Dentists develop their own philosophy of how to best manage the occlusion of every patient they are treating. How they obtain their personal philosophy of occlusion is often from a combination of information from school, journals, lectures and experience. Dr. Gordon Christiansen said in the February 2004 issue of Dentistry Today: “Dentists are afraid of occlusion . . . there is extreme controversy about what concept of occlusion is correct, and I do not see any relief to that controversy.” Occlusion is a discipline that you learn over time and should never stop learning during your entire career.
The first treatment for developing a stable occlusion was outlined in 1858 by Dr. Bonwell. Dentistry is still searching for an ideal treatment 150 years later. Occlusion is a study of function that often times ages from a lean and mean chewing machine into a dysfunctional, pathological image of its former self. The anatomy ages and adapts as gracefully as it can with every chew, swallow, and clench. As an occlusion ages, all the anatomical parts wear flatter, the muscles shorten, the ligaments fatigue, and the condyles compress.
There are three dimensions to consider in an occlusal diagnosis: the teeth, the muscles, and the joints. Most dentists believe that the vertical dimension of occlusion is an equilibrium between the repeated contraction of the elevator muscles and the eruptive force of teeth. Changing the vertical dimension of occlusion could be a good or it could be a bad thing. Therefore, it is a major issue when dentists add to or subtract from the occlusal table. Most of the occlusal management performed by dentistry today consists in decreasing the amount of force on a tooth, or on an arch of teeth. For example, a restorative dentist quickly learns to build fillings and crowns slightly out of occlusion because they know that an adjustment is required if the restoration is perceived as being “too high” by the patient. Also, mobile teeth are often adjusted out of occlusion because the diagnosis is trauma from occlusion. However, you cannot “subtract” forever. When an occlusion finally becomes pathologically flat and the anatomy breaks down, dentists argue over the best way to fix it. Dr. Major Ash, author of numerous books on occlusion, said at the 2000 American Equilibration Society that “science is a battle where ideas compete for acceptance,” and he later asked, “Is there an occlusal scheme with a biological advantage?” What is the truth?
A small percentage of dentists seek out one of the many master philosophies that are taught around the country. Investing the time and money to study a philosophy of occlusion is a major commitment for any dentist, even if you know the direction in which you wish to travel. The major concepts of occlusion available today are:
- Bioesthetics
- Gnathology
- Centric Relation
- Functional
- Neuromuscular
My philosophy is to prevent an occlusion from breaking down in the first place. Saving a bite requires precision dentistry which should incorporate attributes or “pearls” from all five occlusal philosophies. All the philosophies are about excellence and every approach, if executed to perfection, will produce a beautiful, healthy result. The benefits of each occlusal concepts are outlined.
Bioesthetics was developed by the late Dr. Robert Lee, who advocated a fixed anterior guidance based on the skulls of humans with excellent teeth. Dr. Lee taught that the condyles are stabilized with a bite splint worn twenty-four hours a day, seven days a week, for months if needed. The upper orthotic has posterior centric stops and canine disclusion and the patient is required to eat with it. After splint therapy, the dentist will reconstruct the occlusion with these guidelines in mind: the maxillary centrals are 12.0mm in length and the lower centrals are 10.0mm in length. The vertical dimension is fixed by setting the cementoenamel junction of the upper and lower centrals 18.0mm apart. The overbite will be set at 4.0mm and the over jet set at 2.0mm for the centrals and at 1.0mm in the canine region. The steep guidance and open vertical create a posterior space that is reconstructed with very steep posterior crown anatomy. Posterior crowns with sharp cusp anatomy function with less muscle activity, but only if the posterior teeth disclude in every mandibular movement. If the condylar guidance and the anterior guidance are independent of each other in function for the lifetime of a patient, then an exceptional result is possible using this concept of occlusion.
The Gnathology concept was developed in the 1950s by many masterminds, the most prominent being Dr. B.B. McCollum, Dr. Harvey Ballard, and Dr. Charles Stewart. Gnathology is very similar to the Bioesthetic concept in principle, but gnathologists reconstruct the posterior teeth from the opposite direction. Bioesthetic dentists use a pre-set anterior guidance first, and then develop the contours of the posterior teeth, whereas gnathologists use the pathways of condylar movement to develop the pathways and contours of the posterior dentition. The anterior guidance is then designed and created to disclude the posterior teeth. The gnathologists are the ‘fathers’ of occlusion who developed the pantograph, the fully adjustable articulator, and the concept of functionally-generated pathways. The F.A.C.E. Institute (Foundation of Advanced Continuing Education) in Burlingame, California, teaches dentists about the relationship between the teeth and overall jaw and joint function. It also teaches dentists methods for carefully planning and executing complex dental treatment plans. The gnathologists trust their articulators, they prefer gold in the posterior, and focus on the position of the lateral pole of the condyles. They also like to ‘tattoo’ the exact position of the lateral pole on the skin as a reference point for diagnosis and treatment. It is interesting to note that Gnathologic dentists remount and refine the occlusion of their cases on the articulator, not in the mouth. Other philosophies believe the mouth is the best place to do the final adjustments on a prosthetic case.
