Overview of the alloplastic total joint replacement (TJR) of temporomandibular joint (TMJ) with indications for surgical management and efficiency of the treatment is described.

　The indication of TMJ TJR is the end-stage TMJ diseases such as severe bony ankylosis, end-stage of TMJ rheumatic and osteo-arthritis, and severe idiopathic condylar resorption, in consisting with functional/anatomical loss of condylar process.

　Types of TJR in TMJ are consisted with Stock and Custom made system, and the former type is approved as the medical device by PMDA in 2020 in Japan.

　Overall successful outcome ratio of TMJ TJR in oversea country is around 80%. There was no significant differences between two types of TJR.

　Clinical emphasis is made on a skillful and devised team approach to reduce operative time, bleeding and adverse effect. Importance of pre- and post-operative analysis and feedback to next planning. Current topics regarding surgical modification to Asian population and pre-operative embolization is described.

TMJ joint Replacement System by Zimmer Biomet corporation is the only total joint replacement system for temporomandibular joint (TMJ) that is available in Japan.

　This product is stock type prostheses including several sizes of Fossa implants and Mandibular implants that consist TMJ component.

　The surgical procedure should be performed through the steps of condylectomy, coronoidectomy if required, installation of Fossa implant, inter maximal fixation and Mandibular implant installation via combination of pre auricular incision and retro mandibular incision.

　Objectives: The present study aimed to determine the incidence and cure rates of anti-resorptive agentsrelated osteonecrosis of the jaw (ARONJ) and anti-resorptive agents-unrelated osteonecrosis of the jaw (AUONJ).

　Materials and methods: Patients at eight eastern Hokkaido advanced dental care facilities during the period 1 October 2013 to 30 September 2016 were included in this study. We used the results of a partial analysis performed in a multicenter prospective study on ARONJ by the Hokkaido Association of Hospital Dentistry. We also conducted an additional survey on the number and type of bone modifying agent (BMA) prescriptions dispensed during the above 3-year study period at all 574 medical facilities in eastern Hokkaido. These results were used to calculate the incidence and cure rates of ARONJ and AUONJ.

　Results: Eighty-five cases of osteonecrosis of the jaw (ONJ) had been diagnosed during the study period. Low-dose bisphosphonate-related osteonecrosis of the jaw (BRONJ) was observed in 39 patients, high-dose BRONJ in 29 patients, low-dose denosumab-related osteonecrosis of the jaw (DRONJ) in five patients, high-dose DRONJ in three patients, and AUONJ in nine patients. An additional survey regarding BMA prescriptions conducted at all medical facilities in the eastern Hokkaido area yielded a response rate of 96.3% (553/574). High-dose bisphosphonates accounted for 5,778 prescriptions in 1,781 patients; low-dose denosumab (Dmab) for 9,787 prescriptions in 3,756 patients; and high-dose Dmab for 3,268 prescriptions in 986 patients. During the 3-year study period, the estimated incidences of ARONJ due to low-dose BRONJ, high-dose BRONJ, low-dose DRONJ, high-dose DRONJ, and AUONJ were 0.104%, 1.623%, 0.133%, 0.304% and 0.0004%, respectively. The 12-month cumulative cure rate for AUONJ was 100%. The cumulative cure rates for low-dose ARONJ were 46.5% at 12 months, 71.2% at 24 months, and 85.6% at 36 months, and those for high-dose ARONJ were 0% at 12 months and 30.0% at 24 and 36 months. The three groups showed a significant difference (P<0.001).

　Conclusions: The results suggest that the incidence of ARONJ is higher than that of AUONJ in the general population. The cumulative cure rates for AUONJ, low-dose ARONJ, and high-dose ARONJ differ significantly.

Synovial chondromatosis usually develops independently, occurring with other diseases very occasionally. Synovial chondromatosis with osteoma, including epiphysis of a long bone, was not previously reported. We describe an extremely rare case. A 47-year-old man was referred to our department due to pain when he opened his mouth and when biting. The lesion was preoperatively diagnosed as a temporomandibular joint tumor on computed tomography (CT) and magnetic resonance imaging (MRI). When the lower joint cavity was opened during surgery, loose bone-like material was discovered, and subsequently removed at the same time as the mandibular condyle tumor. The pathological diagnosis was peripheral osteoma and primary synovial chondromatosis. There has been no recurrence at 1.5 years after surgery.

