In Dental Practice Report, July / August 2000 issue, the article entitled A Conversation with Dr. Peter Dawson, I find many statements and comments unfounded, misinformed and purposefully ignoring the historical record. Dr. Dawson continues to perpetuate his biased agenda without regard to science nor presents clear evidence regarding his own occlusal concepts. Dr.'s Hornbrook and Dawson have used this publication as a means to antagonize and attack other schools of thought, institutions, trademarked instrumentation as well as FDA and ADA approved bioinstrumentation/ companies. They have used this publication as a means to blatantly misinform the health and dental profession of other competing views and philosophies that are obvious threats to his own arena. They have not gone unnoticed.
There are many doctors in this country that are privy to his manner of operation which is unbecoming of a true professional unwilling to intellectually debate the issues in writing that he has presented unscientifically. I have taken the time to point out a few of the misconceptions that Dr. Dawson and his associates continue to spread around this country for you to read and evaluate. I would request that you give equal opportunity to those of us with another perspective to share our viewpoints as a service to the profession. I would like to preface the following comments with a clear understanding that I have come from a very strong gnathologic background.
Dr. Peter Dawson said, "If we can't record the hinge, we can't correctly alter vertical dimension on any type of instrument, so it's extremely important that the correct axis of condylar rotation is located along with a centric relation bite record."
Dental science, technology and techniques have progressed beyond the outdated teachings of the past. Since the development of computerized jaw tracking instrumentation which allows one to visualize mandibular position and the development of EMG recordings that help visualize muscle activity, it is now possible to take a physiologically optimal bite registration without mechanically deriving the CR position. Since the development of this technology, a new enlightened understanding of how the mandible moves and functions now clarifies the confusion that has plagued this arena of occlusion and temporomandibular joint position for years. Those that understand and have seen this technology used, now realize that recording the hinge axis concept to "correctly" determine vertical dimension without the use of mechanical hinge axis instrumentation (articulators) and determine a physiologic condylar position is possible without the worries of acquiring "centric relation". It is obvious that Dr. Dawson is still in the old traditional mind set of a mechanically derived/ human induced condylar position. Dr. Dawson obviously does not have a complete understanding of this neuromuscular technology or concept and continues to mislead the profession.
In his interview he further states, "Those who support the concept that centric relation is not physiologic also fail to consider that coordinated musculature will routinely position the condyles into centric relation in the absence of occlusal interference's". Question: How does Dr. Dawson determine when muscles are coordinated or uncoordinated? Electromyography is the only objective physiologic modality to record muscle recruitment and coordination. This is exactly the reason the neuromuscular protocol includes the use of electromyography as an objective modality to find an occlusal position synergistic with muscle coordination.
The musculature does not routinely position the condyles in CR unless there is pathology, which can easily be substantiated by recorded data which verifies that the CR concept/ position is not physiologic. Objective data using simultaneous EMG and computerized mandibular scanning (CMS) recordings before and after TENS (Myotronics/ Noromed, Inc.) and tomography clearly proves this with clear supportive evidence. Anyone familiar with muscle physiology will realize that his statement is false and misguided.
The article stated, "Even in the presence of occlusal interference the jaw still repeatedly goes into centric relation as is evident by the fact that the facets of wear always go to that position. If the jaw didn't function in centric relation, the facets of wear wouldn't be worn to that point." The fact that there is presence of posterior wear facets does not mean that it is the physiologic position, but in actuality it is clear evidence of pathology. With posterior as well as anterior faceting and wear it is inferred that occlusal wear would also effect TM Joints. Dr. Dawson strongly emphasizes that the occlusion is connected to the TM Joints as he often illustrates.
As a dentist having had gnathological training, I have taken a hinge axis recording many times. But the question still remains to be answered by the proponents of the centric relation concept, where is the science and objective evidence to support that "centric relation" is the optimal starting point to begin diagnosis and occlusal treatment?
