Effect of labiolingual inclination of a maxillary central incisor and surrounding alveolar bone loss on periodontal stress: A finite element analysis

The effects of clinical crown length on the sagittal movement of maxillary central incisor in clear aligner treatment: a finite element exploration

BACKGROUND

The mechanism of force application in clear aligner treatment involves wrapping the clinical crowns, suggesting that the size of the clinical crowns may impact tooth movement. The present finite element study aimed to explore the impact of clinical crown length on the sagittal movement of maxillary central incisor in clear aligner treatment.

METHODS

The standard maxillary dentition model was developed using computer tomography scanning. Finite element models of the maxillary dentition, alveolar bone, periodontal ligament, and aligners were established. Twelve model groups were divided based on different clinical crown lengths and attachments' position to simulated the tipping and translational movements of the right maxillary central incisor. The dimensions of the short and long clinical crowns were determined based on epidemiological evidence, and appropriate models were constructed by shortening or elongating the normal incisors by 20% along the longitudinal axis of the tooth. Horizontal rectangular attachments were constructed at the clinical crown center of the short, normal and long clinical crowns. These attachments were categorized into four types: no attachment, labial attachment, palatal attachment and labio-palatal attachments. The finite element analysis focused on evaluating the contact pressure distribution on the crown, displacements, rotations, and von Mises stress in PDL of the right maxillary central incisors.

RESULTS

In tipping movement, the long clinical crown exhibited the highest crown displacement and rotation, enhancing the efficiency. In translational movement, the long clinical crown had the lowest TL/CD value, losing less torque during the crown displacement. However, the short clinical crown had the lowest Mx/Fy value, with a greater tendency to move bodily rather than long ones. The von Mises stress distribution in PDL was similar between the two types of movement, while the maximum von Mises stress increased with increasing clinical crown lengths in tipping movement. Labio-lingual attachment had the optimal effect in tipping and translational movement.

CONCLUSIONS

Clinical crown length has considerable influences on the efficiency, movement behavior, and maximum von Mises stress of the PDL in the sagittal movement of maxillary center incisor in clear aligner treatment. Moreover, attachments also influence the movement efficiency of the incisor.

Biomechanical and Biological Multidisciplinary Strategies in the Orthodontic Treatment of Patients with Periodontal Diseases: A Review of the Literature

Orthodontic treatment aims to correct malocclusions and ensure the overall health and stability of the periodontium. The relationship between orthodontic therapy and periodontal health is intricate and multifaceted, and a comprehensive approach is often required to achieve optimal outcomes. Firstly, this article delves into the impact of orthodontic mechanics on periodontal tissues, emphasizing the importance of minimizing iatrogenic effects such as root resorption and gingival recession. Understanding the biomechanical principles allows for the development of treatment plans that mitigate these risks while achieving the desired tooth movement. Effective communication and coordinated treatment protocols are essential for managing periodontal issues before, during, and after orthodontic intervention. To optimize outcomes, periodontal considerations such as gingival biotype, attachment levels, and bone support must be integrated into treatment planning. Additionally, adjunctive periodontal therapies such as selective alveolar decortication and regenerative procedures are explored as valuable tools to enhance periodontal support and optimize treatment outcomes. This narrative review explores strategies to attain periodontal goals in orthodontic patients, thereby facilitating successful treatment. Furthermore, the review examines the role of interdisciplinary collaborations between orthodontists and periodontists. In conclusion, achieving periodontal goals in orthodontic patients requires a comprehensive approach that addresses biomechanical principles, interdisciplinary collaboration, patient education, and adjunctive periodontal therapies. By integrating periodontal considerations into orthodontic treatment planning and execution, clinicians can ensure straight teeth and a healthy and stable periodontium, ultimately leading to successful treatment outcomes and long-term oral health.

