Permanent mucosal discoloration correlated to magnesium-enriched hydroxyapatite: a case report.

Purpose: To describe a clinical case where magnesiumenriched hydroxyapatite (MHA) (SintLife®) used for socket preservation has induced a permanentmucosal discoloration. Methods and materials: After a minimally traumatic extraction of a first maxillary right molar, MHA particulate was inserted into the socket for bone contour preservation. The surgical procedure as the healing process was uneventful. Two months later, the soft tissue areas corresponding to the vestibular sockets of the extracted roots displayed asymptomatic bluish discoloration. The rehabilitation of the area was suspended and the discoloration monitored. Six years later, the pigmentation was still present and the radiographic evaluation of the area showed residual biomaterial particles. The histomorphological evaluation of the soft and hard tissues was consequently performed in order to better comprehend the origin of the mucosal alteration. Results: Histological examination confirmed the presence of residual MHA particles, mainly in direct contact with bone tissue, but partly embedded into the subepithelial fibrotic chorion (see the enclosed picture). There was no melanosis or melanocytic hyperplasia in the epithelium. Mild inflammatory infiltrate was observed, without deposits of haemosiderin. These findings suggest that biomaterial represents the source of discoloration. Since the MHA preparation is white, it can be speculated that, one time into the organic environment, it has gone to a chromatic modification visible through the overlying soft tissues. However this hypothesis did not find a confirmation in the intraoperative observations, where the few particles of biomaterial seen coming out from the surgical areas were all white coloured. Alternatively an explanation of the discoloration can be found in the Tyndall effect, which refers to the fact that different wavelengths of light do not scatter depending on size of substances they encounter: longer redder wavelengths can penetrate more deeply into the soft tissues than shorter blue wavelength before reflecting out. So the light reflecting from tissue over the biomaterial contains less red light than blue, giving the biomaterial a bluish cast. For instance, a similar principle governs why veins appear blue in the skin, despite the red colour of transported blood. Conclusion: In spite of the excellent characteristics of MHA as bone substitute, the potential appearance of permanent mucosal discoloration represents a relevant drawback for oral cavity, especially for those areas with clear aesthetic demand. More investigations are needed in order to confirm the present observations and better comprehend the eventual origin of the mucosal discoloration.