Does Para-chloroaniline Really Form after Mixing Sodium Hypochlorite and Chlorhexidine?

Did in-between rinsing and agitating with distilled water prevents precipitate formation by the interaction between sodium hypochlorite and chlorhexidine canal irrigants?

The interaction of sodium hypochlorite (NaOCl) and chlorhexidine gluconate (CHX) produces an orange-brown precipitate. The present study evaluated the influence of distilled water (H2 O) in different irrigation protocols designed to prevent the formation of precipitate with NaOCl and CHX. Fifty canine teeth were instrumented and split longitudinally. The canal was examined with a stereomicroscope and photographed by canal-thirds. The tooth halves were repositioned and distributed randomly into five groups, according to the final irrigation protocol (n = 10): G1 (control)-Ethylenediaminetetraacetic acid (EDTA) + NaOCl + CHX, conventional irrigation (CI); G2-EDTA + NaOCl + CHX, activated with passive ultrasonic irrigation (PUI); G3-EDTA (PUI) + NaOCl (PUI) + H2 O (CI) + CHX (PUI); G4-EDTA + NaOCl + H2 O + CHX (PUI); G5-EDTA (PUI) + NaOCl (PUI) + H2 O (continuous ultrasonic irrigation [CUI]) + CHX (PUI). The specimens were evaluated with a stereomicroscope and scanning electron microscope (SEM). Energy dispersive x-ray spectroscopy analysis was performed to identify the elemental profile of the irrigated canal walls. The images were scored according to the extensiveness of precipitate. Data were analyzed (Kruskal-Wallis test, α = 5%). Under the stereomicroscope, G1 had significantly higher scores than all the other groups in all canal-thirds (p < .05). All four experimental groups showed similar scores (p > .05). There were no significant differences in precipitate formation among root-thirds in intragroup analysis (p > .05). Upon SEM examination, overall, only G5 had lower scores than G1 (p < .05). Analysis by canal-thirds showed no significant difference among groups and among canal-thirds in the intragroup analysis (p > .05). G1 showed high Cl peaks. In-between irrigation with H2 O activated by CUI is effective in preventing precipitate formation during canal debridement with NaOCl and CHX. RESEARCH HIGHLIGHTS: Continuous ultrasonic irrigation with distilled water was capable to prevent the precipitate formation. The precipitate can be classified as a chemical smear layer.

Current Trends in Regenerative Endodontics: A Web-based Survey

INTRODUCTION

The aim of this study was to ascertain the current trends in regenerative endodontic procedures (REPs) among clinicians, including case selection criteria and clinical protocols.

METHODS

An online questionnaire consisting of provider demographics, case selection criteria for REPs, and clinical protocols was made available to members of the American Association of Endodontists and members of the Endolit website. Data were analyzed using the Fisher exact test.

RESULTS

Two hundred seventy-two responses were analyzed (64.6% were men and 34.7% were women). Of those, 44.5% of respondents practiced in the United States, and 55.5% practiced outside of the Unites States. Most respondents (85.4%) reported performing REPs in their practice, and 92.2% were using sodium hypochlorite as one of their disinfecting irrigants. Calcium hydroxide was the most commonly used intracanal medicament (68.4%), and the majority of respondents use a blood clot alone as the scaffold (73.5%). Most (93%) of the providers reported using a bioceramic material for coronal capping. Practitioners outside the United States were found to be more likely to use adjunctive irrigation activation (P = .003). Younger practitioners preferred REPs over apexification (P = .01). Practitioners outside the United States were more likely to perform an REP in 1 visit (P = .006). Men were found to be more likely to always instrument the canal walls (P = .031). Women were found to be more likely to use manual irrigant activation, whereas men were more likely to use sonic activation (P = .043).

CONCLUSIONS

There is significant heterogeneity within REPs regarding case selection and clinical protocol. Notable differences were observed from the reported findings of REPs from 5 years ago.

