Factors Influencing the Healing of Maxillary Sinusitis of Endodontic Origin After Non-Surgical Endodontic Treatment

<b>Background/Objectives</b>: The purpose of this study was to indicate factors influencing the healing of maxillary sinusitis of endodontic origin (MSEO) after non-surgical endodontic treatment. <b>Methods</b>: The study was performed retrospectively on medical records and CBCT data of 114 teeth in 114 patients, who were referred to endodontic treatment between 2016 and 2024, performed by the same operator and according to the same treatment protocol. Fifteen factors were chosen for their possible influence on the healing of MSEO. <b>Results</b>: The rate of the complete healing of MSEO after RCT was 76.32%. The healing of MSEO was higher when CHX was applied in the final irrigation protocol (<i>p</i> = 0.022) and was less likely when there was a flare-up in-between visits or after obturation of the canals (<i>p</i> = 0.002). MSEO was more likely to heal when a tooth was treated in two appointments than with single-visit RCT (<i>p</i> = 0.012). The number of endodontic interventions significantly influenced the healing of MSEO, as it was less likely to heal when there was more than one endodontic retreatment for a tooth (<i>p</i> = 0.01). <b>Conclusions</b>: Within the limitations of this retrospective study, four factors significantly influenced the healing of MSEO, and these should be taken into consideration in obtaining treatment protocols for dental-induced sinusitis and the better assessment of the possible success of this non-invasive treatment approach.