Biomedical subjects

Mitsuru Motoyoshi

Publications and source records attributed to Mitsuru Motoyoshi.

11 recordsLinked to original sources

PubMed2006

Effects of root morphology on stress distribution at the root apex.

It is thought that the stress concentration at the root apex caused by orthodontic force induces root resorption. The purpose of this study was to investigate stress distribution at the root in cases of deviated root shapes using finite element models (FEMs). To clarify this, five three-dimensional FEMs divided by deviated root shape (normal, short, blunt, bent root apex, pipette shape) were constructed and, experimental orthodontic forces, applied in a vertical (intrusive) and horizontal (lingual) direction to the tooth axis. In the short-root model, significant stress was concentrated at the middle of the root. The blunt-shaped root model showed no significant stress concentration at the root. In the models with a bent or pipette-shaped root, significant stress was concentrated at the root apex. During orthodontic force application, stress concentration was observed in the root of the models with short, bent, and pipette-shaped roots, indicating that attention must be paid to root shape during orthodontic treatment.

Alveolar Process↗

PubMed2006

Inclination of the occlusal plane is associated with the direction of the masticatory movement path.

Using lateral cephalograms and a jaw movement-recording system, the relationship between the masticatory movement path and dentofacial morphology was investigated in 17 subjects (9 males and 8 females, mean age 23.5 years) without a history of orthodontic treatment. The masticatory movement path was measured at the right and left lower first molar while the subjects chewed gum. The angle between the Frankfort horizontal plane and the masticatory axis (FH-masticatory angle), defined as the axis passing the opening and closing turning point on the sagittal masticatory path, was also measured. The correlation between the angular measurements derived from the lateral cephalogram and the FH-masticatory angle was then investigated. A positive correlation was observed in the FH-masticatory, occlusal plane (P < 0.05), and mandibular plane (P < 0.01) angles. Furthermore, it was found that the angle between the masticatory axis and the occlusal plane (69.1 +/- 4.2 degrees) remained constant even as the masticatory axis showed a tendency to incline forward as the mandibular plane angle became steeper; the rates of change of the FH-masticatory and the occlusal plane angles were approximately 1:1. This finding suggests that the masticatory movement path is closely associated with the occlusal plane.

Adult↗

PubMed2006

Recommended placement torque when tightening an orthodontic mini-implant.

To determine an adequate placement torque for obtaining a better success rate of mini-implants that are screwed into the buccal alveolar bone of the posterior region as an anchor for orthodontic treatment, implant placement torque (IPT) was measured. The subjects were 41 orthodontic patients (124 implants), with an average age of 24.9 years (SD 6.5 years), who had surgery to place titanium mini-implants. The peak value of IPT was measured using a torque screwdriver. The success rate of the mini-implant anchor for 124 implants was 85.5%. The mean IPT ranged from 7.2 to 13.5 N cm, depending on the location of the implants. There was a significant difference in the IPT between maxilla and mandible. The IPT in the mandible was, unexpectedly, significantly higher in the failure group than in the success group. Therefore, a large IPT should not be used always. According to our calculations of the risk ratio for failure, to raise the success rate of 1.6-mm diameter mini-implants, the recommended IPT is within the range from 5 to 10 N cm.

Adolescent↗

PubMed2005

Permissible limit for mandibular expansion.

In recent years, mandibular expansion has been increasingly performed in conjunction with orthodontic treatment. Lateral tipping of the molars associated with mandibular expansion should, however, be considered, because excessive expansion may result in excessive buccal tooth inclination, which may disturb the occlusal relationship. This study was conducted to quantitatively clarify molar movement during mandibular expansion using the Schwarz appliance to determine the permissible limit of mandibular expansion as a clinical index for inclination movement. Inclinations in the masticatory surface of the first molar and intermolar width were measured before expansion (T1), after expansion (T2), and before edgewise treatment (T3). Lower plaster models from 29 subjects treated with expansion plates were used and compared with models from 11 control subjects with normal occlusion. The average treatment change (T1-T2) in intermolar width was 5.42 mm (standard deviation 1.98), and the average angle of buccal tooth inclination was 10.16 degrees (standard deviation 3.83). No significant correlation was found between age prior to treatment and the treatment period when they were compared with the intermolar width increments and inclination angles. There was a significant positive correlation between retention duration and the amount of expansion. The regression coefficient of the angle of buccal tooth inclination during expansion to the increment of the intermolar width was approximately 0.2. This means that 1 mm of expansion is accompanied by 5 degrees of molar lateral tipping. This coefficient is clinically useful for estimating the permissible limit for mandibular expansion.

