Biomechanical effect of dual-dimensional archwire on controlled movement of anterior teeth compared with rectangular archwire: A finite element study.

INTRODUCTION: This study aimed to determine and compare the effectiveness of the use of the dual-dimensional archwire and conventional rectangular archwire on tooth movement patterns when combined with various lengths of power arms. METHODS: Displacements of the maxillary central incisor and the deformation of the wire section were calculated when applying retraction forces from different lengths of power arms using the finite element method. RESULTS: Torque control of the incisor could be carried out more effectively when using the dual-dimensional archwire combined with long power arms than with the rectangular archwire. The use of the dual-dimensional archwire produced bodily movement of the central incisor at height levels of the power arm between 8 and 10 mm and lingual root tipping at the level of 10 mm. CONCLUSIONS: The use of the dual-dimensional archwire provided better-controlled movement of the incisor, including bodily movement or root movement, than the rectangular archwire.

Mesial or distal to canine: Which is better for the position of closing loops? Analysis of tooth movements based on numerical simulation.

INTRODUCTION: Although many studies investigating the mechanical behavior of loop mechanics have focused on loop designs to produce a higher moment-to-force ratio, few studies have clarified the effect of loop position on the force system and resultant tooth movements. This study aimed to simulate orthodontic tooth movements during space closure and to compare the effects of loop position in association with different degrees of gable bend on tooth movements using the finite element method. METHODS: Two finite element models of the maxillary dentition were constructed, with the loop placed mesial or distal to the canine. Tooth movements during loop activation were simulated while varying the degree of gable bend. RESULTS: When the loop was placed distal to the canine, the incisor showed uncontrolled tipping even with the gable bend. Placement of the loop mesial to the canine produced controlled tipping or root movement of the incisor, depending on the degree of gable bend. CONCLUSIONS: Placement of the closing loop mesial to the canine in combination with the incorporation of a gable bend into the archwire distal to the canine could provide better control of incisor movements, such as controlled tipping or root movement, as compared with placement of a gable bend into the loop located distal to the canine.

Biomechanical features of tooth movement from a lingual appliance in comparison with a labial appliance during space closure in sliding mechanics.

INTRODUCTION: The objectives of this study were to simulate long-term orthodontic tooth movement in en-masse retraction using the finite element method and investigate the effects of power arms on tooth movements when using a lingual appliance in comparison with a labial appliance. METHODS: A 3-dimensional finite element model of the maxillary dentition was constructed with 0.018-in brackets and 0.016 × 0.022-in stainless steel archwire. An en-masse retraction was performed by applying retraction force at various lengths of the power arm (4, 6, 8, and 10 mm) to the second molar tube, and long-term tooth movements with the lingual and labial appliances were analyzed using the finite element method. RESULTS: Although lingual crown tipping of the incisor was more marked with the lingual appliance than with the labial appliance in the early phase of space closure, only a slight difference was evident after space closure. Although the power arm was effective for achieving better-controlled tooth movement and reducing vertical and transverse bowing effects, bodily movement of the incisor could not be achieved, and bowing effects could not be eliminated. CONCLUSIONS: To provide better torque control of the incisor or prevent a vertical bowing effect, the incorporation of extra torque into brackets of incisors was recommended, and the use of power arms for the lingual appliance. To prevent a transverse bowing effect, incorporation of the antibowing bend or application of retraction force from both buccal and lingual sides or temporary skeletal anchorage devices was recommended.

Visualization of mandibular movement relative to the maxilla during mastication in mice: integration of kinematic analysis and reconstruction of a three-dimensional model of the maxillofacial structure.