Effects of Oral Appliances for Obstructive Sleep Apnoea in Reduced Periodontium: A Finite Element Analysis

BACKGROUND AND OBJECTIVE

In the literature, no studies correlate the effects of mandibular advancement devices (MADs) with different titration systems to periodontitis. Through a finite element analysis (FEA), this study investigates the effects generated on periodontal ligaments (PDLs) and teeth by four commercial MADs in periodontal health and with 15% bone resorption.

METHODS

Four MADs (Somnodent Flex™, Somnodent Avant™, Orthoapnea™, and Herbst™) were digitalised starting from the impressions of a patient's dental arches. A force of 11.18 N, representing an advancement of 9.5 mm, was applied, and a FEA was subsequently performed. After measuring the stresses and displacements on the PDLs and teeth in healthy periodontal conditions, the vertical dimension of the alveolar bone was reduced by 15%, and measurements were repeated.

RESULTS

In terms of PDL stress, Herbst™ is the device which guarantees a more uniform increment in case of the first stage of periodontitis (+7% for mandibular and maxillary PDLs compared to the healthy condition). For Somnodent™ devices, the PDLs stress increment is almost null for mandibular PDLs but much higher than Herbst™ for maxillary PDLs (+17% and +21% for Flex™ and Avant™). Orthoapnea™ determines a PDL stress augmentation between the other devices (+16% and +7%, respectively, for maxillary and mandibular PDLs). Concerning teeth movement, Herbst™ and Orthoapnea™ determine a lower and more uniform displacement than Somnodent devices.

CONCLUSIONS

The stress distribution and teeth displacement are strictly related to MAD geometry. Since its minor effects on teeth and PDLs, the Herbst™ could be more appropriate in patients with periodontitis.

Biomechanical Considerations in the Orthodontic Treatment of a Patient with Stabilised Stage IV Grade C Generalised Periodontitis: A Case Report

Orthodontic treatment of periodontally compromised patients presents unique challenges, including controlling periodontal inflammation, applying appropriate force, designing an effective dental anchorage, and maintaining treatment results. Deteriorated periodontal support leads to alterations in the biological responses of teeth to mechanical forces, and thus orthodontists must take greater care when treating patients with periodontal conditions than when treating those with a good periodontal status. In this article, we report the case of a 59-year-old woman with stabilised Stage IV grade C generalised periodontitis characterised by pathological tooth migration (PTM). The assessment, planning, and treatment of this patient with orthodontic fixed appliances is described. Moreover, the anchorage planning and biomechanical considerations are detailed. Specific orthodontic appliances were employed in this case to produce force systems for achieving precise tooth movement, which included a cantilever, mini-screws, and a box loop. Careful application of those appliances resulted in satisfactory aesthetic and functional orthodontic outcomes in the patient. This case highlights the importance of multidisciplinary collaboration in the treatment of patients with severe periodontitis and the potential for tailored biomechanical approaches in orthodontic treatment to furnish good outcomes.

The Hydrostatic Pressure Distribution in the Periodontal Ligament and the Risk of Root Resorption-A Finite Element Method (FEM) Study on the Nonlinear Innovative Model

Excessive orthodontic force can induce inflammatory tooth root resorption due to sustained high stresses within the periodontal ligament (PDL). This study aimed to analyze the PDL pressures during upper incisor retraction using the en masse method with TISAD. The finite element method (FEM) ensured consistent conditions across cases. The models included bone geometry, adjacent teeth, PDL, and orthodontic hardware, analyzed with LS-Dyna. The pressure ranged from 0.37 to 2.5 kPa across the dental arch, with the central incisors bearing 55% of the load. The pressure distribution remained consistent regardless of the force or hook height. The critical pressure (4.7 kPa) was exceeded at 600-650 g force, with notable pressure (3.88 kPa) on the palatal root wall of the right central incisor. Utilizing 0.017 × 0.025 SS archwires in MBT 0.018 brackets provided good torque control and reduced the root resorption risk when forces of 180-200 g per side were applied, maintaining light to moderate stress. Triple forces may initiate resorption, highlighting the importance of nonlinear finite element analysis (FEA) for accurate oral cavity simulations.