Analysis of Variance↗

PubMed2005

Biomechanical effect of abutment on stability of orthodontic mini-implant. A finite element analysis.

The biomechanical influences of primary factors on titanium mini-implant, which is used as an anchorage for orthodontic tooth movement, were quantified using the three-dimensional finite element method. Six types of finite element models were designed to show various thread pitches from 0.5 to 1.5 mm. Three models were designed with abutment and three other models without abutment. A traction force of 2 N was applied to the head of the mini-implant or abutment to be at 45 degrees to the bone surface. No remarkable differences were observed in the stress distribution patterns regardless of thread pitch variance. However, the stress distribution was remarkably different between models with abutment and without abutment. The maximum stress of the model with abutment and thread pitch 0.5 mm was the least as compared with the other models. Areas of high-level stress were obviously smaller than in the models without abutment. The plots of the displacement distributions of the models with abutment also presented significant pattern differences as compared with the models without abutment. The high-level area was localized to the head of the implant and the abutment in models with abutment. Therefore, the existence of the abutment is significantly useful in decreasing the stress concentration on the bone, while the effect of thread pitch was uncertain.

Biomechanical Phenomena↗

PubMed2003

Tongue pressure on loop of transpalatal arch during deglutition.

The purpose of this study was to measure tongue pressure exerted on the loop of the transpalatal arch (TPA) during deglutition and to consider the influence of the distance of the loop of the TPA from the palatal mucosa and the anteroposterior position of the loop. Tongue pressures of 4 subjects with normal occlusion were measured with subminiature pressure sensors fixed on the TPA. The distances from the palatal mucosa to the surface of the pressure sensor were set at 2, 4, and 6 mm. The loop of the TPA was placed at the level of the middle of the maxillary second premolars (P), first molars (M1), or second molars (M2). Nine types of TPA devices were measured for each subject. The maximum recorded tongue pressure was taken from each act of deglutition. The minimum pressure value was exerted at position P when the distance from the palatal mucosa to the surface of the pressure sensor was 2 mm. The maximum value was obtained at position M2 and a distance of 6 mm from the palatal mucosa. When distances of 2, 4, and 6 mm were compared, significant differences between 2 and 4 mm, and between 2 and 6 mm were found. Significant differences were observed in comparisons between the positions P and M1, M1 and M2, and P and M2.

Adult↗

PubMed2003

Stresses on the cervical column associated with vertical occlusal alteration.

The biomechanical effects on cervical vertebral columns (C1-C7) during mastication were calculated using a three-dimensional (3D) finite element method. To verify the biomechanical influences of vertical occlusal alteration to the cervical column, three finite element models (FEM) showing a normal (model A), a steep (model B), and a flat occlusal plane (model C) were constructed. The occlusal stress distribution showed various patterns for the three models; the stress extended to the anterior area as the occlusal plane became steeper. The plots of the stresses on the mid sagittal section of the cervical columns showed different patterns for the three models; the stress converged at the odontoid process in models A and B, whereas the stresses at C7 in model B tended to decrease compared with model A. Concentrated stress was observed at C5 in model C, supporting the hypothesis that vertical occlusal alteration could influence stress distribution in the cervical columns.

Adult↗

PubMed2003

The effect of occlusal alteration and masticatory imbalance on the cervical spine.

