咀嚼初期における下顎運動路の精密測定

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  • A PRECISION METHOD FOR MEASUREMENT OF THE PATHWAY OF MANDIBULAR MOVEMENT AT THE EARLY STAGE OF MASTICATION
  • ソシャク ショキ ニ オケル シタアゴ ウンドウロ ノ セイミツ ソクテイ

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<p>Realizing the practical importance of the task in dentistry to elucidate detailed movement of the mandidle and its dentition, many investigators have so far done effort to establish the method for accurate measurement of the movement. However, owing largely to inadequacy of apparatus used by these investigators, movement of a specific tooth or a specific position of the dental arch only allowed to be guessed as following the movement of mandible as a whole, and could not be determined as to its individual movement during mastication. Although the X-ray method has permitted direct observation on individual movement of atooth, as yet no device is available to provide true precision in recording the pathway of movement. Very recently Sasaki has presented a method for analyzing the pathway of arbitrarily chosen point of the mandible in its masticatory movement, in which Dr. Yokota's cephalometric photo-apparatus was utilized. This method involves taking the movie of the mandibular movement with usual 35mm films projecting the front and side views of the subject's mandible on single frame of the films simultaneously. Prior to taking the movie, an apparatus for orientation is adjusted to the face of the subject, and the movement of the apparatus along with that of the mandible is pictured on the films in both its frontal and lateral views. The orientation apparatus pictured on the two right-angled planes thus afford reading three dimensional movement of the mandible or of any position selected. The key part of the apparatus consists of a marker system connected with the lower dental arch which serves to indicate exact position of the target within the mouth as it moves during mastication. In the present study the author has made further improvement on the precision of the apparatus and has succeeded to analyze the mandibular movement with accuracy of as high as 1/4 mm. As material for the chewing experiment, three kinds of food were used ; the first was of simply soft consistency (like chewing-gum), the second was of highly resistant and brittle nature (like peanut) and the third was of highly resistant and sticky nature (like caramel). Measurement was done during the first stage of mastication, that is during the first 8 or 4 strokes of mandibular movement, directly after the chewing material was ingested into the mouth and when the conscious effort to chew was vigorously encouraged. As the target points for observation, the mesial angle of left central incisor and the mesio-buccal cusp tip of left 1st molar were chosen in the present experiment. The conclusions reached were summarized as follows. The movement observed at the anterior teeth generally coincided with the one at the posterior teeth, although significant variation in its details was observed to occur with the difference of test foods taken by the subject. When a soft kind of food was ingested the target point projected on the frontal plane first opened toward the working side of the jaw and forming there a wide outward curve, finally closed into the original point. On the other hand, when a highly resistant and brittle material was ingested, the locus, residing in the working side, only went up and down on the same way vertically, and when it dealt with a highly resistant and sticky material, the locus first started to open toward the balancing side of the jaw and then returned to the masticating side to be closed there. Observation of the mandibular dental arch as projected on the sagittal plane revealed that there never occurred antero-posterior sliding movement of the mandible as it had been previously claimed to occur when the lower dentition was brought into close contact with the opponent upper dentition. When the subject was allowed to chew the highly resistant and brittle or sticky kinds of food, the mandibular movement at its last stage of closing the mouth assumed an irregular zigzag course</p><p>(View PDF for the rest of the abstract.)</p>

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