Stability of Doxycycline and Chlorhexidine Absorbed on Root Canal Dentin

Introduction: The antimicrobial agents chlorhexidine and doxycycline bind to dentin to provide sustained antimicrobial action. This study measured the stability of these chemicals on dentin adjacent to the root canal. Methods: Extracted human teeth were instrumented and irrigated with either MTAD or Endo-CHX. After aging at 37 degrees C, the canals were enlarged by 0.3 mm, dentin debris was collected, and compounds were extracted. The amount of doxycyline or chlorhexidine was measured by using reverse-phase high-performance liquid chromatography. Results: After 1 day of aging, the canals contained 3.4 +/- 1.3 mu g doxycycline or 43 +/- 20 mu g chlorhexidine. The half-lives of doxycycline and chlorhexidine were calculated to be 3.0 weeks and 14 weeks, respectively. Groups monitoring decomposition of dilute doxycycline or chlorhexidine in water had half-lives of 5.8 weeks and 40 weeks, respectively. The half-life of the antimicrobials on dentin is suspected to be largely due to diffusion of the antimicrobials. Conclusions: Compared with doxycycline, chlorhexidine is more stable on root canal dentin. (J Endod 2010;36:489-492)