The characteristics of mandibular lateral displacement include lateral inclination of the occlusal plane and the differences between the right and left masticatory muscles. The aims of this investigation were to compare the mandibular stress distribution and displacement of the cervical spine using three-dimensional finite element models (3D FEM) to simulate masticatory movements and to clarify the association between morphological and functional characteristics and head posture. A symmetrical standard model was produced (model-A). Model-B had higher masticatory muscle strength on the left side, model-C had symmetrical masticatory muscle strength but the occlusal plane was inclined upwards towards the right and model-D had the occlusal plane inclined upwards towards the right with higher masticatory muscle strength on the left side. Model-A showed a completely symmetrical stress distribution pattern, while in model-B there was an uneven distribution in the mandible with higher stress on the left side. In addition, the stress distribution in the cervical spine was asymmetrical, showing displacement to the right. Model-C showed a similar mandibular tendency to model-B but the opposite tendency in the cervical spine. In model-D, the mandibular stress distribution was markedly asymmetrical, but almost symmetrical in the cervical spine with markedly decreased lateral displacement. These results suggest that lateral inclination of the occlusal plane and imbalance between the right and left masticatory muscles antagonistically act on displacement of the cervical spine, i.e. the morphological and functional characteristics in patients with mandibular lateral displacement may play a compensatory role in posture control.

Adaptation, Physiological↗

PubMed2002

An experimental study on mandibular expansion: increases in arch width and perimeter.

The purpose of this study was to estimate the increase in arch perimeter associated with mandibular lateral expansion. The mandibular expansion was simulated using a three-dimensional (3D) finite element method (FEM) and a computer graphics technique (3D simulation). The centre of rotation of molars during movement accompanied by lateral expansion was calculated using 3D FEM. The geometry of the model was determined using the mandibular bone of an East Indian skeletal specimen and 1 mm computer tomogram (CT) slices. The 3D set-up simulation was then conducted using 3D computer graphics instead of performing a manual set-up. Rotational movement was induced in the buccal segment, from the first premolar to second molar, in the 3D set-up model around the location of the centre of rotation (4.5 mm below the root apex of the first molar) derived from the FEM. According to 3D simulation, the model showed an opening space of 1.43 mm between the canine and first premolar, and thus a change in arch perimeter of 2.86 mm. The tip of the mesio-lingual cusp of the first molar moved 3.88 mm laterally, resulting in a change in inter-molar width of 7.76 mm. These values mean that a 1 mm increase in arch width resulted in an increase in arch perimeter of 0.37 mm. This result would be of value clinically for prediction of the effects of mandibular expansion.

Biomechanical Phenomena↗

PubMed2002

Biomechanical influences of head posture on occlusion: an experimental study using finite element analysis.

The biomechanical influences of head posture on the cervical column and craniofacial complex during masticatory simulation were quantified using three-dimensional (3D) finite element analysis (FEA). Three types of finite element model (FEM) were designed to examine relationships between the position of the head and malocclusion. Model A was constructed to have a standardized cervical column curve, model B a forward inclined posture, and model C a backward inclined posture. The results of the spinal displacements revealed that model B moved in a forward direction and model C in a backward direction during masticatory simulation. The stress distributions on the cervical column (C1-C7) for models A, B, and C showed differences; stress converged at the atlas in model A, high-level stresses were observed at the spinous processes of C6 and C7 in model C, and the stress converged at the anterior edge in the vertebral body of C4 of model B. Stress distribution on the occlusal plane and maxillofacial structure did not show absolute differences among the three models. Alteration of head posture was directly related to stress distribution on the cervical column, but may not always directly influence the occlusal state.

Biomechanical Phenomena↗

PubMed2002

Stresses in mandibular cortical bone during mastication: biomechanical considerations using a three-dimensional finite element method.

This study investigated biomechanical aspects of the action of the biting force during mastication upon the mandibular bone in the lower first molar area. A three-dimensional (3D) finite element model (FEM) consisting of the tooth, periodontal ligament (PDL), alveolar bone, and cortical bone corresponding to the lower first molar area based on computed tomogram (CT) images was constructed. The model was then analyzed while applying a biting force during mastication, which was transmitted from the tooth to the cortical bone, through the PDL and cancellous bone. A compressive stress of 0.3-7.9 MPa acted on the cortical bone during mastication. In the model, the stress in the cortical bone was distributed from the linguo-superior margin to the basal area, and was also observed in the bucco-medial area. These areas completely agreed with the areas that were significantly thicker in the morphological study described by Masumoto et al. (10). It is suggested that there may be a relationship between masticatory force and cortical bone hypertrophy. Further study of the effects of various factors is required.

Alveolar Process↗