Cusp Of First Molar Research Articles

総義歯人工歯排列に関する解剖学的研究 : 臼歯部の歯列・咬合ならびに歯槽形態

In this study, fifty three subjects (male : 11, and female : 42, 18.7±2.9 years old) from five thousand three handred and seventy seven with the individual normal occlusion were selected according to Miyamura's standards, and were mainly examined about the posterior natural dentition, their occlusions and the contour of the buccal alveolar ridges in order to use as the reference materials when constructing complete prostheses, since it is generally said that the arrangement of dental teeth should be placed at the same position as natural teeth grow and the contour of the polished surfaces should be made up in the harmonious form with the surrounding tissues such as the tongue and cheek, just the same as that is found for the alveolar ridge contour of the dentulous. The results obtained were as follows : 1. The occlusal plane showed the inclination to the post-upper direction by 1.18±3.03 degree to the prosthetic plane at the medium of both incisal edges, and that of the right had a tendency to be slightly higher than that of the left. 2. The interconnected straight line between the buccal cusp and the lingual cusp of the upper first premolar passed through the mesial point by 5.6±5.0 mm from the mesio-lingual cusp of the opposite side upper first molar. In only 7%, and about 30% which included positional difference of 1 mm or less, the straight line passed along the just mesio-lingual cusp of the first molar. 3. The vertical distance from the plane which passes through the caspal position of the canine and the disto-buccal cusp of second molar to the mesio- and the disto-buccal cusps of first and second premolars, and first molar, and the mesio-buccal cusp of second molar were 1.0±0.5mm, 1.6±0.5mm, 2.0±0.6mm, 1.6±0.5mm, and 0.9±0.3mm respectively. And so the connected line of each molar buccal cusp made the deepest concave curve at the mesiobuccal cusp of first molar. Meanwhile the vertical distance to each lingual cusp from the same plane were 2.8±0.8mm, 2.8±0.9mmu 2.6±0.9mm, 2.5±0.8mm, 2.3±0.8mm respectively, and 1.6±0.6mm at the mesio-buccal cusp of second molar. 4. The rate of occlusal contact points of the central and the lateral incisal edges and the canal cuspid at the intercuspal position were 34.3%, 38.0%, and 54.6% respectively. On the molar groups, the contact points were found in 96.9% of the first premolar cusps of which the rate was the highest of all, and the contact points in 78.0% of the bucco-central cusp and in 72.0% of the bucco-mesial cusp of the second molars, and the second premolar were found in turn, but no contact point recognized on the lingo-distal cusp of the second molar. And also a-contact was 35.2%, b-contact 61.8%, and c-contact only 3.0%. The horizontal overlap of the last molar was 1.2±0.4mm, and the horizontal overlap and the vertical one were 1.7±0.5mm and 0.8±0.4mm respectively. 5. The lineal distance to the buccal cusp of the first premolar, the most projecting portion and the deepest portion of the buccal alveolar ridge contour from the cervical on the same section were -1.6±0.7mm, 0.6±0.3mm and -0.4±0.6mm, and that of the second premolar -1.9±0.6mm, 1.1±0.5mm and 0.3±1.0mm respectively. In molar portions, however, were observed many cases which gradually underwent a transition to the buccal membrane from the projecting portion of the alveolar ridge without exhibiting undercuts. On the basis of the foregoing findings, it was reconfirmed that the specific contour for the complete prosthesis had been made in the molar portions too, in spite of being made the tooth arrangement and the occlusion for the complete denture according to natural dentitions. The construction of complete dentures with which the patients content themselves will be easier by investigating the difference between natural dentitions and denture contours, and its reasons.

顎関節内障患者の歯列形態の特徴に関する研究 こう合平面の傾斜と歯列わん曲について

The purpose of this study is to investigate the relation between disorder of dental arch form and internal derangement of TMJ. Twenty patients with internal derangement of TMJ and twenty normal subjects were selected for this investigation.We measured the inclination of occlusal plane to Camper's plane and the degree of the occlusal curvature (sagittal and frontal) in two groups, using study casts mounted on an articulator. The results were as follows: 1) There was no significant difference in the inclination of occlusal plane between two groups, but the inclinations of patients tended to range more than those of normal subjects. 2) There was a significant difference in the degree of sagittal occlusal curvature between two groups. 3) There was no significant difference in the degree of frontal occlusal curvature except the mesial cusp of first molar between two groups. 4) In unilateral patients, comparing the degree of occlusal curvature at affected side with that of healthy side, there was no significant difference in the degree of sagittal occlusal curvature between two sides, but the degree of frontal occlusal curvature on second molar of healthy side was larger than that of affected side.

歯牙の排列に関する計測学的研究

Biometric measurements have been conducted on the distances from every incisal edges and occlusal tips of upper and lower dentitions to the Camper′s plane. A total of 94 individuals consisting of 44 males and 50 females from 18 to 23 of age were selected as the subjects according to a criterion that their teeth were sound in every respects, free from marked attrition and erosion, and the occlusion was normal as strictly as possible. Plaster models were prepared from alginate impressions of upper and lower jaws, and these were mounted on the specially designed apparatus following the preparation tecnipue of gnathostatic model routinely used in the orthodontic practice. On this jaw model, the basal plane of upper jaw was placed so as to come parallel to the Camper′s plane. In Fig.1 and 2 the method and apparatus were illustrated. The conclusions were reached as follows. It was confirmed that the plane including the mesial incisal edges of both central incisors and the buccal distal cusps of both second molars in lower jaw was not parallel to the Camper′s plane as it has been supposed so, because the present study has revealed that the former point of jaw were closer than the latter points to the Camper′s plane by 1.5 millimeters. Hence, for the purpose of utilizing the occlusal plane in denture work which is nearest parallel to the Camper′s plane, one would have to select either the one which connects the buccal cusps of both first premolars and the buccal distal cusps of both second molars in lower jaw, or the one which connects the buccal distal cusps of first and second premolars and the buccal distal cusp of first molar in upper jaw. Also it must be noted that in upper jaw the buccal distal cusp of first molar is lower than its mesial cusp, and among all the cusps in buccal side those of the first and second premolars are the lowest, while among all the cusps in lingual side the mesial cusp of first molar is the lowest. In lower jaw, the distal cusp of first molar is lowest among the buccal cusps of all teeth, while among the lingual cusps that of first premolar is lowest. The author believes that these facts as revealed in the present study must be taken into account by the clinicians in the practice of arranging the artificial teeth on denture plate.