Monday, February 2, 2009

The Occlusal Plane

Which Occlusal Plane Do You Undestand? Don't Get Confused
by Clayton A. Chan, DDS, MICCMO

Read my scientific article: "A Review of the Clinical Significance of the Occlusal Plane: Its Variation and Effect on Head Posture" - published in the International College of Craniomandibular Orthopedics Anthology, 2007.

"If you don't stand for anything you will fall for anything...."

Establishing the occlusal plane is an important aspect for every clinician and laboratory technician who desires to create beautiful soft smile lines, stable occlusion and supported normalized head and neck posture. Many of the dental goals and objectives for dental health correlate to esthetics as well as the physiologic function of natures dynamic masticatory system. The artistry and design of the smile is often subjective in nature and does not always lend itself to a cookbook receipe of hard fast numbers and values, but often is visualized by the designers and creators of dental occlusion. So it is the same with establishing the occlusal plane.

Reconstruction by Clayton A. Chan, DDS and Mike Milne, CDT & Team Sunrise Dental Laboratory, Las Vegas, NV

Dentistry is both an art as well as a science. Combining the artistry of tooth position, orientation, embrasure spaces (open or closed), occlusal plane position and arch shape development are all examples of the subjective clinical decision making ("non science", yet scientific) that must conform to good principles and universal laws of form and function. Implementing one's judgment, clinical experience in addition to a keen visual eye does not lessen ones position of being objective and clinically sound, especially in the arena of neuromuscular occlusion, orthodontics and restorative/prosthetic care.

There are basic laws in nature and science to support such and so it is the same when establishing the occlusal plane. There is nothing wrong neither is it any less than scientific with using leveling tools (e.g Fox Occlual Plane Analyser, face bows, leveling tables and photos) to help the clinician and technician visualize and capture the maxillary occlusal plane with a normalized head position as long as they are used properly. Subjective is certainly required when it comes to the art of dentistry, yet balanced with the physiologic neuromuscular sciences that can measure muscle function using EMG and CMS technology. I like to use all the scientific tools available in dentistry in addition to applying my artistic mind to create postural form for healthy function.

Note the various occlusal plane references as noted in dental literature.
Depending on boney landmarks alone as references to establish maxillary relationships is almost similar to using jaw joints to reference the mandible/bite. The astute clinician recognizes that neuromuscular and physiologic paradigms reference to healthy muscles not bones which often present with distortions, torques, skews and asymmetries. Repeated studies have shown that relaxed muscles can change the profile and soft tissue architecture over the hamular notch regions. Studies have also shown that relaxed cervical neck musculature with isotonic mandibular muscles will effect head posture and the occlusal plane, thus testing the occlusal plane teaching paradigms as to how these boney landmarks are actually referenced to horizontal level in a physiologic position, not pathologic ("level").
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. I use the Fox Plane as indicated in the previous blog titled "Mounting the Maxillary Dental Cast Using the Fox Plane".

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.

Students in a recent Level 6 course at Occlusion Connections mounted their maxillary casts using the Fox Plane technique. Note the natural angles that resulted and are represented in this series of mountings. This is key to dental aesthetics.

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!

Not all clinicians have comprehended these simple teachings of the Fox Plane concept and its significance to the head, neck and mandibular physiology. Not all teachers teach from a TMD/orthodontic-orthopedic/restorative perspective. Not all clinicians take cephalograms and cervical neck films to understand and see the relationship of the neck and occlusal plane as it relates to a leveled balanced head position, thus limiting their understanding of the significance of these occlusal plane concepts that are importantly related to head position, mandibular positioning and mandibular trajectory closing paths. Clinicians who have a scientific inquiring mind will have the maturity and desire to pursue these truths with certainty and apply the common sense techniques that naturally become logically apparent. We don't have time to waste when doing clinical dentistry on live patient's using wrong and misleading concepts. We need to take the opportunity and learn proper occlusal concepts that will lead our profession toward bring health to our patients, not for ease and convience of teaching.

"Clinicians and dental laboratory technicians have found it important to DIAGNOSTICALLY identify HIP plane so that the dentist does not restore to a distorted cranial base. Since the patient poplulation with chronic TMD and postural problems obviously has a higher than normal HIP plane variance from normal base plane parameters, it is important that the clinician does not replicate this distorted base. Ergo Hoc Proctor Hoc, if clinicians restore this patient using the HIP reference it will only replicate the anatomic manifestations of the etiologic problems." - Robert Jankelson, Summer 2005 .
Some may laugh, jeer and criticize me for my passion and beliefs of my occlusal plane perspectives as they relate to clinical dentistry, but one day those critics will quiet themselves when our profession begins to further mature to the next level to see that our application of neuromuscular dentistry brings the science as well as the art together. Don't be confused. Change is in the making! Let's be tolerant, thoughtful and respectful of another point of view!
"It's a curious thing that physical courage should be so common in the world and moral courage so rare." - Mark Twain

Neuromuscular Dentistry