BACKGROUND: Mastication is one of the most fundamental functions for the conservation of human life. To clarify the pathogenetic mechanism of various oral dysfunctions, the demand for devices for evaluating stomatognathic function has been increasing. The aim of the present study was to develop a system to reconstruct and visualize 3-dimensional (3D) mandibular movements relative to the maxilla, including dynamic transition of occlusal contacts between the upper and lower dentitions during mastication in mice. METHODS: First, mandibular movements with six degrees of freedom were measured using a motion capture system comprising two high-speed cameras and four reflective markers. Second, 3D models of maxillofacial structure were reconstructed from micro-computed tomography images. Movement trajectories of anatomical landmark points on the mandible were then reproduced by integrating the kinematic data of mandibular movements with the anatomical data of maxillofacial structures. Lastly, 3D surface images of the upper dentition with the surrounding maxillofacial structures were transferred to each of the motion capture images to reproduce mandibular movements relative to the maxilla. We also performed electromyography (EMG) of masticatory muscles associated with mandibular movements. RESULTS: The developed system could reproduce the 3D movement trajectories of arbitrary points on the mandible, such as incisor, molars and condylar points with high accuracy and could visualize dynamic transitions of occlusal contacts between upper and lower teeth associated with mandibular movements. CONCLUSIONS: The proposed system has potential to elucidate the mechanisms underlying motor coordination of masticatory muscles and to clarify their roles during mastication by taking advantage of the capability to record EMG data synchronously with mandibular movements. Such insights will enhance our understanding of the pathogenesis and diagnosis of oral motor disorders by allowing comparisons between normal mice and genetically modified mice with oral behavioral dysfunctions.

Simulation of orthodontic tooth movement during activation of an innovative design of closing loop using the finite element method.

INTRODUCTION: Although many attempts have been made to study the mechanical behavior of closing loops, most have been limited to analyses of the magnitude of forces and moments acting on the end of the closing loop. The objectives of this study were to simulate orthodontic tooth movement during the activation of a newly designed closing loop combined with a gable bend and to investigate the optimal loop activation condition to achieve the desired tooth movement. METHODS: We constructed a 3-dimensional model of maxillary dentition reproducing the state wherein a looped archwire combined with a gable bend was engaged in brackets and tubes. Orthodontic tooth movements were simulated for both anterior and posterior teeth while varying the degree of gable bend using the finite element method. RESULTS: The incorporation of a 5° gable bend into the newly designed closing loop produced lingual crown tipping for the central incisor and bodily movement for the first molar. The incorporation of 10° and 15° gable bends produced bodily movement and root movement, respectively, for the central incisor and distal tipping for the first molar. CONCLUSIONS: Torque control of the anterior teeth and anchorage control of the posterior teeth can be carried out effectively and simply by reducing by half the thickness of a teardrop loop with a height of 10 mm and a 0.019 × 0.025-in cross-section, to a distance of 3 mm from its apex, and by incorporating various degrees of gable bend into the loop corresponding to the treatment plan.

Dual-section versus conventional archwire for en-masse retraction of anterior teeth with direct skeletal anchorage: a finite element analysis.

BACKGROUND: The aim of this study is to compare the biomechanical effects of the conventional 0.019 × 0.025-in stainless steel archwire with the dual-section archwire when en-masse retraction is performed with sliding mechanics and skeletal anchorage. METHODS: Models of maxillary dentition equipped with the 0.019 × 0.025-in archwire and the dual-section archwire, whose anterior portion is 0.021 × 0.025-in and posterior portion is 0.018 × 0.025-in were constructed. Then, long-term tooth movement during en-masse retraction was simulated using the finite element method. Power arms of 8, 10, 12 and 14 mm length were employed to control anterior torque, and retraction forces of 2 N were applied with a direct skeletal anchorage. RESULTS: For achieving bodily movement of the incisors, power arms longer than 14 mm were required for the 0.019 × 0.025-in archwire, while between 8 and 10 mm for the dual-section archwire. The longer the power arms, the greater the counter-clockwise rotation of the occlusal plane was produced. Frictional resistance generated between the archwire and brackets and tubes on the posterior teeth was smaller than 5% of the retraction force of 2 N. CONCLUSIONS: The use of dual-section archwire might bring some biomechanical advantages as it allows to apply retraction force at a considerable lower height, and with a reduced occlusal plane rotation, compared to the conventional archwire. Clinical studies are needed to confirm the present results.

Accuracy of splint vs splintless technique for virtually planned orthognathic surgery: A voxel-based three-dimensional analysis.

