Pathohistological Changes in the Maxillary Sinus Tissues During Long-Term Contact With Ah Plus Epoxy Sealant

The insertion of epoxy resin-based root sealants (e.g., AH Plus) beyond the tooth root into the maxillary sinus is a common complication of endodontic treatment, leading to chronic inflammation, fibrosis, and tissue necrosis. Despite clinical observations, the pathohistological mechanisms of these changes during prolonged contact remain poorly understood. The aim of this study was to analyze markers of inflammation, fibrosis, and toxic effects in maxillary sinus tissue during an experimental model of contact with an epoxy sealant in sheep. Materials and Methods: The experiment was conducted on 16 North Caucasian sheep. Under general anesthesia, access to the Schneiderian membrane was created in the anterior wall of the maxillary sinus, onto which AH Plus sealant was applied; the contralateral side served as a control. Follow-up periods were 1 and 2 years. Histological analysis (hematoxylin and eosin staining, van Gieson and Mallory staining) and immunohistochemistry (markers Ki-67+, NSE+, EMA+, vimentin) were performed. Statistical analysis included group comparisons and correlation analysis. Results: After 1 year, necrosis of connective tissue around the sealant, migration of its fragments, microvascular disturbances (thrombosis, necrosis), vacuolar degeneration of the epithelium, and stromal fragmentation were noted. After 2 years, intense fibrosis with chaotic collagen fiber orientation, complete vascular necrosis, bone trabecular resorption with demineralization, and epithelial desquamation were observed. Immunohistochemistry revealed moderate expression of markers indicating activation of proliferation, neovasculogenesis, and mesenchymal differentiation, but with a predominance of destructive processes (p < 0.05). Conclusions: Long-term exposure to epoxy sealant causes progressive pathohistological changes, including necrosis, fibrosis, and vascular disruption, with partial activation of reparative mechanisms. The results emphasize the need for developing more biocompatible materials and protocols to reduce complication risks in endodontics, which can improve treatment outcomes and reduce economic losses.