Medication-related osteonecrosis of the jaw (MRONJ) is known to be one of the adverse events of antiresorptive drugs such as bisphosphonates and denosumab, but the mechanisms and treatment methods of MRONJ have not been established. It is necessary to perform MRONJ therapy without interfering with the treatment of underlying diseases such as osteoporosis and bone metastasis of malignant tumors.

　For MRONJ, we have made surgical treatment without drug holiday of antiresorptive drugs the first choice, and have reported good treatment outcomes. However, some cases did not obtain complete healing even after surgery. In this study, we compared various clinical factors and pre- and post-operative CT images in healed and non-healed cases, with the aim of establishing an appropriate surgical method for cases with mandibular MRONJ, and investigated factors for poor prognosis. As CT findings, we focused on osteolysis, periosteal reaction, and mixed type of osteosclerosis. The periosteal reaction was classified into none, attached type, gap type, and irregular type, as reported previously. Mixed type of osteosclerosis was newly defined as a mixture of extensive osteosclerosis with multiple small radiolucent areas. As a result, it was found that osteolysis, gap or irregular periosteal reaction, or mixed type of osteosclerosis remained after surgery in most patients without complete healing. On the other hand, drug holiday of antiresorptive drugs did not affect the treatment results.

　Surgical treatment is the first choice for MRONJ, but it is necessary to include osteolysis, gap or irregular periosteal reaction, and mixed type of osteosclerosis on CT images in the resection range. We were able to propose a certain surgical method for MRONJ surgery. Recently, the number of cases without osteolysis has been increasing, and we would like to continue our research to establish surgical methods including other imaging examinations such as MR.

Diffuse sclerosing osteomyelitis of the mandible(DSO) is the intractable inflammatory disease of bone, characterized by recurrent pain, swelling, and trismus in the absence of pus formation, fistula, or sequestration. Radiographically, it presents as intermingled sclerotic and osteolytic lesions with solid periosteal reaction or external bone resorption.

　Various hypotheses have been discussed about the etiology, including an immunologic reaction to microbial stimuli, chronic tendo-periostitis owing to muscular overuse and as part of systemic syndrome such as chronic recurrent multifocal osteomyelitis(CRMO) or SAPHO syndrome.

　This clinical review of DSO focuses on the diagnostic criteria, the relationship with CRMO and SAPHO syndrome, the transition of the etiology and various therapies and the effect. In addition, this review shows the low dose pamidronate disodium therapy for DSO in our facility.

In this review, we describe the diagnosis and treatment of nonbacterial mandibular osteomyelitis, especially SAPHO syndrome which is associated with systemic disease, and diffuse sclerosing osteomyelitis(DSO) and chronic recurrent multifocal osteomyelitis(CRMO), which we are currently having difficulty in treating. Clinical images of CT, MRI and SPECT-CT are the mainstay of diagnosis in nonbacterial submandibular osteomyelitis, and the combination of systemic disease is a major clue. When a definitive diagnosis is obtained by biopsy, drug administration should be given priority and immediate invasive surgical treatment should be avoided.

Spontaneous regression of malignant tumors is an extremely rare phenomenon. In past reports,renal cancer, malignant melanoma, neuroblastoma and hematological tumor accounted for the majority, however spontaneous regression of gingival cancer has not been reported in the past. We report a case of spontaneous regression of maxillary gingival cancer. An 89-year-old female was referred to our department for the examination of a left-sided maxillary gingival mass. A 45 × 30 mm extending tumor was found in the left maxillary gingiva. Imaging showed destruction of the upper left mandible, and blood tests showed elevated SCC antigens. The lesion was diagnosed as squamous cell carcinoma histologically(T3N0M0: Stage Ⅲ). Local excision was possible based on the extent of the lesion, however due to her medical history and advanced age she was not eligible for radical treatment, and she was transferred to the hospital for palliative treatment. However, the tumor disappeared two months later and, after that, she visited our department. No tumor was found, and the SCC antigens had normalized. Spontaneous regression of malignant tumor is an interesting phenomenon, however the mechanism is unknown. Elucidating the mechanism of this process may provide clues to new cancer therapies, and the accumulation of information on similar cases is desirable.

Giant cell arteritis(GCA) is a granulomatous arteritis containing giant cells that occur in the major branches of the aorta. Headache is frequently the first symptom, but oral symptoms may precede it. We report a case where giant cell arteritis presented as pain and swelling of the tongue with necrosis over time.

　The patient was a 78-year-old woman. She became aware of tongue pain and swelling from June 2019 and visited a nearby dental clinic. Her symptoms remained unimproved and was referred to our department in the same month for detailed examination and treatment. At her first visit, a painful, poorly-marginated dark purple mass w as found extending from the left l ateral edge of tongue to the proglossis. A vascular a nomaly of the tongue was suspected, and contrast-enhanced MRI was performed but did not lead to a diagnosis. One week later, necrotic lesions were observed on her tongue and a blood test showed elevated inflammatory markers. A systemic disease was suspected, and medical examination at our hospital led to the diagnosis of GCA. Steroid treatment and remission maintenance therapy with tocilizumab were performed. Two years and six months have passed since the start of treatment, with no recurrence of the symptoms.

Desmoplastic melanoma(DM) is a subtype of malignant melanoma, and there are very few reports on the occurrence of this disease in the oral region. Since DM is mainly composed of achromatic spindleshaped tumor cells, its clinical and histopathological diagnoses are difficult. However, immunohistochemical staining is useful for the diagnosis of DM.

　We herein present a case of DM in the maxillary gingiva of a 69-year-old woman. Swelling had been observed in the gingiva surrounding the upper left six tooth of this patient since 2018, and in 2020 a rapid increase in the swelling was observed. Thus, the patient consulted a nearby dental clinic and underwent resection due to a clinical diagnosis of epulis. Histopathologically, the patient was diagnosed with sarcoma and referred to our department for detailed examination and treatment. We suspected a sarcomatous malignant tumor and performed a partial left upper jaw resection. Histopathological findings revealed that the spindleshaped cells were arranged in an intricate manner. Immunohistochemical staining was positive for S-100 protein, SOX10 and MelanA, and DM was diagnosed.