Effect of sinus proximity, alveolar bone level, and initial buccolingual inclination on behavior of maxillary first molar under expansion force: a finite element analysis

Biomechanical effects of periodontal status on molar sequential distalization with clear aligners: a finite element study

OBJECTIVE

Molar sequential distalization with clear aligners was advantageous. However, the effect of periodontal status on it has yet to be investigated. This study aimed to analyze the influence of the different periodontal states on molar distalization to reduce the adverse mechanical stimulation caused by periodontal states by the different stagings of movement and further explore therapeutic recommendations for clinical practice.

METHODS

To ascertain the initial displacement of dentition and periodontal ligament (PDL) hydrostatic stress, finite element models (FEMs) were developed. These models included the distalization of the second molars (Step A) and the first molar (Step B) in three distinct periodontal conditions (simulating the periodontal state of mild, moderate, and severe periodontitis) and three distinct distances (0.10 mm, 0.18 mm, 0.25 mm).

RESULTS

Periodontal status affected the tooth movement during molar distalization. During the molar distalization with 0.25 mm step distance, the initial displacement of the molar was greater in the model with worse periodontal condition. However, it did not increase the efficiency of tooth movement because the initial displacement is accompanied by tipping. Moreover, the second molar relapse to mesialization for a reaction from the first molar distalization affected efficiency. Fortunately, reducing the step distance could control those undesired tooth movements positively associated with alveolar bone resorption.

LIMITATIONS

The finite element method cannot simulate complex periodontal conditions in clinical practice.

CONCLUSION

To reduce the undesired tipping and relapse, the personalized staging of movement should be designed according to the periodontal condition. Designing 0.18 mm step distance for patients with 1/3 alveolar bone resorption is recommended, whereas patients with 1/2 alveolar bone resorption need 0.1 mm. These recommendations can guide orthodontists in designing effective treatment plans for patients with varying degrees of periodontal disease.

An expansion to the Nägerl's theory of proportionality in reduced alveolar bone height models: a 3D finite element analysis

Introduction

Orthodontic tooth movement is a basic theme in an orthodontic treatment. According to Nägerl, A nearer force application to the center of resistance will bring a farther center of rotation to the center of resistance. The main goal of this study was to evaluate this theory of proportionality by Finite element method (FEM) and find out its applicability in a bone loss situation.

Materials and methods

Three 3D FEM of an upper central incisor were designed in Solidworks 2016, the first one with a healthy bone height (model 1), with 3 mm of bone loss (model 2) and with 4.5 mm of bone loss (model 3). An 0.5 N force was applied in different predefined locations on the labial surface of the crown in model 2. This was 0.2 N for the model 3. The exact location of the center of resistance (Cres), center of rotation (Crot) for each force application point was calculated using a C++ code specially design for this study in all models.

Results

An apical shift of the Cres positions were shown in gradual steps of bone loss from 7.9708 mm incisal from the apex to 6.6292 mm in model 2 and 5.6105 mm in model 3. Modification of the location of the Crot in different force magnitudes and points of force applications were shown whit a constant a*b.

Conclusion

In healthy teeth and teeth with alveolar bone loss, Cres located in the apical third of the root. The product of the distance between the point of force application and Cres (“a”) and the Cres and Crot (“b”) is constant, thus; Nägerl theory is applicable in both healthy and reduced bone height. In this way, applying a single force nearer to the cervical point will result in a more apical location of the Crot, reducing the angle change in the long axis of the tooth.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02476-9.

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.