Precautions and possibilities in orthodontic treatment of periodontally compromised patients: Current recommendations

OBJECTIVE

Orthodontic treatment plays a crucial role in achieving optimal dental esthetics and functional occlusion. However, when periodontally compromised patients are involved, additional precautions and considerations are critical. This article aims to provide up-to-date recommendations for the orthodontic treatment of periodontally compromised patients.

CLINICAL CONSIDERATIONS

Comprehensive diagnosis of the patient's periodontal status, inherent malocclusion, and secondary malocclusion resulting from periodontal disease are essential for achieving optimal esthetics and functional occlusion. This can be facilitated through the use of a simplified checklist. Prior to orthodontic treatment, pre-existing periodontal diseases should be managed. Light and controlled forces should be used to minimize the risk of adverse effects on the periodontium, and any potential traumatic occlusion during tooth movement should be minimized. Furthermore, careful anchorage management is required, and proper application of temporary anchorage devices can significantly expand the scope of orthodontic treatment. Finally, treatment results are maintained by ongoing supportive periodontal therapy even during the retention period.

CONCLUSIONS

This article presents clinical cases demonstrating the importance of accurate diagnosis in orthodontics and periodontics and the positive impact of orthodontic treatment on patients with pre-existing periodontal diseases.

CLINICAL SIGNIFICANCE

An up-to-date orthodontic treatment protocol for periodontally compromised patients is presented.

Factors affecting the maxillary and mandibular incisors' buccolingual inclinations and buccal and lingual cortical plate heights

INTRODUCTION

Orthodontics is closely related to periodontics. The buccolingual inclination (BLI) of the incisors and deficiencies in their buccal (BHd) and lingual (LHd) cortical plate heights may affect orthodontic outcomes. Identifying risk factors that can compromise buccal or lingual bone heights may have clinical value. The literature on BLI/BHd/LHd is not only scarce but also limited to one jaw. We aimed to examine, for the first time, factors affecting BLI/BHd/LHd not evaluated before as well as other factors with scarce literature about them.

METHODS

In this two-phase epidemiological and analytical study, inclinations and cortical heights of 248 incisors (bilateral centrals and laterals) were evaluated blindly on 62 randomly selected high-resolution pretreatment cone-beam computed tomography volumes (30 maxillae [13 men, 17 women], 32 mandibles [13 men, 19 women]). The sample was balanced in terms of sexes, jaws, and ages. The BLI/BHd/LHd of bilateral incisors were measured (intraobserver agreement > 95%). The effects of jaws, sexes, age, sides, and incisor types on each of the anatomical variables (BLI/BHd/LHd) were analyzed using a Mixed-Model Multiple Linear Regression analysis. Correlations among continuous variables were assessed using a Pearson coefficient (α = 0.05).

RESULTS

For the maxillary centrals, BLI, BHd, and LHd were 106.79 ± 5.06, 1.94 ± 0.95, and 1.50 ± 0.76, respectively. These parameters were '110.56 ± 5.97, 1.81 ± 0.83, 1.23 ± 0.69' for the maxillary laterals; '97.64 ± 8.26, 2.98 ± 1.48, 3.46 ± 1.45' for the mandibular centrals; and '95.98 ± 6.80, 3.29 ± 1.72, and 2.73 ± 1.15' for the mandibular laterals. BLI was greater in the maxilla compared to the mandible and in the lateral incisors compared to centrals (P < 0.05). BHd was greater (more deficient) in the mandible (P = 0.000). Age, sex, or side were not associated with BLI (P > 0.05). Age, sex, side, or incisor types were not associated with BHd (P > 0.05). LHd was greater in the mandible, older individuals, and centrals (P < 0.05). There were some significant but weak correlations between BLI with BHd and especially LHd (P < 0.05).

CONCLUSION

In the maxilla, but not in the mandible, incisors' BLI may determine LHd. Maxillary incisors may have greater BLIs as well as greater buccal and lingual alveolar bone heights compared to mandibular incisors. BLI might be greater in the laterals compared to the centrals in both jaws combined.