Acquired hemophilia A (AHA) is a rare bleeding disorder caused by an inhibitor to endogenous factor VIII. The pathogenic mechanism is considered to be the breakdown of the immune system associated with several conditions such as malignancy, autoimmune diseases, and pregnancy. We report a case of AHA that was diagnosed based on a hematoma of the oral floor during follow-up for prostate cancer with medication-related osteonecrosis of the jaw (MRONJ). An 81-year-old man visited our hospital with the chief complaint of bone exposure following extraction of the upper right canine and the first and second premolars. He was diagnosed with MRONJ due to his course involving denosumab treatment for prostate cancer bone metastases. During conservative treatment, dark red swelling of the oral floor and subcutaneous hemorrhaging in his extremities were observed three months after the first visit. Blood test results indicated an endogenous coagulation system abnormality, and he was referred to the department of hematology and diagnosed with AHA. Hemostasis was achieved within a few days using bypassing agents and immune tolerance induction. Factor VIII antibodies disappeared once but were detected again. Therefore, immune tolerance induction is ongoing.

Neurofibromatosis type I (NF1) is a chromosomal dominant hereditary disease characterized by cafe-au-lait spots of the skin and multiple neurofibroma. Oral manifestation of NF1 is relatively infrequent. We report a rare case of huge neurofibroma arising in the palate, associated with NF1. A 39-year-old woman visited our department with the complaint of a painless mass in the hard palate. An elastic-soft swelling measuring 50 x 38 mm was found on the right palate. The tumor was excised under general anesthesia. Histopathological findings revealed neurofibroma. The tumor has not recurred, and the patient has made good progress.

Septic arthritis of the temporomandibular joint (SATMJ) is a rare disease that can lead to life-threatening complications if diagnosed or treated late. We describe a patient who developed an epidural abscess associated with acute SATMJ caused by otitis media. The patient was a 32-year-old female who was referred to our hospital after visiting her local otolaryngologist with the chief complaints of pain in the front of her right ear, swelling, and trismus. Computed tomography and magnetic resonance imaging revealed the presence of an abscess cavity that extended from the right temporomandibular joint to the epidural space. The patient was diagnosed with right-sided acute SATMJ and an epidural abscess, and was admitted for treatment. Pus was removed from the articular cavity of the temporomandibular joint by needle aspiration. Arthrocentesis was performed and antibiotics were administered. The treatment was effective and the patient was followed up for four months, recovering well without developing symptoms in the temporomandibular joint, or neurological complications. It is important to identify systemic symptoms, including in adjacent regions, for early diagnosis and treatment in patients who present with inflammatory disorders of the head and neck region.

We report a case of cyst of the papilla palatina. A 47-year-old man visited a dental clinic due to swelling of the anterior midline palate. He was referred to our department for further investigation of a lesion in the palate. Radiographic examination and computed tomography found no lesion in the palate. Magnetic resonance imaging revealed a 9.5 mm mass located in the anterior midline palate using T2-weighted short inversion time inversion recovery (STIR) imaging. He was given a provisional diagnosis of cyst of the papilla palatina. He underwent surgical removal of the lesion under local anesthesia. Clinical, histopathological, and imaging findings lead to the diagnosis of cyst of the papilla palatina. No evidence of postoperative recurrence in the anterior midline palate has been observed.

Dystrophic calcification is an ectopic calcification with fibrous connective tissue, without general mineral disorders, and is rarely found in the oral and maxillofacial region. We report a case of dystrophic calcification in the masseter muscle. A 57-year-old woman visited our department with the chief complaint of right cheek swelling. CT revealed two calcification lesions in the right masseter muscle. One lesion was intraorally excised under general anesthesia. Layered collagen fiber with calcification nodules was observed histopathologically, and there were no disorders in her blood and breast X-ray examinations, therefore a diagnosis of dystrophic calcification was made. Six months has passed since the operation and no evidence of recurrence or growth of the residual lesion was observed.