Location and first appearance of rat incisor pigmentation.

Abstract

abstract – Maxillary incisors were obtained from rats aged 10 to 70 d. The distribution of iron pigment was studied in a dissection microscope. The incorporation of pigment into the enamel started at the age of 10–12 d about 0.6 mm from theoriginal incisal end of the tooth. While initially very faint, the degree of pigmentation increased gradually, and at 28 d the characteristic orange color was present. A 12‐day specimen was sectioned longitudinally and analyzed by the electron microprobe. The iron content of the surface layer of enamel 0.6 and 0.8 mm from the incisal end was 0.3 % and 0.7 %, respectively. The original incisal tip, devoid of pigmented enamel, was removed by attrition before 21 d. Hence, the pigment extended to the incisal edge at the age when the animals became dependent upon a gnawing and masticatory function. The distance from the pigment incorporation zone to the incisal end increased with age, whereas the distance from the pigment incorporation zone to the developing end of the tooth remained relatively unchanged. Apparently, the processes of differentiation, formation and maturation of rat incisor enamel require a certain period of time or a constant passage from the growing end, regardless of the age of the animal.