Abstract
The purpose of present study was to observe longitudinally the changes of the consecutive curve of the incisal edges, tip and cusp tips (curve of Spee) in order to assess the relationship between the morphological changes of the curve and the occlusal development.
The materials of this study were serial dental casts of 44 children. The casts were obtained at twomonth intervals from early childhood to adolescence. To provide the physiological time scale for each subject, we selected the dental casts for measuring under the following 6 periods of development.
1. immediately after the completion of the deciduous dentition
2. just before the emergence of the mandibular permanent central incisor
3. at the attainment of intercuspation of the permanent first molars
4. at the exfoliation period of the second deciduous molars
5. at the attainment of intercuspation of the permanent second molars
6. at the stable period of the permanent dentition
We measured the height from the base of the dental casts to each landmark point such as the incisal edge, tip, and buccal cusp tip in order to observe the vertical changes of each point by means of digital vermier calipers.
The mean changes of the normal dentition group indicated that the curve of Spee gradually headed downwardly from the deciduous through the permanent dentition. The curve of Spee of 19 crowding cases showed changes similar to normal occlusion.
We compared the amount of changes during the deciduous dentition between the normal dentition group and the crowding group statistically. There were significant differences in the amount of changes in the buccal cusp tip of maxillary left first deciduous molar (X1) which was larger in the normal group than in the crowding group. In contrast, there were significant differences in the amount of changes that the crowding group showed, with larger changes in the edge of the mandibular right deciduous lateral incisor (X2), in the tip of the mandibular right deciduous cuspid (X4), and in the distobuccal cusp tip of the mandibular right first deciduous molar (X3) than that for the normal group. A discriminant analysis was performed to evaluate further the relationship between the changes in these points. This analysis showed that the changes of Xi the most closely related to identifying the crowding cases followed by X2, X4, and X3. In combination, a discriminant function Z=0.1233 +1.2588 X1-0.9483 X2+ 0.0612 X3- 0.7749 X4 was introduced and these four changes explained 77.3% of t-he variation in the subjects.
These findings, in general, demonstrated the possibility that changes of these specific points may be related on to distinguish the crowding cases.
