The most common cancers in oral cavity are squamous cell carcinoma (OSSC), which accounts for more than 90% in oral cancers. The 5-year overall survival rate of early stage of OSCC is over 90%, while that of advanced stages is still poor. It is important to treat precancerous lesions including leukoplakia and erythroplakia to improve the prognosis. Malignant transformation rates of leukoplakia and erythroplakia range from 5% to 10% and 40% to 50%, respectively. Biopsy is performed to microscopically divide these lesions into oral intraepithelial neoplasia (OIN) /CIS and oral epithelial dysplasia. In addition to histological findings, immunohistochemical analysis such as Ki-67, p53, cytokeratin13, 17, and p16, is also helpful for the diagnosis. After surgical treatment, the resected specimens from OSCC patients are examined in details regarding prognostic factors, which are disease staging, resection margin free of diseases, tumor thickness, and extracapsular dissemination of lymph nodes. Furthermore, it is reported that EGFR-, NOTCH-, PI3K-, PTEN-and AKT-mediated pathways are involved in OSCC proliferation, suggesting that these factors can be expected to be promising molecular targets for OSCC treatment.

Computer assisted surgery (CAS) starts from surgical simulation. Then it progressed to surgical navigation system. The major technical components of CAS were registration, tracking, segmentation, and modeling. The volumetric CT image data plays important role in the whole process of CAS. CAS utilized various surgeries including maxillofacial region. While in the field of dentistry, the typical use of CAS was dental implant. There were several unique simulation / navigation systems that specialized to dental implant. The advent of arm-type cone beam CT (CBCT) has paved the way for the general dentists to use CAS. However in compare with medical surgery, CAS based on dental CBCT has several disadvantages. These were in the reproducibility of CT number and standardization of image data.

We report a case of pyostomatitis vegetans associated with ulcerative colitis. The patient was a 25-year-old woman referred to our hospital because of irritative pain of the right side of the buccal mucosa. She had been receiving mesalazine for ulcerative colitis for 4 years. An erosion with a cobblestone appearance and a small ulcer were observed on the right side of the buccal mucosa. Histopathological examination showed subepithelial microabscesses containing lymphocytes and eosinophils in the subepithelial connective tissue. We finally diagnosed pyostomatitis vegetans associated with ulcerative colitis. The oral lesion completely disappeared 1 month after the administration of prednisolone.

Myotonic dystrophy (MyD) is a rare genetic disease characterized by myotonia and muscular atrophy; it is often accompanied by jaw deformity. Orthognathic surgery for MyD has the following disadvantages: various complications can easily occur during general anesthesia, and postoperative mandibular relapse can be caused by masticatory muscle atrophy. We report a case of jaw deformity with MyD treated by orthognathic surgery. A 15-year-old boy visited our department because of abnormal occlusion; mandibular protrusion with anterior open bite was diagnosed. The presence of certain characteristic physical features and the results of genetic examinations led to the diagnosis of MyD. At 18 years of age, he underwent sagittal splitting ramus osteotomy with overcorrection, performed with the patient under general anesthesia in cooperation with related departments. Postoperative intermaxillary fixation was continued for 14 days. The occlusion temporarily stabilized, but a slight anterior open bite appeared 3 months after surgery; therefore, intermaxillary elastic traction was continued for 1.5 years. He has been followed up for 2 years 4 months after surgery, and no relapse has occurred.

Oral focal mucinosis (OFM) is an uncommon disease characterized by mucinous accumulation caused by an overproduction of hyaluronic acid by fibroblasts. Tomich proposed that OFM is the oral counterpart of cutaneous focal mucinosis in 1974. The etiology of the disease is still unclear. We report a case of OFM of the tongue in a 67-year-old man. The lesion was a small white mass of 3 mm in diameter with a smooth surface at the tip of the tongue. The left lower lateral incisor and canine with sharp edges would contact the mass. We clinically diagnosed it as a fibroma and performed tumor extirpation. Histopathological examination showed a well-localized myxoid stroma containing fibroblasts that were positive for vimentin. The stroma was positive on Alcian blue staining, but negative on PAS staining; thus, the presence of hyaluronic acid was suggested. We finally diagnosed this case as OFM. The prognosis after surgery has been favorable, and no recurrence was observed at follow-up after 3 years 3 months.

An osteoma is a benign tumor consisting of well-differentiated mature bone tissue and is classified as either central or peripheral osteoma. It is considered to most commonly appear on, for example, the inner and outer edges of the mandibular angle, the inferior margin of the mental region, and the lingual side of molar teeth of the lower jaw. However, a tumor arising in the mandibular ramus is relatively rare. We report the case of a patient with a peripheral osteoma that arose in the anterior border of the mandibular ramus. A 64-year-old woman consulted our department because of a painless mass of the right buccal mucosa. The right buccal mucosa showed the formation of a hemispherical mass measuring approximately 26 × 16 mm in the oral cavity. On suspecting a soft tissue benign tumor and performing imaging studies, the right mandibular ramus anterior border showed a pedunculated bone torus. We performed enucleation with the patient under general anesthesia for a clinical diagnosis of a peripheral osteoma. The histopathological diagnosis was a cancellous osteoma. Currently, 4 years 3 months after the operation, the patient has had no recurrence.

We report the case of a 35-year-old man with a complex odontoma in the posterior wall of the maxillary sinus. He was referred to our department for further investigations of a dentigerous cyst in the left maxillary sinus. On intraoral examination, an erupted left maxillary third molar was observed, with no swelling in the left maxillary molar region. Computed tomography confirmed thickening of the mucous membrane of the maxillary sinus associated with the left maxillary second molar and a spherical high-density shadow in the posterior wall of the left maxillary sinus. The mass was excised from the left maxillary sinus after extracting the left maxillary second molar with the patient under general anesthesia. Histopathological examinations confirmed the diagnosis of complex odontoma. We considered that the complex odontoma was derived from a distomolar germ because of the eruption of the left maxillary third molar. No evidence of postoperative recurrence of the left maxillary sinus has been observed.

A diverticulum is a pouch of the digestive tract mucosa that penetrates the muscular layer because of a partial defect in the muscle. It has often been reported in the digestive tract mucosa, but is extremely rare in the oral cavity. We report a case of a diverticulum-like lesion of the buccal mucosa. A 60-year-old man visited his regular dentist for dental treatment. An atheroma-like lesion was noted near the papilla of the parotid duct in the right buccal mucosa. The right maxillary molar was extracted because of a suspected odontogenic infection, but his symptoms did not improve, and he therefore consulted our hospital. Two pouches, one measuring 10 mm in depth and the other 5 mm in depth, were noted, and both contained food debris. These lesions were diagnosed as diverticulum-like lesions of the buccal mucosa and were resected with the patient under general anesthesia. A partial defect of the buccinator muscle was recognized under the pouch. Histopathologically, the buccal mucosa penetrated the buccinator muscle and reached the fatty layer, and buccal glands were located at the bottom of the pouches. These findings suggested the etiology of this lesion. No recurrence has occurred as of 1 year 6 months after surgery.