Tissue characteristics in a traumatised immature necrotic incisor after unsuccessful regenerative endodontic treatment: an immunohistological case report.

The present case report aimed to present an immunohistological analysis of newly formed intracanal tissues in a traumatised immature permanent incisor with pulp necrosis and apical periodontitis following RET. A 7-year-old girl sustained a combined traumatic dental injury, an uncomplicated crown fracture and lateral luxation, affecting an immature maxillary central incisor. The tooth subsequently developed pulpal necrosis and apical periodontitis and was treated with RET using calcium hydroxide as an intracanal medicament. A blood clot served as the scaffold, followed by placement of calcium silicate cement (Biodentine®) and a definitive resin composite restoration. During follow-up, the tooth developed ankylosis with progressive infraocclusion. At 13 years of age, the tooth was extracted, and prosthetic rehabilitation was completed using a resin-bonded Rochette bridge. Histological and immunohistological analyses revealed a heterogeneous mixture of mineralised and connective tissues within the root canal space. The tissues demonstrated infiltration of fibroblast-like cells, resorptive cells, blood vessels and nerve fibres. Numerous fibrous cystic structures containing cholesterol crystals were identified in the middle third of the root canal. The newly formed intracanal tissues demonstrated limited similarity to intact odontogenic tissues. Both inflammatory root resorption and ankylosis-related replacement resorption, likely associated with the initial luxation injury, were observed. The presence of cholesterol crystal deposits represents a novel finding that may provide new insights into the biological processes occurring after RET. As cellular events following RET cannot be fully controlled clinically, the risk of unfavourable outcomes should be considered carefully, particularly in cases involving luxation injuries.