SCIENTIFIC ARTICLES A New Solution for the Removal of the Smear Layer

Various organic acids, ultrasonic instruments, and lasers have been used to remove the smear layer from the surface of instrumented root canals. The purpose of this study was to investigate the effect of a mixture of a tetracycline isomer, an acid, and a detergent (MTAD) as a final rinse on the surface of instrumented root canals. Forty-eight extracted maxillary and mandibular single-rooted human teeth were prepared by using a combination of passive step-back and rotary 0.04 taper nickel-titanium files. Sterile distilled water or 5.25% sodium hypochlorite was used as intracanal irrigant. The canals were then treated with 5 ml of one of the following solutions as a final rinse: sterile distilled water, 5.25% sodium hypochlorite, 17% EDTA, or a new solution, MTAD. The presence or absence of smear layer and the amount of erosion on the surface of the root canal walls at the coronal, middle, and apical portion of each canal were examined under a scanning electron microscope. The results show that MTAD is an effective solution for the removal of the smear layer and does not significantly change the structure of the dentinal tubules when canals are irrigated with sodium hypochlorite and followed with a final rinse of MTAD. Microscopic examinations of root canals show that they are irregular and complex systems, with many cul-de-sacs, fins, and lateral canals. Additionally, numerous dentinal tubules open onto the root canal surface. When the dental pulp undergoes pathologic changes caused by trauma or carious invasion, the root canal system becomes susceptible to infection by several species of bacteria, with their toxins and their by-products. The microorganisms present in the root canal not only invade the anatomic irregularities of the root