Many patients report pain in their jaw joints. The pain can be mild, or it can be debilitating for some patients. Regardless of the intensity of the pain, many patients will ask the question, “Why do my jaw joints hurt?”
Historically, many dentists have assumed pain in the jaw joints is due to an improper occlusion where the teeth do not fit evenly. The assumption was since the teeth don't fit evenly the masticatory muscles will have to contract to help the teeth fit together. The continued muscle contraction was the primary source of pain and if the bite could be corrected, the teeth would fit together, and the pain would resolve.
Muscle does play a role in pain and for many patients it plays a very significant role in pain. Fortunately, today we know that other pain sources should be evaluated in addition to muscle. Herniated disks (Fig. 1) can cause pain, as Piero Cascone discussed in his 2010 article in the journal Cranio.
Cascone discussed how anterior displaced disks that move to the medial aspect of the condyle may be responsible for many of the symptoms TMD patients report.
In addition to muscle and disk-based pain, bone is a possible source of pain that must be considered when TMD patients report symptoms. Bone disorders have been recognized for decades with William H. Bauer authoring an early article in 1941.
Special attention should be given to the bone in cases where patients report sharp or stabbing pain. Eroded bone (Fig. 2) is a commonly seen finding on MRI and CBCT imaging.
Isabela Dias wrote about a significant correlation between disk displacement and associated degenerative bone changes such as erosive changes in the condyle. She said the correlation between advanced cases of disk displacement and the occurrence of degenerative bone changes emphasizes the importance of MRI for an accurate diagnosis and the development of an appropriate treatment plan.
In addition to eroded bone, marrow abnormalities (Fig. 3) – as discussed by Robert Chuong and Mark A. Piper in 1993 – can play a role in patients who report pain.
Lastly, small bone (Fig. 4) or bone that does not develop to its complete genetic potential as discussed by Kurt P. Schellhas may contribute to pain.
Misalignments of the upper cervical spine (Fig. 5) can mimic TMD pain and should always be considered a possible course of pain when patients present with frontal pain. Howard R. Epps provides a comprehensive review of different upper cervical conditions that may be present in TMD patients.
Lastly, TMD patients may present not only with structural alterations in the TM joint but also with sympathetic nervous system dysfunction. Hooshang Hooshmand published a paper in 1999 discussing sympathetically mediated pain and Piper has revived interest in this topic for the TM joints.
It would serve all dentists well to become familiar with complex regional pain syndrome (CRPS) to help more accurately diagnose patients who present with pain. As an interesting side note, CRPS can influence muscle dystonia and may be the long-searched answer to why some patients will brux more than other patients.
In the end, TMD can be just muscle or it can be a combination of muscle, herniated disks, bone disorders, upper cervical misalignment, or sympathetically mediated pain. The more we understand each of these topics, the more we can help our patients.
References
Bauer W. Osteo-arthritis deformans of the temporomandibular joint. The American Journal of Pathology. 1941;17(1):129–140.
Cascone P, Fatone FMG, Paparo F, Arangio P, Iannetti G. Trigeminal impingement syndrome: The relationship between atypical trigeminal symptoms and antero-medial disk displacement. Cranio. 2010;28(3):177-180.
Chuong R, Piper MA. Avascular necrosis of the mandibular condyle-pathogenesis and concepts of management. Oral Surgery, Oral Medicine, Oral Pathology. 1993;75(4):428–32.
Dias IM, Coelho PR, Assis NMSP, Leite FPP, Devito KL. Evaluation of the correlation between disc displacements and degenerative bone changes of the temporomandibular joint by means of magnetic resonance images. International Journal of Oral & Maxillofacial Surgery. 2012;41(9):1051-1057.
Epps HR, Salter RB. Orthopedic condition of the cervical spine and shoulder. Pediatric Clinics. 1996;43(4):919-931.
Hooshmand H, Hashmi M. Complex Regional Pain Syndrome (Reflex Sympathetic Dystrophy): Diagnosis and Therapy-A Review of 824 Patients. Pain Digest. 1999;9:1-24.