA. Moreover, the BPA showed the best in achieving bodily control of the second premolars. When the overtreatment was performed, the canines and first molars also showed reduced tipping trends with second premolars attachments. And the stress on the PDL and the alveolar bone was significantly relieved and more evenly distributed in the BPA group.

CONCLUSIONS

Overtreatment is an effective means for anchorage enhancement. However, the biomechanical effect of overtreatment differs across attachment positions. The BPA design performs at its best for stronger overtreatment effects with fewer adverse effects.

The Power of Customized Clear Aligners in Closing Molar Edentulous Spaces: Clinical and Medico-Legal Considerations in a Scoping Review and Case Report

Successful closure of edentulous spaces with clear aligners (CAs) is influenced by many factors. CAs are tailored orthodontic devices whose predictability may have relevant medico-legal implications. This study presents a scoping review about missing molar space closure (MMSC) with CAs and a clinical case. This study aims to highlight the feasibility of molar space closure by mesialization with CAs without hybrid supports. Following PRISMA Sc-review guidelines, English-written randomized/non-randomized/observational clinical studies on PubMed, Scopus, Cochrane and Lilacs were searched. An 18-year-old patient, with upper and lower edentulous spaces due to the loss of two first molars, was rehabilitated with CAs (Sorridi®, Sorridi srl, Latina, Italy) without hybrid supports and attachments. The therapy was carried out over 10 months. Currently, there are no studies documenting MMSC by mesialization with only CAs. Existing articles document the closure of premolar or incisor spaces. The upper and lower left second molars replaced the missing first molars, and erupting third molars replaced adjacent teeth. The biomechanical effects in space closure with CAs related to extraction cases appear as priorities of clinical/medico-legal interest. Our case turns attention to this movement of CAs without attachments/hybrid supports, indicating that even such a complex treatment can be comfortable for patients and safely predictable for specialists.

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.

Improvements of tooth movement efficiency and torque control in expanding the arch with clear aligners: a finite element analysis

Objectives: The purpose of this study was to analyze the effect of different movement strategies, embossment structures, and torque compensation of the aligner on tooth movement during arch expansion using clear aligners by finite element analysis. Methods: Models comprising the maxilla, dentition, periodontal ligament, and aligners were created and imported into a finite element analysis software. The tests were performed using the following: three orders of tooth movement (including alternating movement with the first premolar and first molar, whole movement with second premolar and first molar or premolars and first molar), four different shapes of embossment structures (ball, double ball, cuboid, cylinder, with 0.05, 0.1, 0.15-mm interference) and torque compensation (0°, 1°, 2°, 3°, 4°, and 5°). Results: The expansion of clear aligners caused the target tooth to move obliquely. Alternating movement resulted in higher movement efficiency with lower anchorage loss as compared with whole movement. Embossment increased the efficiency of crown movement but did not contribute positively to torque control. As the angle of compensation increased, the tendency of oblique tooth movement was gradually controlled; however, the movement efficiency decreased concurrently, and stress distribution on the periodontal ligament became more even. For each 1° increase in compensation, the torque per millimeter of the first premolar would decrease by 0.26°/mm, and the crown movement efficiency eliminate decreased by 4.32%. Conclusion: Alternating movement increases the efficiency of the arch expansion by the aligner and reduces anchorage loss. Torque compensation should be designed to enhance torque control in arch expansion using an aligner.

The effect of maxillary molar distalization with clear aligner: a 4D finite-element study with staging simulation

INTRODUCTION

Long-term simulation of tooth movement is crucial for clear aligner (CA) treatment. This study aimed to investigate the effect of maxillary molar distalization with CA via an automatic staging simulation.

METHOD

A finite-element method (FEM) model of maxillary dentition, periodontal ligaments, attachments, and corresponding CA was established, and a prescribed 2-mm distalization with 0.1 mm each step of the second molar was simulated. The long-term tooth movement under orthodontic force was simulated with an iterative computation method. The morphologic changes of CA during staging were simulated with the thermal expansion method.

RESULTS

Twenty steps of molar distalization were simulated. Significant distal tilting of the second molar was revealed, along with the proclination of anterior teeth, which caused the 'reversed bow effect'. For the second molar, 4.63°distal tilting at the 20th step was revealed. The intrusion of the incisors and the second molar were 0.43 mm, 0.39 mm, and 0.45 mm, respectively, at step 20. All the anterior teeth showed a proclination of approximately 1.41°-2.01° at the 20th step. The expression rate of the designed distalization of the second molar was relatively low (approximately 68%) compared to the high efficacy of interdental space opening between molars with CA (approximately 89%).

