Mamoru Sakuda

Three-dimensional finite element analysis for stress in the periodontal tissue by orthodontic forces

This study was designed to investigate the stress levels induced in the periodontal tissue by orthodontic forces using the three-dimensional finite element method. The three-dimensional finite element model of the lower first premolar was constructed on the basis of average anatomic morphology and consisted of 240 isoparametric elements. Principal stresses were determined at the root, alveolar bone, and periodontal ligament (PDL). In all loading cases for the buccolingually directed forces, three principal stresses in the PDL were very similar. At the surface of the root and the alveolar bone, large bending stresses acting almost in parallel to the root were generally observed. During tipping movement, stresses nonuniformly varied with a large difference from the cervix to the apex of the root. On the other hand, in case of movement approaching translation, the stresses induced were either tensile or compressive at all occlusogingival levels with some difference of the stress from the cervix to the apex. The pattern and magnitude of stresses in the periodontium from a given magnitude of force were markedly different, depending on the center of rotation of the tooth.

A three-dimensional finite element model of the mandible including the TMJ and its application to stress analysis in the TMJ during clenching

The purpose of this study was to develop a three-dimensional finite element model of the mandible including the temporomandibular joint (TMJ) and further to investigate stress distributions in the TMJ during clenching. The model consisted of 2088 nodes and 1105 elements, comprising cortical and cancellous bones, articular disc, articular cartilage layer and periodontal ligament. For loading condition, a resultant force of 500 N derived from the cross-sectional areas of the muscles was applied to the model. Compressive stresses were induced in the anterior, middle and lateral areas of the TMJ during clenching, whereas the tensile stresses were induced in the posterior and medial areas. The mean principal stresses on the surface of condyle were -1.642, -0.543, 0.664, -1.017, 0.521 MPa in the anterior, middle, posterior, lateral and medial areas, respectively. The mean stresses on the surface of glenoid fossa were approximately 1/5 to 4/5 those on the surface of condyle, although the patterns of stress distributions were almost similar. In both the articular disc and cartilage layer, the stress distributions were very approximate in qualitative and quantitative aspects. Thus, it is shown that stresses during clenching vary substantially in different structures and areas of the TMJ and that the stresses are reduced by the articular disc and cartilage layer in comparison with actual biting forces exerted by the masticatory muscles, if anatomic relation between various TMJ components is well maintained.

Patterns of initial tooth displacements associated with various root lengths and alveolar bone heights

The present study was designed to investigate the nature of initial tooth displacements associated with varying root lengths and alveolar bone heights. A three-dimensional model of the upper central incisor was developed for the finite element analysis. Tooth displacements were determined at various levels of the tooth and the apicogingival levels of the center of resistance and centers of rotation were calculated. The results showed that moment-to-force values at the bracket level for translation of a tooth decreased with shorter root length and increased with lower alveolar bone height. In addition, apicogingival levels of the center of resistance shifted more gingivally to the cervix, or the alveolar crest with a shorter root. Alveolar bone loss also shifted the center of resistance toward the alveolar crest, whereas its position was more apical relative to the alveolar bone heights exhibited very slight changes in both cases. The centers of rotation from a single force varied substantially with a short root and alveolar bone loss. However, the relative distances of the centers of rotation from the alveolar crest in comparison with the alveolar bone heights were constant at 0.4 mm, with variations in the root length and alveolar bone height. Because this study showed that root length and alveolar bone height affect the patterns of initial tooth displacements both in the center of resistance and the centers of rotation and also in the amount of displacement, forces applied during orthodontic treatment should take into consideration the anatomic variations in the root length and alveolar bone height so as to produce optimal and desired tooth movement.

Biomechanical effect of anteriorly directed extraoral forces on the craniofacial complex: a study using the finite element method.

This study was designed to investigate the biomechanical effect of protractive maxillary orthopedic forces on the craniofacial complex by use of the three-dimensional finite element method (FEM). The three-dimensional FEM model was developed on the basis of a dry skull of a young human being. The model consisted of 2918 nodes and 1776 solid elements. Eighteen cranial and facial sutural systems were integrated in the model. An anteriorly directed 1.0-kg force was applied on the buccal surfaces of the maxillary first molars in both a horizontal parallel direction and a 30 degree obliquely downward direction to the functional occlusal plane. The nasomaxillary complex showed a forward displacement with upward and forward rotation in a horizontal protraction case, whereas a downward force produced almost translatory repositioning of the complex in an anterior direction. High stress levels were observed in the nasomaxillary complex and its surrounding structures. However, the pattern of stress distributions within the complex was different in two force systems. A downward protraction force produced relatively uniform stress distributions, indicating the importance of the force direction in determining the stress distributions from various orthopedic forces.

Integrated information-processing system in clinical orthodontics: An approach with use of a computer network system

A computer network system has been developed in the Orthodontic Clinic, Osaka University Dental Hospital, to improve treatment efficiency and patient service. The system consists of a 32-bit host computer, its peripheral units, and personal computers connected to the host computer by data-transmission circuits, making up a local area network (LAN). It is possible in this system to integrate various types of data, such as the patients basic information, treatment records, image data, and diagnostic analysis results to construct a relational database. It has been shown that the computer system developed in the orthodontic clinic has various clinical advantages.

