Finite element analysis of mandibular molar protraction mechanics using miniscrews

Evaluating the efficiency of mandibular molar protraction using Herbst appliances versus temporary anchorage devices: a retrospective case-controlled study

BACKGROUND

Mandibular second premolar agenesis is a common problem in orthodontics and is often treated in conjunction with maxillary counterbalancing extractions. However, in cases without maxillary crowding or dental protrusion, space closure may pose challenges leading to compromised occlusal results or patient profile. Multiple techniques have been described to treat these patients; nevertheless, there is a paucity of data comparing effectiveness of space closure utilizing various anchorage techniques. The goal of this study is to assess the effectiveness of the Herbst device during mandibular molar protraction and compare it to the use of temporary anchorage device (TADs) in patients with mandibular second premolar agenesis.

MATERIALS AND METHODS

This retrospective study included 33 patients with mandibular premolar agenesis treated without maxillary extractions. Of these patients, 21 were treated with protraction Herbst devices and 12 with TADs. Changes in molar and incisor positions, skeletal base positions and occlusal plane angulations were assessed on pretreatment (T0) and post-treatment (T1) lateral cephalograms. Scans/photographs at T0 and T1 were used to evaluate canine relationship changes representing anchorage control. Space closure and breakage/failure rates were also compared. Data was analyzed with paired and unpaired t-tests at the significance level of 0.05.

RESULTS

Within the Herbst group, changes in mandibular central incisor uprighting and mandibular molar crown angulations were statistically significant. However, no significant differences were noted between the Herbst and TAD groups. Protraction rates as well as overall treatment times were comparable (0.77 mm/month vs. 0.55 mm/month and 3.02 years vs. 2.67 years, respectively). Canine relationships were maintained or improved toward a class I in 82.85% of the Herbst sample, compared to in 66.7% of the TAD sample. Emergency visits occurred in 80.1% of the Herbst group, with cementation failures or appliance breakages as the most common reasons.

CONCLUSION

The Herbst device could be a viable modality in cases with missing mandibular premolars where maximum anterior anchorage is desired, or if patients/parents are resistant to TADs. Furthermore, they could be beneficial in skeletal class II patients with mandibular deficiency who also need molar protraction. However, the increased incidence of emergency visits must be considered when treatment is planned.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Stress-strain and fatigue life numerical evaluation of two different dental implants considering isotropic and anisotropic human jaw

Dental prostheses are currently a valid solution for replacing potential missing tooth or edentulism clinical condition. Nevertheless, the oral cavity is a dynamic and complex system: occlusal loads, external agents, or other unpleasant events can impact on implants functionality and stability causing a future revision surgery. One of the failure origins is certainly the dynamic loading originated from daily oral activities like eating, chewing, and so on. The aim of this paper was to evaluate, by a numerical analysis based on Finite Elements Method (FEM), and to discuss in a comparative way, firstly, the stress-strain of two different adopted dental implants and, subsequently, their fatigue life according to common standard of calculations. For this investigation, the jawbone was modeled accounting for either isotropic or anisotropic behavior. It was composed of cortical and cancellous regions, considering it completely osseointegrated with the implants. The impact of implants' fixture design, loading conditions, and their effect on the mandible bone was finally investigated, on the basis of the achieved numerical results. Lastly, the life cycle of the investigated implants was estimated according to the well-established theories of Goodman, Soderberg, and Gerber by exploiting the outcomes obtained by the numerical simulations, providing interesting conclusions useful in the dental practice.

Orthodontic Management of Severe Hypodontia and Impacted Maxillary Second Molars in a Patient with Sotos Syndrome

Sotos syndrome is a genetic disorder characterized by distinct craniofacial features, overgrowth in childhood, and impaired intellectual development. We herein report the successful orthodontic treatment of a 14-year-old boy with Sotos syndrome caused by a heterozygous mutation in the NSD1 gene. He showed severe hypodontia, impaction of the maxillary second molars and a skeletal Class III jaw-base relationship. Orthodontic management, including space control by protraction of the maxillary first molars and traction of the impacted molars, was performed using fixed appliances and miniscrews. As a result, acceptable occlusion was obtained without any discernible relapse 18 months postretention.

