Exploratory Evaluation of a Sodium Iodide-Based Root Canal Filling Formulation in a Canine Model of Enterococcus faecalis-Induced Periapical Inflammation

Background and Objectives: Premature loss of primary teeth can disrupt occlusal development and oral function. Although iodoform-based materials such as Vitapex® are widely used, concerns remain regarding their cytotoxicity and potential to accelerate root resorption. Sodium iodide (NaI) has emerged as a biocompatible, antibacterial alternative. This study evaluated the feasibility of a NaI-based root canal filling material in a canine model of Enterococcus faecalis-induced periapical inflammation. Methods: Periapical lesions were induced in a healthy male mongrel dog using E. faecalis (106 CFU/mL). After six weeks, the root canals were obturated with NaI paste, Vitapex®, or Calcipex. Untreated teeth and an E. faecalis-only group served as controls. Radiographic lesion sizes were monitored at 4, 8, 12, and 16 weeks post-obturation. Histological analysis at 16 weeks assessed inflammatory area and perimeter, stromal fibrosis, inflammatory cell infiltration, and myeloperoxidase (MPO) expression. Results: Radiographically, all treatment groups showed reduced lesion size relative to the positive control. No significant differences were observed among the NaI, Vitapex®, and Calcipex groups at 4 and 8 weeks; however, significant differences emerged at 12 and 16 weeks (p < 0.05). The NaI group showed lesion reduction until week 8, followed by subsequent expansion thereafter, whereas the Vitapex® and Calcipex groups showed continuous lesion reduction over time. Histologically, the periapical inflammatory area increased in the order of Vitapex® < Calcipex < NaI < positive control (p < 0.05). MPO staining identified neutrophils as the primary inflammatory cells. Conclusions: NaI paste showed favorable early radiographic healing but limited long-term stability compared with conventional materials. With further optimization, it may have potential as an alternative root canal filling material. However, given the single-animal exploratory design, these findings should be interpreted as preliminary rather than definitive evidence.