Thoughts on MIP Position: Is it a Stable Position?

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I was invited by Dr. Sushil Koirala, Founder and Coordinator – MiCD Global Academy, Chief- Editor of MiCD Clinical Journal, as one of many globally renowned clinicians, academicians and researchers to answer 15 exclusive interview question for their clinical e-journal sharing my experience, clinical and research findings on the subjective of “TMDs – Confusion & Consensus: Expert’s Advice“. The following is the eighth of 15 responses to their questions.

8. Do you agree with the concept that the MIP position should not be changed because it develops naturally and therefore is always well adapted? If not kindly explain why? And if yes, how is it possible that MIP can remain stable and well adapted even after severe occlusal wear or the partial/ complete loss of posterior teeth or after orthognathic surgery.

Physiologic occlusion is an understanding of how the mandible relates to the maxilla and even more importantly how the mandible is affecting head posture and all the associated structures that relates to the coming together of the teeth, muscles and joints.  Resting and functional status of muscle health and physiology of the dental patient are routinely overlooked in the diagnostic work-up and comprehensive examination.  Treating to the existing habitual occlusion or MIP is often assumed to be “stable” enough for most dentists when doing restorative or prosthetic dentistry as long as the patient is not complaining of pain, headaches, facial tension or jaw joint clicking/popping.  Reporting any jaw joint pain or tenderness intra or extra-meatally should cause a clinician to pause definitive treatment until one determines the underlying cause of these masticatory dysfunctions, joint derangements and pain problems. Just because teeth are free of cavities or obvious periodontal disease does not mean that everything is OK musculature wise.  When evaluating a patient’s overall dental health, one must also consider the overall physiologic position of the condyles and disc as well as the mandible because the determined structural jaw relationship will impact the restorative or prosthetic treatment outcomes.

Sometimes maxillary teeth are retro-inclined lingually (Class II, division 2) due to tooth size discrepancies. Maxillary incisors that are retrusive in position are often due to narrowing of the arch or missing upper bicuspid from previous extraction orthodontic treatment. The narrowing of the arch will cause the mandible to function in a posterior (forced adapted) position relative to a more anterior physiologic orthopedic muscle rested position relative to the adapted MIP/habitual position.  Facial profiles commonly show a dished in appearance with the upper lip depressed when the maxillary incisors are retracted posteriorly.

Patient’s accommodative capacity over the years can adapt to their existing MIP to a certain degree even though vertical growth patterns of the first molars from early childhood where unknowingly stunted vertically. Vertical growth potential of the lower arch of teeth are often blocked by abnormal tongue habits and upper airway nose breathing obstruction. The tongue abnormally functions over the growing 6-year molars while the nose and airway are restricted from excessive mucous in the nose due to allergies and inflammation. These intra oral growth restrictions are all part of an accommodating response to abnormal growth patterns ( e.g., lower one third of the face is diminished in growth but adapted).

The lower one-third of a child’s face can develop toward a retrusive profile, thus setting the stage in the adult stages of life with a narrow dental arch, over-close bites, deep curve of Spee and forward head posture. Certainly, tooth wear patterns will appear in the lower incisal edges with bicuspids exhibiting wear facets on the buccal and mesial surfaces as the mandible wants to function anteriorly. The neck of condyles over time are forced to accommodate to this over-closed vertical position of the jaws exhibiting anterior bends in the neck of the condyles (abnormal), due to masseter muscle over-use (hyperactivity) with accompany mandibular gonial angle bone deposition. Over time the patient could complain of temporal headaches, occipital tension, facial pain and tenderness, teeth sensitivities, loose mobile teeth and abnormal toothaches to name a few.  Most dentists would then report these clinical problems as having unknow etiologies. Why?

Receding gums in the anterior or posterior regions depending on the abnormal occlusal forces involved, with accompanied clicking/popping jaw joints during opening and closing of the mouth and fracturing cusps are all part of the cycle of unstable occlusion trying to adapt. Is this “Normal”?  Is this physiologically stable occlusion?  Are these musculoskeletal occlusal sign and symptoms being ignored within our profession assuming that MIP is a stable treatment position to our routine daily dentistry?  We are often led to believe that these problems are just the normal evolution of aging, thus dentistry and restorative procedures continue to build about these pathologic adapted MIP relationships.

In general, we know teeth dominate, muscles and temporomandibular joints will accommodate as long as pain, masticatory dysfunctions and joint derangements do not appear.  When pain, masticatory dysfunction and joint derangement present themselves (patients complaining of their pain problems) one must realize that the present intercuspal relationship is no longer sufficient, adequate or healthy to maintain long-term stability. These observed problems in fact are pathologic, impairing and leads to various stages of masticatory dysfunction.

How keen is a dentist’s clinical awareness and understanding about these matters of TMD and dental occlusion?  Today’s dentists must begin to think both gnathicly and neuromuscularly (GNM).  This is how I “think” and I view my cases as a GNM minded clinician.  Today, dentists need to get proper training to update themselves and grasp and implement these principles optimally.  Knowing this will avoid patient harm and dental occlusal failures.

Clayton A. Chan, D.D.S. – Founder/Director

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Leader in Gneuromuscular Dentistry