A. Lozano, L. Forner, C. Llena
Endodontic, Dental Pathology and Therapeutics Unit, Department of Stomatology, Faculty of Medicine and Dentistry, University of Valencia, Spain.
Knowledge of the root-canal systems is essential for diagnosis and treatment. As in other fifields of science, the development of diagnostic imaging techniques in dentistry has been of fundamental importance. The application of such techniques in endodontics allows the definition of root and canal morphology, and particularly the determination of endodontic working length and fifinal verification of the outcome of root-canal treatment (Versteeg et al.19 97).
Technological advances have led to the introduction of digital radiology (DR), with many potential benefits in endodontic practice (Mouyen et al.1989, Shearer et al. 1990, Horner et al.1 990, Shearer et al.19 91, Furkart et al.1992, Sohfiet al.1993).The first commercial integrated digital imaging system was radiovisiography (RVG; Trophy Radiologie, Vincennes, France), involving the use of an intraoral, sensor instead of conventional X-ray film (Mouyen et al.1 989, Benz & Mouyen 1989). The RVG allowed a substantial reduction in the duration of endodontic procedures, because it effectively eliminated the film-processing time. In the same way, the zoom function had the potential to improve the diagnostic performance by magnifying areas such as the apical zone (Duret et al.1988).
By measuring the intra-root-canal length, it was shown that no statistically significant differences exist between the images provided by a rigid sensor such as RVG and the conventional film (Shearer et al.19 90). The digital radiological systems have been compared with conventional images obtained using E-speed film for the diagnosis of experimentally induced periapical lesions (Kullendorf et al.1996). In this context, the direct digital- image quality was comparable to that produced by the conventional film (E-speed), although modification of the basic features of a digitized image (i.e. brightness and contrast) has little advantage when compared with the original image, provided the latter is of high quality. This has also been demonstrated (Kullendorf et al. 1996) with the Visualix/Vixa system (Gendex Dental Systems, Milan, Italy).
One variant of such digital radiological technology is based on the reading of a reusable plate previously exposed to X-rays from a conventional generator (Kashima et al. 1985, Seki & Okano1993, Kashima et al.19 94). This type of DR is known as the photostimulate storage phosphor (PSP) system (Digora, Soredex, Orion Corporation, Helsinki, Finland). Most of the energy from the radiation of the conventional generator is maintained in the surface of the plate; a scanner is then used to read this energy and to convert it into a digital signal that is recognized by the computer and presented on screen.
One of the most significant characteristics of digital radiological systems is the fact that their sensors make it possible to reduce the radiation dose by 60% (Seki & Okano1993, Kashima et al.19 94, Sanderink et al.19 94). Other recently developed sensors allow even lower exposure levels, although possibly, at the expense of the image quality. Never the less, in a study of the endodontic diagnostic utility of the sensors of the Sidexis (Siemens, Erlangen, Germany) and Digora (Soredex, Orion Corporation) systems, involving radiation dose reductions of up to 95%, both systems were able to determine root-canal length in premolars using size20files (Velders et al.19 96).
Observer accuracy in determining the working length has been studied in vitro contrasting the conventional radiography (E-speed) and RVG.N o differences were observed between conventional film images and the printed RVG image, although the former were significantly more precise than the computed image on the high-resolution screen (Hedrick et al.19 94). Some authors reported a limitation in the diagnostic capacity of the digital technique and defined a minimum calibre that could be visualized without difficulty (Sanderink et al.1994) in relation to a size15 file. Other authors suggested that conventional radiography can not be replaced by digital techniques (Lavelle&Wu1995).When comparing RVG and conventional radiography (D- and E-speed) in detecting small intracanal instruments in vitro, it was demonstrated that 2_magnification for visualizing the size 08 and10 file tips was more accurate with conventional radiography than with RVG (Ellingsen et al. 1995). Similar results were obtained contrasting the RVG and conventional film images when performing root-canal measurements in vitro with a size 15 file (Ong & Pitt Ford 1995). In a recent study involving cone-vertical angles of up to 308 for estimating the working length with the conventional (D-speed) and digital radiography, no significant differences were observed in the results afforded by both techniques, with the exception of image shortening at an angle of 308 when using digital radiology (Almenar et al.19 97).
When using the Digora system with different exposure times, it was concluded that endodontic measurements could be obtained at considerably lower exposures than those required with the conventional film systems (Borg & Grondahl 1996).A comparison of the Digora system and conventional film images (E-speed) revealed no significant differences in the estimation of working length, although the former technique was more accurate in visualizing file tips, particularly when small (Cederberg et al.19 98).
The present study compared the diagnostic efficacy of two digital radiological systems in performing rootcanal measurements and correlated them to conventional film radiography whilst assessing the influence of different projection angles and the use of magnification.