The Effect of Various Concentrations of Sodium Hypochlorite on the Ability of MTAD to Remove Smear Layer

By Torabinejad M, Khademi A, Bakland L, Shabahang S

Date: 03/2004
Journal: JOE


•Purpose:  to investigate the effectiveness of various concentrations of NaOCl as a root canal irrigant before the use of MTAD as a final irrigant to remove the smear layer

. •N=   80 extracted maxillary and mandibular single- and multi- rooted teeth. Exclusion: teeth with previous RCT


oTeeth were randomly divided into 7 experimental groups and two control groups according to the type of irrigants and final rinses used during and after instrumentation (Table 1).

oTen operators perform instrumentaion using a combination of passive step-back &rotary  #30-.04 file .

oA total of 10 ml of irrigant was used in each canal penetrated to within 1 to 2 mm from the WL . 2 min exposure time for the final rinse. Three investigators scored the presence or absence of smear layer at the coronal, middle, and apical portion of each canal and the degree of erosion using SEM.

Most highlighted Results: 

1.Root canals irrigated with 5.25% NaOCl and a final rinse of EDTA were significantly cleaner than those irrigated and rinsed with distilled water or 5.25% NaOCl. With EDTA smear layer was completely removed from the middle and coronal thirds and less effective in the apical third of the canals.

2.The amount of smear layer in canals irrigated with MTAD during cleaning &shaping and as a final rinse was significantly less than those irrigated with 5.25% NaOCl or distilled water alone. However, The surfaces were covered with scattered remnants of the organic component of the smear layer. (Fig. 2)

3.No significant differences were noted between canals that were irrigated with 1.3%, 2.6%, or 5.25% NaOCl and a final rinse of MTAD. 4.MTAD is less destructive to tooth structure compared with EDTA when used as a final irrigant

Clinical significance

NaOCl is needed as an irrigant to assist MTAD to completely remove the smear layer. The use of EDTA and NaOCl is an effective method for smear layer removal.