Temporary anchorage devices and the forces and effects on the dentition and surrounding structures during orthodontic treatment: a scoping review

BACKGROUND

Temporary anchorage devices (TADs) offer the clinician an immediate temporary source of skeletal anchorage for a range of orthodontic interventions. It is important to understand forces involved in using TADs and the effects on the dentition and surrounding structures, to improve clinical outcomes.

OBJECTIVE

To examine and qualitatively synthesize literature on the forces involved with the use of TADs and the effects on the dentition and surrounding structures in orthodontic tooth movement, to provide better understanding of the complex interactions and the clinical implications.

SEARCH METHODS

Electronic databases searched included: Cochrane Library [including Central Register of Controlled Trials (CENTRAL)], Embase via OVID, Pubmed, and Scopus. Study screening and selection were conducted in duplicate.

SELECTION CRITERIA

Studies selected were clinical studies, simulation studies (computer or laboratory-based), or animal studies with no restriction over gender, age, study type (excluding case reports), or setting. Studies focusing on the forces involved with the use of TADs in orthodontic treatment and their effects on the dentition and surrounding structures were included.

DATA COLLECTION AND ANALYSIS

A data charting form was piloted and refined. Data charting was performed independently and in duplicate. This consisted of key fields with predetermined options and free text. The extracted data were collated, and a narrative synthesis conducted.

RESULTS

The results from 203 included studies were grouped into seven TAD based interventions combining the clinical, simulation, and animal studies. They were: En masse retraction of anterior teeth, intrusion, movement of a single tooth, orthopaedic interventions, distalisation, maxillary expansion and other types. The forces involved with the use of TADs, and their effects on the dentition and surrounding structures, were presented in descriptive and tabular formats.

LIMITATIONS

This review restricted study language to English. Formal appraisal of the quality of evidence is not a required feature of scoping reviews, as per the PRISMA-ScR guidelines, however it was evident that a proportion of clinical studies were of high risk of bias and low quality and therefore any proposed changes the reader may consider to their clinical practice should be contextualized in light of this.

CONCLUSIONS

Across the seven types of TAD based interventions the effects on the dentition and surrounding structures are described providing a better understanding of the complex interactions. A guide to the level and direction of forces in each type of intervention is provided to aid clinicians in achieving high quality outcomes.

IMPLICATIONS

There is a need to validate future FEA simulation studies by comparing to clinical data. It is also recommended that future scoping reviews incorporate a formal critical appraisal of studies to facilitate the translation of the results into clinical practice. Development of a standard set of terms for TADs is recommended to facilitate future research.

REGISTRATION

Registration of a scoping review is not possible with PROSPERO.

FUNDING

None to declare.

Three Different Fixation Modalities following Mandibular Setback Surgery with Sagittal Split Ramus Osteotomy: A Comparative Study using Three-dimensional Finite Elements Analysis

Background

The provision of sufficient stability after maxillofacial surgery is essential for the reduction of complications and disease recurrence. The stabilization of osteotomized pieces results in rapid restoration of normal masticatory function, reduction of skeletal relapse, and uneventful healing at the osteotomy site. We aimed to compare qualitatively stress distribution patterns over a virtual mandible model after bilateral sagittal split osteotomy (BSSO) bridged with three different intraoral fixation techniques.

Methods

This study was conducted in the Oral and Maxillofacial Surgery Department of Mashhad School of Dentistry, Mashhad, Iran, from March 2021-March 2022. The mandible computed tomography scan of a healthy adult was used to generate a 3D model; thereafter, BSSO with a 3mm setback was simulated. The three following fixation techniques were applied to the model: 1) two bicortical screws, 2) three bicortical screws, and 3) a miniplate. The bilateral second premolars and first molars were placed under mechanical loads of 75, 135, and 600N in order to simulate symmetric occlusal forces. Finite element analysis (FEA) was carried out in Ansys software, and the mechanical strain, stress, and displacement calculations were recorded.

