Morphological, structural and chemical composition study of pulp nodules in human teeth

Pulp stones are mineralized structures that are formed inside the dental pulp of permanent and deciduous teeth in various clinical situations. The formation of these structures may preclude the endodontic treatment. Several microscopic, histological and prevalence studies have already been carried out and have demonstrated that the formation of pulp stones may be due to local, systemic or genetic factors. However, the results are controversial and insufficient to define the etiology of pulp stones. The aim of this paper was to perform a morphological, structural and chemical analysis study of pulp stones for a better understanding of their origins and pathophysiology. Thirteen samples of pulp stones and dentin obtained from unerupted and erupted teeth were part of the sample. All pulp stones were evidenced by periapical radiography. The samples were then analyzed by scanning electron microscopy (SEM) with secondary electron (SEM-SE) and backscatter electron (SEM-BSE) imaging, energy dispersive X-ray spectroscopy (EDX), micro-RAMAN spectroscopy (EMR), micro-diffraction (mDRX) and Argon inductively coupled plasma atomic emission spectroscopy (ICP-AES). As a result, it was noticed that the pulp stones had a great heterogeneity in relation to their morphology and surface, regardless of the clinical situation when they were in the mouth. mDRX and EMR revealed that the predominant crystal phase corresponded to hydroxyapatite. Moreover, dentin and pulp stones were very similar in composition, with no preferential growth direction and no significant differences in crystallite size. The results of EDX showed that dentine and the interior of the pulp stone presented similar chemical structure and consisted mainly of the following chemical elements: O, Ca, C and P. Higher concentrations of C, N, S, Cl, Al, K, Zn, Cu and Pb were found on the outer surface of the pulp stones due to its proximity to the organic matter, vessels and nerves of the pulp tissue. The ICP-AES technique evaluated the nodule completely, with no differentiation between surface and interior. It showed that the amount of Cu, Fe and Zn were significantly higher in the pulp stone than in dentin. In addition, it showed that there is no significant difference between the elemental structure of a pulp stone of an unerupted tooth compared with one of an erupted one. In conclusion, the physicochemical and crystalline structure of the pulp nodules is very similar to dentin, with only morphological variances among them. (author)