Prenatal dental development as a reference standard for embryologic status.

Postnatal dental development may be used as a reference standard in the absence of exact-age information because dental variability is less than variability for other calcified structures (S. M. GARN, A. B. LEWIS, and D. L. POLACHECK, Science 128:1510, 1958; J Dent Res 38: 135-148, 1959) and is not affected much by nutritional status (S. M. GARN, A. B. LEWIS and R. S. KEREWSKY, J Dent Res 44:228-242, 1965; L. R. FESS, Tooth Eruption and Nutrition, PhD thesis, Tulane University, 1965). It is reasonable, therefore, to consider the value of tooth formation as a prenatal reference standard by first testing its validity at various developmental horizons. We used nearly 5,000 5 to 15 micrometer ("sm) histologic jaw sections of 52 first-trimester human embryos in the 14 to 58 mm crownrump (C-R) range. The data for 440 deciduous teeth from 22 male embryos were separated from the data for 600 deciduous teeth from 30 female embryos. A series of eight 'stages" of dental development was used (cf A. R. BuRm, S. M. GARN and R.L. MILLER, J Dent Res 49:644, 1970) for both left and right teeth. Dental-stage data, C-R length data, and restricted gestational age data (based on last menstrual periods) were stored on standard 80-column IBM punch cards. Since preliminary analysis of the relationships between C-R length and tooth stage showed linear relationships for each of the 20 deciduous teeth in both sexes, computation of correlation coefficients was appropriate and values of r for left and right sides could be pooled. As shown in the table, Pearsonian correlation coefficients for tooth stage and C-R length were uniformly high, for all classes of teeth and for both sexes, averaging 0.90 overall. The relationship between C-R length and tooth stage proved systematically higher for