The optimal orthodontic displacement of clear aligner for mild, moderate and severe periodontal conditions: an in vitro study in a periodontally compromised individual using the finite element model

Effect of force direction and impaction angulation during dilaceration impacted central incisor traction: a finite element analysis

BACKGROUND

The effects of traction forces at different angles on impacted central incisors(ICI)with varying inverted angles (IA) may be different. The objective of this study was to analyze the biomechanical effects of different force directions (FD) on developmentally inverted ICI with multi-angle variations and to offer insights and guidance for the treatment of inverted ICI.

METHODS

Three-dimensional finite element method was employed to simulate clinical scenarios of inverted ICI traction. As such, 0.2 N of force (direction: antero-superior angles of 90°, 100°, 110°, 120°, and 130° relative to the long axis of the inverted ICI crown) was applied to the inverted ICI with inverse angles (IA) of 40°, 30°, 20°, 10° and 0°. Inverted ICI apical displacement and Von Mises stress on periodontal ligament (PDL) and alveolar bone were compared.

RESULTS

IA and FD showed minimal influence on the stress distribution in the PDL, as higher stresses were concentrated in the apical region. The higher stresses in the alveolar bone are focused on the cervical and apical regions of the tooth. In particular, IA exerts a more significant impact on stress distribution in the alveolar bone than FD. The influence of IA on the apical displacement of inverted ICI is larger than that of FD.

CONCLUSIONS

To promote the health of the root and periodontal tissues, it is recommended to use an angle of 100°-110° relative to the long axis of the ICI crown when dealing with a large IA (> 20°) developmentally inverted ICI. Conversely, an angle of 110°-120° can be used.

Effects of different tooth movement patterns and aligner thicknesses on maxillary arch expansion with clear aligners: a three-dimensional finite element study

Objectives

The objective of this study was to investigate the biomechanical effects of different tooth movement patterns and aligner thicknesses on teeth and periodontal tissues during maxillary arch expansion with clear aligners, to facilitate more precise and efficient clinical orthodontic treatments.

Methods

Three-dimensional models including teeth, maxilla, periodontal ligament, and aligner were constructed and subjected to finite element analysis. Tooth displacement trends and periodontal ligament stresses were measured for seven tooth displacement patterns (divided into three categories including overall movement of premolars and molars with gradually increasing molar expansion in each step; distributed movement of premolars and molars; and alternating movement between premolars and molars at intervals) and two aligner thicknesses (0.5 mm and 0.75 mm) during maxillary arch expansion with clear aligners.

Results

When expanding the maxillary arch with clear aligners, the effective expansion of the target teeth mainly showed a tilting movement trend. Increasing the amount of molar expansion increased the buccal displacement of the first molar but decreased the buccal displacement of the premolars. The mean buccal displacement of the target teeth was greater in the posterior teeth interval alternating movement group (0.026 mm) than in the premolar/molar distributed movement group (0.016 mm) and the overall movement group (0.015 mm). Increasing aligner thickness resulted in greater buccal displacement of the crowns and increased stress on the periodontal ligaments.

Conclusion

Increasing the amount of molar expansion reduces the efficiency of premolar expansion. Alternating movement of premolars and molars at intervals achieves a higher arch expansion efficiency, but attention should be paid to the anchorage of adjacent teeth. Increasing the thickness of the aligner increases the expansion efficiency but may also increase the burden on the periodontal tissues.

Maxillary molar distalization treated with clear aligners combined with mini-implants and angel button using different traction force: a finite element study

OBJECTIVES

To evaluate the biomechanical system of molar distalization with clear aligner therapy (CAT) combined with angel button using interradicular mini-implants (IRMIs) with varying elastic forces.

MATERIALS AND METHODS

FE models including maxilla, complete maxillary dentition, periodontal ligaments (PDL), composite attachments, mini-implants (MI), and dedicated orthodontic aligner, were constructed. Three groups were created in accordance with the sagittal position of MI. Elastic forces (0 N,1 N,1.5 N,2 N) were applied.

RESULTS

CAT without elastics caused labial tipping and intrusion of the anterior teeth. Initial labial tipping and the von Mises stress of the maxillary anterior teeth decreased as the elastic forces increased.