Results

The FEA contours revealed that stress was mainly concentrated in the fixation units. Although bicortical screws presented better rigidity than miniplates, they were associated with higher stress and displacement readings.

Conclusion

Miniplate fixation demonstrated the most favorable biomechanical performance, followed by fixation with two and three bicortical screws, respectively. Intraoral fixation with miniplates in combination with monocortical screws can serve as an appropriate fixation arrangement and treatment option for skeletal stabilization after BSSO setback surgery.

Effects of Rigid and Nonrigid Connections between the Miniscrew and Anchorage Tooth on Dynamics, Efficacy, and Adverse Effects of Maxillary Second Molar Protraction: A Finite Element Analysis

Introduction

Direct, rigid indirect, and nonrigid indirect absolute anchorages using temporary anchorage devices (TADs, mini-implants/miniscrews) can provide promising opportunities for challenging, yet common, orthodontic tooth movements such as molar protraction. Rigid rectangular wire and ligature wire are the most common methods of attaching a tooth to a miniscrew in indirect anchorages. We aimed to provide a comparison of the rigidity of the connecting wire in terms of stress on the miniscrew, the anchorage loss, and the risk of root resorption using finite element analysis (FEA).

Methods

The maxillary right second molar was protracted into the proximal space at a 150 g load (1) using direct absolute anchorage with a tapered miniscrew implanted between the premolar roots and using indirect absolute anchorage with the second premolar reinforced by the miniscrew through (2) a rigid stainless steel (SS) wire or (3) a nonrigid SS ligature wire (4) at different elastic moduli. Stresses and displacements of 4 models' elements were measured. The risk of external root resorption was evaluated.

Results

Connecting the tooth to the miniscrew using rigid full-size wire (model 2) compared to ligature (model 3) can give better control of the anchorage (using the ligature wire, the anchorage loss is 1.5 times larger than the rectangular wire) and may reduce the risk of root resorption of the anchorage unit. However, the risk of miniscrew failure increases with a rigid connection, although it is still lower than with direct anchorage. The miniscrew stress when using a ligature is approximately 30% of the rigid model using the rectangular wire. The miniscrew stress using the rectangular wire is approximately 82.4% of the miniscrew stress in the direct model. Parametric analysis shows that the higher the elastic modulus of the miniscrew-tooth connecting wire in the indirect anchorage, the less the anchorage loss/palatal rotation of the premolars/and the risk of root resorption of the anchorage teeth and instead the stress on the miniscrew increases.

Conclusions

Direct anchorage (followed by rigid indirect anchorage but not nonrigid) might be recommended when the premolars should not be moved or premolar root resorption is a concern. Miniscrew loosening risk might be the highest in direct anchorage and lowest in nonrigid indirect anchorage (which might be recommended for poor bone densities).

Effects of Mandibular Canine Intrusion Obtained Using Cantilever Versus Bone Anchorage: A Comparative Finite Element Study

Background This study was conducted to assess and compare the effects of mandibular canine intrusion obtained using a cantilever having different toe-in bends and with mini-implants using the three-dimensional (3D) finite element method (FEM). Methodology 3D models of the mandibular right quadrant were created using FEM. Brackets and molar tubes were also modeled. In the first model, the mandibular canine intrusion was produced using a cantilever loop with compensatory toe-in bends (0°, 4°, 6°, and 8°). In another model, the intrusion was done using two mini-implants. Force was applied using an elastic chain. The amount of intrusion and the associated labial tipping of canine that occurred in both the models was assessed and compared using FEM analysis. Results The pure intrusion of the canine was produced by the 6° toe-in bend of the cantilever. The labial tipping of the canine was also reduced. The highest amount of periodontal ligament stress was observed around the canine root with a 0° toe-in bend. In the posterior segment, the molar displayed a slight tendency for extrusion and distal crown tipping. Conclusions The intrusion mechanics using a cantilever simulated in this study may achieve pure mandibular canine intrusion with minimal labial tipping when a compensatory toe-in of 6° is incorporated into the cantilever.

