effect of duration of irrigation with sodium hypochlorite in clinical protocol of mtad on removal of smear layer and creating dentinal erosion

background and aims. the aim of the present study was to compare 1.3% sodium hypochlorite (naocl) in mtad (mixture of tetracycline isomer, acid, and detergent) for the removal of the smear layer and induction of canal erosion. materials and methods. 38 maxillary incisors were divided in three experimental groups of 10 and two positive and negative control groups of each 4 teeth, and prepared using rotary files. in test groups, 1.3% naocl was used for 5, 10 and 20 minutes during preparation followed by mtad as the final rinse. in negative control group, 5.25% naocl was used for 10 minutes followed by 17% ethylenediamine tetra-acetic acid (edta) as the final rinse. in positive control group, dis-tilled water was used for 10 minutes during preparation and then as the final rinse. the samples were examined under scan-ning electron microscope, and the smear layer and dentinal erosion scores were recorded. results. five and 10 min groups had significant differences with 20 min group (p < 0.05). in apical third, 5 and 10 min groups had also significant differences with 20 min (p < 0.05). in the coronal thirds, when the time of irrigation with 1.3% naocl increased from 5 min to 20 min, erosion also increased significantly. however, 5 and 10 min groups had no signifi-cant differences with negative control group. conclusion. the use of 1.3% sodium hypochlorite for 5 and 10 minutes in the mtad protocol removes the smear layer in the coronal and middle thirds but does not induce erosion.