The Interaction of Two Widely Used Endodontic Irrigants, Chlorhexidine and Sodium Hypochlorite, and Its Impact on the Disinfection Protocol during Root Canal Treatment

In recent years, sodium hypochlorite and chlorhexidine digluconate have been the gold standard of irrigation solutions utilized within the disinfection protocol during root canal treatments. Nowadays, it is known that, during chemical disinfection of the root canal, consecutive application of sodium hypochlorite and chlorhexidine digluconate leads to the formation of an orange-brown precipitate. This precipitate is described as being chemically similar to para-chloroaniline, which is suspected to have cytotoxic and carcinogenic effects. Concerns also exist regarding its influence on the leakage of root canal fillings, coronal restorations, and tooth discoloration. The purpose of this article is to review the literature on the interaction of sodium hypochlorite and chlorhexidine digluconate on the tooth and its surrounding tissues, and to discuss the effect of the precipitate formed during root canal treatment. We further address options to avoid the formation of the precipitate and describe alternative irrigation solutions that should not interact with sodium hypochlorite or chlorhexidine digluconate.

Effect of irrigation protocols on chemical smear layer formation over the post-space dentin

This study evaluated the effect of irrigation protocols using 95% ethanol (ET) or 1% peracetic acid (PA) prior the use of 2% chlorhexidine (CHX) compared to distilled water (DW) on the chemical smear layer (CSL) formation and incidence of open dentin tubules at the apical, medium, and cervical third of the post-space dentin. Scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) images were used. Forty bovine roots were endodontically treated. After, post-space preparation was performed and the roots were randomized in four groups (n = 10) according to the irrigation protocol: DW, CHX, CHX-ET and CHX-PA. The chemical composition of CSL and the incidence of open dentin tubules at the post-space thirds were evaluated by EDS (500× magnification) and SEM (2000× magnification) images, respectively. Data from chemical composition of CSL were descriptively analyzed, while the incidence of open dentin tubules was evaluated by scores and submitted to Kruskal-Wallis and Dunn test (p = .05). Cl, Bi, and Si were the chemical elements most found over the dentin after the irrigation with CHX and CHX-ET. Moreover, CHX and CHX-ET showed the highest incidence of CSL (p < .05), but without difference between them (p > .05), regardless of the post-space third. DW and CHX-PA showed similar incidence of CSL (p > .05). No difference on the incidence of open dentin tubules was found for any irrigation protocol and post-space third (p > .05). The use of 1% PA prior the post-space irrigation with CHX decrease the incidence of CSL. RESEARCH HIGHLIGHTS: The post-space irrigation with chlorhexidine results in the formation of chemical smear layer. Ethanol is not capable to remove the chemical smear layer. Peracetic acid is more effective to remove the chemical smear layer.

The effects of final irrigants on the push-out bond strength of two calcium silicate-based root canal sealers: an in vitro study

Purpose:

The purpose of the present study was to investigate the effect of the different irrigant combinations used in final irrigation on the push-out bond strength of root canal sealers that have different compositions.

Materials and methods:

In total 60 dentinal slices in 1 mm thickness were collected from 15 extracted mandibular premolar teeth; 4 slices from each tooth. 3 canal-like artificial cavities were opened on each dentinal slice. Samples were divided into 4 experimental groups, each of which consisted of 15 samples. In group 1, samples were immersed in 5.25% NaOCl and 17% EDTA solutions respectively; in group 2, immersed in 5.25% NaOCl and 2% CHX solutions respectively; in group 3, immersed in 5.25% NaOCl, 17% EDTA and 2% CHX solutions respectively; and in group 4 immersed in distilled water. After drying with absorbent papers, each cavity in dentinal slice sample was filled with different sealer (Endoseal MTA, Tech Biosealer Endo or AH Plus). Two days later, the push-out bond examination was performed.

Results:

AH Plus showed higher push-out bond strength value in two combinations (group 2 and 3) in which final irrigants contained CHX (p<0.001). Dentinal push-out bond strengths of root canal sealers from Endoseal MTA and Tech BioSealer Endo were not affected by final irrigant (p=0.965).

Conclusion:

Using CHX after NaOCl in final irrigant increases push-out strength of epoxy resinbased sealer but, did not create any difference in dentinal push-out bond strength of calcium silicate-based sealers.