CONCLUSION

A novel method of simulating long-term molar distalization with CA with FEM was developed. The FEM results suggested distal tilting of the second molar and the proclination of anterior teeth during the molar distalization.

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.

Effectiveness of clear aligners in achieving proclination and intrusion of incisors among Class II division 2 patients: a multivariate analysis

BACKGROUND

The predictability of incisor movement achieved by clear aligners among Class II division 2 patients is poorly understood. The aim of this retrospective study was to determine the effectiveness of clear aligners in proclining and intruding upper incisors and its influencing factors.

METHODS

Eligible patients with Class II division 2 malocclusion were included. For clear aligner therapy, three types of incisor movements were designed: proclination, intrusion and labial movement. Pre-treatment and post-treatment dental models were superimposed. The differences between predicted and actual (DPA) tooth movement of incisors were analyzed. Univariate and multivariate linear regression were used to analyze the potential influencing factors.

RESULTS

A total of 51 patients and their 173 upper incisors were included. Actual incisor proclination and intrusion were less than predicted ones (both P < 0.001), while actual labial movement was greater than predicted one (P < 0.001). Predictability of incisor proclination and intrusion was 69.8% and 53.3%, respectively. Multivariate linear regression revealed that DPA of proclination was significantly positively associated with predicted proclination (B = 0.174, P < 0.001), ipsilateral premolar extraction (B = 2.773, P < 0.001) and ipsilateral canine proclination (B = 1.811, P < 0.05), while negatively associated with molar distalization (B = - 2.085, P < 0.05). The DPA of intrusion was significantly positively correlated with predicted intrusion (B = 0.556, P < 0.001) while negatively associated with labial mini-implants (B = - 1.466, P < 0.001). The DPA of labial movement was significantly positively associated with predicted labial movement (B = 0.481, P < 0.001), while negatively correlated with molar distalization (B = - 1.004, P < 0.001), labial mini-implants (B = - 0.738, P < 0.001) and age (B = - 0.486, P < 0.05).

CONCLUSIONS

For Class II division 2 patients, predicted incisor proclination (69.8%) and intrusion (53.3%) are partially achieved with clear aligner therapy. Excessive labial movement (0.7 mm) of incisors may be achieved. Incisor movement is influenced by predicted movement amount, premolar extraction, canine proclination, molar distalization, mini-implants and age.

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

INTRODUCTION

Compared with fixed treatments, clear aligners (CAs) have the advantages of comfort, esthetics, and hygiene, and are popular among patients and orthodontists. However, CAs exhibit control deficiencies in extraction patients because of insufficient root control and retention effects. These deficiencies can magnify biomechanical differences in bimaxillary dentition, further causing different orthodontic requirements between maxillary and mandibular dentition. This study aimed to elaborate on the biomechanical characteristics of bimaxillary dentition in extraction space closure and provided feasible biomechanical compensation strategies for use in clinical practice.

METHODS

We constructed a 3-dimensional (3D) bimaxillary model based on patient data. Several 3D modeling-related software was used to generate a standard first premolar extraction model, CAs, and attachments. Subsequently, finite element analysis was performed to demonstrate the biomechanical effects.

RESULTS

The maxillary and mandibular dentition showed a roller coaster effect during space closure. Compared with the maxillary dentition, the mandibular posterior teeth exhibited stronger relative anchorage causing greater anterior teeth retraction. The tipping and vertical movements of the anterior teeth were related to tooth length. The longer the anterior tooth, the less tipping and greater vertical displacement occurred. Generally, when having the same retraction distance, the mandibular dentition exhibited greater retroclination and fewer extrusions. Both mechanical and retention compensations should be considered to prevent these unwanted tipping movements. Adding specific attachments to bimaxillary dentitions compensated for the retention and root control deficiencies of CAs.

CONCLUSIONS

When applying CAs to extraction patients, different biomechanical effects can present in the bimaxillary dentition because of specific dentition morphologies. To effectively treat these patients, mechanical compensation through overcorrection of the target position should be designed on the basis of bimaxillary control deficiencies, and retention compensation by adding specific attachments should also be considered according to the overcorrections.

Effects of different distalization directions and methods on maxillary total distalization with clear aligners: a finite element study

OBJECTIVES

To analyze the effects of maxillary tooth distalization by clear aligner (CA) treatment with variations in the angular direction of the distalization force, presence of attachments, and force-application method used.

