Mitosis in Secretory Ameloblasts

Abstract

Our objective is to test the dictum that secretory ameloblasts cannot divide. Dental biology textbooks often present this idea without citation or evidence; its source seems to be studies of rodent incisors from the 1960's. However, rodent incisors are ever‐growing, and not acceptable models for enamel epithelia in other mammals. There are two reasons to expect that ameloblasts divide. First, recent studies show that tensile forces induce mitosis in epithelia, and enamel epithelia likely undergo tension as enamel is deposited and the surface area of the growing crown expands. Second, we now know that ameloblasts are subject to the same biorhythms that synchronize proliferation of osteoblasts. If ameloblast division is also coordinated by the brain and occurs at night, it is unlikely to have been observed since most experimental protocols occur in daylight.To test the hypothesis, we first measured enamel area from surface and enamel‐dentine junction in Saimiri sciureus tooth sections. We also measured enamel rod width at both sites, as a proxy for ameloblast width. We found an average 9% greater area at the tooth surface, but no difference in enamel prism width. We also searched for mitotic figures in tooth buds of perinatal Saguinus spp. with random times of death, but found none. In conclusion, increasing tooth surface area from deep to superficial and no change in cell size suggests that ameloblast mitosis is likely. However, we did not find any mitotic figures, possibly because of sample size and lack of control over time of death.