Establishment of an optimized ex vivo system for artificial root canal infection evaluated by use of sodium hypochlorite and the photodynamic therapy.

ABSTRACT

AIM: To establish a refined model of artificially infected root canals and confirm its suitability as a sensitive ex vivo method to assess the efficacy of disinfecting agents. Disinfection was evaluated using sodium hypochlorite (NaOCl), either blocked or unblocked by sodium thiosulphate, and a recently promoted method of disinfection, the antibacterial photodynamic therapy (PDT). METHODOLOGY: The roots of bovine incisors were sectioned into three parts, the canals of coronal and middle regions were filled with a suspension of Enterococcus faecalis and the apical region with culture medium. After 7 days, coronal sections were disinfected using NaOCl (0.5%, 1.0% and 3.0% for 30, 60 and 600 s) or a system for photoactivated chemotherapy (PACT; Cumdente, Tübingen, Germany) for antibacterial PDT. Apical sections served as sterile controls and middle sections as bacterial growth controls. In half of the NaOCl-treated specimens, disinfection was arrested. Dentine chips from biopsies at different depths from the central canal towards the periphery were plated and assessed for colony-forming units (CFU). Disinfection was considered biologically relevant if the reduction of CFU was at least three log10 orders of magnitude. RESULTS: Colony-forming units of 10³ - 104 in growth controls indicated effective artificial infection. A biologically relevant reduction of CFU was accomplished with unblocked NaOCl, but not after blocking with NaOCl nor with PDT. CONCLUSIONS: The system reliably detected disinfection of the root canal and dentinal tubules and proved suitable for ex vivo testing of root canal disinfection. The effect of NaOCl depended on the duration of impact. Under the present experimental conditions, the antibacterial PDT system did not achieve sufficient disinfection.