Kazuo Tanne

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.

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.

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.

FEM-Studie zum biomechanischen Vergleich von labialem und palatinalem Kraftangriff an oberen Inzisivi

The present study was designed to compare the biomechanical response of upper incisors to labial and lingual force applications. A three-dimensional finite element model was developed to analyze tooth displacement and stress distribution in the periodontal ligament. Lingually and apically directed forces of 1 N were applied at one point on the labial and at three points on the lingual surface of the crown. Tooth displacement and stress distribution resulting from lingual force applications were compared with those from the labial side. The following results were obtained: 1. Lingual horizontal forces produced similar patterns of tooth displacement and stress distribution, irrespective of the point of application (labial--lingual). 2. Apically directed vertical forces applied at the lingual points produced more uniform tooth displacements and stress distributions, although the force applied on the lingual side close to the CEJ, which happened to be most distant from the tooths long axis, generated a pattern of movement somewhat different from the remaining two lingual force applications. The present results suggest the crucial role of the positional relation between the long axis of the tooth, respectively the center of resistance, and the point of force application. It can be deduced that lingual force application may produce more optimal tooth movement in terms of intrusion and subsequent stress distributions in the periodontal ligament.ZusammenfassungDie vorliegende Studie wurde durchgeführt, um die initiale Zahnbewegung und die Spannungsverteilung im Parodontium bei labialer beziehungsweise palatinaler Kraftapplikation zu vergleichen. Zu diesem Zweck wurde ein dreidimensionales Finite-Elemente-Modell eines mittleren oberen Schneidezahnes entwickelt und darauf palatinal bzw. apikal gerichtete Kräfte von 1 N appliziert. Die Berechnungen wurden für einen labialen und drei palatinale Angriffspunkte durchgeführt. Zusammenfassend ergaben sich die folgenden Ergebnisse: 1. Palatinal gerichtete Kräfte führen zu sehr ähnlichen Zahnbewegungen und Streßverteilungen unabhängig davon, ob die Kraft labial oder palatinal ansetzt. Dabei hat die Höhe des Kraftangriffs nur einen relativ geringen Effekt. 2. Bei vertikalen Kräften, die parallel zur Zahnlängsachse wirken, ist der Abstand des kraftvektors von der Zahnlängsachse von ausschlaggebender Bedeutung für die resultierende Zahnbewegung und Spannungsverteilung.SummaryThe present study was designed to compare the biomechanical response of upper incisors to labial and lingual force applications. A three-dimensional finite element model was developed to analyze tooth displacement and stress distribution in the periodontal ligament. Lingually and apically directed forces of 1 N were applied at one point on the labial and at three points on the lingual surface of the crown. Tooth displacement and stress distribution resulting from lingual force applications were compared with those from the labial side. The following results were obtained: 1. Lingual horizontal forces produced similar patterns of tooth displacement and stress distribution, irrespective of the point of application (labial-lingual). 2. Apically directed vertical forces applied at the lingual points produced more uniform tooth displacements and stress distributions, although the force applied on the lingual side close to the CEJ, which happened to be most distant from the tooths long axis, generated a pattern of movement somewhat different from the remaining two lingual force applications. The present results suggest the crucial role of the positional relation between the long axis of the tooth, respectively the center of resistance, and the point of force application. It can be deduced that lingual force application may produce more optimal tooth movement in terms of intrusion and subsequent stress distributions in the periodontal ligament.

Biomechanical Responses of Craniofacial and Alveolar Bones to Mechanical Forces in Orthodontics

Stress patterns and levels were analysed by use of the three-dimensional finite element method in association with orthodontic and orthopaedic forces applied to the upper canine and the craniofacial complex in human beings. Stress distributions in the periodontium and the craniofacial bones were directly related with actual changes of the tooth and craniofacial skeleton observed in orthodontic treatments. Thus, it is shown that the mechanical stress in living structures may be a trigger to induce biological remodelling of bones.

Biomechanical Behaviour of Articular Disc in Adult Dogs: A Measuring Method and Preliminary Results

Biomechanical behaviour of temporomandibular joint (TMJ) disc was investigated by means of a tensile test. Articular discs derived from eight adult dogs were used as experimental materials. Each disc was further divided into medial, middle and lateral parts, in parallel to the antero-posterior direction. The whole articular disc exhibited a non-linear stress-strain relationship, where the point of inflexion was around 150 gf/mm2. It was found that elastic modulus of the disc was approximately 3.23 ± 0.85 kgf/mm2 and 6.34 ± 1.19 kgf/mm2 in lower and higher stress regions, respectively. In addition, mechanical properties of the articular disc varied in different areas of the disc. It is shown that the disc plays an important role in reducing stress induced in the TMJ space and its susceptibility to internal stress may be different in the lateral, middle and medial regions.