Molar space closure: To do or not to do?

Missing or compromised permanent molars can complicate orthodontic treatment planning and mechanics. Molar extraction should be considered in appropriate situations, but clinicians must decide between closing and regaining the edentulous space. Several factors should be taken into consideration to achieve appropriate molar space management, such as the need for space, asymmetry, periodontal status, sinus pneumatization, and the terminal molar position. Herein, three sample cases are reported to demonstrate the treatment options for molar space closure and maintenance with these factors taken into consideration during treatment planning. The understanding of mechanics played a crucial role in anchorage preparation and side effect prevention. If the third molar substitution was managed in advance and adequate space between the ramus and third molar was obtained via second molar protraction, the tooth spontaneously erupted in a favorable position without requiring further treatment. This case series can aid clinicians in molar space management. Regardless of whether the space is to be closed or regained, the treatment plan should conform to the patient’s expectations and improve occlusion with minimal side effects and treatment duration.

Modelling and evaluating periodontal ligament mechanical behaviour and properties: A scoping review of current approaches and limitations

This scoping review is intended to synthesize the techniques proposed to model the tooth-periodontal ligament-bone complex (TPBC), while also evaluating the suggested periodontal ligament (PDL) material properties. It is concentrated on the recent advancements on the PDL and TPBC models, while identifying the advantages and limitations of the proposed approaches. Systematic searches were conducted up to December 2020 for articles that proposed PDL models to assess orthodontic tooth movement in Compendex, Web of Science, EMBASE, MEDLINE, PubMed, ScienceDirect, Google Scholar and Scopus databases. Although there have been many studies focused on the evaluation of PDL material properties through numerous modelling approaches, only a handful of approaches have been identified to investigate the interface properties of the PDL as a complete dynamical system (TPBC models). Past reviews on the analytical and experimental determination of the PDL properties already show a concerning range in reported output values-some nearly six orders of magnitude in difference-that strongly suggested the need for further investigation. Surprisingly, it has not yet been possible to determine a narrower range of values for the PDL material properties. Moreover, very few scientific approaches address the TPBC as an integrated complex system model. In consequence, current methods for capturing the PDL material behaviour in a clinical setting are limited and inconclusive. This synthesis encourages more systematic, pragmatic and phenomenological research in this area.

Effects of Skeletally Supported Anterior en Masse Retraction with Varied Lever Arm Lengths and Locations in Lingual Orthodontic Treatment: A 3D Finite Element Study

Objective

This study is aimed at analyzing different points of force application during miniscrew supported en masse retraction of the anterior maxillary teeth to identify the best line of action of force in lingual orthodontic treatment.

Materials and Methods

Three-dimensional (3D) finite element models were created to stimulate en masse retraction with different heights and positions of the miniscrew and lever arm to change the force application points; a 150 g retraction force was applied from the miniscrew to the lever arms, and the initial tooth displacements were analyzed.

Results

Lingual crown tipping and occlusal crown extrusion were seen at all heights and positions of the miniscrew and lever arm, but when the miniscrew height was at 8 mm and the power arm was located between the lateral incisors and canines, these tipping patterns were less than those obtained with a 4.5 mm high miniscrew and a lever arm located distal to the canines.

Conclusion

All miniscrew heights and lever arm positions showed initial lingual crown tipping and labial root tipping with occlusal crown extrusion. However, the 8 mm miniscrew height and the lever arm located between the lateral incisor and canine showed fewer amounts of these tipping patterns than a 4.5 mm miniscrew height and lever arm located distal to the canines. Therefore, this could be the preferred point of force application during en masse retraction in lingual treatment with additional torque control methods.

