Abstract
It is important to know the influences of the supernumerary teeth in the upper incisor region on the arch form and occlusion. If we use some materials independently such as X-ray films or dental casts, it is not so easy to analyse their influences precisely. Therefore we devised a new method to observe such cases three-dimensionally, applying Ishikawa's method (1977) in which one could calculate three-dimensional coordinates of the anatomical landmarks that were able to be traced in the lateral and frontal cephalograms simultaneously.
61 cases which had supernumerary teeth and were in the stage after the eruption of the lateral incisor were investigated, the mean age being 9 years and 1 month. We drew tripartite diagrams of all cases using three-dimensional coordinates of the measuring points and examined the interrelation between the central incisors and the supernumerary teeth. Of all the tripartite diagrmas, we superimposed some of the supernumerary teeth which were shown by arrows according to their number and crown direction, and measured the angles between supernumerary teeth and palatal plane.
The results are as follows.
1. The tripartite diagram expressed by the three views such as lateral, frontal and occlusal makes it possible to evaluate three-dimensionally the precise position of the supernumerary teeth in the upper jaw and relationship to central incisors, especially in case of their maleruption.
2. As to the distribution area of the supernumerary teeth, there was some difference according to the types.
3. The degrees of the crown direction of the supernumerary teeth were distributed gently sloping and continuously. In the lateral view, noninverted types were a little more right-angled than the inverted types.
4. In cases of delayed eruption of the central incisors, the tripartite diagrams suggested that the supernumerary teeth were just under or around the path of incisor's eruption, and it seems to be one of the main reasons that supernumerary teeth should be removed at an early stage.