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 effects of different staging and attachment designs in maxillary molar distalization with clear aligner: a finite element study

BACKGROUND

In the present study, the effects of distalizations of one and two molars with different step distances and attachment designs have been analyzed.

METHODS

A 3D finite element analysis model has been developed in order to determine the tendency of tooth displacement and stress distribution with clear aligner treatment.

RESULTS

Under the condition of single-molar distalization, when the step distance was set to 0.25 mm, the total displacement was 0.086 mm for central incisors, 0.080 mm for lateral incisors, 0.084 mm for canines, 0.102 mm for the first premolar and 0.076 mm for the second premolar. The von Mises stress of roots and the principal stress of the periodontal ligament was slightly lower than in the control group when the step distance was set to 0.130 mm. Under the condition of two-molar distalization, when the step distance was set to 0.130 mm, the total displacements for central incisors, lateral incisors and canines as well as both the first and second maxillary molars were basically the same as with a distance of 0.250 mm for one-molar distalization. In addition, when the step distance was 0.130 mm with two-molar distalization, the rotation center of the first and second molar was closer to the apex of the root indicating that the smaller step distance led to more bodily movement during the two-molar distalization. However, displacement tendencies of the first molar and the second molar were basically the same whether horizontal or vertical rectangular attachments were added.

CONCLUSIONS

A step distance of moving two molars to 0.130 mm can achieve the same reaction force on the anterior teeth as moving one molar 0.250 mm without effects on horizontal or vertical rectangular attachments.

CLINICAL RELEVANCE

Our results provide a theoretical basis and guidance for simultaneously moving two molars backward in clinical practice using a clear aligner.

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.

Three-dimensional finite element analysis of retracting pathological migration of the right upper central incisor with a clear aligner

We aimed to explore the best orthodontic step distance of the right upper central incisor with mild, moderate, and severe pathological displacement achieved via a clear aligner. Three-dimensional models of maxilla-tooth-periodontal ligament clear aligner of the right upper central incisors with five different steps of 0.1, 0.125, 0.15, 0.165, 0.25 mm and three different alveolar bone heights were established via finite element analysis. We analysed the changing trends in initial displacement, the periodontal ligament, the alveolar bone, and apical stress of right upper central incisor. In the process of retraction, the right upper central incisor a movement trend of the crown deviating from the distal root to the mesial, and with the decrease of the height of the alveolar bone and the increase of the displacement, the crown would appear distal labial torsion with a deepening trend of vertical overlay.The maximum stress distribution of the periodontal ligament and alveolar bone showed a positive correlation. The overall stress distribution of the periodontal ligament and apical stress increased with decrease of alveolar bone height and the increase of alveolar bone displacement. In patients with mild, moderate, and severe pathological displacement of the right upper central incisor, the best step distance of anterior tooth retraction is 0.165, 0.15, and 0.125 mm, respectively.

Effective contribution ratio of the molar during sequential distalization using clear aligners and micro-implant anchorage: a finite element study

INTRODUCTION

This study aims to investigate the biomechanical effects of anchorage reinforcement using clear aligners (CAs) with microimplants during molar distalization. And also explores potential clinical strategies for enhancing anchorage in the sequential distalization process.

METHODS

Finite element models were established to simulate the CAs, microimplants, upper dentition, periodontal ligament (PDL), and alveolar bone. In group set I, the 2nd molars underwent a distal movement of 0.25 mm in group set II, the 1st molars were distalized by 0.25 mm after the 2nd molars had been placed to a target position. Each group set consisted of three models: Model A served as the control model, Model B simulated the use of microimplants attached to the aligner through precision cuts, and Model C simulated the use of microimplants attached by buttons. Models B and C were subjected to a series of traction forces. We analyzed the effective contribution ratios of molar distalization, PDL hydrostatic stress, and von Mises stress of alveolar bone.

RESULTS

The distalization of the 2nd molars accounted for a mere 52.86% of the 0.25-mm step distance without any reinforcement of anchorage. The remaining percentage was attributed to the mesial movement of anchorage teeth and other undesired movements. Models B and C exhibited an increased effective contribution ratio of molar distalization and a decreased loss of anchorage. However, there was a slight increase in the undesired movement of molar tipping and rotation. In group set II, the 2nd molar displayed a phenomenon of mesial relapse due to the reciprocal force produced by the 1st molar distalization. Moreover, the efficacy of molar distalization in terms of contribution ratio was found to be positively correlated with the magnitude of force applied. In cases where stronger anchorage reinforcement is required, precision cuts is the superior method.