PURPOSE: This study compared two transferring methods for virtually planned orthognathic surgery - the CAD/CAM intermediate splint and the customized surgical guide with fixation plates. METHODS: This was a prospective clinical study in which participants were consecutively recruited and underwent bimaxillary orthognathic surgery. They were divided into two groups based on the transferring method used. The pre- and postoperative CBCTs were aligned using voxel-based landmark-free registration, and the discrepancies for selected points were compared with the planned displacement of the virtually planned surgery. The maxilla and mandible were analyzed separately, and translation and rotation movements were considered. RESULTS: A total of 16 patients, divided into two groups of eight patients each, were included in this study. The splintless group was significantly more accurate for the translation movement along the x-axes for points A (p = 0.008; mean absolute error 0.527 ± 0.387 for the splint group and 0.137 ± 0.067 for the splintless group) and Ans (p = 0.045; mean absolute error 0.535 ± 0.446 for the splint group and 0.156 ± 0.002 for the splintless group). For the mandible there was a significant difference in accuracy along the x-axes for points B (p = 0.049; mean absolute errors 1.728 ± 1.181 and 0.697 ± 0.519 for the splint and splintless groups, respectively), LL3 (p = 0.049; mean absolute error 1.629 ± 0.912 and 0.851 ± 0.797 for the splint and splintless groups, respectively), LR3 (p = 0.049; mean absolute error 1.711 ± 0.906 and 0.844 ± 0.780 for the splint and splintless groups, respectively), with the splintless group being more accurate. For the rotation the splintless group was significantly more accurate along the y-axes (p = 0.04; mean absolute error 1.62 ± 0.78 and 0.49 ± 0.31 for the splint and splintless groups, respectively) and z-axes (p = 0.04; mean absolute error 0.63 ± 0.45 and 0.17 ± 0.05 for the splint and splintless groups, respectively) for the maxilla, while no significant difference was found for the mandible. CONCLUSIONS: Overall, the customized fixation plate system is more accurate than the intermediate CAD/CAM splint for transferring the virtual plan into the operation room.

Development and evaluation of a jaw-tracking system for mice: reconstruction of three-dimensional movement trajectories on an arbitrary point on the mandible.

BACKGROUND: Mastication is one of the most fundamental functions for the conservation of life. The demand for devices for evaluating stomatognathic function, for instance, recording mandibular movements or masticatory muscle activities using animal models, has been increasing in recent years to elucidate neuromuscular control mechanisms of mastication and to investigate the etiology of oral motor disorders. To identify the fundamental characteristics of the jaw movements of mice, we developed a new device that reconstructs the three-dimensional (3D) movement trajectories on an arbitrary point on the mandible during mastication. METHODS: First, jaw movements with six degrees of freedom were measured using a motion capture system comprising two high-speed cameras and four reflective markers. Second, a 3D model of the mandible including the markers was created from micro-computed tomography images. Then, the jaw movement trajectory on the certain anatomical point was reproduced by integrating the kinematic data of the jaw movements with the geometric data of the mandible. RESULTS: The 3D movements at any points on the mandible, such as the condyle, molar, and incisor during mastication, could be calculated and visualized with an accuracy > 0.041 mm in 3D space. The masticatory cycle was found to be clearly divided into three phases, namely, the opening, closing, and occlusal phases in mice. CONCLUSIONS: The proposed system can reproduce and visualize the movements of internal anatomical points such as condylar points precisely by combining kinematic data with geometric data. The findings obtained from this system could facilitate our understanding of the pathogenesis of eating disorders or other oral motor disorders when we could compare the parameters of stomatognathic function of normal mice and those of genetically modified mice with oral behavioral dysfunctions.

Multifunctionality in coating films including Nb-doped TiO2 and Cs x WO3: near infrared shielding and photocatalytic properties.

Various types of coating films were obtained from hydrothermally synthesized Nb-doped TiO2 (NTO) and Cs x WO3 (CWO) nanoparticles. The coating films possessed multifunctionality including near infrared (NIR) absorption and photocatalysis abilities. The NTO and CWO nanoparticles were synthesized by a unique solvothermal reaction in which water induced by an esterification reaction between alcohol and carboxylic acid can act as a hydrolyzing agent for metal precursors. NTO was synthesized by the unique solvothermal reaction for the first time. The reaction accompanied by the reduction of Ti4+ to Ti3+ led to the formation of nanoparticles with both NIR absorption and photocatalytic properties. The effect of the ethanol-acetic acid ratio on the morphology of the obtained NTO was investigated, and the larger amount of acetic acid led to a larger nanoparticle size, indicating the size controllability. The two types of coating film, including CWO and NTO nanoparticles, were obtained for comparison: (1) coexistent coating film: one side of the quartz glass was coated with a dispersion, including both CWO and NTO nanoparticles, and (2) double-sided coating film: a quartz glass coated with a CWO dispersion on one side and an NTO dispersion on the other side. The double-sided coating led to higher multifunctionality. Furthermore, the optimized condition for the double-sided coating was investigated by using various NTO particles obtained using different ethanol-acetic acid ratios.