3D Finite Element Study of the Physiological Anchorage Control Concept on Anchorage Molars in Lingual Orthodontics

Objective. To study the effect of the physiological anchorage control concept on anchorage molars in lingual and labial orthodontic techniques. Methods. Three-dimensional finite element models, including the right maxillary first molar, periodontal ligament, alveolar bone, and buccal tube, were established. The models were divided into the McLaughlin–Bennett–Trevisi (MBT™) straight-wire model with 0-degree maxillary first molar axial inclination and the physiologic anchorage Speewire system (PASS) model with −7-degree maxillary first molar axial inclination. Simulated sliding retraction forces (1 N, 1.5 N, and 2 N) were loaded on the buccal side and lingual side, and retraction forces (0.5 N, 0.75 N, and 1 N) were loaded on the buccal and lingual sides simultaneously. The displacements, principal stresses, and von Mises stresses of the periodontal ligament under different conditions were derived. Results. The anchorage molars showed different degrees of rotation, tipping, intrusion, and extrusion. As the force increased, these displacement trends also increased. The mesial displacement of the buccal + lingual force loading was less than that of the other two groups. Under the same force load method, the mesial displacement of the PASS group was less than that of the MBT group. Tilt movement increases the tensile stress of the distal cervical margin and root mesial apical third and the compressive stress of the mesial cervical margin and root distal apical third. The maximum stress of the periodontal ligament was less than that of the other two groups when the lingual force was loaded. Conclusion. The physiological anchorage control concept in lingual orthodontics provides better sagittal anchorage control than in labial orthodontics, but there is no significant difference numerically. Attention should be given to the control of torsion, torque, and arch width. Tilt movement increases the PDL stress of the cervical margin and root apical third. The sliding retraction force should be loaded lingually to maintain the force value of 1∼1.5 N.

Change in crown inclination accompanying initial tooth alignment with round archwires

OBJECTIVE

To evaluate, in-vitro, the change in crown inclination that occurs during orthodontic leveling and alignment using different archwire-bracket-ligation combinations.

MATERIALS AND METHODS

Four archwire types were tested: (1) 0.012-in stainless steel and (2) 0.0155-in stainless steel multi-stranded, (3) 0.012-in nitinol Orthonol® and (4) 0.012-in nitinol Thermalloy®. Combinations with five types of 0.022-in slot orthodontic brackets were tested: SmartClipTM and Time3® self-ligating brackets, Mini-Taurus® and Victory SeriesTM conventional brackets, and Synergy® conventional-low friction bracket. Conventional brackets were ligated with both stainless steel and elastomeric ligatures. The simulated malocclusion comprised 2.0mm gingival and 2.0mm labial displacements of a maxillary right central incisor. Rotation around the Y-axis (representing labio-palatal inclination) was measured for the different archwire-bracket-ligation combinations.

RESULTS

The largest rotation was measured whith Orthonol® and Thermalloy® wires when combined with SmartClipTM brackets (8.07±0.24º and 8.06±0.26º, respectively) and with Synergy® brackets ligated with stainless steel ligatures (8.03±0.49º and 8.0±0.37º, respectively). The lower rotation was recorded when Thermalloy®, multi-stranded, and Orthonol® wires were ligated with elastomeric rings to Mini-Taurus® brackets (1.53±0.18º, 1.65± 0.23º and 1.70±0.28º, respectively) and to Victory SeriesTM brackets (1.68± 0.78º, 2.92± 1.40º and 1.74±0.46º, respectively).

CONCLUSIONS

All archwire-bracket-ligation combinations produced lingual crown inclination; however, lower changes were observed when the conventional brackets were ligated with elastomeric rings. The multi-stranded archwire produced less rotation with nearly every bracket-ligation combination, compared to the other archwires. The effect of the archwire-bracket-ligation combination on tooth inclination during leveling and alignment should be considered during planning treatment mechanics.

