Development of an ex-vivo model for endodontic antibacterial protocols assessment

Background: The in-vivo quantification of root canal bacteria for efficacy assessment of antibacterial regimens applied in endodontic treatments often creates inconvenience for patients and treatment providers. Objectives: To develop an ex-vivo model that would allow bacterial quantification under clinically simulated conditions. Methods: Immediately after extraction, 36 single-rooted teeth were transferred to a humidified incubator and stored at 37°C. The teeth were divided into 4 groups (n=9), those treated immediately and those treated after 2d, 4d or 6d. The tooth crown was disinfected and the root canal accessed. A bacteriological sample was taken by aspirating the root canal contents (S1). The root canal was sealed and the tooth was returned to the incubator. After 1 week, the canal was re-accessed, sampled (S2), debrided and enlarged and sampled again (S3). After further storage for 1 week, the canal was re-accessed and re-sampled again (S4). Quantification of the bacterial contents of each sample was determined using CFU counts and epifluorescence microscopy (EFM). Mean-intra and inter-group counts were calculated and compared using exact permutation tests for small samples. Results: the CFU counts and those obtained by epifluorescence staining showed similar trends, with EFM showing significantly higher densities (counts per µL of root canal) than the CFU (1.94x102 ± 3.33x102 and 7.62x105 ± 1.05x106, respectively). In all groups, no re-growth of bacteria occurred between S1 and S2, or between S3 and S4. Conclusion: This study suggested that ex-vivo treatment after extraction of naturally infected teeth has the potential for assessing one-visit endodontic treatment regimens. Grants: American association of endodontists, International Federation of Endodontic Associations, Canadian Academy of Endodontics and Alpha omega foundations.