1. REFERENCES INTRODUCTION The periapical lesion is a localized inflammation of periapical tissues. In some cases the periapical radiography doesn’t permit clear visualization of these lesions (1). In these situations, cone beam computed tomography (CBCT) is the preferred method to assess endodontic lesions, and the correct identification of these images is very important for the diagnosis, treatment planning, follow-up and clinical management (2). This study aims to describe from a clinical report, the use of post-processing tomographic image software to follow-up periapical lesion after endodontic treatment. CLINICAL REPORT / TECHNICAL DESCRIPTION A 20-year-old healthy white young man was referred for the endodontic treatment of tooth #21. The patient reported dental trauma with crown fracture 9 years prior. The patient was asymptomatic and the tooth reacted negatively to the thermal test. Periapical radiography was undertaken using the Schick 33 sensor (Schick Technologies, Long Island City, NY, USA) and failed to clearly show the periapical lesion (figure 1). USE OF POST-PROCESSING TOMOGRAPHIC IMAGE SOFTWARE TO FOLLOW-UP PERIAPICAL LESION: CLINICAL REPORT AND TECHNICAL DESCRIPTION Eduardo Murad Villoria, Antonio Renato Lenzi, Kyria Spyro Spyrides, Sandra Rivera Fidel, Alexandre Perez Marques Figure 1. Crown darkening on tooth 21 (A) and radiographic image before the endodontic treatment (B). Diagnosis and Surgery Department - Oral Radiology - School of Dentistry - State University of Rio de Janeiro (UERJ) Dentistry Department - Pontificial Catholic University of Minas Gerais (PUC-MG) Following this stage, the virtual 3D models were exported to the.STL format (STerioLitography) and imported into the MeshLab 64-Bit v.1.3.3 (free and open source software, www.meshlab.sourceforge.net) to permit the alignment and overlap of these 3D models. Figure 4. Virtual 3D models aligned and overlapped. Figure 5. Quantitative assessment by color maps and “Point Value” tool Figure 2: Digital radiography and CBCT performed just after the treatment (A and B). CBCT performed four months later (C). CONCLUSION The software described in this paper can assist in the follow-up of periapical lesions. It is important for the cases that the investigation of the healing should be more rigorous and when the periapical radiography doesn’t clearly show the lesion. However, it is necessary further studies to assess the accuracy of the segmentation. The endodontic treatment was performed and soon after the patient was referred to perform a CBCT. The CBCT showed the radiolucent image associated with the root apex. However, this periapical lesion presented next to the nasal cavity and a new CBCT scan was carried out to follow-up four months later. The PreXion 3D system (Terarecon, San Mateo, CA, USA) was used at 90 kV, 4 mA and an exposure time of 19 seconds. Scanning was performed with a field of view (FOV) volume of 8.0 x 7.5 cm and isotropic voxel size of 0.1mm. To assist this tomographic evaluation the DICOM (Digital Imaging and Communications in Medicine) files were imported into ITK-SNAP 3.0 (free and open source software, www.itksnap.org) to segment the periapical lesion and anatomic structures, and to construct virtual 3D models. The virtual models were then saved in.STL format and imported into the 3DMeshMetric v.1.4.3 (free and open source software, www.nitrc.org) to perform the quantitative assessment of dimensional changes of periapical lesion after the treatment. B A B C Figure 3. Segmentation and construction of 3D virtual models just after the treatment (red) and four months later (yellow). 1. Borden W, Wang X, Wu M et al. Area and 3-dimensional volumetric changes of periapical lesions after root canal treatments. J Endod 2013;39(10):1245-9. 2. Scarfe WC. Use of cone beam computed tomography in endodontics joint position statement of the American Associate of Endodontists and the American Academy of Oral and Maxillofacial Radiology. Oral Surg Oral Med Oral Pathol Oral Radiol and Endod 2011;111(2):234-7. A