The substitution of chlorhexidine for doxycycline in MTAD: the antibacterial efficacy against a strain of Enterococcus faecalis.

The antimicrobial effect of MTAD has been largely attributed to the presence of doxycycline. In the present study, chlorhexidine was added to or substituted for doxycycline to compare these three formulations in their ability to disinfect extracted human teeth infected with Enterococcus faecalis. Ten teeth were used in each group along with positive and negative controls. The teeth were treated according to previously published protocols. None of the samples treated with MTAD or MTAD + chlorhexidine showed the presence of residual bacteria. In contrast, 7 of 10 samples treated with MCAD (chlorhexidine substituted for doxycycline) showed positive cultures of E. faecalis. The results clearly showed that although the addition of chlorhexidine did not negatively impact the efficacy of MTAD, the substitution of this antimicrobial agent for doxycycline significantly reduces the efficacy of the solution.