The Elastic Modulus of the Temporomandibular Joint Disc from Adult Dogs

The present study was designed to measure the elastic properties of temporomandibular joint (TMJ) discs from six adult dogs. Each disc was divided mediolaterally into medial, middle, and lateral parts. Under tension, the articular disc exhibited a non-linear stress-strain relationship, which could be represented as two lines (two moduli of elasticity) connected at a point of stress around 1.5 MPa. These two elastic moduli of the disc were approximately 44 MPa and 92 MPa in the lower- and higher-_stress regions, respectively. Elastic moduli of the articular disc in the middle area were significantly different from that in the lateral area of the disc. The reaction to external force appeared to be different in the medial, middle, and lateral regions of the disc.

Biomechanical and clinical changes of the craniofacial complex from orthopedic maxillary protraction.

The present study was designed to investigate biomechanical and clinical changes in the craniofacial complex resulting from orthopedic maxillary protraction by means of finite element and cephalometric analyses, respectively. An analytical model developed from a young human dry skull was used for finite element analysis. Three principal stresses were determined in the complex and its sutures. For evaluating morphological changes of patients, lateral cephalograms taken before and after maxillary protraction therapy were analyzed. Tensile stresses were produced in the maxillary and zygomatic bones in an anterior direction with corresponding compressive stresses in a perpendicular direction. In the sutural systems, compressive stresses were induced by counter-clockwise rotation of the complex. Cephalometric investigation demonstrated that significant improvement of the maxillo-mandibular relationship was obtained by maxillary protraction, however, maxillary growth and repositioning were not as great when compared to mean growth in the control group.

Tongue, Jaw, and Lip Muscle Activity and Jaw Movement during Experimental Chewing Efforts in Man

The electromyographic (EMG) activity of the human genioglossus (GG) muscle during chewing efforts is not fully understood. In this study, the EMG activity of the human GG muscle during unilateral gum chewing was illustrated and correlated with the activities in the anterior temporalis (AT), the anterior digastric (DG), and the inferior orbicularis oris (OI) muscles. GG muscle activity was measured with customized surface electrodes, while other muscles were recorded with conventional surface electrodes. EMG activities during tongue displacement and the articulation of long vowels, recorded by the customized electrodes, were consistent with the recordings obtained by fine wire electrodes placed in the GG muscle. Jaw displacement was monitored by means of a kinesiograph with a transducer attached to the mandibular central incisors. Mean normalized GG muscle activity showed an onset in the last one-fifth of the intercuspal phase, gradually increasing during jaw-opening, and at its greatest immediately before the maximum jaw-opening position. It then decreased during jaw-closing and ceased in intercuspation but showed a small rebound in the third fifth of the intercuspal phase. The GG muscle burst showed phase lags with the DG and 01 muscles and an opposite phase with the AT muscle (all P < 0.0001). All correlations were statistically significant (all P < 0.0001, r values between 0.88 and 0.97). The results suggest central coordination of the timing of the activities of the jaw, lip, and tongue muscles in chewing.

The Effect of Local Application of 1,25-Dihydroxycholecalciferol on Osteoclast Numbers in Orthodontically Treated Rats

Orthodontic tooth movement requires remodeling of periodontal tissues, especially alveolar bone. 1,25-(OH)2D3, the active form of vitamin D 3, is known to be a potent stimulator of osteoclastic bone resorption. The purpose of this study was to investigate the effect of local application of 1,25-(OH)2D3 on osteoclast numbers induced by experimental tooth movement. A piece of orthodontic elastic band was inserted between the first and second upper molars of male Wistar rats weighing about 200 g each. Twenty μL of 1,25-(OH)2D3 (10-12-10 -7 mol/L) was injected locally into the submucosal palatal area of the root bifurcation of the right first molar. The left side was injected with phosphate-buffered saline (PBS). The number of osteoclasts was counted in a 700 x 1050 μm2 area of the interradicular septum. The local injection of 1,25-(OH)2D3 caused a dose-dependent increase in osteoclast number. The effect of 1,25-(OH)2D3 reached a response plateau at 10-10 mol/L when greater than a threefold rise in osteoclast number was attained compared with the PBStreated controls. While the insertion of a piece of elastic band for three days induced a significant increase in osteoclasts in the alveolar bone, daily injections of 20 μL of 10-10 mol/M 1,25-(OH)2D 3 for three days markedly stimulated the numbers of osteoclasts induced by the insertion of an elastic band. 1,25-(OH)2D3 was apparently synergistic with mechanical stimuli, resulting in enhancement of the numbers of osteoclasts induced by mechanical stimuli alone. These findings suggest that the local application of 1,25-(OH)2D 3 acted directly to increase osteoclast number and to potentiate osteoclastic bone resorption induced by mechanical stimuli.

Insolubilized properties of UV-irradiated C03 apatite-collagen composites

To examine the response to biological hard tissues, a carbonate-containing hydroxyapatite with chemical composition and crystallinity similar to those of bone was synthesized at pH 7.4 and 60 degrees C. The apatite powder was mixed with collagen solution, whose antigenicity had been removed by enzymatic treatment, and formed into apatite-collagen pellets. After insolubilization by UV-irradiation for 4 h, the composites showed remarkably reduced disintegration and maintained their shape under 3.6 MPa of stress after 1 wk incubation in 0.9% NaCl solution. They showed good biocompatibility when implanted beneath the periosteum cranii of rats. The UV-irradiated sample kept its features well and was packed with newly created material 3 wk after implantation.