Gingival inflammation around abutment teeth in patients with overdentures is primarily caused by accumulation of plaque and debris due to inadequate oral hygiene. The abutment teeth are more prone to periodontal issues because they retain the denture and create niches where bacteria thrive. Maintaining proper oral hygiene, including regular cleaning of abutments and denture hygiene, is essential to prevent inflammation. Other causes like allergic reactions or denture overextensions are less common and typically present differently. Therefore, poor oral hygiene remains the most likely cause of gingival inflammation in overdenture patients.

Reference: Prosthodontics, Anil Singh, 2nd Edition.