Much talk about "evidence-based care" is discussed in his writings of occlusal issues, but where is the hard evidence about his views and the traditional concepts? Where is the hard scientific evidence proving that "proper manipulative procedures" even if it is gentle and not forceful, is physiologically sound as far as determining an optimal starting point? Show the scientific data. Show the objective evidence that it is truly physiologic. The discussion on centric relation is obviously fraught with confusion since it has been changed numerous times over the years. Dr. Dawson states that 30 years ago that he and a group of 40 clinicians met in Las Vegas to clarify the definition of centric relation. Dr. Dawson relates "By the end of the meeting, the group reached unanimous agreement that the definition should be changed, and it has been in the glossary of prosthodontic terms ever since that time."
Despite Dr. Dawson's attempt to defend his CR position the OFFICIAL prosthetic committee responsible for clarification of terminology determines that Dr. Dawson's definition "is in TRANSITION TO OBSOLESCENCE." What Dr. Dawson fails to tell the reader is that this definition has officially been in TRANSITION TO OBSOCLSCENCE." 17 years after Dr. Dawson's meeting, the nomenclature committee of the academy of denture prosthetics defined centric relation as "A maxillo-mandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the complex in the anterior- superior position against the slopes of the articular eminences. This position is independent of tooth contact. This position is clinically discernable when the mandible is directed superiorly and anteriorly and restricted to a purely rotary movement about a transverse horizontal axis. This term is in transition to OBSOLESCENCE." Published in the Glossary of Prosthodontic Terms, Journal of Prosthetic Dentistry, CV Mosby Company, 1987. On its way to obsolescence, the confusion regarding the definition of CR becomes ever greater. (The Glossary of Prosthodontic Terms, sixth edition, GPT-6, 1994.)
Dr. Dawson has changed his definition over the past (references i.e. his first and second edition textbooks), trying to understand physiological and anatomical structures that are dynamic. For anyone to continue to stand on such a belief as a leader in this country on occlusion, one must clearly present strong supportive evidence to prove that centric relation is necessary when obtaining a bite for consistency and reproducibility. He must also prove that centric relation is physiologic. Any student that carefully reads his writings will realize that what he is purporting is in reality a pathologic and habitual starting point rather than an optimal physiologic starting point for optimal treatment. Scientific evidence proves this.
Once one begins to understand that there is a way to determine a "physiologic" starting point without the use of mechanical manipulation, the concept of centric relation and condylar hinge axis concerns no longer are a concern to the treating clinician. These are just terms and concepts that have been created over the years among academicians and teachers of occlusion who have been searching to understand the mysteries of occlusion, mandibular movement, the physiology and anatomy of jaw function from their perspective. These views and opinions come only from the minds of those with the traditional mechanical perspective and are not supported with objective evidence neither science.
Medical and dental science today have progressed beyond the old traditional thinking. Dr. Dawson's philosophy continues to linger in the old thinking. Objective recording instrumentation, that is accessible now to dentistry, have clearly removed the doubts with scientific evidence that rings the bell of confirmation to many clinicians who are interested in learning about occlusion and the related structures of the stomatognathic system scientifically.
It is clear that the authors do not have science nor evidence to justify their rationalized concepts. Even though these concepts have been around for ages, these concepts and views lack physiologic understanding of the stomatognathic system as medical science has proven. Their understanding is not only mechanically based, but opinionated with no complete understanding of the neuromuscular views. This is obviously the best they can do to bring a rational understanding to support their erroneous theories and speculations. It is way short of sound biophysiologic and occlusal principles. They lack an ability to present data, facts and evidence. Both Dr. Hornbrook and Dr. Dawson have an agenda to ignore the facts and perpetuate the dogma.
Their discussion about electronic pulsing of the muscles that activate the lateral pterygoid do not create an incoordination of muscle activity. The writers severe lack of understanding and ignorance of electronic instrumentation and muscle physiology is clearly shown. Their illustrative diagrams are only their biased perceptions and concepts. It does not represent nor depicts scientific physiologic reality. They again lack the scientific bases to support their views. Do they expect dental professionals to believe their misguided illustrations to be the truth?
