The general objective of this observational study is to clarify the clinical, microbial, and tissue characteristics, aetiology, and risk factors behind severe TMJ pathology. The main questions it aims to answer are:

• What are the clinical and histologic characteristics of patients with severe pathology of the TMJ?
• Can microbial DNA be found in TMJ tissue from patients with severe pathology of the TMJ, and if so, does this correlate to the outcome of the surgery?

The temporomandibular joint (TMJ) is a synovial joint characterized by a combination of rotation and translation during mouth opening. Unlike other joints in the body, the joint cartilage is fibrous and innervated by cranial nerves. Normal TMJ function is essential for vital functions such as eating, including proper mouth opening capacity, as well as for social activities such as talking, laughing, singing, and kissing. Several studies have reported a severe impact on the quality of life for patients with impaired and painful TMJ function.

Temporomandibular joint disorders (TMD) are common, affecting approximately 20% of the population with a strong, as yet unexplained, female predominance. The aetiology of internal derangement of the TMJ is unknown, but trauma and local or general joint hypermobility have been discussed as possible predisposing factors.

In a small proportion of patients, severe TMJ pathology, including ankylosis, develops. If ankylosis occurs, the condylar process of the mandible becomes fused to the fossa by fibrotic or bony tissue, resulting in severely restricted mouth opening ability. This can lead to a total inability to move the jaw, which can, in turn, be potentially life-threatening due to compromised airways in case of nausea.

In developing countries, TMJ ankylosis usually develops during early childhood as a complication of otitis media (inflammation of the middle ear). In the industrialized world, the condition is more frequent in adults. Factors suggested to cause severe TMJ disease, including ankylosis, are local or systemic infections or rheumatic diseases. According to some studies, a common etiological factor is trauma through intra-articular hematoma, tissue scarring, and excessive bone formation. Since most TMJ trauma resolves uneventfully, this does not explain the individual susceptibility to developing severe TMJ pathology. Thus, the aetiology and epidemiology of these conditions remain unknown.

Previous data point in different directions regarding the role of bacteria in TMJ pathology. However, knowledge regarding the role of chronic, low-virulent microbial challenges in post-surgically deteriorating cases with severe arthritis or ankylosis is lacking. Furthermore, the histopathologic presentation of these conditions is largely unknown, and systematic approaches for tissue categorization and diagnostics are lacking.

There are different surgical procedures available for these severe TMJ conditions, including osteoarthrectomy (removal of the joint bone), interpositional osteoarthrectomy using the temporalis muscle, and/or joint reconstruction using alloplastic materials or autogenous grafts. The choice of surgical technique is debated, and supporting long-term follow-up studies are lacking.

Previous studies have mainly focused on surgical interventions in a series of patients with TMJ disease without accounting for diagnosis or clinical presentation, leading to uncertainties regarding treatment decisions and efficacy. Knowledge of the mechanisms behind severe TMJ disease will improve the understanding, prediction, management, and prognosis of these conditions.

Inclusion Criteria:

• Patients subjected to open TMJ surgery such as arthroplastic surgery with or without autogen or allogen reconstruction
• Preserved biobank material (resected bone and soft tissue).

Exclusion Criteria:

• Absence of biobank material.
• Inability to give informed consent.

Consecutive patients (n=20) offered open TMJ surgery such as arthroplasty surgery with or without autogen or allogen reconstruction due to TMJ ankyloses or severe osteoarthritis. Patients treated at Karolinska University Hospital, Örebro University Hospital or Lund University Hospital. Exclusion criteria: suspicion of malignancy, inability to give consent.