Anchorage effects of ligation and direct occlusion in orthodontics: A finite element analysis

Biomechanical analysis of maxillary first molar intrusion using 3D printed personalized device combined with clear aligner: a finite element study and clinical application

OBJECTIVES

The aim of this study is to compare the biomechanical effects of maxillary first molar intrusion using the fixed appliance, microimplant, and clear aligner with or without 3D printed personalized device, and to demonstrate the effect of this device through a relevant clinical case.

METHODS

A clinical patient with an overerupted maxillary molar was selected to construct a patient-oriented three-dimensional model of the four intrusion patterns. The initial displacement of the teeth and the stress distribution of the PDL were compared. The 3D printed personalized device was used in this case, and the data of the case was collected to assess the therapeutic effect.

RESULTS

The side effects of target tooth tilt and adjacent tooth displacement were obvious in fixed appliance and clear aligner, while the side effects were smaller in 3D printed personalized device, and the intrusion efficiency is slightly higher than that of microimplant. In clinical practice of 3D printed personalized device, a favorable intrusion effect was achieved.

CONCLUSIONS

The 3D printed personalized device had relatively high intrusion efficiency and stress relaxation on the target tooth and reduced the displacement and stress concentration on the anchorage teeth to a certain extent.

CLINICAL RELEVANCE

In clinical practice, clear aligner with 3D printed personalized device has a good therapeutic effect on molar intrusion.

Measurement of the root surface area in rat molars through three-dimensional modeling

OBJECTIVES

Rats are used as animal models for basic and applied research related to orthodontic tooth movement (OTM). The magnitude of mechanical force in OTM rat models mainly depends on the supporting capability of the periodontal ligament (PDL), which is highly associated with the root surface area (RSA). But the size of rat RSA remains unknown, which is the reason why there are still debates on the magnitude of mechanical force in OTM rat models. This study aimed to explore a method for measuring the RSA in rat molars.

DESIGN

The maxillary and mandibular samples of rats were scanned by Micro-CT to generate three-dimensional (3D) images, followed by 3D reconstruction of every molar through Mimics Medical 21.0. Geomagic Wrap 2021 and Unigraphics NX 12.0 were utilized to smooth teeth surface and mark the cementoenamel junction (CEJ). Finally, the RSA in rat molars was measured.

RESULTS

The results showed that for the six-, eight-, or ten-week-old rats, the average RSA of maxillary first, second, and third molars was 25.90 ± 2.29 mm2, 15.92 ± 2.14 mm2, and 10.34 ± 1.94 mm2. The RSA of mandibular first, second, and third molars was 27.03 ± 2.63 mm2, 17.16 ± 1.61 mm2, and 11.39 ± 2.13 mm2.

CONCLUSIONS

Through 3D modelling, we provided data of rat RSA, and observed the trend of increasing RSA mean values with age. These data are pivotal for determining the magnitude of mechanical force required to move rat molars, especially when conducting research related to OTM using rat models.

Root-crown Ratio of Maxillary and Mandibular Anterior Permanent Teeth in Yemeni Adults using CBCT

AIM

To assess the root-crown ratio (RCR) of maxillary and mandibular anterior permanent teeth from cone-beam computed tomography (CBCT) acquired from a sample of Yemeni adults.

MATERIALS AND METHODS

This was a retrospective radiographic observational cross-sectional study. The study included 233 CBCTs. Root length, crown length, and RCR of all anterior teeth were measured using Ez-3Di software. Factors considered for correlation included gender differences, skeletal classifications (class I, II, and III), overjet (OJ), and overbite (OB). The data were entered and analyzed using the Statistical Package for the Social Sciences software. Significance was set at a value of p < 0.05.

RESULTS

Mean RCR of maxillary and mandibular anterior teeth ranged between 1.2 and 1.3 for central incisors, 1.3 and 1.4 for lateral incisors, and 1.5 and 1.6 for canines. The length of roots and crowns was generally greater in males, except for the mean crown length of the left mandibular central incisor. Class III participants exhibited the longest root length for maxillary and mandibular canines, 15.75 and 14.7 mm, respectively, compared with class I and II participants. Participants with increased OJ (>4 mm) showed the lowest root and crown lengths in all canines and lateral incisors while displaying the highest root length in all central incisors. However, no statistically significant variances were observed in root length and the RCR (p > 0.05). Those with a deep bite had the longest roots for maxillary lateral and central incisors and the shortest roots for maxillary canines. In contrast, participants with an open bite displayed the opposite measurements.

