| Popis: |
The curve symbol in the mandibular central incisor on the cross-sections of the tooth crown was observed quantitatively, based on the two methods by Muhlreiter. Fifty extracted incisors were examined. To identify the individual incisors as belonging to the right/left quadrant, moire topography was applied to the proximal surface of the root before measuring. The most common morphological combination pattern of the proximal surfaces on the root was ridge-groove type (78.0%). In all teeth in the present study the mesial/distal surface could be identified from the difference of the concavo-convex level on the root surface. The cross-sectional outlines were obtained by a tht ee-dimensional measwing instrument system (VECTRON), and the measurements were made on the cross-sections output by X-Y plotter.Comparison of the angles: When the distolabial angle is larger than the mesiolabial angle, the curve symbol is evident. On the cervical and cervical third of the tooth crown, the reverse curve symbol was evident. On the middle and incisal third of the tooth crown, the curve symbol was exhibited. Inclination of the perpendicular line: When the line perpendicular to the segment between the mesio-and disto-labial angle inclines toward the distal, the curve symbol is evident. The angle between the perpendicular line and labiolingual axis was within 5°. There tended to be a slight increase in the percentage of “distal” from the cervical to the incisal third. Therefore, the curve symbol was apt to occur near the incisal edge. On the cervical and cervical third, in any case of inclination of the perpendicular line, the mesiolabial angle was larger than the distolabial. On the middle and incisal third, when the line was toward the distal, the distolabial angle was larger than the mesiolabial, and the two methods agreed with each other. A comparison of the degree of the curve symbol judged by the angles in the three cases of the perpendicular line showed that on the every cross-section there was a general increasing trend from “mesial” to “coincident” to “distal”, and the two methods showed a similar tendency. In the relationship between the curve symbol and tooth morphology, it was suggested that the size factor correlated significantly with the curve symbol, while the shape factor did not. The curve symbol appeared more distinctly in the larger teeth. |
