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by Clayton A. Chan,  D.D.S.
This short posting appear as a 2nd part to an original posting made on the former genR8TNext internet forum under the subject: Re: [CROWNS] TMD/Wear, No Anterior Guidance on Monday, September 04, 2000 9:44 AM.

The physiology of mastication and swallowing has always promoted a great deal of interest in dentistry.  The result has been extensive research in mandibular movements, mandibular posturing, chewing, chewing forces, chewing efficiency, muscle activity and tooth contact patterns.  As a result many authorities believe that almost all the research has shown that tooth contact rarely occurs in a border movement position, but rather during chewing and swallowing.  Most of the contacts have been shown to occur in an occlusal position slightly anterior to centric occlusion, the so-called maximum intercuspation (habitual occlusion).  When observing our patients natural dentition and looking at the anterior incisal wear either on the lower incisal edges or the upper anteriors, we clinicians should ask ourselves where did the mandible have to position itself for that to occur?  How many thousands of times did the mandible move to that position to wear away the natural hard enamel during habitual functioning moments of posturing, swallowing, smiling, speaking, even repose.  But, then suddenly it had to move to another position (an avoidance position) due to the malocclusions and discrepancies in intercuspation for maximum bracing.  Skids occurred, rubs, strains, forces were exerted, crowding, tooth rotations and eventual breakage of tooth structures and/ or restorations occurred in the regions of the mouth, we could only see after obvious damage was done.  The muscles of mastication naturally posture the mandible within the confines of their resting length.   They are most comfortable and least resistant during resting, speaking and swallowing when functioning within the “physiologic zone” typically anterior and inferior to the habitual CO position.

It is the acquired/ habitual occlusal schemes that dictate the habitual intercuspating of teeth resulting in further rubs, wear and tear on tooth structure.   When the muscles of mastication want to posture the mandible to its physiologic position while the teeth, the dominating structures, force the bite and mandible into another position, disharmony occurs.

It is important to recognize that the functioning forces applied during chewing and swallowing are relatively small compared with the maximum biting forces which can be applied as a result of isometric muscle contraction.