CONCLUSIONS

Gender differences in RCR were insignificant except for the mandibular right central incisor. No significant differences were observed among the three skeletal classes in all study parameters. Furthermore, RCR variations based on OJ and OB were not statistically significant, except for the mandibular left lateral incisor in relation to OB.

CLINICAL SIGNIFICANCE

Understanding RCR variations supports clinicians in treatment planning, especially in anchorage selection, force application, and predicting treatment outcomes. This knowledge is important for minimizing potential complications and improving treatment effectiveness in various orthodontic cases. How to cite this article: Alhaidary SA, Al-Haddad KA, Al-Harazi GA, et al. Root-crown Ratio of Maxillary and Mandibular Anterior Permanent Teeth in Yemeni Adults using CBCT. J Contemp Dent Pract 2024;25(12):1118-1126.

The crucial role of periodontal ligament's Poisson's ratio and tension-compression asymmetric moduli on the evaluation of tooth displacement and stress state of periodontal ligament

The hydrostatic stress in the periodontal ligament (PDL) evaluated by finite element analysis is considered an important indicator for determining an appropriate orthodontic force. The computed result of the hydrostatic stress strongly depends on the PDL material model used in the orthodontic simulation. This study aims to investigate the effects of PDL Poisson's ratio and tension-compression asymmetric moduli on both the simulated tooth displacement and the PDL hydrostatic stress. Three tension-compression symmetric and two asymmetric PDL constitutive models were selected to simulate the tensile and compressive behavior of a PDL specimen under uniaxial loading, and the resulting numerical results were compared with the in-vitro PDL experimental results reported in the literature. Subsequently, a tooth model was established, and the selected constitutive models and parameters were employed to assess the hydrostatic stress state in the PDL under two distinct loading conditions. The simulated results indicate that PDL Poisson's ratio and tension-compression asymmetry exert substantial influences on the simulated PDL hydrostatic stress. Conversely, the elastic modulus exhibits minimal impact on the PDL stress state under the identical loading conditions. Furthermore, the PDL models with tension-compression asymmetric moduli and appropriate Poisson's ratio yield more realistic hydrostatic stress. Hence, it is imperative to employ suitable Poisson's ratio and tension-compression asymmetric moduli for the purpose of characterizing the biomechanical response of the PDL in orthodontic simulations.

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.

Efficacy of a four-curvature auxiliary arch at preventing maxillary central incisor linguoclination during orthodontic treatment: a finite element analysis

BACKGROUND

Correct torque of the incisors is beneficial in the assessment of the effects of orthodontic treatment. However, evaluating this process effectively remains a challenge. Improper anterior teeth torque angle can cause bone fenestrations and exposure of the root surface.

METHODS

A three-dimensional finite element model of the maxillary incisor torque controlled by a homemade four-curvature auxiliary arch was established. The four-curvature auxiliary arch placed on the maxillary incisors was divided into four different state groups, among which 2 groups had tooth extraction space retracted traction force set to 1.15 N. Initial displacements and pressure stresses of the periodontal tissue in the maxillary incisors and molars were calculated after torque forces (0.5, 1, 1.5, and 2 N) were applied to the teeth at different stable states.

RESULTS

The effect of using the four-curvature auxiliary arch on the incisors was significant but did not affect the position of the molars. Given the absence of tooth extraction space, when the four-curvature auxiliary arch was used in conjunction with absolute anchorage, the recommended force value was < 1.5 N. In the other 3 groups (i.e., molar ligation, molar retraction, and microimplant retraction groups), the recommended force value was < 1 N. The application of a four-curvature auxiliary arch did not influence the molar periodontal and displacement.

CONCLUSION

A four-curvature auxiliary arch may treat severely upright anterior teeth and correct cortical fenestrations of the bone and root surface exposure.