Evaluation of Chronic Periapical Lesions by Digital Subtraction Radiography by Using Adobe Photoshop CS: A Technical Report Fabiola B. Carvalho, DDS, MSc,* Marcelo Gonçalves, DDS, MSc, PhD, † and Mário Tanomaru-Filho, DDS, MSc, PhD* Abstract The purpose of this study was to describe a new technique by using Adobe Photoshop CS (San Jose, CA) image-analysis software to evaluate the radiographic changes of chronic periapical lesions after root canal treatment by digital subtraction radiography. Thirteen upper anterior human teeth with pulp necrosis and radiographic image of chronic periapical lesion were endodontically treated and radiographed 0, 2, 4, and 6 months after root canal treatment by using a film holder. The radiographic films were automatically de- veloped and digitized. The radiographic images taken 0, 2, 4, and 6 months after root canal therapy were submitted to digital subtraction in pairs (0 and 2 months, 2 and 4 months, and 4 and 6 months) choosing “image,” “calculation,” “subtract,” and “new docu- ment” tools from Adobe Photoshop CS image-analysis software toolbar. The resulting images showed areas of periapical healing in all cases. According to this meth- odology, the healing or expansion of periapical lesions can be evaluated by means of digital subtraction radi- ography by using Adobe Photoshop CS software. (J Endod 2007;33:493– 497) Key Words Digital subtraction, periapical lesion, radiograph C hronic periapical lesions associated with root-filled teeth are usually monitored by conventional periapical radiography (1, 2). However, the suggested radiographic criteria, including lesion persistence and increase of periapical lesion size, are quali- tative and subjective (3). Several methods have been described to measure periapical radiolucencies, including measurement of the diameter, distance between root surface and radiolucency outlines, use of a specific classification, and determination of the area by means of tracing (4). Digital radiographic techniques and computed analysis methods allow measuring of the periapical lesion area and provide a correlation among the images obtained at different follow-up periods (3). Digital subtraction radiography with specific software is considered as a valuable tool for evaluation of periapical lesions because they are capable of detecting extremely small bone alterations. It increases the accuracy for assessment of bone gain or loss during or after root canal treatment (5). In addition, this technique almost duplicates the sensibility in detecting lesions in comparison to conventional radiographic interpretation (6). The importance of digital subtraction radiography as an evaluation tool of the healing process of periapical lesions has been shown in follow-up studies with en- dodontically treated teeth (7–10). The results of those studies show that image sub- traction is a good tool to be used in reliable diagnoses of minimal changes of periapical tissues during short-time intervals. However, the technology involved in digital subtrac- tion radiography together with the need of additional equipment (specific software like X-PoseIt [XP, Torben Jorgensen, Lystrup, Denmark] and the EMAGO [Oral Diagnostic Systems, Amsterdam, The Netherlands]) and computer support make this technique complicated for use in daily practice (5). Nonspecific image-analysis software can represent an alternative for the digital subtraction radiographic technique in the evaluation of healing or increase of periapical lesions. Adobe Photoshop CS image-analysis software allows digital subtraction of two superposed images (11). The aim of this study was to describe a new technique performed by using Adobe Photoshop CS image-analysis software to evaluate the radiographic changes of chronic periapical lesions after root canal treatment by digital subtraction radiography. Materials and Methods Thirteen upper anterior human teeth with pulp necrosis, asymptomatic, in normal masticatory function, and a radiographic image of chronic periapical lesion larger than 5 mm in diameter measured in its largest long axis were selected for this study. Patient written informed consent was obtained after the nature of the procedures and possible discomforts and risks had been fully explained. In each specific case, the root canal was prepared according to the crown-down technique by using manual instrumentation and irrigation with 2.5% sodium hypochlo- rite. After biomechanical preparation, a calcium hydroxide-based paste (Calen PMCC; SS White, Rio de Janeiro, Brazil) was placed as root canal dressing for at least 15 days. Final obturation was done by lateral condensation of gutta-percha points and Sealapex root canal sealer (SybronEndo/SDS, Glendora, CA). Radiographs were taken 0, 2, 4, and 6 months after root canal filling by using Rinn XCP film holder (Rinn Corp, Elgin, IL) stabilized with spherical rubber silicone impression From the *Department of Restorative Dentistry, Arara- quara Dental School, São Paulo State University, UNESP, Araraquara, SP, Brazil; and † Department of Radiology, Arara- quara Dental School, São Paulo State University, UNESP, Araraquara, SP, Brazil. Address requests for reprints to Dr. Mário Tanomaru Filho, Rua Humaitá, 1680, Caixa Postal 331, Centro, 14801-903 Araraquara, SP, Brazil. E-mail address: tanomaru@uol.com.br 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2006.12.015 Case Report/Clinical Techniques JOE — Volume 33, Number 4, April 2007 Chronic Periapical Lesions 493