Assessment of the cytotoxic effects and chemical composition of the insoluble precipitate formed from sodium hypochlorite and chlorhexidine gluconate

AIM

To investigate (1) the cytotoxic potential of the brown precipitate (BP) formed with sodium hypochlorite (NaOCl) and chlorhexidine gluconate (CHX), using both a small animal model of Caenorhabditis elegans (C. elegans) and cultured human gingival fibroblasts; and (2) the chemical composition of BP using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

METHODOLOGY

Brown precipitate was obtained by mixing equal volumes of 6% NaOCl and 2% CHX and separating the BP from clear supernatant by centrifugation. The brown precipitate was weighed and solubilized in dimethyl sulfoxide for cytotoxicity experiments. The cytotoxic effect of BP was assessed using C. elegans larvae and primary immortalized human gingival fibroblasts-hTERT (hTERT-hNOF) cells. Various dilutions of BP (25 ng/µL-150 ng/µL), supernatant (0.15% v/v), NaOCl (1:100-1:1000 dilutions of 6% NaOCl) or CHX (1:500-1:1000 dilutions of 2% CHX) along with vehicle control (0.5% v/v ethanol and 0.15% v/v DMSO) or untreated control (growth medium) were tested on C. elegans larvae and hTERT-hNOF cells. Viability was assessed in C. elegans larvae using stereomicroscopy and in hTERT-hNOF cells using dehydrogenase-based colorimetric assay. ToF-SIMS was used to assess the chemical composition of BP in comparison with CHX and para-chloroaniline (PCA). The C. elegans and cell line data were analysed using Log-Rank test and Student's t-test, respectively (p < .05).

RESULTS

BP-75 ng/µL and BP-150 ng/µL were significantly more toxic to C. elegans larvae than the untreated, vehicle, supernatant or CHX treatment groups (p < .0001). Similarly, in hTERT-hNOF cells, BP-50 ng/µL, BP-75 ng/µL and BP-150 ng/µL induced significant cytotoxicity within 2 h compared with untreated, vehicle, supernatant and CHX treatments (p < .05). ToF-SIMS analysis of BP revealed ion composition characteristic of both CHX and the carcinogen PCA.

CONCLUSIONS

Brown precipitate was toxic in both C. elegans larvae and hTERT-hNOF cells. The ToF-SIMS analysis of BP revealed ions characteristic of CHX and PCA that could account for the toxicities observed in C. elegans larvae and human gingival fibroblasts. Because of the insoluble and toxic nature of BP, consecutive use of CHX and NaOCl irrigants should be avoided in root canal treatment.

Bacterial Contamination of Gutta-Percha Points From Different Brands and the Efficacy of a Chairside Disinfection Protocol

OBJECTIVE

To evaluate the bacterial contamination of different brands of Gutta-Percha (GP) points routinely used in clinical practice and the efficacy of a chairside disinfection protocol with sodium hypochlorite.

METHODS

GP points (n=240), in sizes A, B, C, D, K15, K20, K25, K30, K35, K40, F1, F2, F3 (Dentsply®, Proclinic®, ProTaper® and R&S®), were randomly sampled from commercial packages already in use. These were added directly to Fluid Thioglycolate Medium (one GP point per tube) and incubated at 37ºC for 21 days. During this period, the presence/absence of turbidity was evaluated. To evaluate the efficacy of a chairside disinfection protocol, all detected contaminated GP points were immersed for 1 minute in 10 mL of 5.25% sodium hypochlorite, followed by 5 minutes in 10 mL of detergent solution (3% Tween 80 and 5% sodium thiosulfate) and a final rinse with 10 mL of sterile distilled water and incubated. The data was analysed using the chi-square test and differences between characteristics of dichotomic variables were performed using the binomial test. The significance level was set at P<0.05.

RESULTS

Bacterial growth was observed in 22.9% of the total study samples. Dentsply® and R&S® showed the highest level of contamination, 47.3% each, although without significant differences to the other commercial brands. The most contaminated GP point size was K30 (16.4%). The chairside disinfection protocol was effective in disinfection of 76.4% of GP points (P<0.001).

CONCLUSION

A real small number of GP points in clinical use harboured bacteria, including after the Chairside Disinfection Protocol that, anyway, proved to be effective. No significant difference was observed between tested commercial brands.

Decoding the Perplexing Mystery of Para-Chloroaniline Formation: A Systematic Review

Objective

The objective of this article was to understand and decode the mystery of the formation of para-chloroaniline (PCA). The ingredient of the brown precipitate after mixing sodium hypochlorite (NaOCl) and chlorhexidine gluconate (CHX) is still in debate.

