Electron microprobe analysis of iron content of incisor enamel in some species of rodentia

Abstract

Enamel from maxillary incisors of six species was analysed. In those species where pigmentation was observed in the outermost layer of enamel, a corresponding iron-rich zone was demonstrated by elemental analysis. The enamel of squirrel and beaver contained about 10 per cent of iron close to the enamel surface and the concentration gradually decreased to less than 0.1 per cent within 20–30 μm from the surface. Through the same zone, the calcium and phosphorus concentration profile lines showed a gradual increase until a plateau was reached (about 36 per cent calcium and 17 per cent phosphorus) at the point where iron had decreased below a detectable level. This inverse relationship between iron on one hand and calcium and phosphorus on the other was clearly seen in incisor enamel of hamster and mouse which contained a maximum of 5–6 per cent iron near the enamel surface, but was not observed in the lemming (maximum 3 per cent iron). In the non-pigmented enamel of the guinea-pig, iron was not detected at the 0.1 per cent level, and the calcium and phosphorus profile lines followed a horizontal course through the entire width of the enamel. The sum of iron, calcium and phosphorus was approximately equal in all analysed areas. The results indicate that a clear relationship exists between pigmentation and iron content of rodent incisor.