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Orthodontic Jaw Wiring Position of lowerJaw
(OJW Position of Physiologic Rest)
THE OJW POSITION OF PHYSIOLOGIC REST is a parted resting position of the mandible at which the muscles of mastication are in a minimally contracted position thereby allowing the lower jaw to be suspended from the maxillary teeth in a condition of "weightlessness". Inter-occlusal wiring (connecting the upper teeth to the lower teeth) permits the mandible to move 2.0 mm - 4.0 mm laterally, vertically and antero-posteriorly thereby minimally impeding speech and minimizing the possibility of TMJ stiffening. This position is often congruent with an observable inter-occlusal space of 2.0 mm - 4.0 mm and closely approximates the position we know as the "physiologic jaw resting" position, the initial position from which all speech and chewing begin and ends. It is this condition of jaw "weightlessness" that precludes the possibility that the upper/lower teeth are extruded during the time the OJW device is in place.
More than likely as are reading this document your jaw is in the “physiologic rest position”. The muscle that allow/permit/cause you to open your mouth are in a state of complete relaxation. However, the muscles that allow/permit/ cause your mouth to be shut are slightly active. If they were full active you would be clenching your teeth. Try speaking from this clenched position (upper and lower teeth touching) and you will see that your speech is greatly distorted. Now let your muscle relax and allow your teeth to part if only just a little and you will see how much more clearly your speech becomes. Look around you at people and notice how they posture their mouth. Very few, if any at all, can be observed that allow the mouth to remain gaping open wide, That is because the muscle that close the mouth (Masseter and Temporalis Muscles) are normally in a state of mild contraction. Excessive contraction leads to clenching which if prolonged can cause TMJ-like pain. When these muscles lose their ability to contract, as occurs with some medicaments and pathologies, the mouth falls agape.
In normal healthy persons the Masseter and Temporalis muscles are remain in state of mild (unconscious) contraction thereby holding the lower jaw up in a state of “physiologic rest” Most often the lips are slightly apart while sometimes the lips are lightly touching. This is the position in which the jaws are wired “apart”. It is called the “OJW Position of Physiologic rest”. You can find this position by saying the word “emma” or “momma” and then bring your lips into a very light touching position. Hold the position and you will note that your teeth are slightly parted (the very same position you were in when you began reading this document, and congruent with the position that your lower jaw is in at this very moment.
I ask you to consider whether this position is socio-cultural (taught/ learned position, or whether it is simply built-in to “our” genes.
In any case, when the jaws are interlaced in OJW they are in the position of physiologic rest. The lower jaw in not “suspended” from the upper jaw like a sack of potatoes being held from your hand. Au contraire, the lower jaw puts no weight on the upper jaw/teeth at all. That is the reason you can be in OJW for as long as necessary to achieve your weight goal. OJW per se can not cause your teeth to elongate because the wires are not tugging on them. Every dentist is keenly aware of this position especially those that fabricate dentures for their edentulous patients.
May 10, 2012
Dr. Ted Rothstein
Specialist in Orthodontics
Specialist in Orthodontic Jaw wiring
(718) 852 1551