Of various factors indicated for effective use of straight wire appliances, there was a great lack of studies both domestic and international about the curvatures of tooth crowns. This study was performed to investigate the labio/ buccal clinical crown curvatures of Korean permanent teeth.
For this study, three-dimensional laser scanning was performed on 36 dental casts with normal anatomic structures. Andrews. plane and Facial axis of clinical crown (FACC) were designated as horizontal and vertical reference planes respectively. 2 or 3 lines, 1 mm apart, were drawn superior, inferior, left and right of these reference planes. A threedimensional coordinate table was made for points formed by crossing these lines, and averages of each coordinate point on the 36 dental casts were obtained. The curvature equation was made using three-dimensional coordinate points (x,y,z) and by this curvature equation, the curve ratio of each tooth was obtained. Curve ratio changes of each section of teeth were calculated by curve ratios of simplified curves. These two dimensional curves were simplified horizontally and vertically.
Conclusions for this study are as follows.
1. The basic data of labial and buccal clinical crown curvatures were obtained about Korean permanent teeth. 2. No significant difference was found between male and females.
3. Individual tooth characteristics
1) In maxillary central incisors, the difference in the curve ratio between the gingival and incisal sides was greater than for the other teeth. And the gingival side showed a greater curve ratio.
2) Maxillary canines showed more curvatures in the mesio-occlusal surface than the other surfaces.
3) In maxillary 1st premolars, more curvatures were found in mesio-occlusal and disto-gingival surface, thus showing
a twisted crown surface, but in maxillary 2°d premolars, the crown curvatures of mesial and distal ends became
parallel to each other.
4) No significant difference in crown curvatures was found between mandibular central and lateral incisors.
5) Occluso-gingival curvatures of m andibular 2°d premolar turned out to be more rounded than mandibular 1$t premolars or maxillary 2"d premolars.
From the above conclusions, it can be deduced that the same bracket bases can be used for mandibular central and lateral incisors. But for maxillary Is` and 2" d premolars and for mandibular I" and 2"d premolars, because crown curvatures showed significant differences, when making bracket bases there is ample reason to make bracket base curves differently for each type of tooth.
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