Apical force distribution due to orthodontic forces: a finite element study

Overall stress in periodontal ligament under orthodontic movement during a periodontal breakdown

INTRODUCTION

This research aimed to assess qualitatively and quantitatively the overall stress in the periodontal ligament during gradual periodontal breakdown (0-8 mm) under orthodontic movements. Correlations between the applied forces, the level of bone loss, the decrease of force magnitude, and the increase of stress were also assessed.

METHODS

On the basis of cone-beam computed tomography examinations (voxel size, 0.075 mm), nine 3-dimensional models of a mandibular second premolar with intact periodontium were created and then individually subjected to various levels of horizontal bone loss. Orthodontic forces (intrusion at 0.2 N; extrusion, rotation, and tipping at 0.6 N; translation at 1.2 N) were applied on the brackets. Finite elements analysis was performed, and von Mises (VM) stresses were quantitatively and qualitatively determined.

RESULTS

Rotation and translation induced the highest stress apically and cervically, whereas intrusion determined the lowest. Apical stress was lower than cervical stress. In intact periodontium, VM stress was under maximum hydrostatic pressure (MHP) and maximum tolerable stress (MTS). In reduced periodontium, VM stress was lower apically than MHP, whereas cervically, the rotation, translation, and tipping exceeded MHP.

CONCLUSIONS

A force of 1.2 N seemed safe to be used in the intact periodontium. Forces higher than 0.6 N could produce stresses exceeding MHP and MTS endangering the reduced periodontium. VM stress failure criterion (despite its limited use) seemed to be more adequate for accurate quantitative results. An overall correlation between the applied force, VM stress increase, and periodontal breakdown applicable to all 5 movements could not be established. This was possible only for individual movements.

Compressive stress in periodontal ligament under orthodontic movements during periodontal breakdown

INTRODUCTION

This analysis aimed to assess quantitatively and qualitatively the compressive stress (S3) in periodontal ligament in a gradual periodontal breakdown (0-8 mm) under orthodontic movements. Correlations between the applied forces, the level of bone resorption, the decrease of force magnitude, and S3 increase were also conducted.

METHODS

On the basis of cone-beam computed tomography examinations (voxel size, 0.075 mm), nine 3-dimensional models of the second mandibular premolar with intact periodontium were created and then individually subjected to various levels of horizontal bone loss. Orthodontic forces (intrusion: 0.2 N; extrusion, rotation, tipping: 0.6 N; translation: 1.2 N) were applied on the brackets. Finite elements analysis was performed, and S3 stresses were quantitatively and qualitatively determined.

RESULTS

Translation and rotation induced the highest stress apically and cervically, whereas intrusion determined the lowest. Apical stress was lower than cervical stress. In intact periodontium, only intrusion and extrusion exhibited S3 stresses lower (apically and cervically) than maximum hydrostatic pressure (MHP) and maximum tolerable stress (MTS). In reduced periodontium, S3 stress (except for intrusion) exceeded MHP and MTS.

CONCLUSIONS

In reduced periodontium, forces of 0.2 N seems safe to be used. Forces of 0.6-1.2 N may produce stresses exceeding both MTS and MHP, endangering the periodontium. S3 failure criterion (despite its widely use) seems not to be adequate for accurate quantitative results when evaluating the stress in the periodontal ligament while remaining adequate for qualitative results. An overall correlation between the applied force, S3 increase, and periodontal breakdown applicable to all 5 movements could not be established-this was possible only for sole movements.

Determination of stress distribution on periodontal ligament and alveolar bone by various tooth movements - A 3D FEM study

Aim

The purpose of this study was to evaluate the stress distribution on the maxillary central incisors by various tooth movements using three-dimensional finite element modeling with varying periodontal ligament (PDL) thickness and different alveolar bone height (at the apex and alveolar crest).

Material and methods

A Finite Element Modeling model was created using surface data of the tooth using SolidWorks Software. Different types of force (intrusion, extrusion, tipping, and bodily movement) were applied on the maxillary central incisor, with two different periodontal ligament thickness (0.15 mm and 0.24 mm) and alveolar bone height (at the apex and alveolar crest). Stress generated due to force applied due to different types of tooth movement was calculated and compared.

Results

Maximum stresses generated under intrusion, extrusion, tipping, bodily movement were 9.0421 E^-003 N/mm² for 0.15 mm pdl at alveolar bone, 7.2833 E^-5 N/mm²for 0.24 mm pdl labio-lingually, 9.1792 E^-002 N/mm² at 0.15 mm pdl at alveolar bone height and 6.2208 E^-6 N/mm² for 0.24 mm pdl at alveolar crest respectively.

Conclusion

The stress pattern seen was nearly the same in all the cases in both PDL thickness. The maximum stress pattern was found to be at the apex of the central incisor, reducing from apex to the cervical region. Intrusion, extrusion, and tipping movement showed the greatest amount of relative stress at the apex of the maxillary central incisor. The bodily movement produced forces at root apex and distributed it all over.

Correlation between Dental Vestibular-Palatal Inclination and Alveolar Bone Remodeling after Orthodontic Treatment: A CBCT Analysis

The aim of this study was to evaluate the correlation between dental vestibular-palatal inclination changes and the cortical bone remodeling after fixed orthodontic treatment using cone beam computed tomography (CBCT). Twenty-two patients with Angle Class I malocclusion, permanent dentition, and mild to moderate dental crowding were included in the present three-dimensional (3D) analysis. Bone dimensions were evaluated by CBCT scans obtained before and after orthodontic treatment, whereas the torque values were calculated by means of digital models using the 3D VistaDent software. A paired t-test was used to compare the changes between the pretreatment and post-treatment measurements. The correlations between variables were analyzed with linear regression analysis. A significant correlation between torque variations and bone thickness changes was observed for the apical buccal level of the anterior side (P < 0.05). Limited and not significant alveolar bone resorption for the apical thickness of anterior teeth occurred at ± 5 degrees of torque variation, while for tooth inclination exceeding +5 or -5 degrees, the bone remodeling was more evident. The present study demonstrated that anterior region was the most affected area by bone remodeling and that torque variation was highly related to apical bone thickness adaptation for maxillary and mandibular incisors and maxillary canines.