Analysis of stress in periodontium associated with orthodontic tooth movement: a three dimensional finite element analysis

It is well known that the initiating factor for the biologic changes is the stress induced in the periodontal tissue; but as of now there is no gauge to measure the stress in the PDL directly. Therefore finite element model can be used to study the stress-strain relation through simulation of the PDL. The aim of the study was to simulate the stress response in the periodontium for different moment to farce ratios induced by tipping, translation, rotation, intrusion, extrusion and root torque by means of finite element method. The three-dimensional finite element model of the mandibular first molar was constructed. The pattern of Von misses stress and the maximum displacement of the mandibular molar was recorded on application of different combination of moment to force ratio. The periodontium was sensitive to changes in the load values. The stress pattern in the periodontal ligament for a lingually directed force without counterbalancing moments showed high concentration at the cervical level of the root. With addition of counter-tipping and counter-rotation moments, a relatively even distribution of stress throughout PDL was obtained. Additionally, high stress concentration was observed on the root surface at the furcation level for forces applied parallel to the long axis. Translation type of tooth movement showed relatively even distribution of the stress in the PDL and makes the tooth less susceptible to root resorption.

Autotransplanted premolars with incomplete root formation in a growing patient with multiple missing teeth

A boy aged 8 years 11-months with 4 missing teeth in his mandibular arch and with a skeletal Class II pattern was treated with autotransplantation of developing premolars from his maxillary arch with the aid of temporary skeletal anchorage devices. The active treatment duration was 25 months. After treatment, he had a normal occlusion, and his profile was improved. Posttreatment records at 12 months showed stable occlusion and successfully autotransplanted premolars.

Displacement and stress distribution of Kilroy spring and nickel-titanium closed-coil spring during traction of palatally impacted canine: A 3-dimensional finite element analysis

OBJECTIVE

To compare the stress distribution and initial displacements during traction of palatally impacted canine between Kilroy and nickel-titanium (NiTi) closed-coil springs by means of the finite element analysis.

SETTING AND SAMPLE POPULATION

A finite element method analysis of two traction methods for a maxillary impacted canine.

MATERIALS AND METHODS

The corresponding periodontal ligaments (PDLs), brackets, molar tubes and a 0.019 × 0.025-in base stainless-steel (SS) wire were modelled and imported to ANSYS SpaceClaim version 2020 R1. Traction was simulated under two different set-ups with equal force magnitude (60 g); (1) the Kilroy spring, which is made of 0.016-inch SS, and (2) the NiTi closed -coil spring. Von Mises stress distributions and initial displacements of the maxillary teeth were analysed.

RESULTS

In both mechanics, while the highest stress was seen on the impacted canine (Kilroy, 10.41 kPa; NiTi closed-coil, 5.27 kPa), the stress distribution decreased as the distance from the impacted canine increased. The Kilroy spring showed a greater total displacement (465.60 μm) on the impacted canine. The higher stresses on the adjacent lateral (5.29 kPa) and premolar (6.41 kPa) occurred with the Kilroy spring.

CONCLUSIONS

The Kilroy spring yielded higher stresses than the NiTi closed-coil spring on the impacted canine and the adjacent teeth. The difference between distribution of the stresses over the impacted canine induced greater displacement with the Kilroy spring, particularly in the vertical direction.

Effect of Bracket Slot and Archwire Dimension on Posterior Tooth Movement in Sliding Mechanics: A Three-dimensional Finite Element Analysis

Introduction

Space closure by molar protraction has always been a challenge in orthodontic treatment due to larger root surface area which requires additional anchorage. Ideally, there should be little or no tipping. However, the protraction forces, being occlusal and buccal to the centre of resistance (CR) of the tooth, cause tipping and rotations.

Aim

The aim of the study was to assess the effect of bracket slot and archwire dimensions on posterior tooth movement during space closure in sliding mechanics and evaluate the length of power arm to bring about translatory movement of teeth using three-dimensional finite element analysis.

