The effect of root canal irrigation regimens on dentin collagen

Abstract

Objectives: Dentin exposed to endodontic chemicals such as sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) demonstrates a detrimental effect on its matrix characteristics. The effects of different irrigation sequences remain to be investigated in detail. The aim of this study was to characterize the effect of 2 possible irrigation sequences with NaOCl and EDTA on the ultrastructural and matrix characteristics of root dentin. Methods: Root canals (n=10) were prepared with rotary instruments, using 3% NaOCl as the irrigant, and rinsed with 3% NaOCl (30 minutes) and 17% EDTA (2 minutes). The specimens were randomly divided into two groups for the final rinse: Group 1, 0.9% saline; Group 2, 3% NaOCl (2 minutes). Five untreated teeth served as controls (Group 3). The root canal walls were analyzed under scanning electron microscopy (SEM). The percentage of open dentinal tubules (ODT %) and smear layer were graded and statistically analyzed using Kruskal-Wallis test (P=0.05). Decalcified, stained specimens were observed under light microscopy and polarized light microscopy. Results: SEM analysis of the control group revealed thick deposits of tissue debris, obliterating the dentinal tubules. Group 1 and 2 showed significantly higher ODT %, and less smear scores, compared to the control (P<0.05), with no significant difference between Groups 1 and 2 (P>0.05). Both groups showed evidence of dentinal erosion, with Group 2 demonstrating tunnelling dentinal erosion and wider dentinal tubular opening. Light microscopic analysis revealed superficial and subsurface collagen exposure in Group 1, while Group 2 exhibited surface collagen damage and increased density of hydroxyapatite-encapsulated collagen in the subsurface. Both groups showed increased birefringence, characteristic of disorganized collagen structure to varying depths. Conclusions: This is the first study to demonstrate that chemicals used for contemporary irrigation sequences significantly altered the dentin matrix, both at the surface and/or subsurface levels. The transitional impact of this effect is under investigation.