Effects of concentration of sodium hypochlorite as an endodontic irrigant on the mechanical and structural properties of root dentine: A laboratory study

Haiping Xu, Zhou Ye, Anqi Zhang, Fei Lin, Jing Fu, Alex S.L. Fok

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AIM: The use of high-concentration sodium hypochlorite (NaOCl) as an endodontic irrigant remains controversial because of its potential impact on the fracture strength of endodontically treated teeth. This study evaluated the effects of using different NaOCl concentrations, with 2-min-ethylenediaminetetraacetic acid (EDTA) as the final active irrigant, on the biomechanical and structural properties of root dentine.

METHODOLOGY: A new test method, which is more clinically relevant, was utilized to calculate the fracture strength of root dentine. Bovine incisors were used to obtain root dentine discs. The root canals were enlarged to mean diameter of 2.90 mm with a taper of 0.06. The resulting discs were divided into five groups (n = 20) and treated with different concentrations of NaOCl (5.25%, 2.5%, and 1.3%) for 30 min plus 17% EDTA for 2 min. The discs were then loaded to fracture by a steel rod with the same taper through the central hole. The fractured specimens were examined by scanning electron microscopy to evaluate changes in the dimensions of the remaining intertubular dentine and the tubular radius. Micro-hardness was also measured with a Knoop diamond indenter along a radius to determine the depth of dentine eroded by the irrigation. Results were analysed by one-way anova and the Tukey test. The level of significance was set at α = 0.05.

RESULTS: The damage by NaOCl increased with its concentration. 5.25% NaOCl greatly reduced the fracture strength of root dentine from 172.10 ± 30.13 MPa to 114.58 ± 26.74 MPa. The corresponding reduction in micro-hardness at the root canal wall was 34.1%. The damages reached a depth of up to 400 μm (p < .05). Structural changes involved the degradation of the intratubular wall leading to enlarged dentinal tubules and the loss of intertubular dentine. Changes in the microstructural parameters showed positive linear relationships with the fracture strength.

CONCLUSIONS: With the adjunctive use of EDTA, NaOCl caused destruction to the intratubular surface near the root canal and, consequently, reduced the root dentine's mechanical strength. The higher the concentration of NaOCl, the greater the effect. Therefore, endodontists should avoid using overly high concentration of NaOCl for irrigation to prevent potential root fracture in endodontically treated teeth.

Original languageEnglish (US)
Pages (from-to)1091-1102
Number of pages12
JournalInternational Endodontic Journal
Issue number10
StatePublished - Oct 2022

Bibliographical note

Funding Information:
Haiping Xu would like to thank the Minnesota Dental Research Center for Biomaterials and Biomechanics for hosting her visit, during which this study was performed. This work was supported by the National Natural Science Foundation of China (No. 81600903).

Publisher Copyright:
© 2022 The Authors. International Endodontic Journal published by John Wiley & Sons Ltd on behalf of British Endodontic Society.


  • fracture strength
  • root canal irrigation
  • root dentine
  • root fracture
  • sodium hypochlorite

PubMed: MeSH publication types

  • Journal Article


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