3-DIMENSIONAL ARRANGEMENT OF ENAMEL PRISMS AND THEIR RELATION TO THE FORMATION OF HUNTER-SCHREGER BANDS IN DOG TOOTH

The three-dimensional architecture of enamel prisms and their relation ship to Hunter-Schreger bands were examined in the developing enamel o f several dog teeth by light and electron microscopy, and computer-ass isted reconstruction. Sections were prepared from a single demineraliz ed tooth germ. Longitudinal semithin sections parallel to the meridian of the tooth showed parazones and diazones of the Hunter-Schreger ban ds in alternate rows at equal intervals. On sections vertical to the t ooth crown through the middle region of parazone or diazone, a row of parallel prisms were angulated with the largest tilting angle being 55 degrees to the enamel-dentin junction: running in opposite directions in the respective zones. Tangential sections parallel to the enamel-d entin junction showed numerous belt-like zones arranged perpendicular to the meridian of the tooth. Each belt-like zone consisted of a group of enamel prisms oriented in the same direction, those in the neighbo ring zones being oriented in an opposite direction. The densely staine d boundaries between the adjacent belt-like zones corresponded to the interface between parazone and diazone. Computer-reconstructed enamel prisms in the adjacent two zones were oriented in the opposite sidewar ds direction with occasional confluence and divergence. Scanning elect ron-microscopic observation of the developing enamel surface exposed b y dissolution of the enamel organ revealed band-like arrangements of g roups of pits encasing the Tomes' processes of secretory ameloblasts. The secretory faces of the pits inclined uniformly in the same sidewar ds direction, with those in the neighboring groups, in the opposite di rection.