To understand TMD, we first want to help patients understand the anatomy and function of the TMJ and joint space.
The lower jaw articulates in a space of the skull called the mandibular fossa (temporal bone of the skull). The lower jaw, called the mandible, has a vertical (green in the picture below) and horizontal (grey in the picture below) component. The horizontal component houses the teeth, and the vertical component is what articulates in the mandibular fossa. The end of the vertical component has an oval shape to it that’s longer left to right than up and down. This is called the condyle (marked with an arrow).
The condyle is covered with a thin layer of hard connective tissue. Housed between the condyle and mandibular (temporal) fossa is the articular disc. A fibrous tissue that resembles a donut, it allows the condyle 360 degrees of support due to the thinness in the middle with a thick, fibrous connective tissue ring.
The temporomandibular joint is encapsulated in a connective tissue sling that’s completely sealed so synovial fluid can lubricate the moving parts. The articular disc is attached from behind by inelastic connective tissue (retro-discal tissue) and in front by a muscle (the lateral pterygoid muscle).
As the jaw moves, the lateral pterygoid muscle must contract in order to keep the disc on top of the condyle. When the lateral pterygoid releases and the mandible closes, the inelastic connective tissue (that is attached from behind) is tight, allowing the disc to stay on top of the condyle as the jaw closes.
The masticatory system is composed of four compensating parts. All four on dependent on each other. They are:
- Teeth
- Periodontium (gums and bone)
- Temporomandibular joint
- Neuromuscular system
The teeth are the only part of the masticatory system that will not accommodate. For the system to work in physiologic harmony, the gears of the teeth must line up when the TMJ and neuromuscular system are in physiologic equilibrium.
The neuromuscular system is an intricate network of nerves and muscles controlled by neural feedback loops. There are 26 muscles attached to the mandible (lower jaw). They have a proprioceptive control mechanism where their action is controlled mainly by the arrangement of the gearing of the teeth. When the gearing of the teeth causes shifting of the mandible, the neuromuscular system responds rapidly by accommodating to the needs of the teeth, allowing them to “line up.” Any small, accommodating shifts will begin the process of joint derangement.
The signs and symptoms of TMD can be divided into three categories: muscle, non-muscle, and musculoskeletal.
Muscle pain is caused by a sustained accommodating muscle contraction, leading to constricted blood flow followed by depleted oxygen to the muscles.
The head postures above the atlas and ondontoid process. The atlas and ondontoid process are the first two cervical vertebrae. The head rotates in all dimensions atop the atlas. Forty-two muscles are attached to the skull — short ones from the cervical vertebrae to the base of the skull and long ones from the sacrum up to the base of the skull.
This intricate system can contribute to the onset of TMD because of fatigue, injury, or general dysfunction. Thankfully, Dr. Udoff can serve as a personal guide for his patients, helping you understand the intricacies of your musculoskeletal health and how your symptoms relate to the presence of TMD. Effective therapy options will not be far behind once we’ve pinpointed the severity and cause of your condition.
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