CONCLUSIONS

The utilization of microimplants in conjunction with CAs can facilitate the effective contribution ratio of molar distalization. However, it is important to note that complete elimination of anchorage loss is not achievable. To mitigate undesired movement, careful planning of anchorage preparation and overcorrection is recommended.

Actual contribution ratio of maxillary and mandibular molars for total molar relationship correction during maxillary molar sequential distalization using clear aligners with Class II elastics: A finite element analysis

INTRODUCTION

Class II elastics, in combination with clear aligners (CA), are efficient for molar distalization. However, the effects of this combination on intermaxillary molar relationship correction have yet to be investigated. This study aimed to investigate the actual contribution ratio of the maxillary and mandibular molars for total molar relationship correction during maxillary molar distalization using Class II elastics with CA and further explore therapeutic recommendations for clinical practice.

METHODS

Finite element models (FEMs) were established, including the distalization of the second molars (Set I), followed by the distalization of the first molars (Set II). Model A simulated elastics attached by precision cutting, whereas Model B simulated elastics attached to buttons. Force magnitudes of 100 g, 150 g, and 200 g of force were applied. We recorded the contribution ratio of the maxillary and mandibular molars for total molar relationship correction, effective distalizing distance in 0.25 mm step distance, tipping and rotation angles, and the hydrostatic stress in the periodontal ligament.

RESULTS

During maxillary molar distalization, mesialization of the mandibular molar had a notable contribution ratio for molar relationship correction. The mandibular first molar was mesialized with mesiolingual rotation tendency. Approximately half of the 0.25 mm step distance was occupied by maxillary molar distalization; the remainder was occupied by anchorage teeth mesialization and tipping or rotation. When traction forces increased, the total molar relationship correction and effective distalization increased; the mandibular molars mesialization contribution ratio also increased, as did rotation and inclination tendency. Precision cutting had a higher total molar relationship correction and more effective distalization than a button but also had a larger contribution ratio of mandibular molar mesialization and inclination or rotation.

CONCLUSIONS

Mandibular molar mesialization should be considered when correcting the molar relationship using CA with intermaxillary elastics during maxillary molar distalization. It is also important to consider the anchorage teeth mesialization and undesired tipping or rotation.

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.

Clear Aligner Therapy: Up to date review article

The advantages of Clear Aligners Therapy (CAT) include the braces being virtually invisible, comfortable to wear, and removable for eating and brushing; that way, CAT can be used to treat a wide range of orthodontic issues. In 1999, the company Align Technology introduced the frst commercial clear aligner system called Invisalign. The Invisalign system was initially only available to orthodontists, but later became available to general dentists as well. The system quickly gained popularity among patients who were looking for a more discreet and comfortable alternative to traditional braces. In 2000, Align Technology received FDA clearance for the Invisalign system, which further increased its popularity. The biomechanics of clear aligners involve the use of custom-made tooth aligners that are specifcally shaped to guide teeth into desired positions. These aligners are typically made from flexible materials such as polyurethane or ethylene vinyl acetate and are adjusted to apply the necessary forces for tooth movement. Attachment devices, such as power ridges or buttons, are often used to enhance or assist in specifc tooth movements and for retention of the aligner. The use of attachments allows for the exertion of desired force on the teeth, which is crucial for the success of Clear Aligner Therapy. CAT should be used if patients are concerned about the esthetic appearances of their teeth-for example, actors and other individuals that rely on their appearances in public in a professional context-and if the misalignment is not severe, so that clear aligners can still work. One should not use CAT in cases of severe crowding or spacing issues that require extractions. If the patient has complex jaw discrepancies or skeletal issues or if teeth need to be moved extensively in multiple directions, CAT is likely not going to be strong enough. In conclusion, Clear Aligner Therapy is a safe, effective, and convenient orthodontic treatment option that offers patients a virtually invisible way to achieve a straighter, more beautiful smile. With continued advancements in technology and a growing body of research supporting its effectiveness, the future of Clear Aligner Therapy looks bright.