Their conclusion that "the myocentric approach invariably leads to increasing vertical, which rarely is necessary and too often results in over treatment", again is their opinionated view which lacks scientific and objective facts. The authors of the article do not explain how they have come to this conclusion. What evidence do they have to prove that the myocentric approach leads to overtreatment? What is viewed as overtreatment to them is in actuality their neglect and their concept to perpetuate pathology. Their claim that clinicians who are increasing the vertical dimension in their patients' bites is over treatment is their biased opinion with no founded bases. Many of our patients have lived with pathologic over-closed bite conditions for years and are ready to proceed to an optimal mode of treatment by increasing their vertical dimensions either by restorative or orthodontic/ orthopedic means, thus calming spastic hyperactive musculature and restoring a proper supportive occlusion. Again, the authors do not support their opinionate views with evidence again.
Those that are treating myocentrically can prove that increasing vertical is not over treatment, but in reality normalizing a physiologic mandibular position which has been over closed, by use of EMG recordings and jaw tracking instrumentation. Objective data clearly shows that by establishing a myocentric position with low rested muscle activity as a starting point to establish an occlusal position is certainly not over treatment. Any clinician who understands the meaning of objective data gathering protocols using electromyography and mandibular scanning will conclude that the evidence is overwhelming in favor of re-establishing a more normalize mandibular position that was formerly over-closed with high unrested muscle activity (pathologic). These statements I am making are factual and not my opinion.
Dr. Dawson continues to make many erroneous statements as they relate to the "myocentric approach". His comment "The error in thinking is that the open "rest" vertical is the correct vertical dimension of occlusion but teeth aren't supposed to be in contact at the rest position. The vertical dimension of occlusion is established by the repetitive contracted length of the elevator muscles" is absurd! The author's statements are again erroneous, biased and show an obvious lack of understanding of muscle function and physiology. When muscles are rested via TENS, the elevator muscles and the depressor muscles are neutralized thus at their lowest muscle activity. It is often found that the mandible is more open then the habitual acquired occlusion presents. When low EMG readings of both the elevator and depressor muscles are objectively recorded the mandible is neither being pulled down or pulled up. It is in this neutralized zone that the informed neuromuscular clinician can assuredly establish his/ her occlusal/ mandibular position. It is in this physiologic rested position, that one can visualize with instrumentation, that occlusion will be stable. Any other position other than a true rested physiologic position will result in instability, further tooth movement and as the author states "It will self-adapt back to where it was" (pathologic)". They agree that the literature supports these consistent findings. It is obvious that Dr. Dawson does not understand nor use electromyography (EMG), computerized jaw tracking and electrosonography (ESG). If he did he would have a completely different perspective. That seems to be the author's problem, the lack of not knowing the status and position of their mandibles when treating.
Dr. Dawson speaks further and states "I don't believe in arbitrary measurements." Yet he tries to discuss the "neutral zone, the zone of neutrality between the outer forces of the tongue and the inward forces of the lips." How does he establish the neutral zone? He also indicates that he can't go along with arbitrarily verticalizing anterior teeth. What evidence does Dr. Dawson provide in determining his occlusal position? Is he not arbitrarily assuming that his centric relation position is correct? Again where is his scientific evidence and objective data to prove his opinionated assumptions? He says he doesn't believe in arbitrary measurements - then what measurements and evidence does he use to support his mandibular position and concept?
Dr. Dawson stated, "The rules of evidence-based dentistry are going to eliminate much of the hype and get down to factual statements that are better researched". I challenge the authors to begin to show evidence, facts and proof rather than continue to perpetuate biased attacks to those that are scientifically sound and have the hard data. Where is his burden of proof to continue to support his theories? If he could only present actual evidence to substantiate his beliefs with science and objective data, it will truly help bring these controversial issues to rest. I would encourage the leaders of occlusion to start presenting the facts rather than perpetuating biased opinions in the name of evidence. I am optimistic that science and objective data gathering technology will prevail to bring our professions to new heights in the clinicians world of diagnosis and optimal treatment.
Sincerely,
Clayton A. Chan, DDS, FICCMO, DACFE, DABFM, DABFD, Dipl.CFO
Fellow International College of Craniomandibular Orthopedics
Diplomat American College of Forensic Examiners
Diplomat American Board of Forensic Medicine
Diplomat American Board of Forensic Dentistry
Diplomat College of Forensic Orthopedics
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