Conservative orthodontic treatment for severe pathologic migration following total glossectomy: A case report

Glossectomy combined with radiotherapy causes different levels of tongue function disorders and leads to severe malocclusion, with poor periodontal status in cancer survivors. Although affected patients require regular access to orthodontic care, special considerations are crucial for treatment planning. This case report describes the satisfactory orthodontic management for the correction of severe dental crowding in a 43-year-old female 6 years after treatment for tongue cancer with total glossectomy combined with radiotherapy, to envision the possibility of orthodontic care for oral cancer survivors. Extraction was performed to correct dental crowding and establish proper occlusion following alignment, after considering the possibility of osteoradionecrosis. Orthodontic mini-implants were used to provide skeletal anchorage required for closure of the extraction space and intrusion of the anterior teeth. The dental crowding was corrected, and Class I occlusal relationship was established after 36 months of treatment. The treatment outcome was sustained after 15 months of retention, and long-term follow-up was recommended.

To Compare the Stress Magnitude on Roots of Mandibular Incisors at Different Inclinations With Different Arch Wires During Intrusion Mechanics—A Fem Study

Introduction:

Force is applied through brackets in fixed mechanotherapy which generates stress in periodontal ligament and root of the teeth and is difficult to measure directly. Finite element analysis is used as a solution for understanding this biomechanical response. So the aims and objectives of this study were to evaluate the stress magnitude induced in the labial and lingual surface of mandibular incisors using superelastic NiTi arch wires of different cross-section at different inclination through finite element analysis.

Materials and Methods:

Finite element model of all mandibular teeth including periodontal ligament, alveolar bone, buccal tubes, brackets, and arch wire were constructed using mechanical elastic properties of the materials. Three different NiTi arch wires, round (0.016″), square (0.016″ × 0.016″), and rectangular (0.016″ × 0.022″), were placed into the bracket slots and models were constructed which were analyzed for stress distribution on root surface and periodontal ligament with 3 different cross-sections at 90°, 100°, and 110° with Ansys Version 14 software.

Conclusion:

Labial stress was found highest in round arch wire as compared to square and rectangular wire. Lingual stress was found to be slightly more in rectangular wire as compared to round and square arch wire.

Orthodontically induced root resorption: A critical analysis of finite element studies' input and output

INTRODUCTION

Orthodontically induced inflammatory root resorption (OIIRR) constitutes an undesirable risk connected to orthodontic treatment. Finite element analysis (FEA) is a powerful tool to study the risk of OIIRR. However, its efficiency in predicting OIIRR depends on the insertion of the correct inputs and the selection of an output coherent with the clinical failure mechanism.

METHODS

By combining a systematic review with a 3-dimensional FEA, this article discusses which are the implications of using certain periodontal ligament (PDL) properties (linear and nonlinear models) and failure criteria. Six orthodontic loading regimes were simulated in a maxillary premolar: pure intrusion, buccal tipping, and their combination applied with either a light (25 cN) or a heavy (225 cN) force. Three stress parameters in the PDL were compared: von Mises stress, minimum principal stress_, and hydrostatic stress (σ_H).

RESULTS

The comparison between linear and nonlinear models showed notable differences in stress distribution patterns and magnitudes. For the nonlinear PDL, none of the light-force models reached the critical compressive hydrostatic stress of 4.7 kPa, whereas all the heavy-force models reached it. In addition, the regions of critical compressive σ_H matched with the regions with resorption craters in clinical studies. In linear models, the σ_H critical value of 4.7 kPa was reached even in the light-force scenario.

CONCLUSIONS

Only compressive hydrostatic stress in PDL satisfied the requirements to be used as an FEA indicator of OIIRR. However, the requirements were satisfied only when a nonlinear PDL model was considered.

