下顎の前後的位置変化に関する基礎的研究 : 特に顎関節の生物力学的性状について

Abstract

Investigation of biomechanical behavior of the temporomandibular joint of persons with stabilized occlusion was made to establish a means for determining whether the mandible has stabilized in its new position after its anterior or posterior displacement due to orthodontic treatment. For this purpose, an apparatus which enables detailed measuring of the anterior or posterior positional change of the mandible was devised. Measurements with the apparatus were taken of adults with normal occlusion first and studied. The results obtained were as follows : 1. The extents of the anterior displacements brought about by the subjects' own muscles were 7.4 to 12.9mm (average : 10.8mm) on Frankfort Horizontal Plane. The posterior displacements were 0.1 to 1.9mm (average : 1.2mm). These values were 82.9 to 99.2% (average : 90.0%) and 0.8 to 17.1% (average : 10.0%) of the total mandibular displacements respectively. 2. When the mandible was pulled using a chin-retractor toward Pogonion to Porion direction, the extents of the posterior displacements of the mandible were 0.11 to 0.37mm (average : 0.27mm) on the Pogonion to Porion line with the traction load of 2, 000g. With the traction load of 4, 000g, the figures were 0.23 to 0.84mm (average : 0.59mm). With an increase in the traction load, the extents of the movements also increased. The extents of increase, however, showed individual differences. 3. As to the biomechanical behavior after the removal of the traction load, every subject showed viscoelastic movement consisting of instant and creep recovery. The behavior could be shown by 3 element model with the spring and voigt model in series. The biomechanical behavior of the temporomandibular joint showed elastic behavior in which a full recovery was made when the application time of the external force was quite short (about 2 minutes). 4. Observations of the extent of displacements (creep recovery) of the mandible after the removal of the traction load showed that individual differences in full creep recovery time were great even among the subjects with normal occlusion, and that the time varied from very short (4 to 6 seconds) to relatively long (4 to 6 minutes). 5. In every subject, the higher the traction load and the longer the traction time, the longer was the full creep recovery time after the removal of traction load. 6. The biomechanical behavior of the temporomandibular joint was similar to the behavior of the supporting tissue of the teeth, which has already been reported.