Materials and methods

A model of the maxillary teeth was created and converted to a finite element format through a meshing software, Hypermesh. Two three-dimensional models, each with a combination of 0.017”× 0.022” archwire in 0.018” slot (model 1) and 0.019”×0.025” archwire in 0.022” slot (model 2), were generated. Power arms of different lengths were attached to the first molar. Miniscrew was inserted between the canine and first premolar.

Results

In model one, the power arm of 10-mm height provided controlled tooth movement than the one with 6 mm height, and in model two, power arms of both 6-mm and 10-mm height produced controlled tooth movement.

Conclusions

As the force was raised apically from the slot, more translation was observed. Power arm of 6-mm height can be used due to anatomic limitation of the vestibule.

Two distalization methods compared in a novel patient-specific finite element analysis

INTRODUCTION

Orthodontic mini-implants aid in the correction of distocclusions via direct anchorage (pull from mini-implant to teeth) and indirect anchorage (teeth pulled against other teeth anchored by the mini-implant). The aim of this study was to compare stress levels on the periodontal ligament (PDL) of maxillary buccal teeth in direct and indirect distalization against orthodontic mini-implants and accounting for individual variation in maxillary anatomy and biomechanical characteristics of the compact bone.

METHODS

A 3D model of the maxilla containing the different components (teeth, PDL, trabecular and cortical bones) was generated from a computed tomographic scan. Cortical bone was divided into several areas according to previously defined zones. Bone stiffness and thickness data, obtained from 11 and 12 cadavers, respectively, were incorporated into the initial model to simulate the individual cortical bone variation at the different locations. Subsequently, a finite element analysis was used to simulate the distalization modalities.

RESULTS

Stresses at the buccal, palatal, mesial, and distal surfaces were significantly different between adjacent teeth under stiffness but not thickness variation. In both distalization modalities, low or no significant correlations were found between stress values and corresponding cortical bone thicknesses. High significant and inverted correlations were observed at the first molar between stress amounts and cortical bone stiffness (direct modality: -0.68 < r < -0.72; indirect modality: -0.80 < r < -0.82; P <0.05).

CONCLUSIONS

With the use of a novel finite element approach that integrated human data on variations in bone properties, findings suggested that cortical bone stiffness may influence tooth movement more than bone thickness. Significant clinical implications could be related to these findings.

Finite element analysis of the effect of power arm locations on tooth movement in extraction space closure with miniscrew anchorage in customized lingual orthodontic treatment

INTRODUCTION

More patients are choosing customized orthodontic appliances because of their excellent esthetics. It is essential that clinicians understand the biomechanics of the tooth movement tendency in customized lingual orthodontics. This study aimed to evaluate the tooth movement tendency during space closure in maxillary anterior teeth with the use of miniscrew anchorage in customized lingual orthodontics with various power arm locations.

METHODS

Three-dimensional finite element models of the maxilla were created with miniscrews and power arms; the positions were varied to change the force directions. A retraction force (1.5 N) was applied from the top of the miniscrews to the selected points on the power arm, and the initial displacements of the reference nodes of the maxillary teeth were analyzed.

RESULTS

After applying force in different directions, power arms located at the distal side of the canines led to larger initial lingual crown tipping and occlusal crown extrusion of the maxillary incisors compared with power arms located at the midpoint between the lateral incisors and canines, and caused a decreasing trend of the intercanine width.

CONCLUSIONS

In customized lingual orthodontic treatment, power arms located at the distal side of the canines are unfavorable for anterior teeth torque control and intercanine width control. Power arms located at the midpoint between the lateral incisors and canines can get better torque control, but still cannot achieve excepted torque without extra torque control methods, no matter whether its force application point is higher than, lower than, or equal to the level of the top of the miniscrews.

