1. CASE 1 CASE 2CASE 3CASE 4CASE 5 Orthokeratinized odontogenic cystKeratocystic odontogenic tumor CASE Ⅱ CASE 2 Comparison of radiographic features of orthokeratinized - odontogenic cyst and kerotocystic odontogenic tumor Materials and Methods Results Conclusion Objectives Introduction Ju-Hee Kang, Sae-Rom Lee, Gyu-Tae Kim, Yong-Suk Choi, Eui-Hwan Hwang Department of Oral and Maxillofacial Radiology and Institute of Oral Biology, School of Dentistry, Kyung Hee University, Seoul, Republic of Korea Orthokeratinized odontogenic cyst (OOC) was initially defined by the World Health Organization (1992) as the orthokeratinized type of odontogenic keratocyst (OKC). The WHO new classification (2005) for head and neck tumors has reclassified parakeratinized type of OKC as Keratocystic Odontogenic Tumor (KOT). Since then, OOC is not a part of the spectrum of KOT and should be considered as a separate entity. The aim of this study is evaluation the radiographic features of orthokeratinized odontogenic cyst (OOC) compared with as keratocystic odontogenic tumor (KOT). Three OOC cases (CASE Ⅰ ~ Ⅲ, 2maxilla and 1mandible) and six KOT cases (CASE1~6, 2maxilla and 4mandible) were reviewed retrospectively. The definitive diagnosis of OOC and KOT were confirmed by oral pathologist. Plane radiography and cone beam computed tomography were evaluated for all cases. Radiographic features according to border, shape, peripheral cortication, internal structure, cortical plate thinning & expansion, and displacement of tooth were compared. All OCC cases had non-painful swelling, whereas 3 cases of KOT had no symptom. OOC revealed monolocular radiolucency, absent of internal septa, relatively smooth border and thick corticated margin without transient zone. 2 cases of OOC present prominent thinning and expansion of cortical plate with tooth displacement, has shown oval shape contour related to fluid-filled balloon effect. KOT revealed mono- multilocular appearance with internal septa on 2 cases and thin demarcated margin with week cortication. All cases of KOT has shown prominent mesial-distal expansion compared with bucco-lingual expansion and undulate into interadicular space than tooth displacement. All cases of OOC were associated with adjacent impacted tooth, while 3 cases of KOT were associated. Histopathological entity and growth potentiality make different radiographic appearance between OOC and KOT. Proliferative and anti-apoptotic activity in KOT makes scalloped outline and undulating border dissimilar to OOC. Orthokeratinized odontogenic cyst exhibits distinctive clinical and radiological features that vary substantially from KOT. It must be considered in the differential diagnosis. Fig 1. OOC case and KOT case. H-E stain X100 Table 1. Radiographic features of OOC & KOT cases Fig 2. Panoramic radiographs and CBCT images of OOC cases. Fig 3. Panoramic radiographs and CBCT images of KOT cases. CASE Ⅰ CASE Ⅱ CASE Ⅲ OOC (n=3)KOT (n=6) Shape Border Peripheral condition Internal structure Unilocular Multilocular Adjacent teeth Displacement of tooth Resorption of tooth Association with impacted tooth oval shape smooth thick corticated margin 3 0 2 0 3 prominent mesio-distal expasion undulating thin corticated margin 4 2 0 3