The Effect of QMix, an Experimental Antibacterial Root Canal Irrigant, on Removal of Canal Wall Smear Layer and Debris Lin Dai, DDS, MS,* Khaled Khechen, MD, † Sara Khan, BS, ‡ Brian Gillen, DMD, § Bethany A. Loushine, DMD, § Courtney E. Wimmer, BS, MS, k James L. Gutmann, DDS, PhD, ¶ David Pashley, DMD, PhD, # and Franklin R. Tay, BDSc (Hons), PhD §# Abstract Introduction: This study examined the ability of two versions of QMix, an experimental antimicrobial irrigant, on removal of canal wall smear layers and debris using an open canal design. Methods: Cleaned and shaped single-rooted human root canals were irrigated with NaOCl as the initial irrigant and one of the following as the final irrigant: (1) QMix I (pH = 8), (2) QMix II (pH = 7.5), (3) distilled water, (4) 17% EDTA, and (5) BioPure MTAD (Dentsply Tulsa Dental Specialties, Tulsa, OK). Smear and debris scores were evaluated in the coronal, middle, and apical thirds of longitudinally fractured canal spaces using scanning electron microscopy and analyzed using Cochran- Mantel-Haenszel statistic. Results: Smear scores, when the overall canal was considered, differences were observed among groups except groups 1 versus 4 and groups 2 versus 4. After adjusting for canal levels, all groups differed significantly from each other (p < 0.005) with the exception of groups 2 versus 5. For the debris scores, no significant difference was observed among the treatment groups when the overall canal was considered and after adjusting for the effect of canal level. Conclu- sion: Within the limitations of an open-canal design, the two experimental QMix versions are as effective as 17% EDTA in removing canal wall smear layers after the use of 5.25% NaOCl as the initial rinse. (J Endod 2011;37:80–84) Key Words Antimicrobial, canal level, chelation, debris, root canal irrigant, smear layer, surfactant I t is impossible to create a sterile space in infected root canals with mechanical prep- aration alone because of the complexity of root canal systems (1–3). Pulpal tissue remnants and inorganic debris remain even in well-shaped canals, especially in those areas with which the instruments do not come in contact (4). Rotary instruments that used a conventional single-shaft design, regardless of the instrumentation technique, never contacted canal walls completely (5). The amount of residual tissues was much more in canals that were treated without irrigation than those in which root canal irrigants were used (6). Thus, irrigants are essential for successful debridement of the root canals after mechanical shaping procedures (7). Although canal wall smear layers may reduce dentin permeability and prevent bacterial penetration into dentinal tubules (8, 9), they may prevent irrigants and medications from accessing infected dentinal tubules (10). An infected smear layer containing bacteria and necrotic tissue may also act as a substrate for the multiplication of those bacteria (11, 12). The use of NaOCl and EDTA has been reported to be effective in removing pulpal tissue remnants and the organic and inorganic components of the smear layer (13, 14). BioPure MTAD (Dentsply Tulsa Dental Specialties, Tulsa, OK), has shown promise as an antimicrobial against Enterococcus faecalis (15–18) and as a smear layer removal agent (19–21) after the use of 1.3% NaOCl as the initial rinse. However, the antimicrobial efficacy and substantivity of this irrigant combination has been challenged (22–24). BioPure MTAD is also relatively ineffective against E. faecalis biofilms (25–27), which are more difficult to eliminate and more resistant to antimicrobial agents than planktonic bacteria (28, 29). It is effective in removing canal wall smear layers but demineralizes intraradicular dentin (30). An experimental antimicrobial root canal irrigant (QMix) and its modifications containing a mixture of a bisbiguanide antimicrobial agent, a polyaminocarboxylic acid calcium-chelating agent, saline, and a surfactant have been found to be more effec- tive than BioPure MTAD against bacterial biofilms (Dr Markus Haapasalo, personal communication, August 2010). As little information is available on the ability of QMix in removing pulpal debris and canal wall smear layers, the objective of the present study was to evaluate its effectiveness in removing canal wall debris and smear layer from the coronal third, middle third, and apical third of root canals. The null hypothesis tested was that there are no differences in the ability of two versions of QMix, BioPure MTAD, and 17% EDTA as final irrigants to remove canal wall debris and smear layer from different parts of the root canals. Materials and Methods Fifty extracted human single-rooted teeth were radiographed to ensure that each tooth contained one canal and that an equal number of narrow (33%) and wide canals (67%) were present in the experimental groups. Each tooth was decoronated at 17 mm from the anatomic apex. Working length was established at 1 mm short of the apical foramen. Each tooth was prepared using a crown-down technique to size 50, 0.06 taper using the stainless steel hand files and ProTaper Universal nickel titanium rotary instru- ments (Dentsply Tulsa Dental Specialties). Because the objective of the study was to evaluate the effectiveness of the irrigants instead of the efficacy of root canal irrigation (20, 21), an ‘‘open-system’’ design (31) with an unsealed root apex (13) that permits air and vapor communication between the From the *Department of Stomatology, The First Hospital of Wuhan, Wuhan, China; † Dentsply Tulsa Dental Specialties, Tulsa, OK; ‡ School of Dentistry, Medical College of Georgia, Augusta, GA; § Department of Endodontics, School of Dentistry, Medical College of Georgia, Augusta, GA; k Department of Biostatistics, Medical College of Georgia, Augusta, GA; ¶ Department of Endodon- tics, Baylor College of Dentistry, Texas A&M University System Health Science Center, Dallas, TX; # Department of Oral Biology, School of Dentistry, Medical College of Georgia, Augusta, GA. Supported by Dentsply Tulsa Dental Specialties. Dr Khaled Khechen is Clinical Research Manager of Dents- ply Tulsa Dental Specialties. Address requests for reprints to Dr Franklin Tay, Department of Endodontics, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129. E-mail address: ftay@mcg.edu 0099-2399/$ - see front matter Copyright ª 2011 American Association of Endodontists. doi:10.1016/j.joen.2010.10.004 Basic Research—Technology 80 Dai et al. JOE — Volume 37, Number 1, January 2011