[Not Available]

Le Pr Ravindra Nanda a obtenu une licence et une maîtrise en dentisterie et en orthodontie du King George's Medical College, Lucknow University. En 1967, il a intégré l'Université Catholique de Nimègue, aux Pays-Bas, où il a obtenu un doctorat en philosophie en 1969. Il a rejoint la nouvelle école dentaire de Loyola à Chicago en 1970, après avoir occupé le poste de Professeur assistant en orthodontie dans le service dirigé par Frans van der Linden. En 1972, il fut promu au Département d'Orthodontie de l'Université du Connecticut à Farmington, CT, et y reçu son certificat en orthodontie sous la direction de Charles Burstone. Professeur adjoint, puis professeur titulaire à partir de 1979, il a assumé le poste de Chef du Département d'Orthodontie à partir de 1992 et a été promu pour diriger le Département des Sciences Craniofaciales en 2004, dont les divisions de chirurgie orale et maxillo-faciale, de dentisterie pédiatrique, de l'enseignement supérieur en dentisterie générale et en orthodontie.

Il est membre et ancien président de la composante Atlantique Nord de la Edward H. Angle Society of Orthodontists. Il occupe actuellement la fonction de rédacteur en chef de Progress in Orthodontics, de rédacteur associé du Journal of Clinical Orthodontics et est membre du comité éditorial de neuf revues d'orthodontie nationales et internationales. Il est membre de l'Association dentaire américaine, de l'Association dentaire de l'État du Connecticut, de la Hartford Dental Society, de l'Association américaine des orthodontistes, de la Société européenne d'orthodontie, de l'Association internationale de recherche dentaire et du College of Diplomates of American Board of Orthodontists.

Il a rédigé et publié sept manuels et plus de 200 articles dans des revues à comité de lecture. Il a donné des conférences magistrales dans plus de 40 pays et a reçu de nombreux prix et honneurs pour ses contributions en dentisterie et en orthodontie, aux États-Unis et de la part d'organisations internationales d'orthodontie. Il est membre d'honneur des Jordan Orthodontic Society, Czech Orthodontic Society, Taiwanese Orthodontic Society, Central American Orthodontics Society et membre d'honneur à vie de l'Indian Orthodontic Society.

Ravindra Nanda a été honoré du Life Time Achievement Award (University of Connecticut Foundation), et il est Senior Research Fellow (Japan Promotion for Science, Sendai, Japan − Tohoku University). Il a prononcé de nombreuses conférences d'honneur : la John Taylor Lecture, lors de la réunion annuelle de l'Australian Society of Orthodontics Foundation, la Sheldon Friel Memorial Lecture lors de la réunion annuelle de l'European Orthodontic Society, la Gordon Kirkness Memorial Lecture lors de la réunion annuelle de l'Australian Society of Orthodontics, la John Mershon Memorial Lecture, Boston, Massachusetts lors de la réunion annuelle de l'American Association of Orthodontics et la Wendell L. Wylie Memorial Lecture, à l'Université de San Francisco, Californie.

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Numeric simulation model for long-term orthodontic tooth movement with contact boundary conditions using the finite element method

INTRODUCTION

Although many attempts have been made to simulate orthodontic tooth movement using the finite element method, most were limited to analyses of the initial displacement in the periodontal ligament and were insufficient to evaluate the effect of orthodontic appliances on long-term tooth movement. Numeric simulation of long-term tooth movement was performed in some studies; however, neither the play between the brackets and archwire nor the interproximal contact forces were considered. The objectives of this study were to simulate long-term orthodontic tooth movement with the edgewise appliance by incorporating those contact conditions into the finite element model and to determine the force system when the space is closed with sliding mechanics.

METHODS

We constructed a 3-dimensional model of maxillary dentition with 0.022-in brackets and 0.019 × 0.025-in archwire. Forces of 100 cN simulating sliding mechanics were applied. The simulation was accomplished on the assumption that bone remodeling correlates with the initial tooth displacement.

RESULTS

This method could successfully represent the changes in the moment-to-force ratio: the tooth movement pattern during space closure.

CONCLUSIONS

We developed a novel method that could simulate the long-term orthodontic tooth movement and accurately determine the force system in the course of time by incorporating contact boundary conditions into finite element analysis. It was also suggested that friction is progressively increased during space closure in sliding mechanics.