Growth and Calcification in the Prenatal Human Primary Molars

¹ Department of Operative Dentistry, School of Dentistry, University of Washington, Seattle, Washington

It was the purpose of this study to examine the relationship between growth of the tooth bud crown and its extent of calcification. The investigation was conducted on the 4 primary molar tooth buds of 69 human fetuses. A total of 519 tooth buds was examined. A direct technique of dissection and staining to permit quantitative measurement was employed.

Two sets of observations were used as the basis for this investigation: (1) a series of microscopic measurements of crown size were recorded; (2) the extent of calcification of the crown of the tooth was determined and assigned a standard value.

The relationship between these two sets of measurements—size and calcification—was analyzed statistically. The two sets of measurements were plotted against each other on a linear regression graph and on a curvilinear regression graph. A measure of their relationship was achieved by this means. The analysis of variance was used to determine the significance of differences of the regression lines.

From the data obtained from the sample it was concluded for the human primary molars that: (1) a statistically significant linear relationship exists between the growth of the tooth bud crown and the extent of its calcification; (2) the tooth bud crown continues to increase in size after the onset of calcification; (3) the distance between the cusp tips continues to increase after the onset of calcification; (4) there is no appreciable increase in the distance between two cusp tips after their coalescence.