T M J is the first letters of the three anatomic parts of the head. T= Temporal bone (skull), M= Mandible (lower jaw), J= Joint (connects two bones together) and called temporo-mandibular-joint.
TMJ(s) are a large group of delicate small muscles, nerves, blood vessels, ligaments, tendons, sympathetic fibers, disc, synovial fluid, and work together as a system. There are two TM joints in the mandible, which move as one. Thus, if one joint is injured or out of its joint socket, the other joint will usually become affected.
The function of the TM Joint is to hold the jaw and the head within a certain boundary, and guide the jaw movements for chewing, talking, singing, yawning, and swallowing, keeps open the airway for breathing while you are asleep, and maintains the body balance.
TMD simply means TMJ Disorders: a collection of symptoms when it results in various pain and dysfunctions of the body, which result when the chewing muscles and jaw joints do not work together correctly; often times use interchangeably with TMJ.
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MJ may be the most active part in our body next to the heart and lungs. An average person moves the TM joint 2,000-2,500 times a day/night. If someone likes to talk excessively or chew gum habitually, it may move 5,000 times or even 10,000 times a day/night.
All body joints (TMJ, hip, knee, wrist, ankle, finger etc.) have either hinge movement or circular, movement, or a combination of the two. However, TMJ has not only hinge and circular movement, but also has a sliding movement, which moves in and out of the joint socket: Ginglimoarthroidal (hinge-gliding) joint.
If this joint-complex receives constant distress beyond the adaptive capacity, the harmony of the system can be disturbed, disc can become displaced, joint can be damaged and clinical symptoms can be manifested to the face, head, neck, shoulder, back, and to the whole body through the musculo-skeletal-nervous system.
Perhaps, TMJ is the least respected joint in the human body because of its complex anatomical structure, complicated internal mechanical movements, lack of understanding of its mysterious influence to the body, and difficulty in correcting/treating/managing when it develops intractable pains and symptoms.
WHAT CAUSES TMJ/TMD?
Medical-Dental researchers and clinicians all agree that there are multiple causes for TMD. Well known causes are: malocclusion (a bad bite), low vertical dimension (deep bite), bruxism (grinding teeth), para-functional habit (chewing gum, fingernail bite, pencil bite, habitual clenching, habitual jaw support on one side, using one side for a prolonged period of time etc.), post major surgery, automobile accident, whiplash, falls/injury, trauma (macro and micro) to the jaw, underdeveloped dental arch, structural imbalance (short leg, short arm), chronic stress, emotional related, clenching, grinding, degenerative arthritis, internal organ dysfunction, nutritional imbalance, poor posture, and problems with the Atlas Vertebra (first bone of the neck, located at the base of the skull), etc. In other words,
"Anything can cause TMD!"
The fact is, "TMJs are inert objects". They are not capable of initiating any movement on their own until attached muscles are contracted and pull it to move. If TMD symptoms begin to develop, it must be a result of unusual muscular activities beyond their adaptable capacity. Muscles or ligaments do not have an intelligence of their own; they can only do what they are told to do by the nerves which control them. Therefore, with the exception of cases that have seen some type of severe blow to the jaw or accident, a muscular imbalance with consequential joint distortion must be caused by a neurological disturbance, which results in spasmodic muscles.
The next question which must be asked is: What causes the neurological disturbance and what nerves are involved?
The answer is: "Dental Distress, Malocclusion, and Trigeminal Nerve".
DENTAL DISTRESS SYNDROME: Teeth are inserted into the jaw bone and at the end of the jaw are TMJs. The ligaments, tendons and muscles of TMJ which hold the jaw to the skull are small and very delicately balanced. If chronic distress is placed upon them and distract the adaptive limit to the muscles and joint, it goes into a protective spasm (cramp). This continuous spasm can become part of a cycle: muscle tenderness, pain, and more spasm, that results in tissue damage. Any dental distress, which disturbs the harmony of this complex "neuro-musculo-skeletal system" (nerves, muscles, bones and joints working together in harmony), can result in TMJ Disorder. The number one cause of dental distress syndrome is malocclusion.
MALOCCLUSION (BAD BITE): TMJ position is established by the upper and lower arch relationship. This relationship is dictated by the bite of the teeth. If you have a physiologically, functionally well balanced bite, you may not notice any discomfort, dysfunction or pain while the joint is in movement. However, if you have a bad bite, this can cause dental distress and force TMJs to move to a non-physiologic position.
BAD BITES ARE: Deep bite, missing molar teeth, multiple missing teeth, poorly aligned teeth, crooked teeth, under development of dental arch, badly decayed or broken teeth, excessively worn down teeth, loose teeth, poor dental work, poor orthodontic treatment, etc.
Every time we chew, swallow, move our head around, walk, work, drive, exercise, play, lift things up, and even during breathing and fall asleep, the upper and lower teeth constantly meet together lightly or clench hard. If there is a bad bite, this not only distresses the trigeminal nervous system, but also forces the TMJ to move away from its balanced physiologic position. A bite changes throughout one's lifetime and so does the TMJ balance. (Note: Not all bad bite cause TMJ disorders, and this is one of the big debates among dental professionals).
This following is excerpted from Edwin A. Ernest, III, DMD's article: The 'bite' aspect of the term describes the influence of the upper and lower teeth. This influence includes the 'fit' of the upper and lower teeth and whether that fit helps to support or hinder the articulation of the jaw joint and thus its stability. In fact, it is accurate to describe each tooth in the maxillary bone and in the mandible to also be a 'joint.' In the human adult, anywhere from 28 to 32 teeth normally play a pivotal role in the health and or disease of the TMJ. An injury to a tooth affecting its position of height, maloccluded teeth, tooth extraction and progressive dental instability, extrinsic injury to the muscles or ligaments that move the joint, or internal derangement within the joint can all alter normal joint arthrokinesis. Arthrokinesis is the ligamento-neuro-muscular reflex mechanism that allows a movable joint anywhere in the body to work either effectively or to exhibit some degree of dysfunction, injury, or disease. In arthrokinesis, it is the ligament -- via its mechano-receptors -- that directs spinal and CNS activity that serves to protect as well as signal joint-related injury. Joint-related injury often results in muscular reflex restriction and pain, and the pain often includes pain referral to distant sites.
TRIGEMINAL NERVOUS SYSTEM (TNS): The trigeminal nerve (fifth cranial nerve) is the largest cranial nerve among twelve cranial nerves. It has three branches, innervated with all other cranial nerves and directly innervated to all teeth, upper jaw, lower jaw, mouth, gums, tongue, nose, eyes, ears, face, head, and neck region. Trigeminal nervous system is associated with brainstem's reticular formation function, which influences the autonomic nervous system, limbic system, hypothalamus and cerebellum. Additionally, recent EMG (electromyogram) research demonstrates that postural stability of the head and the neck can be influenced by a TMJ problem or, conversely, the TMJ can be affected by changes in the axial cervical structures.