Spherulitic brushite stone in the dental pulp of a cow

Pulp stones of human teeth usually contain biological apatite. In the dental pulp of a cow, aged 12 years, we observed spherulitic pulp stones, up to approximately 200 microns in diameter, consisting of radially arranged crystals with several kinds of light microscopy and scanning electron microscopy including the secondary electron and the backscattered electron signals. The crystals extending fan-like towards the periphery showed a rectangular shape, and they had subunits of elongated crystallites and fine slits of NaOCl-dissolved substances, probably including organic matter and amorphous mineral. By using energy-dispersive X-ray microanalysis, large amounts of Ca and P, and trace elements of Na, Mg, Cl, and Fe were detected from the stones. The calcium phosphate crystals were identified as biological brushite by shape, Ca/ P molar ratio, and electron diffraction pattern. Core regions of the stones containing granular structures, probably erythrocytes, were always present in blood vessels, and rectangular crystals frequently penetrated the vessel walls. Under the decalcified sections, the nidi were completely or incompletely dissolved, but the peripheries showed a radial arrangement of erythrocytes. Thus, the nidi may be thrombus or necrotic blood cells including erythrocytes. Such calcospherulites in the dental pulp of a cow were similar to the spherulitic pulp stones in human deciduous teeth reported previously, however, their nidi were present in different regions.