The mandibular and cervical head mechanism PROPRIOCEPTIVELY responds to subtle occluding contacts (distal facing or mesial facing) of the teeth. The occlusal plane and its orientation to the cervical neck and base of the skull also proprioceptively responds to each individual occlusal form and incline plane in total as well as how the occlusal plane is designed in an attempt to seek a balance of forces between the teeth, joints and musculature of the temporalis, masseters and even more so with the suprahyoid/digastricus and the semispinius cervicalis, capitus, trapezius, scalene, levator scapula muscles. Teeth and the occlusal plane do not function independently from the supporting musculature.
Classic HIP mount with fence post and incive pin.
Many technicians still don’t get it, thinking that it doesn’t matter if the doctor Rx/presribes a case for HIP or Fox plane mounting, because they believe they are artists and can customize any occlusal plane to any orientation of the maxillary case with a curve of Spee and make it look esthetic. That may seemly be true superficially, but they fail to realize the clinical outcomes dentist may or may not be aware of. Here are just a few important factors:
2) When building the case to HIP, the lab technicians all admit that the upper posterior crowns are shorter with longer looking lower posterior crowns. This is not just against golden proproptional crown to root ratio principles, but further contributes to abnormal vector of musculo-occlusal forces (abnormal form leads to abnormal function) since the occlusal plane tends to be flatter and does effectively support an isotonic perpendicular closure path of the mandible to support a normalized head posture, thus…
3) A relapse of the closing path will naturally occur over time posterior of an optimized NM trajectory with an accompanying upward head tilt tendency further confirming a level occlusal plane with accompanying relapse of musculo-occlusal signs and symptoms (UNRESOLVED)!
The laboratory technicians all know the truth about the mounting problems and occlusal plane design problems they have with HIP! They admit that it produces odd crown length ratios for years. But may not realize the impact it has on the patients subtle proprioceptive responses to the musculature of the mandible and head and neck posture.
Since they fail to openly admit this to doctors they knowingly and or unknowingly contribute to confusion to the learning dentist, thus confusion in the ranks of our dental profession.
Every doctor has choices and will chose what is best for themselves as well as for their patients. I can only share what I am aware of. Perhaps it may make a difference to some.
Time is a real tester of concepts and principles. It is unrelenting and the TRUTH WILL PREVAIL. You don’t have to take my word for it. Your patients will let you know and the evidence will become obvious in time. It’s a matter of one’s awareness.
For further reading see: Fox Plane and HIP Mounting Considerations Blog
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