METHOD OF CALCULATING THE SPEED OF MOVEMENT OF AMELOBLASTS DURING RAT INCISOR AMELOGENESIS

Ameloblast migration rates during secretion of enamel in rat incisors were calculated from measurements of (1) certain angular and linear parameters pertaining to the prism pattern, (2) the length of the zones of enamel secretion, (3) the impeded eruption rate of rat incisors, and (4) the diameters of the circles of which the rat incisors are parts. It is assumed that the ameloblasts move along the path of the prisms, that the incisors of adult rats erupt along the are of a stationary circle, and that the length of the zones of enamel secretion does not change with age. From data in the literature, the transverse component of ameloblast migration was calculated to be 9.9 /gmm/day in the upper incisor and 13.4μm/day in the lower. If adjacent rows of ameloblasts move in opposite directions, each ameloblast will in 1 day slide past five ameloblasts of the adjacent row in the upper incisor and past seven ameloblasts in the lower incisor. The results obtained for the component of ameloblast migration from the dentine surface were 9.0μm/day in the upper incisor and 12.3 μm/day in the lower, which are below the 16 /gmm/day enamel apposition rate of other workers. Due to the gingival inclination of enamel prisms, the ameloblasts move gingivally faster than the tooth erupts. This movement is faster during secretion of outer enamel than that of inner enamel. The increased inclination of prisms in the outer enamel zone may be effected by an increase in the gingivo-basal diameter of ameloblasts as they enter the zone of outer enamel secretion. © 1979.