Effect of sodium hypochlorite on human root dentine--mechanical, chemical and structural evaluation.
OBJECTIVE
To investigate the mechanical, chemical and structural alterations of human root dentine following exposure to ascending sodium hypochlorite concentrations.


METHODS
Three-point bending tests were carried out on standardized root dentine bars (n = 8 per group, sectioned from sound extracted human third molar teeth) to evaluate their flexural strength and modulus of elasticity after immersion in 5 mL of water (control), 1% NaOCl, 5% NaOCl or 9% NaOCl at 37 degrees C for 1 h. Additional dentine specimens were studied using microelemental analysis, light microscopy following bulk staining with basic fuchsin, and scanning electron microscopy (SEM). Numerical data were compared using one-way ANOVA. Bonferroni's correction was applied for multiple testing.


RESULTS
Immersion in 1% NaOCl did not cause a significant drop in elastic modulus or flexural strength values in comparison to water, whilst immersion in 5% and 9% hypochlorite reduced these values by half (P < 0.05). Both, carbon and nitrogen contents of the specimens were significantly (P < 0.05) reduced by 5% and 9% NaOCl, whilst 1% NaOCl had no such effect. Exposure to 5% NaOCl rendered the superficial 80-100 mum of the intertubular dentine permeable to basic fuchsin. Three-dimensional SEM reconstructions of partly demineralized specimens showed NaOCl concentration-dependent matrix deterioration. Backscattered electron micrographs revealed that hypochlorite at any of the tested concentrations left the inorganic dentine components intact.


CONCLUSIONS
The current data link the concentration-dependent hypochlorite effect on the mechanical dentine properties with the dissolution of organic dentine components.
Marending
M
M
Division of Endodontology, Department of Preventive Dentistry, Periodontology, and Cariology, University of Zürich Center of Dental Medicine, Zürich, Switzerland.
Luder
H U
HU
Brunner
T J
TJ
Knecht
S
S
Stark
W J
WJ
Zehnder
M
M
D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D019551:Dental Disinfectants / Q000008:administration & dosage*; D003804:Dentin / Q000737:chemistry / Q000187:drug effects* / Q000648:ultrastructure; D006801:Humans; D008964:Molar, Third / Q000187:drug effects*; D012973:Sodium Hypochlorite / Q000008:administration & dosage*
D019551:Dental Disinfectants; D012973:Sodium Hypochlorite