Effect of a pH-modified Low-concentration EDTA Irrigant on Smear Layer Removal and Dentin Demineralization

Abstract

 Purpose: Instrumented root canal walls are covered with a smear layer, which can harbor bacteria, provide an avenue for leakage and limit the disinfection of intratubular bacteria by preventing the penetration of intracanal irrigants and medicaments. Although ethylenediaminetetraacetic acid (EDTA) is most widely used for smear layer removal, high concentrations of EDTA can induce hyper-demineralization (erosion) of intraradicular dentin. This study aimed to evaluate the smear layer removal effect of a pH-modified low-concentration EDTA irrigant, and examine whether it induces dentin hyper-demineralization.

 Methods: Dentin slices prepared from extracted human teeth were ground with #600 SiC paper to create an experimental smear layer. Each specimen was treated with one of the following solutions: 3% EDTA solution (Smear Clean, Nippon Shika Yakuhin, pH=9.5: SC), 14.3% EDTA solution (Morhonine, Showa Yakuhin Kako, pH=7.2: MH), or 20% citric acid solution (Ultradent citric acid, Ultradent Japan, pH=1.4: CA). Smear layer removal and dentinal erosion were examined by scanning electron microscopy (SEM). Dentin slices treated with SC or MH for up to 30 min were examined with Ca and P mapping with energy dispersive X-ray spectrometry (EDX). Root canals of single-rooted human teeth instrumented with Ni-Ti rotary instruments (EndoWave, Morita) were also examined with SEM to evaluate the effect of SC irrigation on smear layer removal.

 Results: SC, MH and CA effectively removed the smear layer created on dentin slices. Dentinal erosion was hardly seen on SC- and MH-treated specimens, while it was frequently detected on CA-treated specimens. Thirty-minute treatment by MH caused severer dentinal decalcification compared with that by SC. Following intracanal irrigation with SC, the smear layer generated by Ni-Ti rotary instrumentation was almost completely removed in the middle portion of tooth roots, although a small amount of the smear layer remained in the apical portion.

 Conclusions: The 3% EDTA solution (SC) showed a smear layer removal effect comparable to that of the 14.3% EDTA solution (MH) and 20% citric acid solution (CA), and effectively removed the intracanal smear layer generated by Ni-Ti rotary instrumentation. Among the three irrigants, SC induced the mildest dentinal erosive changes.