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.

Types of tooth movement, bodily or tipping, do not affect the displacement of the tooth's center of resistance but do affect the alveolar bone resorption.

OBJECTIVE: To investigate how types of tooth movement, bodily or tipping, influence the displacement of the center of resistance in teeth and alveolar bone resorption. MATERIALS AND METHODS: Ten-week-old female Wistar rats were divided into eight groups of different factors, as follows: type of movement (bodily and tipping) and force magnitude (10, 25, 50, and 100 cN). The maxillary left first molars were moved mesially with nickel-titanium coil springs for 28 days. Micro-computed tomography (micro-CT) images were taken before and after tooth movement. The position of the center of resistance was determined by using finite element models constructed from the micro-CT image. The displacement of the center of resistance and the volume of alveolar bone resorption were measured. RESULTS: The displacement of the center of resistance showed no significant difference between the bodily and tipping groups. The displacements of the center of resistance were increased with force magnitude at 10 and 25 cN, whereas they were not further increased at 50 and 100 cN. On the other hand, cervical alveolar bone resorption was significantly greater in the tipping group than in the bodily group. CONCLUSIONS: Displacement of the center of resistance was not influenced by the types of tooth movement. However, volume of cervical alveolar bone resorption was greater in the tipping movement group than in the bodily movement group.

Innovative design of closing loops producing an optimal force system applicable in the 0.022-in bracket slot system.

INTRODUCTION: Most closing loops designed for producing higher moment-to-force (M/F) ratios require complex wire bending and are likely to cause hygiene problems and discomfort because of their complicated configurations. We aimed to develop a simple loop design that can produce optimal force and M/F ratio. METHODS: A loop design that can generate a high M/F ratio and the ideal force level was investigated by varying the portion and length of the cross-sectional reduction of a teardrop loop and the loop position. The forces and moments acting on closing loops were calculated using structural analysis based on the tangent stiffness method. RESULTS: An M/F ratio of 9.3 (high enough to achieve controlled movement of the anterior teeth) and an optimal force level of approximately 250 g of force can be generated by activation of a 10-mm-high teardrop loop whose cross-section of 0.019 × 0.025 or 0.021 × 0.025 in was reduced in thickness by 50% for a distance of 3 mm from the apex, located between a quarter and a third of the interbracket distance from the canine bracket. CONCLUSIONS: The simple loop design that we developed delivers an optimal force and an M/F ratio for the retraction of anterior teeth, and is applicable in a 0.022-in slot system.

Biomechanical aspects of segmented arch mechanics combined with power arm for controlled anterior tooth movement: A three-dimensional finite element study.

The porpose of this study was to determine the optimal length of power arms for achieving controlled anterior tooth movement in segmented arch mechanics combined with power arm. A three-dimensional finite element method was applied for the simulation of en masse anterior tooth retraction in segmented power arm mechanics. The type of tooth movement, namely, the location of center of rotation of the maxillary central incisor in association with power arm length, was calculated after the retraction force was applied. When a 0.017 × 0.022-in archwire was inserted into the 0.018-in slot bracket, bodily movement was obtained at 9.1 mm length of power arm, namely, at the level of 1.8 mm above the center of resistance. In case a 0.018 × 0.025-in full-size archwire was used, bodily movement of the tooth was produced at the power arm length of 7.0 mm, namely, at the level of 0.3 mm below the center of resistance. Segmented arch mechanics required shorter length of power arms for achieving any type of controlled anterior tooth movement as compared to sliding mechanics. Therefore, this space closing mechanics could be widely applied even for the patients whose gingivobuccal fold is shallow. The segmented arch mechanics combined with power arm could provide higher amount of moment-to-force ratio sufficient for controlled anterior tooth movement without generating friction, and vertical forces when applying retraction force parallel to the occlusal plane. It is, therefore, considered that the segmented power arm mechanics has a simple appliance design and allows more efficient and controllable tooth movement.