MATERIALS AND METHODS

A finite element model containing alveolar bone, dentition, and periodontal ligament was constructed. Analytical model groups were as follows: (1) distalization with buttons (without attachments), (2) buttons on canines (with attachments), (3) precision cuts on the canines (without attachments), and (4) precision cuts on the canines (with attachments). A distalization force of 1.5 N was applied to the button or precision cut at -30°, -20°, -10°, 0°, 10°, 20°, and 30° to the occlusal plane.

RESULTS

As the direction of force approached +30°, the dentition inclined posteriorly. The posterior movement pattern was significantly influenced by the presence of an attachment and the direction of force, rather than the area where the force was applied. Distal inclination was dramatically reduced with attachments. A disengagement or deformation of the CA may reduce the distalization efficiency of the dentition or move the dentition in an inappropriate direction.

CONCLUSIONS

Attachments for efficient distalization by the CA are necessary. The use of miniscrews in the direction of force parallel to the occlusal plane is more advantageous than the use of Class II elastics. Due to CA deformation, distalization with the button on the canines can be more effective for distal movement of the maxillary dentition.

Torque recovery of the maxillary incisors with a modified double J retractor in a Class II division 2 case treated with clear aligners

A patient with a Class II division 2 malocclusion is presented, illustrating the application of a modified double J retractor (DJR) and palatal miniscrews along with clear aligners to correct the malocclusion and normalize the incisor torque. In terms of incisor torque recovery, a nonextraction approach might be a good choice if the Class II correction could be successfully achieved with total arch distalization. When maxillary molar distalization was limited by anatomical boundaries, the treatment plan was changed to bilateral maxillary first premolar extractions, which led to even more retroclination of the maxillary incisors after space closure. Anterior interdental miniscrews were used to intrude the maxillary incisors. A modified DJR and palatal miniscrews were used to regain torque and achieve palatal root movement of the maxillary incisors. The treatment effects and biomechanical designs were evaluated for torque recovery of the retroclined maxillary incisors.

Optimal sites and angles for the insertion of orthodontic mini-implants at infrazygomatic crest: a cone beam computed tomography (CBCT)-based study

BACKGROUND AND OBJECTIVES

Both cortical and overall bone thicknesses of the infrazygomatic crest (IZC) were measured to determine the optimal areas for mini-implants into the IZC. The impact of insertion sites, heights and angles, sex and age on bone thickness were evaluated.

MATERIALS AND METHODS

In this study, cone beam computed tomography (CBCT) images of 32 patients were included. The cortical bone thickness (CBT) and overall bone thicknesses (OBT) of IZC were measured at different insertion sites between the maxillary first and second molars (site 61, 62, 63, 67, 71, 72 and 73), different heights (0 to 12 mm from alveolar bone crest) and different angles (0 to 90 degrees from the reference line).

RESULTS

OBT was the thickest at site 63, followed by site 73. For each site, the insertion height where OBT was the thickest decreased with the increase of angle CBT and OBT were significantly influenced by sex and age. The percentage of root contact was significantly influenced by insertion heights and angles, not by sites. The recommended regions in the IZC for mini-implants were mapped.

CONCLUSIONS

Both CBT and OBT in the infrazygomatic crest were influenced by insertion sites, heights, and angles. Sex and age had an impact on CBT and OBT. The optimal insertion heights and angles were 12 mm to 18 mm from the occlusal plane, and 40 to 70 degrees for mini-implants at IZC.

Different biomechanical effects of clear aligners in bimaxillary space closure under two strong anchorages: finite element analysis

Background

Clear aligner (CA) treatment has been gaining popularity, but the biomechanical effects of CAs in bimaxillary dentition have not been thoroughly investigated. Direct and indirect strong anchorages are two common anchorage control methods, but the underlying biomechanical mechanism has not yet been elucidated. This study aimed to investigate the different biomechanical effects of CAs in closing the bimaxillary space under different anchorage controls, further instructing the compensation strategies design and strong anchorage choice in clinical practice.

Methods

Three-dimensional (3D) bimaxillary models of different anchorage controls were created based on cone-beam computed tomography and intraoral scan data. Four first premolars were extracted using 3D modeling software. Finite element analysis was conducted to simulate the space closure process of the CAs.