The goal of the Centric Relation occlusal concept is to work toward healthy condylar and anterior guidance developed around patients’ neuromuscular requirements. Centric Relation (CR) is taught at the Pankey and Dawson Institutes in Florida. The Pankey-Dawson philosophy is 40 to 50 years old and is preached as gospel by numerous clinicians around the world. Centric Relation refers to a positional relationship of the TM joints and is a hard concept to master because the position can change over time. CR is a mandible to maxilla relationship in which the condyles can rotate on a fixed axis even when the teeth are separated. Clinicians who are taught at the Pankey and Dawson centers learn that the restoration of the teeth should be in harmony with all the structures of the mastication system. The diagnostic strategy begins with a healthy physiologic position of the condyle and its relationship to the occlusal table, muscles, ligaments, envelope of function, neutral zone, and vertical dimension. This is basic occlusion that every dentist should study because four of the five philosophies are totally committed to seating the condyles into a stable, biometrically-seated, closed-pack condyle disc position. It is this closed-pack relationship of the condyle, articular disc, and fossae during function that the orthopedics refer to as Centric Relation. However, if a dentist is trying to re-establish a healthy closed-pack condyle disc position, it is named Adaptive Centric Posture.
Functional Occlusion is a concept that is only 10 years old and developing rapidly. Dr. John Kois, from the Seattle area, is focused on the biology of the joints, muscles, teeth, and periodontium. He developed a true horizontal facebow (Acculiner) as opposed to the traditional or arbitrary earbow and simplified the diagnostic process. Functional Occlusion is what I call the “new wave” approach to the CR concept already described. He teaches dentists not to “think outside the box,” but to “start with a bigger box.” The important diagnostic criteria that Dr. Kois emphasize are the envelope of function, parafunction, and dysfunction. Additionally, biologic considerations like enamel microhardness, quality of bone, quality of saliva, and hereditary factors are important in the physiology of occlusion. A diagnostic anterior deprogramming retainer is used to quickly seat the condyles and allow the dentist to simplify the splint therapy. This concept allows the dentist to remain conservative and re-establish a healthy centric relation occlusion for the patient.
Neuromuscular Occlusion is a 25 year-old concept that was created by a company named Myotronics in Seattle, Washington. Dr. Robert Jankelson is the father of this concept which seemed radical two decades ago. However, his concept is gaining in popularity now that the Las Vegas Institute has embraced it and teaches his technique. The neuromuscular concept begins with the traditional gnathologic theory based only on hard tissues (teeth and bone) and their static relationships. It expands to include the nerves and muscles into a dynamic relationship, related to posture and physiologic range of motion. Appling computer-age technology [electromyography (EMG), mandibular position recordings, and TENS] helps find a physiologic rest position of the mandible. Technology allows the clinician to view the dynamic bio-mechanisms of the stomatognathic system in real time.
The neuromuscular concept is the only philosophy that does not believe in placing the condyles into centric relation or adaptive centric posture before restoring the teeth or the occlusal table. Proponents believe that a true centric relation does not exist and that the condyles do not rotate on a fixed axis. CR dentists believe that a braced condyle on a fixed axis allows the clinician to find a repeatable position that is not possible with a neuromuscular technique. Neuromuscular dentists say that their concept has a very precise, scientific, repeatable position in space. This position is found with the myomonitor and approximately opens the bite 3 to 5mm and allows the mandible to protrude 1 to 2mm. A full-mouth restoration is required to reconstruct the occlusal table to a position believed to be optimally synergistic for the teeth, the TM joints, and the mastication muscles.
Every concept contains powerful information that requires precision dentistry and an excellent command of models, materials, bite registrations, and articulators to make a successful case. Every occlusal philosophy has the same goals to diagnose the anatomy and then correct or improve the health of the system. Occlusion has two meanings in dentistry. It can be defined as the touching of the teeth because “occlude” means “come together.” Or, it can be defined as an occlusal philosophy, such as the ones outlined in this article. Treatment must satisfy both meanings of the word occlusion. A successful result means that there is less stress on the dentition when the teeth come together and that the system is working more efficiently. Dr. Gordon Christiansen said in the February 2004 issue of Dentistry Today: “After many years as a practicing prosthodontist, teacher, and researcher, and after experimentation with almost all concepts of occlusion, I can candidly state that it is not the concept of occlusion that allows success, it is the knowledge and experience and the clinical skills and honesty of the clinician that are important factors to success with occlusion. Therefore, no matter what your philosophy of treatment is, the study of occlusion is a never-ending process with one goal in mind, providing the best treatment for all patients.”