## 2 Case Report  
A five-year-old boy was referred to the Department of Oral and Maxillofacial Surgery at Seoul National University Dental Hospital from another hospital with suspicion of ameloblastoma. Upon extraoral clinical examination, facial asymmetry was observed, with swelling on the right side of the mandible (Figure 1a). Meanwhile, the intraoral examination revealed buccal vestibule swelling and displaced teeth #82, #83, #84, and #85 (Figure 1b). The panoramic radiograph revealed a large unilocular radiolucency in the right mandible (Figure 1c). Computed tomography (CT) and 3D imaging Cone beam computed tomography (CBCT) showed an avoid corrected lesion 37.06 \(\times\) 20.44 mm in size, extending from the apex of #31 to #85 and expanded in the buccal and lingual directions (Figure 1d,e). Most of the lesion was filled with an enhanced solid portion, and partial fluid attenuation was observed. Anamnesis and lab result were negative for any history of serious medical conditions such as diabetes mellitus, hepatitis or drug allergy. The treatment was proceeded with the conservative surgery without pretreatment biopsy due to several considerations: (1) Radiographically, the growth pattern of the lesion represented benign characteristic, (2) the lesion was embedded in the bone, in which the required sufficient tissues for biopsy would be difficult to obtain, (3) the pretreatment biopsy would give additional injuries. Considering young patient's low tolerance to postoperative pain can affect the cooperation to the upcoming treatment, the treatment stages should be as efficient as possible. Under general anesthesia, surgery was performed. The right mandibular vestibule was infiltrated with 2% lidocaine, 1:100.000 epinephrine. An incision was created in the right retromolar area using a #15 blade, and extended to #41 with a crevicular incision. A mucoperiosteal flap was elevated, and mass excision was performed with a molt curette (Figure 2a-c). After mass excision, the inferior alveolar nerve (IAN) was identified and carefully preserved. A silastic drain for decompression was inserted and sutured with 4-0 Polyglactin 910 Vicryl(Johnson & Johnson Co., Johnson, NJ, USA) (Figure 2d,e). Primary closure with 4-0 Vicryl and pressure dressing was performed. Two days after surgery, a sensory assessment ensured the normal nerve function. Copious routine irrigation with warm saline was performed every day for one week after surgery and was repeated for every two weeks for seven months. The silastic drain was regularly changed to prevent infection. Figure 1: Preoperative view. (**a**) Extraoral photograph. (**b**) Intraoral photograph. (**c**) Panoramic radiograph showed unilocular radiolucency extending from #31 to the mesial root of #46, surrounding the crown of the #43 tooth bud. (**d**) The axial CT radiograph. (**e**) The 3D imaging CBCT showed the extent of the lesion in the mandible. An excised gray-white mass containing tooth #43 4.6 \(\times\) 3.1 \(\times\) 1.8 cm in size was obtained (Figure 2c) and stained with hematoxylin and eosin (H&E) for histopathologic examination. Microscopically, the excised mass was solid and surrounded by a thin fibrous capsule (Figure 3a). The tumor cells of odontogenic epithelial proliferated in long anastomosing cords bounded by columnar or cuboidal ameloblast like cells with inconspicuous stellate reticulum, forming a plexiform pattern. The stroma was composed of fibrous connective tissue with some cyst-like stromal degeneration in several areas (Figure 3b). Therefore, the final diagnosis was plexiform ameloblastoma. Monthly radiograph examination follow-ups were performed following the principle of as low as reasonably achievable (ALARA) for the first 10 months after surgery to evaluate healing of the right mandible (Figure 4a-c).