Orthodontic treatment of periodontal patients: challenges and solutions, from planning to retention

Introduction:

There is an increasing number of adult patients with sequelae of periodontal diseases seeking orthodontic treatment to improve their occlusion and quality of life. However, it is important to highlight that the patient who has vertical bone loss has unique needs, arising from the frequent related pathological migrations. Therefore, it requires an individualized orthodontic treatment in terms of anchorage, biomechanics, and multidisciplinary planning, which raises doubts in the hierarchy of priorities and organization of the treatment plan.

Objectives:

It was proposed a stratified hierarchy of the needs of orthodontic-periodontal treatment in six levels, which were illustrated with examples of clinical cases in which biomechanical planning and a multidisciplinary approach made it possible to obtain a balanced occlusion, aesthetic improvement and stabilization of the results.

Conclusion:

Orthodontic treatment of periodontal patients with a multidisciplinary approach is increasingly frequent and should be planned individually, considering bone losses suffered by each patient. Respecting some limitations, it is possible to improve the level of bone insertion, smile aesthetics and masticatory function, to facilitate oral hygiene through the orthodontic treatment of adult patients with little bone support. It is also important to highlight that there are unique aspects in the orthodontic retention in these cases.

Prosthetic Correction of Proclined Maxillary Incisors: A Biomechanical Analysis

In some cases of proclined maxillary incisors, the proclination can be corrected by a fixed prosthesis. The aim of this study was to investigate the magnitude and distribution of (i) principal stresses in the adjacent alveolar bone and (ii) direct and shear stresses that are normal and parallel, respectively, to the bone-tooth interface of a normal angulated maxillary incisor, a proclined one, and a proclined one corrected with an angled prosthetic crown. 2D finite-element models were constructed, and a static load of 200 N on the palatal surface of the maxillary incisor at different load angles was applied. Load angles (complementary angle to interincisal angle) ranging from 20° to 90° were applied. The results indicate that the load angle could have a more significant impact on the overall stress distributions in the surrounding alveolar bone and along the bone-tooth interface than the proclination of the maxillary incisor. Provided that the resulting interincisal angle is 150° or smaller, the stresses in the surrounding bone and at the bone-tooth interface are similar between a proclined maxillary incisor and the one with prosthodontic correction. Hence, such a correction, when deemed appropriate clinically, can be undertaken with confidence that there is little risk of incurring additional stresses over that already in existence, in the supporting bone and at the tooth-bone interface.

Influence of bone loss and inclination of incisor on periradicular stresses due to simulated bite force

Abstract Introduction Adults with sequelae of periodontal disease tend to have bone loss, with consequent flaring of the maxillary incisors. Objective The influence of bone loss and the inclination of the maxillary incisor in the distribution of stresses due to simulated bite forces was studied. Material and method Models in epoxy resin were made in three conditions (without bone loss and with bone loss of 5mm and 8mm). Increases in the labial inclination of the maxillary incisor of 10° and 20° were obtained with a beveled metallic block. Loads of 100N were applied five times in each condition using a universal test machine. The models were observed and filmed with a circular polariscope. Orders of isochromatic fringes (stresses) on the labial, lingual, and apex surfaces were recorded. The agreement of the data was evaluated using the weighted kappa test, and the results were 0.89 and 0.82 for intra- and inter-examiners, respectively. Result The results of the Kruskal–Wallis and SNK tests indicated higher stresses (2.0) with increased labial inclination in the labial surface; higher stresses (2.67) with increased bone loss; higher greater stresses with the association of bone loss and labial-inclination (3.6); and the highest stresses tended to concentrate on the labial surfaces, except in cases of normal inclination and without bone loss (0.45). Conclusion It was concluded that increases in both the labial inclination of the maxillary incisors and bone loss increase periradicular stresses, and the combination of these factors further increases the stresses due to bite forces, with the highest concentration on the labial side.

