The effect of initial irrigation with two different sodium hypochlorite concentrations on the erosion of instrumented radicular dentin.
OBJECTIVE
This study evaluated the effects of different NaOCl concentrations and contact times on removal of the organic phase from mineralized dentin with and without the adjunctive use of EDTA, and the effect of NaOCl concentrations on canal wall erosion after the use of EDTA as the final active irrigant.


METHODS
Dentin powders were immersed in 5.25% or 1.3% NaOCl for different contact periods and then rinsed with 17% EDTA for 2 min. Before and after the use of 17% EDTA as the final rinse, the NaOCl-treated dentin powders were examined using ATR-FT-IR spectroscopy to analyze the relative loss of organic and inorganic components. Scanning (SEM) and transmission electron microscopy (TEM) were used to examine the erosion of instrumented canal walls irrigated with 5.25% NaOCl/EDTA or 1.3% NaOCl/EDTA.


RESULTS
Compared with 1.3% NaOCl, less intact collagen remained within the subsurface of the mineralized dentin powder after the use of 5.25% NaOCl, irrespective of subsequent rinsing with 17% EDTA. Canal wall erosion was apparent only under SEM when root canals were irrigated 5.25% NaOCl followed by 17% EDTA. Under TEM examination, subsurface erosion extended 10-15 microm beneath the sealer-bonded dentin surface after the use of 5.25% NaOCl for 20 min.


CONCLUSIONS
The superficial destructive effect of NaOCl on mineralized dentin is irreversible and is present irrespective of whether EDTA is subsequently employed as the final active irrigant. The EDTA removes the collagen-depleted apatite phase to expose the underlying cause of destruction that is morphologically perceived as canal wall erosion.
Zhang
Kai
K
Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China.
Tay
Franklin R
FR
Kim
Young Kyung
YK
Mitchell
Jan K
JK
Kim
Jong Ryul
JR
Carrilho
Marcela
M
Pashley
David H
DH
Ling
Jun-qi
JQ
D001031:Apatites / Q000032:analysis; D002614:Chelating Agents / Q000008:administration & dosage; D024042:Collagen Type I / Q000032:analysis / Q000648:ultrastructure; D003786:Dental Pulp Cavity / Q000737:chemistry / Q000187:drug effects* / Q000648:ultrastructure; D003804:Dentin / Q000737:chemistry / Q000187:drug effects* / Q000648:ultrastructure; D004338:Drug Combinations; D004492:Edetic Acid / Q000008:administration & dosage; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008903:Minerals / Q000032:analysis; D012388:Root Canal Irrigants / Q000008:administration & dosage*; D012973:Sodium Hypochlorite / Q000008:administration & dosage*; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D013997:Time Factors
D001031:Apatites; D002614:Chelating Agents; D024042:Collagen Type I; D004338:Drug Combinations; D008903:Minerals; D012388:Root Canal Irrigants; D004492:Edetic Acid; D012973:Sodium Hypochlorite