The quasi-fixed point for the linearised deciduous dentition plot.

Abstract

As Masuyama has indicated, the existence of a quasi-fixed point on the linearised dentition plot is useful in forecasting the age at which subsequent teeth will erupt, once the first eruption was observed. He proposed two methods (direct and indirect) for finding this quasi-fixed point. The direct method is based on individual data obtained by longitudinal research, and the indirect method is to estimate it from the mean and standard deviation of the age of eruption. We first examined whether the two methods give the same result with Kitamura's data, which lists the ages of eruption for individuals. When we used the indirect method, the estimates in both sexes were not valid and did not coincide with those from the direct method. However, when we considered a selected group of subjects with good linearization of dentition, the results obtained from the two methods were sufficiently close. Secondly, we attempted to determine the quasi-fixed point (C, C) in many other reports published in the past. Since almost all papers on dentition have not published individual data, we could only use the indirect method. The estimates of C differed considerably, but all of the quasi-fixed points occurred in the late stages of dentition. When we excluded deciduous central incisor from the data, the range of C narrowed and the value varied from about 1.3 (20 months) to about 1.5 (31.6 months).