Materials and Methods

Various studies adopt a different methodology to substantiate that it may contain PCA, which is a carcinogenic agent. The purpose of this systematic review is to evaluate the relationship between PCA and brown precipitate. Two reviewers independently conducted a comprehensive literature search. The MEDLINE, Embase, Cochrane, and PubMed databases were searched. In addition, the bibliographies were manually searched. There was no disagreement between the two reviewers. This review was reported and conducted in step with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

Results

Of 233 articles, only 13 articles met the inclusion criteria. Available scientific evidence was more supportive that the brown precipitate form after mixing NaOCl and CHX may form para-chloroamide moiety rather than free PCA, and PCA may be the by-product of CHX degradation.

Conclusion

On the basis of the current evidence and data extracted from the various databases, it can be concluded that the mixture of sodium hypochlorite and chlorhexidine does not form PCA, and PCA may be the by-product of high concentrated chlorhexidine. Further studies are required to substantiate the evidence.

Proton Nuclear Magnetic Resonance Spectroscopy Analysis of Mixtures of Chlorhexidine with Different Oxidizing Agents Activated by Photon-Induced Photoacoustic Streaming for Root Canal Irrigation

Objective: The aim of this in vitro study was to investigate the possible interactions between photon-induced photoacoustic streaming (PIPS™)-activated oxidizing agents and 2% chlorhexidine digluconate. Background data: There is no information about the safety of laser-activated oxidizing agents in combination usage with chlorhexidine gluconate. Materials and methods: Groups were designed as follows G1: 98% para-chloroaniline (PCA); G2: 2% chlorhexidine (CHX); G3: 5.25% sodium hypochlorite (NaOCl) +2% CHX; G4: 5.25% NaOCl (30 sec PIPS activated) +2% CHX; G5: 5.25% NaOCl (60 sec PIPS activated) +2% CHX; G6: 3.5% chlorine dioxide (ClO₂) + 2% CHX; G7: 3.5% (ClO₂) (30 sec PIPS activated) +2% CHX; G8: 3.5% (ClO₂) (60 sec PIPS activated) +2% CHX. The laser-irrigation protocol was performed with an erbium:yttrium-aluminum-garnet laser with a wavelength of 2940 nm equipped with a 140 mm long endodontic fiber tip (PIPS) using 10 mJ at 15 Hz (0.15 W), per pulse operating outputs. Groups were analyzed with proton nuclear magnetic resonance spectroscopy, using PCA as an internal standard. Results: No free PCA was formed in any groups of mixtures or after PIPS activation. Conclusions: Mixing of 3.5% ClO₂ and 2% CHX does not form bulky precipitates, unlike the mixture NaOCl + CHX. PIPS activation does not cause changes in reactions of oxidizing agents.

Dentinal Tubule Penetration and Dislocation Resistance of a New Bioactive Root Canal Sealer Following Root Canal Medicament Removal Using Sonic Agitation or Laser-Activated Irrigation

Objective:

To investigate the influence of sonic agitation or laser-activated irrigation techniques on the removal chlorhexidine (CHX) and modified triple antibiotic paste (mTAP) on the sealer penetration depth and dislocation resistance of Guttaflow Bioseal.

Methods:

Single-rooted mandibular premolars (n=96) were prepared with rotary nickel titanium instruments and randomly divided into two groups (n=48) based on the intracanal medicaments used: Group 1, mTAP; Group 2, CHX gel. After 7 days, the specimens in each group were divided into three subgroups (n=16) based on the supplementary irrigation technique used to remove the medicaments: laser activated irrigation (Er, Cr: YSGG laser, Waterlase MD, Biolase Technology Inc., San Clemente, CA, USA), sonic agitation (EndoActivator, Dentslpy Sirona Endodontics, PA, USA) and syringe-and-needle irrigation (control) techniques. Canals were filled with single matched-taper gutta-percha cone and a calcium silicate-based sealer (GuttaFlow® Bioseal, Coltène/Whaledent, Langenau, Germany). At the end of three weeks, sealer penetration was investigated using confocal microscopy (n=6), and dislocation resistance was calculated by measuring the push-out bond strength (n=10). Statistical analysis was performed using three-way analysis of variance (ANOVA) and Tukey post-hoc test (P=0.05).

Results:

Laser activated irrigation resulted in significantly higher depth of sealer penetration compared to sonic agitation and syringe irrigation (P<0.01). The average sealer penetration depths were recorded as 846.6 µm, 786.5 µm and 505 µm in the Er, Cr: YSGG laser, EndoActivator and control groups, respectively. The mean bond strength obtained in group 3 (syringe-and-needle irrigation) was significantly less than the other groups (P<0.05). The mean values were 9.08 in the Er, Cr: YSGG laser group, 8.44 in the EndoActivator group and 5.08 in the needle group.

