Extra oral comparison of smear layer removal from root canals when using phosphoric acid and RCprep- NaOCL: A SEM study

The smear layer is a thin layer of microcrystalline and organic debris which forms due to instrumentation of canal walls. Today, it is known that the smear layer contains bacteria as well as the nutrients necessary for bacteria. However, it is at the same time a barrier against penetration of irrigants and filling materials into dentinal tubules. Thus it is a factor that can cause micro-leakage and treatment failure. Smear layer removal will increase the adaptation between filling material and canal walls, and therefore it improves the overall sealing quality. Obtaining the cleanest canal possible before obturation is one of the goals of Endodontic treatment. The purpose of this in vitro study was to evaluate the smear layer removal ability of the 10% phosphoric acid and RCprep-5.25% NaOCL in the middle third of the root canals. Twenty freshly extracted human mature anterior teeth with single root canals were used in this study. Then the teeth were divided into three groups. Root canal instrumentation was conducted after decrownation of teeth at the CEJ level. Normal saline was used as irrigants during instrumentation in group 1. After final preparation, the canals were irrigated by 10 ml 10% phosphoric acid for 5-min. In group 2, the irrigants used during instrumentation by files coated with RCprep was 2 ml 5.25% NaOCL. At the end, both groups were irrigated with 5 ml normal saline. In 2 control specimens (teeth), normal saline was the only irrigants used during instrumentation. The roots were first split longitudinally, and then one section was randomly selected for further analysis under the electron microscope. The photomicrographs were evaluated by two different investigators (in group 1) and three different investigators (in group 2). Statistical analysis was performed to detect group differences and student-t test was used to determine the significance level. Canal walls were covered with smear layer in control group. The results showed that canals irrigated with 10% phosphoric acid had less smear layer throughout the canal walls compared with the group prepared with RCprep that contained 5.25% NaOCL. This difference was statistically significant in method used in group one (P<0.05) only. Based on the findings of this study, 10% phosphoric acid is superior to RCprep - 5.25% NaOCL in terms of removing smear layer from root canal walls.