Longitudinal observation of the changes of the consecutive curve of the incisal edge, tip and cusp tip from deciduous and permanent dentition — Comparison between normal and crowded dental arch —

We observed changes in the consecutive curve of the incisal edge, tip and cusp tip using serial dental casts from the deciduous to permanent dentition period in the same 44 individuals showing normal dentition at the time of the completion of deciduous dentition. In addition, in both the maxilla and mandible, the curvature gradually increased from the deciduous to permanent dentition period. Changes in the superoinferior position of each measurement site were similar between the normal and crowded dentition groups; however, at 4 measurement sites, the amount of change from the completion of deciduous dentition to immediately before the transition to mixed dentition significantly differed between the two groups (P < 0.01); therefore, using values at the 4 measurement sites, discriminant analysis was performed. When the amount of change at the 4 measurement sites showing significant differences was indicated by variables X1–X4, the discriminant function was: Z = 0.1233+1.2588X1–0.9483X2+0.0612X3–0.7749X4. Normal dentition (Z > 0) could be discriminated from crowded dentition (Z < 0) with a probability of 77.3%. These results suggest that this amount of change is a factor facilitating discrimination between normal and crowded dentition.