Scanning electron microscope study of cat and dog enamel structure.

Scanning electron microscopy revealed several similarities as well as significant differences in the enamel structure between cat and dog teeth. Three enamel layers were present in both species; a surface rodless (aprismatic) layer, an outer layer of parallel rods (only at some sites), and an inner layer with prominent Hunter-Schreger bands. In the inner layer of both carnivores, the diameter of individual rods varied significantly and frequently their course changed abruptly with respect to neighboring rods. In dog teeth the cross-sectional shape of inner enamel rods was pleomorphic, but hexagonal in outer enamel. In contrast, cat enamel rods were rounded in both inner and outer enamel layers. Hunter-Schreger bands of cats circumscribed the teeth in relatively straight segments, but these bands showed pronounced waviness in dog teeth. In cats and dogs the surface rodless layer was structurally continuous with subjacent interrod enamel and covered all tooth surfaces with the exception of the cervical areas. The data show that the structure of inner and outer enamel layers differ between these two carnivore species and that the enamel structure of the cat was most similar to that described in humans. One principal difference between carnivore and human teeth is that the growth lines of carnivores do not terminate at perikymata on the tooth surface.