Results

In the two strong anchorage groups, the bimaxillary dentition presented different movement patterns during the space closure process, and the lower dentition was more vulnerable to elastic force. From the vertical view, direct strong anchorage with elastic force had the advantage of flattening the longitudinal occlusal curve and resisting the roller-coaster effects, whereas indirect strong anchorage could lead to a deep longitudinal occlusal curve. From the sagittal view, indirect strong anchorage with metallic ligaments had a greater instantaneous anchorage protection effect, particularly in the lower dentition, which reduced the mesial movement of the posterior teeth by nearly four times that of the direct anchorage group. In addition, indirect strong anchorage presented better anterior teeth torque/tipping control, while direct strong anchorage could aggravate lingual tipping of the upper central incisors. Due to the differences in anterior–posterior anchorage and arch shape, compared with the upper dentition, anchorage preservation and vertical control effects were amplified in the lower dentition.

Conclusions

The biomechanical effects of CAs differed between the two strong anchorage groups. Due to the differences in dentition morphology, anterior–posterior anchorage, and dental arch shape, CAs present different biomechanical effects in bimaxillary space closure. Orthodontists should consider the corresponding mechanical compensation according to specific anchorage control methods and dentitions.

Effectiveness of the attachment position in molar intrusion with clear aligners: a finite element study

Objective

To evaluate the biomechanical effects of different attachments’ position for maxillary molar intrusion with clear aligner treatment by finite element analysis.

Methods

Cone-beam computed tomography images of a patient with supra-eruption of the maxillary second molars were selected to construct three-dimensional models of the maxilla, periodontal ligaments, dentition, and clear aligner. The models were divided into four groups depending on the attachment location on the first molar: (1) no attachment (NA), (2) buccal attachment (BA), (3) palatal attachment (PA), and (4) bucco-palatal attachment (BPA). After applying an intrusion of 0.2 mm on the second molar, displacements and stress distributions of the teeth, aligner, and periodontal ligament were analyzed with the finite element software.

Results

All groups displayed equivalent movement patterns of aligners. The NA and BA groups showed buccal tipping of the second molar, while the PA group showed palatal tipping. The BPA group had the highest intruding value and the lowest buccal/palatal tipping value. All groups showed mesial tipping of the second molar. Stress distribution in the periodontal ligament strongly correlated with the attachment position. The BPA group showed the best stress distribution.

Conclusion

Combined BA and PA could effectively prevent buccal and palatal tipping and showed the best efficiency in intruding the second molar. The second molar showed an unavoidable tendency to tip mesially, regardless of the attachment position.

Three-dimensional finite element analysis of upper anterior teeth retraction and intrusion using clear aligners and mini-implants

OBJECTIVES

This study aimed to investigate the differences in treatment outcomes of upper anterior teeth retraction and intrusion with clear aligners and different types of elastics on mini-implants via the 3D finite element method.

METHODS

Cone-beam computed tomography (CBCT) was conducted to construct a 3D finite element model of maxillary bone, dentition, and clear aligners using Mimics, Geomagic, Solidworks, and Ansys. Four model groups were developed. Group 1 was the control group. Group 2 implanted a mini-implant between the upper second premolar and the upper first molar with a force of 0.98 N applied to the canine cut along the retracting direction for each side. Group 3 was based on Group 2, which implanted an additional mini-implant between the upper central incisors with a force of 0.98 N applied to the upper anterior teeth cuts. Group 4 was also based on Group 2, which implanted 2 additional mini-implants between the upper central and lateral incisors with a force of 0.56 N applied to the upper anterior teeth cuts for both sides. Anterior teeth torque changes, displacement patterns, and stress distributions were analyzed.

RESULTS

Among all the experimental groups, the anterior teeth demonstrated intrusion and distal inclination, accompanied with varied degrees of torque loss. In Group 3, the maxillary and lateral incisors had the smallest sagittal coronal displacement. In Group 4, the intrusion values of the maxillary and lateral incisors were the largest among all the experimental groups. The maximum stress concentration in Group 2 was the most significant among all the experimental groups.

CONCLUSIONS

Implanting the mini-implant between the central incisors for traction is conducive to torque control. By contrast, implanting the mini-implants between the central incisors and lateral incisors combined with vertical traction is conducive to simple intrusion, avoiding the "bowing effect" to a certain extent.

