No abstract

Palamara J, Phakey PP, Raehinger WA, Oratns HJ. Ultrastrueture of the intaet surfaee zone of white spot and brown spot earious lesions in human enamel. J Oral Paihol 1986: \5: 2X-,35.Electron microscopy of the intact surface zone of white spot and brown spot carious lesions showed that in general their ultrastructure was similar. Their outermost erystalline surface consisted of small erystals similar to those in healthy enamel, erystals with central eore dissolution, and rounded crystals. Below this, surfaee demineralization of enamel was observed as the enlargement of mieropores, the eentral eore dissolution of crystals, the formation of channels and the enlargement of spaees at prism boundaries. Remineralization of enamel was observed as the partial oeelusion of voids, the rounding and enlargement of crystals, and some new needle-shaped erystals. Some other features indieated eombined demineralization and remineralization. The occlusion of spaces at prism boundaries was a tnore eomnion feature in brown spot lesions, whereas the poekets of rounded crystals were more common in white spot lesions. A relatively uniform distribution of needleshaped erystals throughout the intact surface zone was a feature of some brown spot lesions only.

Teeth of three macropod species, M. giganteus, W. bicolor and P. concinna, have been studied using the techniques of light microscopy, scanning- and transmission-electron microscopy and hardness measurement. Light microscope observations showed that the teeth of these species had a translucent enamel region close to the dentine and an outer opaque enamel region at the tooth's surface. These regions were not related to the presence or absence of tubules which are a characteristic feature of marsupial enamel. Hardness tests showed that the opaque enamel was softer than the translucent enamel. Scanning electron microscope observations revealed that there was no correlation between any particular prism packing or orientation and the opaque and translucent enamel regions. Transmission electron microscope observations showed that the translucent enamel region consisted of well defined prisms and well packed, lath-like crystals, whereas the opaque enamel was disrupted by voids (which ranged in size from enlarged micropores to about 2 microns in diameter in extreme cases) between crystals and some randomly oriented, loosely packed crystals. This disruption within the opaque enamel region was more common at prism boundaries but pockets of disrupted enamel were also found within prisms and interprismatic regions. The opacity of the enamel was caused by scattering of light from the voids. The ultrastructure of the opaque enamel region indicated that this region was hypomineralized; hardness tests and polarized light microscope observations were consistent with these results.

The ultrastructural localization and gradient of activity of alkaline phosphatase were studied with respect to cell differentiation, matrix synthesis, and matrix mineralization in the incisor and molar teeth of 4-day-old Sprague-Dawley rats. The animals were perfused intracardially at room temperature with 2.5% glutaraldehyde in 0.1M sodium cacodylate (pH 7.4) with 3-4% sucrose. The jaws were dissected, immersion-fixed for 24 h, and the incisor and molar tooth germs removed. These were determined in 10% EDTA in NaOH (pH 7.4) with 7% sucrose. After reactivation of the enzyme with 0.1M MgCl in Tris-maleate buffer (pH 7.4) at 4 degrees C, the medium consisting of 6 ml 3% sodium beta-glycerophosphate, 4 ml 0.2M Tris-HCl buffer (pH 9.2), 3 ml 1.6% MgSO4, 12 ml 0.5% lead citrate (pH congruent to 12), and 2.1 g sucrose. The pH was adjusted to 9.2 with 0.2M HCl, the volume made up to 30 ml, and the solution centrifuged for 10 min at 5000 rpm. Control teeth were incubated in medium minus the substrate. Finally, the specimens were routinely post-fixed and embedded for sectioning and examination with a Philips 300 electron microscopy. A gradient of alkaline phosphatase activity was mapped along the developing teeth in the cells of the stratum intermedium, the proximal borders of the ameloblasts, the early dentine matrix, the predentine-dentine border, matrix vesicles, and the plasma membranes of odontoblasts and subodontoblast cells. The gradient of alkaline phosphatase activity was evident in the forming tooth from the cervical loop to the crown apex and was related to the cellular events, matrix synthesis, and matrix mineralization occurring during odontogenesis.

Selected areas of early enamel caries (‘White spot’ lesion) in human teeth were argon‐ion‐beam thinned and examined by transmission electron microscopy. A systematic examination of areas which were histologically defined as the translucent zone and the dark zone showed that the pattern of early caries was consistent with that of demineralization of the tissue commencing with a widening of the micropores and of the inter‐rod spaces and gradually progressing to a severe destruction of the original enamel crystals, with possibly some remineralization. Observations indicate that the intercrystalline micropores and inter‐rod spaces are the pathways by which acidic agents reach the crystals causing carious dissolution.