Mineralization patterns in the dentine of the floor of the pulp chamber of porcine molars

The relationship between the arrangement of the matrix fibre bundles and the shape of the mineralization front (mineralization pattern) were observed in the dentine of the subpulpal wall of porcine molars. The observations were made using mainly light microscopy and scanning electron microscopy on the primary dentine excluding the secondary dentine. The results obtained shows that the dentine of the subpulpal wall consists of two parts, a surface layer and the circumpulpal dentine. The surface layer can be divided into two sublayers according to the arrangement of it's matrix fibres. The mineralization pattern was also observed to have another two sublayers which did not correspond with the two fibrous subdivisions. Adjacent to the dentine-cement junction, there is a layer, measuring about 3 microns in thickness, in which the matrix fibres run parallel to the junction. The second layer is characterized by two types of fibre bundles which run perpendicularly to the dentine-cement junction. These outer radially oriented fibres are about 1-2 microns in diameter, and the inner radially oriented fibre bundles are coarse, 10 microns in diameter. In the outermost 10 microns, mineralization begins as an aggregation of mineral granules, and forms a hypermineralized layer which overlays the junctional region between the fibres which are oriented parallel and perpendicular to the dentine-cement junction. Except for the most-superficial layer, mineralizing cones surround the radial fibre bundles at the mineralizing front. The circumpulpal dentine, which forms the floor of the pulp chamber, can also be divided into two layers by the differences in their fibrous matrix. The fibres of both of these layers lay in the plane of the predentine surface. However, in the outer layer the fibres of the matrix are randomly arranged around and between the dentinal tubules, whereas in the inner layer the fibres have a preferred orientation extending radially from a central region between the roots. In the outer layer, calcospherites, which are the units of the mineral aggregation, appear at the mineralizing front. In the inner layer, at the mineralizing front, ridges, measuring approximately 10-15 microns in width, 10 microns in height and 100 microns in length, also have a preferred orientation, 90 degrees to the fibre direction. Microradiographs show that a higher mineralized "lamellae-like' region exists in the center of each ridge-crest. X-ray diffraction indicates two preferred crystallite orientation, one is parallel to the matrix fibres and the other perpendicular to the predentine surface. The latter seems to be situated in the highly mineralized lamellae. In the circumpulpal dentine, therefore the mineralizing units have a spheritic shape in the outer layer, and a columner shape in the inner layer. As far as the author is aware the columnar mineralization unit in mammalian dentine has not been described before.