“If you don’t stand for anything you will fall for anything….”

After studing numerous cephalometrics and lateral cervical spine films of patients it is clearly evident that the hamular notch and incisive papilla (HIP) landmarks actually are more closely parallel to the the Ala-Tragus plane, and Campers Plane, NOT parallel to horizontal level as some teach. This is a big misnomer! True HIP of the maxilla in a true physiologic head and cervical relationship actually angles or slants at a 6 to 10 degrees (average) relative to horizontal (see literature references in above article).Key Point: The lab technicians are challenged when mounting the maxillary casts by artistically guessing because dentists fail to sending the necessary recordings that are essential to reliably fabricate the aesthetic restorative case. They do not rely on stick bites, inaccurate impressions, inadequate photos, distorted models (hamular notches) and wrong fox plane recordings. The artistic eye often comes into play regardless of advocated techniques.

Clinical and laboratory studies have shown when using the boney landmarks of the maxilla to mount the maxillary cast is in fact incorrect and will simulate an unnatural upward head tilt position with the maxillary cast displaying an anterior upward cant 57.6% of the time. That is why most labs ultimately do not complete the restorative cast to these references, but may use it as a guide. Anyone who honestly questions this can check for themselves by mounting the final restorations on the solid mounted maxillary cast to see the type of occlusal plane and what mounting position was actually used.

Labs will say they mount the case to HIP, but will often not dare finish the case to these references because of their experience and realization that this mount will lead to long toothy looking smiles. The technicians realize that the maxilla is not naturally oriented in that manner, thus they make the decision to change the cant of the cast purposely to avoid remakes and an undesirable result for the dentist. The maxillary cast mount should be determined by the dentist, but reality shows that the lab technicians will subjectively and artistically alter the doctors HIP recording to one that is more subtable for finishing the restorative case.

A flat/level HIP mount leads to a pathologic referenced position. A slanted/angled HIP mount is what nature designed physiologically. I advocate the second HIP mount (slanted or angled) which nature intends and is similar to Campers plane or ala tragus plane. This will lead to golden proportions not only in the anterior regions, but also will result in a more idealized crown to root ratio of both the upper to lower posterior molar regions. (Interesting to note that with the classic HIP mount it is often observed that the upper posterior molar crowns will typically look short (staulky) with longer looking lower molar crowns (This is not gold proportions, but results when the maxilla is erroneously mounted to a pathologic relationship). Neuromuscular science supports natures golden proportions and recognizes pathologic distortions! I prefer not to use the fence post and incisive pin as my mounting references to orient the HIP.

 

 

Note: A)Pathologic neck posture: Kyphosis resulting in a more flatter occlusal plane. B) Physiologic neck posture: Lordosis resulting in a normalized occlusal plane (angled slant).

If we were to establish boney maxillary cast references such as the hamular notch and incive papilla as some prefer to dogmatically advocate as scientifically objective and mount the maxillary cast to those references the dentist and technician will ultimately be reproducing an undesireable relationship (often resulting in a maxillary cast occlusal plane that appears level and often with the anterior incisal edges vertically upward relative to the posterior teeth). This does not truly represent what nature intended as dental health. Although this idea may appear to be simple to learn and easy to teach this maxillary cast mounting method is in fact one that ignores natures isotonic neutral head position. What we clinicians want to do is replicate healthy relationships of the head, neck and mandible as it relates to the cranum and not pathologic relationship when treating our patients occlusion.

The Fox Plane technique I advocate is a simple means to subjectively analyze and capture what nature intended (an angled HIP mount not flat or level). This is well supported by literature and the orthodontic and prosthetic community. It is a convenient way to capture a proper maxillary recording when the patient is stable and ready to move to the next phase of restorative dentistry. (The classic face bow also works, but is historically more complex and involved and not laboratory friendly). Objective science will always advocate healthy form to support healthy function. The neuromuscular minded clinician needs to learn to use their best judgement skills and understanding and not rely solely on pathologic boney references as their guide. “Nature does not think in mechanical terms”. We need to learn from nature, its beauty,design, form and how it functions.

My View and Opinion: Use the Fox Plane technique to reference a physiologic occlusal plane, not depending on maxillary boney references. Capture a correct maxillary slant or angled HIP (Physiologic) keeping the Fox Occlusal Plane Analyzer level and parallel to the ground. Make sure the head is level (see Fox Plane Mount blog for technique). This will allow the clinician to easily capture a proper occlusal plane, not a flat or “level” occlusal plane (pathologic). Frontally the fox plane is perpendicular to the long axis of the face. I am sure the laboratory technician understands these techniques and the esthetic significance better then most clinicians since they actually have first hand experience of mount your dental casts daily!