Qualitative Analysis of Precipitate Formation on the Surface and in the Tubules of Dentin Irrigated with Sodium Hypochlorite and a Final Rinse of Chlorhexidine or QMiX Kamil P. Kolosowski, HBSc, DDS,* Rana N.S. Sodhi, BSc, MSc, PhD, † Anil Kishen, BDS, MDS, PhD,* and Bettina R. Basrani, DDS, MSc, PhD* Abstract Introduction: Interaction of sodium hypochlorite (NaOCl) mixed with chlorhexidine (CHX) produces a brown precipitate containing para-chloroaniline (PCA). When QMiX is mixed with NaOCl, no precipitate forms, but color change occurs. The aim of this study was to qualitatively assess the formation of precipitate and PCA on the surface and in the tubules of dentin irrigated with NaOCl, followed either by EDTA, NaOCl, and CHX or by saline and QMiX by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Methods: Dentin blocks were obtained from human maxillary molars, embedded in resin, and cross-sectioned to expose dentin. Specimens in group 1 were immersed in 2.5% NaOCl, followed by 17% EDTA, 2.5% NaOCl, and 2% CHX. Specimens in group 2 were immersed in 2.5% NaOCl, followed by saline and QMiX. The dentin sur- faces were subjected to TOF-SIMS spectra analysis. Lon- gitudinal sections of dentin blocks were then exposed and subjected to TOF-SIMS analysis. All samples and analysis were performed in triplicate for confirmation. Results: TOF-SIMS analysis of group 1 revealed an irregular precipitate, containing PCA and CHX break- down products, on the dentin surfaces, occluding and extending into the tubules. In TOF-SIMS analysis of group 2, no precipitates, including PCA, were detected on the dentin surface or in the tubules. Conclusions: Within the limitations of this study, precipitate contain- ing PCA was formed in the tubules of dentin irrigated with NaOCl followed by CHX. No precipitates or PCA were detected in the tubules of dentin irrigated with NaOCl followed by saline and QMiX. (J Endod 2014;-:1–5) Key Words Chlorhexidine, hypochlorite, parachloroaniline, TOF- SIMS, tubules M icrobial infections are the most common cause of an endodontic disease (1). To critically reduce bacterial loads, endodontic treatment regimens combine me- chanical instrumentation with chemicals, namely irrigation and medication (2, 3). The most commonly used irrigation solution is sodium hypochlorite (NaOCl). It is antimicrobial and an effective tissue-dissolving agent (4–6). It is used at a concentration varying between 0.5% and 6% (4). One disadvantage of NaOCl is its inef- fectiveness in removing the smear layer (7). Chlorhexidine digluconate (CHX) has also been suggested as a possible irrigation solution in endodontic treatment (4, 6). It exhibits antimicrobial activity in addition to substantivity (4, 6, 8). The concentrations used vary from 0.12% to 2% (4, 6). Its mode of action is a cationic binding, which causes bacterial cell membrane disruption (9). As a disadvantage, CHX is ineffective in removing the smear layer and possesses no tissue-dissolving ability (10). EDTA is a chelating agent that dissolves inorganic components of the dentin but not the organic components (4, 6, 7). Concentration used is normally 17% (4). Although its main function is to remove smear layer, dentin erosion can occur with pro- longed exposures of 10 minutes (4, 11). QMiX is a novel irrigation compound containing EDTA, CHX, and a nonspecified detergent (12). It is antimicrobial and has been shown to remove smear layer. The detergent’s function is to decrease surface tension and increase surface wettability (12, 13). In vitro studies showed that NaOCl and CHX can diffuse into dentinal tubules (DTs) to a depth of 300 mm (14, 15). Interestingly, the effect of QMiX on bacteria in 2 studies was reported to extend deeper into the tubules than CHX and similar to NaOCl, up to 500 mm (16, 17). In endodontics, irrigation solutions are used in succession, and it is crucial to discern that irrigation solutions used in succession can react with each other. This is especially evident when NaOCl is mixed with CHX. This interaction breaks down CHX, produces a brown precipitate containing para- chloroaniline (PCA) (18–20), and can occlude DTs (21). The amount of PCA is directly proportional to the concentration of NaOCl used (18). A reaction also occurs when QMiX is mixed with NaOCl, resulting in a visually detectable color change but without precipitate formation (pilot study). Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a method used in surface chemistry that has been successfully adapted to analyze mineralized tissue such as dentin (22). It consists of ion gun pulsing high-energy ions into the target surface. This bombardment causes collision cascades, disrupting atoms in the top 1 or 2 monolayers, causing an ejection and emissions of secondary ions from the sur- face. The charged ion mass is determined by the flight time from the surface to the detector (23). Mass spectra with multiple peaks that arise as a result of molecular From the *Discipline of Endodontics, Faculty of Dentistry, University of Toronto; and † Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Canada. Address requests for reprints to Dr Bettina R. Basrani, Co-Director MSc Endodontic Program, Faculty of Dentistry, University of Toronto, 124 Edward Street, Room 348C, Toronto, ON, M5G 1G6 Canada. E-mail address: Bettina.basrani@dentistry.utoronto.ca 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.08.017 Basic Research—Technology JOE — Volume -, Number -, - 2014 Parachloroaniline in Dentinal Tubules 1