An in vivo evaluation of clear aligners for optimal orthodontic force and movement to determine high-efficacy and periodontal-friendly aligner staging

Objectives

To investigate the effect of aligner displacement on tooth movement and periodontal health to improve the efficiency of aligner treatment and explore the mechanism in vivo.

Methods

A two-tooth site was established by a finite element (FE) model to virtually evaluate aligner staging. A randomized controlled experiment was conducted when the tooth sites in beagles were treated with fixed or aligner appliances with different movement and force, and tooth movement and internal structure were recorded during the alignment. After sacrificing five dogs, bone-periodontal ligament (PDL)-tooth specimens were removed and processed to conduct uniaxial compression and tensile tests as well as micro-CT imaging and histological analysis.

Results

Three displacements of 0.25, 0.35 and 0.45 mm were obtained from FE analysis and applied in beagles. In general, aligners had poorer performance on movement compared to fixed systems in vivo, but the aligner with a staging of 0.35 mm had the highest accuracy (67.46%) (P < 0.01). Loaded with severe force, fixed sites exhibited tissue damage due to excess force and rapid movement, while aligners showed better safety. The PDL under a 0.35-mm aligner treatment had the highest elastic modulus in the biomechanical test (551.4275 and 1298.305 kPa) (P < 0.05).

Conclusions

Compared to fixed appliances, aligners achieve slightly slower movement but better periodontal condition. Aligners with an interval of 0.35 mm have the highest accuracy and best PDL biomechanical and biological capacities, achieving the most effective and safest movement. Even with complexity of oral cavity and lack of evaluation of other factors, these results provide insight into faster displacement as a method to improve the efficacy of aligners.

Biomechanical factors in the open gingival embrasure region during the intrusion of mandibular incisors: A new model through finite element analysis

Introduction: Open gingival embrasure (OGE) is a common complication in adults following clear aligner therapy and the influence of gingival or alveolar bone biotype on OGE is of great concern. Unfortunately, due to the limited number of patients with clearaligner therapy and the clinical methods to distinguish the gingival biotype of patients being invasive, it is difficult to carry out clinical studies on the gingival or alveolar bone biotype of the OGE. In the meanwhile, the detailed biomechanics of the occurrence of OGE remains unknown. The goal of this study was to establish a new model to simulate the virtual space region, namely, the OGE region, to investigate the relationship between alveolar bone biotype and the occurrence of OGE, and explore potential biomechanical factors related to OGE.

Methods: The OGE region in the interproximal space was established using a filler with a very low modulus of elasticity (1 × 10−6 MPa). To illustrate the biomechanics of OGE more exhaustively, a line was created at the top of the alveolar crest along the proximal tooth root. FEA was then used to analyze the biomechanics of the surrounding tissues, the OGE region and the line at the top of the alveolar crest along the proximal tooth root of the central incisor under two different labial bone thicknesses (thick and thin) with an axial inclination of 80°, 90° and 100°.

Results: During intrusion of the incisors in clear aligner therapy, as inclination increased or bone tissue became thinner, the stress in the surrounding tissues [tooth root, alveolar crest, and periodontal ligament (PDL)] was greater. In the OGE region and interproximal alveolar crest, the strain increased with increasing inclination and labial bone thinning. The results from the line at the top of the alveolar crest along the proximal tooth root showed more detailed biomechanics: In all groups, stress and strain were focused on the mesial-labial alveolar crest. Interestingly, our results also demonstrated that when OGE occurs, other complications may arise, including root resorption and bone dehiscence.

The mechanical effect of geometric design of attachments in invisible orthodontics

INTRODUCTION

In invisible orthodontics, attachments are used with aligners to better control tooth movement. However, to what extent the geometry of the attachment can affect the biomechanical properties of the aligner is unknown. This study aimed to determine the biomechanical effect of attachment geometry on orthodontic force and moment using 3-dimensional finite element analysis.

METHODS

A 3-dimensional model of mandibular teeth, periodontal ligaments, and the bone complex was employed. Rectangular attachments with systematic size variations were applied to the model with corresponding aligners. Fifteen pairs were created to move the lateral incisor, canine, first premolar, and second molar mesially for 0.15 mm, respectively. The resulting orthodontic forces and moments were analyzed to compare the effect of attachment size.

