Laser Fluorescence Assessment of the Root Canal Using Plain and Conical Optical Fibers Quan V. Ho,BDSc, Roy George, MDS, PhD, Andrew L. Sainsbury, BDSc, MDSc, William A. Kahler, MScDent, and Laurence J. Walsh, PhD, DDSc Abstract Introduction: Traditional culture-based techniques for assessing infection of the root canal system are difficult to use and prone to error. Real-time assessment of the microbial status of the root canal system using laser fluorescence would help address these limitations. Methods: This study evaluated the performance of thin optical fibers of different diameters, with either plain or conically modified ends, connected to a KaVo KEY 3 laser with an inbuilt 655-nm laser fluorescence diagnostic system. Penetration was tested on sectioned extracted teeth. Fluorescence recordings were made ex vivo in the canals of extracted teeth with known periap- ical pathology. Several endodontic medicaments and irrigants were also tested for autofluorescence. Results: The fibers could reach the apical third of the root canal, unless the canals had distal curvatures greater than 15  . Penetration was greater for conical than for plain fibers. Fluorescence readings were significantly higher in infected canals (range, 19-99) than in noninfected canals and sound radicular dentin (range, 2-8). Of the medicaments examined, only tetracycline-based medi- caments gave false-positive fluorescence signals. Conclusions: Fluorescence analysis of root canals with optical fiber probes has the potential for real- time assessment of the microbial status of the root canal system in clinical practice. (J Endod 2010;36:119–122) Key Words Bacteria, diagnosis, fluorescence, infection, laser, optical fibers L aser fluorescence techniques have potential uses for endodontic diagnosis (1-4). Visible red light–induced fluorescence (using the 655-nm wavelength of the DIAG- NOdent; KaVo, Biberach, Germany) has recently been shown to identify single-species bacterial biofilms in the root canal under laboratory conditions and biofilms in the coronal third of root canals in freshly extracted teeth (3, 4). This previous work used short rigid sapphire probes that were unable to access the entire length of the root canal system. In contrast, small-diameter optical fibers should be able to negotiate the root canal system to the apical third, the region in which persistence of microor- ganisms is likely after instrumentation (5-8) because of anatomic complexities (9, 10). Recent developments in optical fiber technology allow manufacture of conical fiber ends, with efficient lateral emission and lateral collection of light (11-13). Such conical tips should be suitable for fluorescence diagnostics in the narrow confines of the root canal space. The present study was undertaken to evaluate the ability of both various plain and conical-tipped fibers to negotiate the root canal system and detect bacterial deposits in extracted teeth. Potential confounding factors in fluorescence diagnosis were also assessed. Materials and Methods The KEY3 laser system (KaVo) was used because this has an inbuilt 655-nm laser fluorescence diagnostic system for detecting subgingival calculus and dental caries as well as removable optical fibers for endodontic procedures. The debridement laser in this system is an erbium-yttrium-aluminum-garnet (Er:YAG) with a wavelength of 2,940 nm. In the present study, the thinnest commercially available 300- and 400-mm diameter germanium-doped silica fibers for this laser were used. Half the fibers were modified by tube etching to create conical ends and to improve their lateral emis- sion and collection of light (11-13). To assess the penetration of fibers into the root canal, 20 extracted single-rooted teeth of varying canal curvatures were used in a longitudinal split tooth model. After removing the crowns, the canals were instrumented to the apical foramen using hand files to size #30, and the roots were then split longitudinally. Digital x-ray images of the split roots (using Schick CDR, Schick Technologies, Long Island City, NY) were used to measure the canal curvature and classify roots into groups using the Schneider technique (14). In brief, canal curvatures of #5  divergence between the apical foramen and the long axis of the root were considered straight; canal curvatures of >5  and #15  were considered moderately curved; and canal curvatures of >15  were considered severely curved. The split half roots were mounted horizontally into plaster blocks and glass microscope slides attached to the cut surface so that negotiation of the half diameter of root canal by the fiber could be observed directly using a stereo microscope fitted with a digital camera. Although not anatomically correct, this arrange- ment was preferable to using epoxy resin blocks with curved canals because in the latter the canal walls are much smoother than those in natural teeth. Each fiber was inserted into the root canal with a light force until resistance was felt, and a digital photograph was then taken to record the distance from the tip of the fiber to the anatomic apex. This assessment was undertaken for 300- and 400-mm optical fibers, with either plain or conically modified ends. Data for distance were analyzed for normality by using the Kolmogorov-Smirnov test; differences between From the University of Queensland School of Dentistry, Brisbane, QLD, Australia. Supported by grants from the Australian Dental Research Foundation and the Australian Society for Endodontology. No financial affiliation exists for any author. The intellectual prop- erty rights relating to the technology described in this paper have been assigned to The University of Queensland through a provisional patent application. Address requests for reprints to Laurence J. Walsh, PhD, DDSc, The University of Queensland School of Dentistry, 200 Turbot Street, Brisbane, QLD 4000, Australia. E-mail address: l.walsh@uq.edu.au. 0099-2399/$0 - see front matter Copyright ª 2010 by the American Association of Endodontists. All rights reserved. doi:10.1016/j.joen.2009.09.024 Basic Research—Technology JOE — Volume 36, Number 1, January 2010 Laser Fluorescence Assessment Using Plain and Conical Optical Fibers 119