The risk of intentional dissolution of the smear layer after mechanical preparation of root canals

The root canals of 27 caries-free human cuspids were divided into 3 groups of 9 teeth each. Group I was mechanically prepared with reamers and files. Alternate irrigation with 5.25% NaOCl and 3% hydrogen peroxide was used between each instrument. The group II root canals were prepared with the use of alternate irrigation with the same concentrations of NaOCl and hydrogen peroxide and finally flushed with 17% EDTA and NaOCl solution. Group III was prepared mechanically with the use of sterile distilled water as an irrigant followed by a final flush with 17% EDTA solution. The root canals of all specimens were obturated with gutta-percha points and Tubliseal by means of the lateral condensation technique. After the root canals were obturated, samples of each of the three groups were immersed in separate flasks containing Streptococcus mutans, Staphylococcus epidermidis, and Corynebacterium hofmannii. All the microorganisms tested invaded the coronal dentin--where the access cavity had been sealed with Fynal--and/or the main foramen.