Conclusion:

Er,Cr;YSGG laser irrigation to remove the medicaments was advantageous to other irrigation techniques in sealer penetration and dislocation resistance of the sealer.

In vitro assessment of interaction between lidocaine hydrochloride and sodium hypochlorite on root canal dentin before and after chemomechanical instrumentation procedures

Introduction

To investigate the effect of resultant precipitate formed on interaction between 2% lidocaine hydrochloride with adrenaline (LA) and 2.5% sodium hypochlorite (NaOCl) on root canal dentin before and after chemomechanical preparation, using scanning electron microscopy (SEM).

Methods

Sixty mandibular premolars were decoronated, and the root length was standardized. All specimens were randomly distributed into the following three groups: Group I (control): 2% LA mixed with sterile water without root canal instrumentation, Group II: 2% LA with 2.5% NaOCl and no instrumentation, and Group III: 2% LA with 2.5% NaOCl, followed by mechanical instrumentation with rotary files. Teeth samples were sectioned into three parts, split and SEM analysis of the root canal wall was done at cervical, middle, and apical root thirds.

Results

SEM images revealed patent dentinal tubules with no precipitate occlusion in the control group, whereas there was occlusion of dentinal tubules with a precipitate in all the specimens in Group II and Group III at all the three root levels studied.

Conclusions

The precipitate formed on the interaction between 2% LA solution and 2.5% NaOCl tends to occlude the dentinal tubules at the coronal, middle, and apical root thirds. The chemomechanical rotary instrumentation procedure did not effectively remove the precipitate from all the three levels of the root specimens studied. LA/sterile water group did not result in any precipitate formation on root canal dentin.

Nuclear magnetic resonance spectroscopy and infrared spectroscopy analysis of precipitate formed after mixing sodium hypochlorite and QMix 2in1

Background

Mixing sodium hypochlorite (NaOCl) with chlorhexidine (CHX) forms a brown precipitate. QMix-2in1 (QMix) was introduced as a final irrigant. Manufacturer recommends interim flushing with saline between the application of NaOCl and QMix to prevent formation of precipitation. This study assessed whether para-chloroaniline (PCA) is formed after mixing NaOCl with QMix.

Methods

Commercially available, 5.25% NaOCl solution, 2% CHX, QMix, 15% ethylenediaminetetraacetic acid (EDTA) and 98% PCA in powder form were used. Groups were prepared at room temperature. Group 1, 98% PCA in powder form; Group 2, 2% chlorhexidine (CHX); Group 3, QMix; Group 4, 5.25% sodium hypochlorite (NaOCl) mixed with QMix; Group 5, 5.25% NaOCl mixed with CHX; Group 6, 15% EDTA mixed with CHX. The precipitates were extracted and analysed with Proton Nuclear Magnetic Resonance (1H-NMR) and Infrared (IR) Spectroscopy, using PCA as an internal standard.

Results

No PCA was found in any of the irrigant-mixture groups tested.

Conclusions

This study used the interpretation of spectral results for the amino signals of precipitate formed after mixing QMix with 5.25% NaOCl using different nondestructive analysis methods, with PCA as an internal standard (control). We conclude that mixing QMix or 2%CHX with 5.25% NaOCl does not yield free PCA.

Alkaline Sodium Hypochlorite Irrigant and Its Chemical Interactions

Endodontic irrigating solutions may interact chemically with one another. This is important, because even when solutions are not admixed, they will come into contact with one another during an alternating irrigation technique, forming unwanted by-products, which may be toxic or irritant. Mixing or alternating irrigants can also reduce their ability to clean and disinfect the root canal system of teeth by changing their chemical structure with subsequent loss of the active agent, or by inducing precipitate formation in the root canal system. Precipitates occlude dental tubules, resulting in less penetration of antimicrobials and a loss of disinfection efficacy. Sodium hypochlorite is not only a very reactive oxidizing agent, but is also the most commonly used endodontic irrigant. As such, many interactions occurring between it and other irrigants, chelators and other antimicrobials, may occur. Of particular interest is the interaction between sodium hypochlorite and the chelators EDTA, citric acid and etidronate and between sodium hypochlorite and the antimicrobials chlorhexidine, alexidine, MTAD and octenisept.