Evaluation of Smear Layer: A Comparison of Automated Image Analysis versus Expert Observers Roy George, BDS, MDS, Edward B. Rutley, BSc, BDSc, MDSc, and Laurence J. Walsh, PhD, DDSc Abstract Consistent and reproducible evaluation techniques of the smear layer in root canals in scanning electron microscopy studies are needed when comparing various instruments and techniques. In this study, the perfor- mance of 3 experienced blinded evaluators applying the Hulsmann technique was compared with a digital anal- ysis method. Smear layer in the apical third of root canals of 35 freshly extracted teeth prepared by using nickel-titanium rotary instruments, Er:YAG and Er,Cr: YSGG lasers was scored on coded images. There was good agreement between the digital analysis method and the different evaluators (kappa analysis) across the range of the Hulsmann scores. Image analysis might be useful for evaluating the degree of smear layer removal in endodontic research. (J Endod 2008;34:999 –1002) Key Words Dentinal tubules, digital imaging, lasers, smear layer S mear layer has been defined as a layer of debris on the surface of dental tissues created by cutting a tooth. It varies in thickness, roughness, density, and degree of attachment to the underlying tooth structure, according to the instruments and mate- rials used, with some techniques that use irrigants such as ethylenediaminetetraacetic acid (EDTA) recognized to give effective removal of smear layer (1). A smear layer might partially or completely occlude dentinal tubules, and the bacteria, endotoxins, and debris contained within it could contribute to ongoing peri- apical inflammation. Moreover, as well as containing bacteria, smear layer might pre- vent medicaments from adequately diffusing from the root canal space into the dentinal tubules (2). For these reasons, complete removal of the smear layer is seen as desirable, and accordingly, irrigants such as EDTA (3), sodium hypochlorite (4, 5), chlorhexidine gluconate (6), organic acids, MTAD (Biopure; Dentsply Tulsa Dental, Tulsa, OK) (7), and combinations of these are used clinically (8, 9). Physical techniques for smear layer removal include ultrasound (endosonics) and pulsed middle infrared lasers, both of which cause cavitations and pressure waves within the root canal space (8, 10). Comparing the effectiveness of smear layer removal methods typically involves scoring high magnification (1000) photomicrographs from scanning electron mi- croscopy (SEM) studies, particularly of the apical third of the root canal. The images are coded and then scored by blinded evaluators by using qualitative or semiquantitative scales such as those described by Prati et al. (11) and Hulsmann et al. (12), with the latter the most commonly used. Other methods have involved tracing SEM photomicro- graphs onto graduated tracing paper for subsequent measurement (13) and using resin replicas of the surface under examination (14). The use of digital image analysis methods in dentistry is becoming more popular, with reports of its use for assessing the curvature of root canals (15), dentin removal during root canal preparation with various techniques (16), and the efficiency of obturation methods (17). In 2007, Ciocca et al. (18) described a computerized auto- mated analysis technique for counting dentinal tubules; however, the use of this method for characterizing a prepared dentinal surface has not been evaluated. The purpose of the present study was to validate an image analysis method for evaluating smear layer removal, comparing this with the well-established gold standard of the ordinal scoring system with 3 observers of Hulsmann et al. (12). Materials and Methods A total of 35 single-rooted extracted human teeth had their crowns removed at the cementoenamel junction. The roots were randomly allocated into 5 groups of 7 each as follows. The positive control groups (groups 1 and 5) were prepared by using K3 files (Sybron Endo, West Collins, CA) in a 4:1 reduction handpiece (WE-66 EM; W & H, Buermoos, Austria), by using the variable taper, variable tip-size technique recom- mended by the manufacturer. In group 1 (control for smear layer removal), irrigation with 1% sodium hypochlorite and 15% EDTAC (1 mL of each) was used between the introductions of files. In group 5 (control for the presence of smear layer), only water was used for irrigation, ensuring a smear layer was present. Samples in group 2 were treated with an Er:YAG laser (KEY3; KaVo, Biberach, Germany), with a fiberoptic endodontic handpiece with 200-, 320-, and 400-m di- ameter fibers, at panel settings of 500, 450, and 450 mJ, respectively, at a pulse fre- quency of 4 Hz. The Er:YAG laser was used in an experimental technique developed by Rutley (19). In brief, the coronal two thirds of the root canals were treated sequentially From the School of Dentistry, University of Queensland, Brisbane, Australia. Address requests for reprints to Professor L. J. Walsh, School of Dentistry, The University of Queensland, 200 Turbot St, Brisbane QLD 4000, Australia. E-mail address: l.walsh@ uq.edu.au. 0099-2399/$0 - see front matter Copyright © 2008 American Association of Endodontists. doi:10.1016/j.joen.2008.05.003 Basic Research—Technology JOE — Volume 34, Number 8, August 2008 Evaluation of Smear Layer 999