Vertical Growth Rates of the Deciduous Teeth

Most of what we know about the growth of teeth comes from serial radiographic studies. As many as 15 stages in growth of the permanent lower first molars were seen by Gleiser and Hunt. ' They are of the opinion that occlusal growth has one maximum rate during crown formation and another as the root is developing. Phases of acceleration and deceleration also seem to mark early stages of growth of the deciduous teeth. Kraus2 has shown that early calcification proceeds more rapidly mesiodistally than occlusally. Moss and Applebaum5 applied the concept of differential growth to several developing incisors and molars. They remark on the proportional increases in occlusal length and labiolingual width, beginning during the fifth month of fetal life. Recent data on growth and resorption of three of the deciduous teeth (mandibular canines and the two molars) by Moorrees, et al.4 are based on serial oblique or lateral radiographs of nearly 250 children; these were taken every 3 or 6 months at the Fels Research Institute. Some aspects of crown growth cannot be seen because of the intervals between observations. This study, however, adds greatly to our knowledge of the rate of growth of these teeth. Reference has been made to both longitudinal and cross-sectional studies, but for observations on isolated teeth only the latter type is possible (and then only when postmortem material is available, together with data on the pathologic factors, so that teeth in which dental growth appears retarded can be set aside from those selected as "normal"). The present study was made possible by collecting deciduous dentitions with the cooperation of a pathology department. It was designed, as far as possible, to exclude the minority of teeth in which retarded dental growth was presumed. An attempt has been made to describe fetal dental growth in terms of the simplest of mathematical relationships. These were evaluated, where necessary, by modifying units of measurement so that proportional changes in the variables could be followed. Measurements that were found to increase proportionately were occlusal lengths and labiolingual widths; lengths and cube roots of weights; ages and square roots of weights, and root lengths and ages. These relationships applied to selected periods of tooth growth and were not shown to apply to all types of deciduous teeth. The rates of vertical growth of all ten types were evaluated, however, as were the rates of increase in weight (dry mineralized tissues only). The proportionality of growth in two dimensions of the central incisors5 was confirmed, and this finding was complemented by a comparison of changes in the occlusal dimension in incisors and first molars. Proportional growth of central incisors in occlusal length and labiolingual width is shown (Fig. 1). The comparison is limited to the dentin caps, free of enamel, and to a period when the direction of curvature of the lingual surface does not change. Relative growth of the two types of incisor, as expressed by their weights, is best seen on a semi-logarithmic plot (Fig. 2). The relationship that indicates that square roots of weights increase in direct proportion to age was not applicable to the smallest incisors (fetal age, 26 weeks) because enamel deposition was still relatively slight. Neither was it applicable after birth, when enamel deposition on these teeth no longer continued at the prenatal rate. Weights of enamel and dentin deposited intermediate to these stages were found to be almost identical, however (Fig. 3).