See Dr Bixby's videos on
The Cosmetic Channel
|
ATLANTIC CENTER FOR ADVANCED DENTISTRY |
Health, Beauty, Confidence ... for you |
TMJ / TMD
What is It?
The temporomandibular joint is the jaw joint and is frequently referred to as the TMJ. There are two TMJs, one on either side, which work in unison. The name is derived from the two bones which form the joint: the upper temporal bone which is part of the skull, and the the lower jaw bone called the mandible. The unique feature of the TMJs is the articular disk. The disk is composed of fibrocartilagenous tissue ( like the firm but flexible cartilage of the ear ) which is positioned between the two bones that form the joint. The disk divides each joint into two.
The lower joint compartment formed by the mandible and the articular disk is involved in rotational movement ( opening and closing movements. ) The upper joint compartment formed by the articular disk and the temporal bone is involved in translational movements ( sliding the lower jaw forward or side to side. ) The part of the mandible which mates to the under-surface of the disk is the condyle and the part of the temporal bone which mates to the upper surface of the disk is the glenoid ( or mandibular ) fossa.
The left temporomandibular joint, viewed from the outside
The condyle articulates with the temporal bone in the mandibular fossa. The mandibular fossa is a concave depression in
the lower part of the temporal bone. These two bones are actually separated by the articular disc, which divides the TMJ
into two distinct compartments. The lower compartment allows for pure rotation of the jaw, which corresponds to the
first 20 mm or so of the opening of the mouth. After the mouth is open to this extent, the mouth can no longer open
without the upper compartment of the TMJ becoming active.
At this point, if the mouth continues to open,
not only is the condylar head rotating within the lower compartment of the TMJ, but the entire apparatus ( condylar head
and articular disc ) slides forward , thus incorporating a forward movement into the further opening of the mouth.
In order to work properly, there are neither nerves nor blood vessels within the central portion of the articular disc. Were there any nerve fibers or blood vessels in the TMJ joint, people would bleed whenever they moved their jaws; however, movement itself would be too painful.
Normal movements of the jaw during function, such as chewing, are known as excursions. There are two lateral excursions ( left and right ) and the forward excursion, known as protrusion, the reversal of which is retrusion.
When the jaw is moved into protrusion, the lower incisors or front teeth are moved so that they first come edge to edge with the upper incisors, and then move past them, producing a temporary underbite. This is accomplished by sliding of the condyle down the articular eminance ( in the upper portion of the TMJ ) without any more than the slightest amount of rotation taking place ( in the lower portion of the TMJ ), other than that necessary to allow the lower incisors to come in front of the upper incisors without running into them.
The left temporomandibular joint, viewed from the inside
During chewing, the jaw moves in a specific manner as delineated by the two TMJs. The side of the mandible that moves sideways is referred to as either the working or rotating side, while the other side is referred to as either the balancing or orbiting side. The latter terms, although a bit outdated, are actually more precise, as they define the sides by the movements of the respective condyles.
When the jaw is moved into a lateral excursion, the working side condyle ( the condyle on the side of the jaw that moves outwards ) only performs rotation ( in the horizontal plane ), while the balancing side condyle performs translation. During actual functional chewing, when the teeth are not only moved side to side, but also up and down when biting of the teeth is incorporated as well, rotation ( in a vertical plane ) also plays a part in both condyles.
The jaw is moved primary by four muscles: the masseter, medial pterygoid, lateral pterygoid and the temporalis. These four muscles work in different groups to move the mandible in different directions. Contraction of the lateral pterygoid acts to pull the disc and condyle forward; thus, the action of this muscle serves to open the mouth. The other three muscles close the mouth; the masseter and the medial pterygoid by pulling up the angle of the mandible and the temporalis by pulling up on the coronoid process.
The temporomandibular joint is arguably the most complex set of joints in the human body, and is susceptible to a number of problems. Temporomandibular joint disorder ( TMJD, TMJ or TMD ), or TMJ syndrome, is an umbrella term covering acute or chronic inflammation of the temporomandibular joint. The disorder and resultant dysfunction can result in significant pain and impairment. Because the disorder transcends the boundaries between several health-care disciplines - in particular, dentistry, neurology, physical therapy, and psychology - there are a variety of quite different treatment approaches.
Neuromuscular dentistry is a medical paradigm in which TM joints, muscles, and central nervous system mechanisms are treated together. It is a form of dentistry that objectively focuses on correcting misalignment of the jaw at the temporomandibular joint (TMJ). Neuromuscular dentistry acknowledges the signs and symptoms that relate to problems involving the lower jaw. Neuromuscular dentistry recognizes the need to solve the root of the misalignment problem(s) by understanding the relationships of the tissues which include the muscles, teeth, temporomandibular joints, and nerves.
some parts adapted from Wikipedia
reviewed and edited by Dr Bixby
Our entire team has had advanced training at the world-renowned
Las Vegas Institute for Advanced Dental Studies
Proudly serving Monmouth County for over 30 years