The success or failure of root canal therapy depends upon the ability to remove all or most of the debris in the canal during instrumentation. Sodium hypochlorite (NaOCl) is the solution most commonly used to irrigate the canal. NaOCl used in dentistry has a 5.25 percent concentration, which can be diluted to 2.60 percent, 1.3 percent, or .66 percent concentration. As pulp solubilizers, the 5.25 percent and 2.60 percent concentrations of NaOCl were equally effective (greater than 90 percent), and 5.25 percent NaOCl was capable of dissolving virtually the entire organic component of dentin (Beltz et al 2003). NaOCl alone, however, does not remove the smear layer left behind from the instrumentation process. Ethylene diamine tetra-acetic acid (EDTA) is commonly used to remove this smear layer. Studies have shown the effectiveness of EDTA in removing up to 70 percent of the inorganic material in dentin.
Recently, a new intracanal irrigant has come on the market to compete with EDTA. MTAD is a mixture of tetracycline isomer (doxycycline), an acid (citric acid), and a detergent (Tween 80). The protocol for clinical use of MTAD is 20 minutes with 1.3 percent NaOCl followed by 5 minutes of MTAD. The solubilizing effects of MTAD on pulp and dentin are somewhat similar to those of EDTA. The major difference between the actions of these solutions is a high binding affinity of the doxycycline present in MTAD for the dentin. (Beltz et al J Endod 2003) The benefit of the doxycycline in MTAD can be seen in the study by Torabinejad et al comparing it to NaOCl and EDTA in the ability to kill E. faecalis. MTAD is found to be as effective as 5.25 percent NaOCl and significantly more effective than EDTA. Furthermore, MTAD is significantly more effective in killing E. faecalis than NaOCl when the solutions are diluted. MTAD is still effective in killing E. faecalis at 200x dilution, but NaOCl ceases to be effective at 32x dilution. EDTA did not exhibit any antibacterial activity. Shabahang et al conducted a study to compare the abilities of MTAD and NaOCl in disinfecting human root canals that had been contaminated with whole saliva. Twenty-three of sixty teeth treated with NaOCl remained infected. Only one of sixty teeth treated with MTAD remained infected.
With every new product we are always concerned about the cytotoxicity to the underlying tissue and the effect it may have on the strength of dentin. MTAD was compared with commonly used irrigants and medications in a study by Zhang et al in 2003. The results showed MTAD to be less cytotoxic than eugenol, 3 percent H2O2, Ca(OH)2 paste, 5.25 percent NaOCl, Peridex, and EDTA. It is more cytotoxic than NaOCl at 2.63 percent, 1.31 percent, and 0.66 percent concentrations.
Machnick et al conducted a study to evaluate the effect of MTAD on the flexural strength and modulus of elasticity of dentin. The result showed no significant difference in flexural strength and modulus of elasticity between the dentin bars exposed to saline or MTAD when applied according to clinical protocol as stated above.
According to all these studies, MTAD seems to be an excellent intracanal irrigant if used according to clinical protocol. It is better than EDTA in killing bacteria and less cytotoxic than most irrigants. This new irrigant may help increase the success rate of root canal therapy in infected root canals.
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