RESULTS

Expansion in the attachment size showed a continuous increase in force and moment. Considering the attachment size, the moment increased more than the force, resulting in a slightly higher moment-to-force ratio. Expanding the length, width, or thickness of the rectangular attachment by 0.50 mm increases the force and moment up to 23 cN and 244 cN-mm, respectively. The force direction was closer to the desired movement direction with larger attachment sizes.

CONCLUSIONS

Based on the experimental results, the constructed model successfully simulates the effect of the size of attachments. The larger the size of the attachment, the greater the force and moment, and the better the force direction. The appropriate force and moment for a particular clinical patient can be obtained by choosing the right attachment size.

Effects of upper-molar distalization using clear aligners in combination with Class II elastics: a three-dimensional finite element analysis

INTRODUCTION

The effects of upper-molar distalization using clear aligners in combination with Class II elastics for anchorage reinforcement have not been fully investigated yet. The objective of this study is to analyze the movement and stress of the whole dentition and further explore guidelines for the selection of traction methods.

METHODS

Three-dimensional (3D) finite element models are established to simulate the sequential molar distalization process, including the initial distalization of the 2^nd molar (Set I) and the initial distalization of the 1^st molar (Set II). Each group set features three models: a control model without Class II elastics (model A), Class II elastics attached to the tooth by buttons (model B), and Class II elastics attached to the aligner by precision cutting (model C). The 3D displacements, proclination angles, periodontal ligament (PDL) hydrostatic stress and alveolar bone von Mises stress in the anterior area are recorded.

RESULTS

In all of the models, the maxillary anterior teeth are labial and mesial proclined, whereas the distal moving molars exhibit distal buccal inclination with an extrusion tendency. With the combination of Class II elastics, the anchorage was effectively reinforced; model C demonstrates superior anchorage reinforcement with lower stress distribution in comparison with model B. The upper canines in model B present an extrusion tendency. Meanwhile, the mandibular dentition in models B and C experience undesired movement tendencies with little discrepancy from each other.

CONCLUSIONS

Class II elastics are generally effective for anchorage reinforcement as the upper-molar distalization is performed with clear aligners. Class II elastics attached to an aligner by precision cutting is a superior alternative for maxillary anchorage control in cases that the proclination of upper incisors and extrusion of upper canines are unwanted.

The three-dimensional displacement tendency of teeth depending on incisor torque compensation with clear aligners of different thicknesses in cases of extraction: a finite element study

Background

Despite 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.

Methods

Three-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.

Results

Distal 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.

Conclusions

The 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.

Torque movement of the upper anterior teeth using a clear aligner in cases of extraction: a finite element study

Background

Clear aligner treatment has become popular over recent years. It is necessary to identify methods by which we could avoid the bowing effect in extractions with clear aligner. The present study was to identify the appropriate method to design torque movement involving the upper anterior teeth of extraction cases, in order to maintain or improve the axis and torque of the upper anterior teeth with a clear aligner during movement and closure of the extraction space.

Results

As the height of the power ridge increased, the rotation angle of the upper central incisor in the sagittal direction decreased gradually and the location of the rotation center changed significantly; the rotation center moved in the apical direction and then changed to the crown side. The highest von-Mises stress of the upper central incisor root, periodontal ligaments, and alveolar bone, showed little change as the power ridge height increased. When the axial inclination of the upper central incisor was normal (U1-SN = 105°), the tendency of movement for the upper central incisor approached translation with a power ridge height of 0.7 mm (corresponding distorted angle: 5.8415). When the axial inclination of the upper central incisor was oversized (U1-SN = 110°), the axial inclination of the upper central incisor reduced to normal following completion of the anterior segment retraction with a power ridge of 0.4 mm (corresponding distorted angle: 3.4265).

Conclusion

Analysis indicates that pure palatal tipping movement of the upper anterior teeth is generated without torque control, thus resulting in the bowing effect. The required torque control of the upper anterior teeth with oversize axial inclination is weaker than that of the upper anterior teeth with normal axial inclination because limited torque loss is expected for oversize axial inclination teeth. Variation sensitivity of the rotation center should be considered carefully due to biological problems when designing translation of the upper anterior teeth with normal axial inclination.