Facemask performance during maxillary protraction: a finite element analysis (FEA) evaluation of load and stress distribution on Delaire facemask

BACKGROUND

To evaluate load and stress distribution on Delaire facemask (FM) during maxillary protraction in class III growing patients by means of finite element analysis (FEA). A three-dimensional geometry of a Delaire FM was reconstructed from the original CAD 3D prototype, using software package (ANSYS 5.7). FM presented forehead and chin supports and stainless steel framework characterized by two lateral vertical bars connected to a crossbar with two pawls for elastic attachment. Two traction intensities (7.8 and 9.8 N) were applied on the FM pawls along three different downward inclined directions with respect to the occlusal plane (0°, 30°, or 50°, respectively). Resulting stresses and deformations were then tested through the von Mises yield criterion in order to underline the FM wear performance.

RESULTS

The analysis showed that higher stresses and deformations are mostly related to axial forces of 9.8 N rather than 7.8 N. Stresses also progressively increased with increasing downward force inclinations (0°, 30°, and 50° with respect to the occlusal plane). The overall tensions were inferior to the limit of the elastic behavior (yield point) characterizing the material they are applied on. Thus, the FM structure absorbed the load applied with an elastic deformation of the lateral and horizontal bars.

CONCLUSIONS

Resulting stresses and deformations were directly proportional to protraction load amounts and to increasing downward inclination of forces. In all tested conditions, protraction forces were not able to determine plastic deformation on FM structure compromising its performance and efficiency.

Wide Linear Corticotomy and Anterior Segmental Osteotomy Under Local Anesthesia Combined Corticision for Correcting Severe Anterior Protrusion With Insufficient Alveolar Housing

BACKGROUNDS

This article presents an alternate surgical treatment method to correct a severe anterior protrusion in an adult patient with an extremely thin alveolus. To accomplish an effective and efficient anterior segmental retraction without periodontal complications, the authors performed, under local anesthesia, a wide linear corticotomy and corticision in the maxilla and an anterior segmental osteotomy in mandible.

METHODS

In the maxilla, a wide linear corticotomy was performed under local anesthesia. In the maxillary first premolar area, a wide section of cortical bone was removed. Retraction forces were applied buccolingually with the aid of temporary skeletal anchorage devices. Corticision was later performed to close residual extraction space. In the mandible, an anterior segmental osteotomy was performed and the first premolars were extracted under local anesthesia.

RESULTS

In the maxilla, a wide linear corticotomy facilitated a bony block movement with temporary skeletal anchorage devices, without complications. The remaining extraction space after the bony block movement was closed effectively, accelerated by corticision. In the mandible, anterior segmental retraction was facilitated by an anterior segmental osteotomy performed under local anesthesia. Corticision was later employed to accelerate individual tooth movements.

CONCLUSIONS

A wide linear corticotomy and an anterior segmental osteotomy combined with corticision can be an effective and efficient alternative to conventional orthodontic treatment in the bialveolar protrusion patient with an extremely thin alveolar housing.

Finite-element analysis of the center of resistance of the mandibular dentition

Objective

The aim of this study was to investigate the three-dimensional (3D) position of the center of resistance of 4 mandibular anterior teeth, 6 mandibular anterior teeth, and the complete mandibular dentition by using 3D finite-element analysis.

Methods

Finite-element models included the complete mandibular dentition, periodontal ligament, and alveolar bone. The crowns of teeth in each group were fixed with buccal and lingual arch wires and lingual splint wires to minimize individual tooth movement and to evenly disperse the forces onto the teeth. Each group of teeth was subdivided into 0.5-mm intervals horizontally and vertically, and a force of 200 g was applied on each group. The center of resistance was defined as the point where the applied force induced parallel movement.

Results

The center of resistance of the 4 mandibular anterior teeth group was 13.0 mm apical and 6.0 mm posterior, that of the 6 mandibular anterior teeth group was 13.5 mm apical and 8.5 mm posterior, and that of the complete mandibular dentition group was 13.5 mm apical and 25.0 mm posterior to the incisal edge of the mandibular central incisors.

Conclusions

Finite-element analysis was useful in determining the 3D position of the center of resistance of the 4 mandibular anterior teeth group, 6 mandibular anterior teeth group, and complete mandibular dentition group.