Histological reconstruction of crown formation times and initial root formation times in a modern human child

Previous qualitative studies on root growth in hominoids have suggested that the early stages of root growth in modern human teeth are slower than in great apes, but no quantitative data on root extension rates exist for modern human teeth. The primary objective of this study was to use incremental markings in the crowns of teeth to provide information about crown formation times and early root formation times. This study provides a detailed description of a single unaged child from Spitalfields, London, and presents an internally consistent model of incremental growth in crowns and roots of different teeth of this individual. We describe methods for determining times of initial mineralization in different teeth in the same individual. Scanning electron micrographs of perikymata on tooth surfaces and histological sections of teeth were prepared and analyzed. Total crown formation times were 4.4 years in the lower I1, 4.9 years in the lower 12, and 3.1 years in the upper M1. Average root extension rates indicate that during the first 2 or 3 mm of root growth in the lower permanent incisors and upper first permanent molar the average root extension rate was between 2.9 and 3.8 μm per day. This rate is similar to the rate of enamel extension in the last portion of cervical enamel formed in modern human anterior teeth. These root extension rates are approximately four times slower than similar rates calculated for ape teeth (Beynon et al: Am. J. Phys. Anthropol., 1991), a highly significant difference. The implications of these findings for comparative studies of dental development in early hominids and modern humans are discussed.