The Effect of Preparation Size on Efficacy of Smear Layer Removal; A Scanning Electron Microscopic Study

Enlargement of the root canal may potentially affect efficient smear layer (SL) removal. The aim of the present in vitro study was to compare SL removal following canal preparation with two different sizes/tapers by means of scanning electron microscopy (SEM).

A total of 50 extracted human mandibular premolars were decoronated. The teeth were randomly divided into two experimental groups (n=20) and two negative control groups. In groups 1 and 2 the sizes of master apical file (MAF) were #25 and 40, respectively. Coronal part of the canals were flared with #2 Piezo drills in group 1 and sizes #2 to 6 in group 2. Finally FlexMaster NiTi rotary instruments were used to complete canal preparation (25/0.04 and 35/0.06 in groups 1 and 2, respectively). The irrigation protocol consisted of 10 mL of 17% ethylenediaminetetraacetic acid (EDTA) for 1 min followed by 10 mL of 5.25% NaOCl for 3 min. The patency of dentinal tubules was evaluated under SEM with Hülsmann scores. Data were analyzed with the Kruskal-Wallis and Mann-Whitney U tests.

The number of patent dentinal tubules in coronal third of the group 1 was significantly more than group 2 (P<0.001). However, this difference was not significant for the middle and apical segments. There was a significant difference in the number of patent dentinal tubules between coronal, middle and apical thirds (P<0.05).

Increasing the canal preparation size did not lead to better cleanliness of the canal walls and more efficient smear layer removal.