Relating developing surface to adult ultrastructure in Chiropteran enamel by SEM.

Abstract

The developmental basis for a newly discovered feature of adult Chiropteran (bat) enamel has been explored. Developing enamel surfaces of tooth germs of Chalinolobus gouldii have been examined after either plasma-ashing or NaOCI immersion to remove cellular material superficial to the surface. Maintenance of dimensional stability of the anorganic surface was promoted either by prior embedding in methacrylate for plasma-ashing or by subsequent critical-point-drying for wet preparation. Stereo-pair scanning electron micrographs were analyzed in a stereo-comparator and profiles reconstructed in directions parallel with the electron beam. A novel feature of the developing surface is described which accounts for the additional crystallite discontinuity line (minor boundary plane) found in the central cervical region of each horseshoe-shaped prism in what is essentially a Pattern 2 enamel. The feature is a consistent groove in the more superficial part of the developing floor wall of the Tomes' process depression, reflecting the absence of the most prominent parts of the developing enamel at the border between adjacent (Pattern 2) pits in the direction of their longitudinal alignment. The existence of a cervical floor groove was predicted from earlier observations of adult material as a result of our previously having constructed three-dimensional models utilizing the stereo-sketch approach. The present observations satisfactorily complete a conceptual cycle involving initial description of a new feature of adult bat enamel; prediction of the necessary developmental basis for it; and finally, analysis and confirmation of that developmental feature.