Facial Scanning Accuracy with Stereophotogrammetry and Smartphone Technology in Children: A Systematic Review

The aim of the study was to systematically review and compare the accuracy of smartphone scanners versus stereophotogrammetry technology for facial digitization in children. A systematic literature search strategy of articles published from 1 January 2010 to 30 August 2022 was adopted through a combination of Mesh terms and free text words pooled through boolean operators on the following databases: PubMed, Scopus, Web of Science, Cochrane Library, LILACS, and OpenGrey. Twenty-three articles met the inclusion criteria. Stationary stereophotogrammetry devices showed a mean accuracy that ranged from 0.087 to 0.860 mm, portable stereophotogrammetry scanners from 0.150 to 0.849 mm, and smartphones from 0.460 to 1.400 mm. Regarding the risk of bias assessment, fourteen papers showed an overall low risk, three articles had unclear risk and four articles had high risk. Although smartphones showed less performance on deep and irregular surfaces, all the analyzed devices were sufficiently accurate for clinical application. Internal depth-sensing cameras or external infrared structured-light depth-sensing cameras plugged into smartphones/tablets increased the accuracy. These devices are portable and inexpensive but require greater operator experience and patient compliance for the incremented time of acquisition. Stationary stereophotogrammetry is the gold standard for greater accuracy and shorter acquisition time, avoiding motion artifacts.

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.

Root resorption followed by orthodontic treatment in individuals with anterior open bite. A complete vision focused on different treatment alternatives: A review

The aim of this review was to determine the incidence of different types of treatment and the prevalence of root resorption in incisors induced by orthodontic treatment in patients with open bite. Libraries and electronic databases were searched, with 322 articles being selected and 55 articles considered regarding PRISMA checklist. It has been shown that apical root resorption of the incisors is more frequent in patients with premolar extractions than in those treated without extractions, due to greater apical displacement during retraction of the anterior teeth in the space closure phase. On the other hand, it has been described that intrusion of posterior teeth is four times more likely to cause root resorption than extrusion movement, thereby increasing the risk of root resorption in posterior teeth compared to conventional orthodontic treatment not requiring molar intrusions. Finally, aligners, such as orthodontic treatments with fixed appliances, have not been shown to induce clinically significant root resorption in open bite individuals. Literature on root resorption in open bite treatments is scarce making difficult conclusions difficult. However, the amount of root loss in cases of open bite seems to be similar to that of individuals without open bite.

Clear aligners with differentiated thickness and without attachments - A case report

Background

Most clear aligner systems use straight or scalloped gingival margin aligners that are replaced weekly and that mainly use attachments to guide many movements. Yet in the literature some studies show the effectiveness of the aligner margin extended beyond the gingival margin, and divots instead of attachments and the biological advantage given by the use of aligners with differentiated thickness.

Material and Methods

A female patient (23 years old) with a pronounced proclination of the upper and lower incisors and moderate crowding who was treated with aligners weekly replaced with differentiated thickness, divots, no attachments and a straight margin beyond the gingival margin.

Results

The therapy was carried out in 5 months and did not need any refinements. A total of 40 aligners were used (20 with soft thickness and 20 with hard thickness for each arch).

Conclusions

Invisible aligners without attachments and with other therapeutic strategies such as divots and differentiated thickness are a valid alternative to traditional aligners that cannot be ignored. Key words:Orthodontics, clear aligners, appliances design.

Does Sex, Skeletal Class and Mandibular Asymmetry Affect Tooth Length and Asymmetry in Tooth Length?

Introduction: The aim of our cross-sectional study is to determine whether there is a link between sex, skeletal class and mandibular asymmetry in orthodontic patients, with tooth length and asymmetry in tooth length on contralateral sides of the mandible. Methods: As the source for relevant data to answer this question, 3D cone-beam tomography (CBCT) images of a total of 95 future orthodontic patients were retrospectively selected from private practice records and were analyzed. The CBCT images were part of routine orthodontic diagnosis. Patients were divided into three groups (Class I, Class III with asymmetry and Class III without asymmetry) based on skeletal variables assessed on orthodontic cephalometric images and frontal photos of the face. Three null hypotheses were developed, and a series of statistical tests was performed in order to support or reject them. Results: We have established that there exists a sexual dimorphism in some of the teeth’s lengths in our sample. Furthermore, we failed to find a link between mandibular asymmetry and asymmetry in tooth length. We have also found a link between skeletal class and tooth length differences in some of the analyzed measurements. Conclusions: Computational models used to design orthodontic appliances and to plan orthodontic treatment should be more individualized to consider a patient’s sex and skeletal class.