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.

Study on the Effects of Orthodontics on Anterior Tooth Displacement in Patients

Objective

The purpose of this study was to investigate the therapeutic effect of orthodontic treatment on anterior tooth displacement caused by periodontal disease.

Methods

A prospective study was performed in 86 patients with anterior tooth displacement caused by periodontal disease. These patients were divided into the experimental group and the control group according to the intervention methods. For the control group, patients were treated with conventional therapy. The experimental group used straight wire orthodontic technique for orthodontic treatment on the basis of conventional treatment. Comparisons were performed between two groups in term of bleeding index, alveolar bone height, anterior tooth coverage, periodontal pocket depth, probing depth, clinical crown length, tooth root length, inflammatory cytokines levels, and orthodontic satisfaction.

Results

Comparison of bleeding index, alveolar bone height, anterior tooth coverage, periodontal pocket depth, probing depth, clinical crown length, tooth root length, and inflammatory cytokines levels between two groups before treatment indicated that there were no statistical differences (all P > 0.05). After treatment, bleeding index, alveolar bone height, anterior tooth coverage, periodontal pocket depth, probing depth, clinical crown length, and serum levels of IL-6 and TNF-α in the experimental group were lower than those in the control group (all P < 0.05), while the serum level of IL-2 in the experimental group was more than that in the control group (P < 0.05). Also, there was no difference for tooth root length between two groups. Moreover, compared with the control group, orthodontic satisfaction in the experimental group was significantly increased.

Conclusion

The efficacy of orthodontic treatment in patients with anterior tooth displacement caused by periodontal disease is higher than that of only using conventional therapy, as it helps improve their periodontal health, alveolar bone height, clinical crown length, inflammatory factor levels, and orthodontic satisfaction of patients.

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.

Predictability of Root Movements Using Virtual Root Setup in a Patient With Periodontal Disease Treated With Clear Aligners

Aims:

The aim of the study was to show a case with a midline diastema in a patient with high periodontal risks and gingival recessions treated with clear aligners. The objective was to predict and quantify root movements using a dedicated software that extrapolates data from the Cone Beam Computed Tomography (CBCT).

Case Presentation:

A 31-year-old female with a mandibular midline diastema asked for an aesthetic treatment. She had vertical bone loss on the lower central incisors, so a CBCT was necessary in order to plan the root movements. The purpose of the treatment was to avoid an uncontrolled tipping of the incisors and, therefore, a vestibular movement of the roots, which could cause serious periodontal problems.

Conclusion:

At the end of the treatment, the complete closure of the diastema and the radiographic healing of the vertical bone loss between mandibular central incisors were achieved. The superimpositions with the virtual setup demonstrated predictability of root movements of 76%.

Using FEM to Assess the Effect of Orthodontic Forces on Affected Periodontium

Orthodontic treatment in patients with no periodontal tissue breakdown vs. horizontal bone loss should be approached with caution even though it can bring significant benefits in terms of periodontal recovery and long-term success. We used the finite element method (FEM) to simulate various clinical scenarios regarding the periodontal involvement: healthy with no horizontal bone loss, moderate periodontal damage (33%) and severe horizontal bone loss (66%). Afterwards, forces of different magnitudes (0.25 N, 1 N, 3 N, and 5 N) were applied in order to observe the behavioral patterns. Through mathematical modeling, we recorded the maximum equivalent stresses (σ ech), the stresses on the direction of force application (σ c) and the displacements produced (f) in the whole tooth–periodontal ligament–alveolar bone complex with various degrees of periodontal damage. The magnitude of lingualization forces in the lower anterior teeth influences primarily the values of equivalent tension, then those of the tensions in the direction in which the force is applied, and lastly those of the displacement of the lower central incisor. However, in the case of the lower lateral incisor, it influences primarily the values of the tensions in the direction in which the force is applied, then those of equivalent tensions, and lastly those of displacement. Anatomical particularities should also be considered since they may contribute to increased periodontal risk in case of lingualization of the LLI compared to that of the LCI, with a potential emergence of the “wedge effect”. To minimize periodontal hazards, the orthodontic force applied on anterior teeth with affected periodontium should not exceed 1 N.