Three-dimensional structure of Tomes' processes and enamel prism formation in the kitten.

The Tomes' processes of ameloblasts in the kitten were examined with both transmission and scanning electron microscopes and their three-dimensional structure demonstrated. In general, Tomes' process can be envisaged as the upper part of a diagonally cut column. It was established that the flat crescent face of the process which is slanted cervically, it is the secretory surface (S-face) and the curved crescent surface which is cuspally directed, is the nonsecretory surface (N-face). The cervical border of the S-face is confluent with the free apical surfaces of cervically adjacent ameloblasts. Only the S-face and the adjoining small part of the next ameloblasts produce enamel and arrange crystallites into prisms as evidenced by the perpendicular orientation of crystallites to the S-face of Tomes' process and the free ameloblast surface. Crystallite arrangement within prisms and prism arrangement within enamel are determined by the three-dimensional morphology of the Tomes' processes. The processes are schematically represented and their relationship to other ultrastructural features as seen in sections is discussed.