In this blog article, Dr. Peter Dawson responds to a comment made on a previous article. The following was the comment:
It has been demonstrated repeatedly since 1997 that the relationship of bruxism to chronic craniofacial pain is non-linear. [1-4] In fact, 20% of the Raphael, et al, pain sample showed no bruxism. Lavigne lists among his finest work the discovery that sleep bruxism begins from an open mouth position with the action of the depressors.  This is not an “occlusal” problem beyond tooth wear, should the patient so decide.
That being said, the nature of the pain is such, particularly as it relates to headache, that keeping the posterior teeth apart with an appliance can prevent headache. As Mahan and Alling pointed out in their text , we have known that since 1960. 
Sessle, Dubner and colleagues have shown repeatedly that the pain of chronic M/TMD is not inflammatory.  Masticatory muscles are fatigue resistant over time, [9, 10] and the excess substance found is glutamate, not hydrogen ions from lactic acid in chronic craniofacial muscle pain. 
The blog post of April 25 is not supported by the current science.
Dr. Peter Dawson’s Response
In the blog, “How to Discover Occlusal Muscle Disorders” we presented a time-tested process for observing when a patient has symptoms of an occluso muscle disorder. The Dawson Academy curriculum teaches dentists to follow a simple protocol of discovery in every new patient examination. That protocol includes evaluation of masticatory muscles to see if specific muscles are tender or painful. The rationale for muscle palpation makes perfect sense because tenderness or pain in any masticatory muscle is a sign that some disharmony or disfunction may exist within the system.
The second step in the protocol is to determine if specific muscle discomfort is related to disharmony between the occlusion and the TMJs. Occluso muscle pain is a very specific response to occlusal interferences that deflect the condyles on a determinable path from centric relation to MIP when the teeth are clenched together. Such disharmony is a common factor in masticatory muscle pain and many headaches, as well as a principal cause of excessive wear, sore teeth, hypermobility, and other signs of occlusal disease. Because of the detrimental effects of occluso muscle disorder, evaluation of all signs of disharmony is considered an essential part of every dental examination.
The fact that so little attention is paid to a proper examination of the occlusion and the effects of occlusal disharmony in most dental practices is a serious omission. The effectiveness of occlusal correction is so predictable in properly diagnosed occluso muscle pain patients, it seems counterproductive to obfuscate the rationale for a complete examination by claiming it lacks scientific support.
A Forum for Research, Discussion & Critiques
We appreciate any and all critique of what we teach because it stimulates discussion that can be beneficial. A major strength of the Dawson Academy has been its objective analysis of clinical concepts by a multidisciplinary think tank approach that evaluates differing viewpoints. With that in mind I must disagree with any idea that downplays the role of occlusal disharmony as a strong, potential factor in specific types of craniofacial pain. The key to treatment is proper diagnosis. If a correlation between occlusal deflections and specific muscle responses can be ascertained (we can do that) a proper diagnosis can be made. Treatment effectiveness is predictable IF proper occlusal correction is precisely completed (we can also do that).
It must be pointed out however, that the position and condition of the TMJs is a critical factor that requires precise classification of the TMJs as an essential step in the examination process. Use of the term “TMD” without a specific classification has led to an overload of invalid research and erroneous conclusions about diagnosis and treatment of orofacial pain.
Having shared visiting professorship duties with Parker Mahan at Emory University School of Postgraduate Dentistry, I am very familiar with his agreement with the role that lactic acid plays as a factor in muscle pain. To quote his words regarding the value of muscle palpation:  “In patients with pain associated with malocclusion, the pterygoids are usually tender to palpation”. He also states in the third edition of his text, Facial Pain: “Two apparent signs of bruxism are elevator muscle tenderness and more pronounced wear facets on the teeth”
Lactic Acid Buildup's Role in Muscle Pain
The exact action of lactic acid is currently being reevaluated, as extracellular buildup of lactic acid has recently been shown to have force – restoring effects on muscle . What is known however, as certain at this time, is that acidosis does contribute to muscle pain and it is probable that lactic acid plays a role.
There is reason to question the adversarial concept that excessive interstitial glutamate is a dominant factor in craniofacial muscle pain . In fact, the article cited to support that point presents contrary evidence stating: “There were no significant correlations between glutamate concentrations in the masseter muscle and pain scores”. Several studies [4, 5, 6, 7] have reported that muscle pain and fatigue are not associated with an altered release of glutamate.
We will welcome more research to determine if glutamate is or is not a factor. Whether it is or is not, does not alter, in any way, the advice in the Dawson Academy blog on the clinical evaluation of occluso muscle disorders.
It has been scientifically verified through numerous EMG studies that even minute occlusal interferences can activate masticatory muscle hyperactivity. It is a consistent clinical finding that prolonged muscle hyperactivity results in palpable tenderness. These are signs that every complete examination should be looking for. The goal of complete dentistry should be a peaceful neuromusculature. Clinicians who understand the TMJ/occlusion relationship to the neuromuscular system can predictably achieve that goal, or know when they can’t because of specific intracapsular structural disorders of the TMJ.
- Mahan,PE,Ailing,CC.Facial Pain 3rd Edition 1991,Philadelphia: Lee and Febiger
- Bandschapp O et al. Lacticacid restores skeletal muscle force in an in vitro fatigue model: Am J Physiol Cell Physiol,2012 Apr 1
- Castrillon,EE,and Sessle,B.Interstitial glutamate concentration is elevated in the masseter muscle of myofascial temporomandibular disorder patients:J Orofac Pain 2010
- Ashina M et al. No release of interstitial glutamate in experimental human model of pain. European J of Pain. Vol 9, Issue 3
- Dawson A,Ghafouri B,et al. Pain and intramuscular release of algesic substances in the masseter muscle after experimental tooth-clenching excercises in healthy subjects.J Orofac Pain 27 (4) 2013
- Emberg M,Castrillon EE et al. Experimental myalgia induced by repeated infusion of acidic saline into the masseter muscle does not cause the release of algesic substances: Euro J Pain,Apr (4) 2013
- Dawson A. Experimental tooth clenching: A model for studying mechanisms of muscle pain.Swed Dent J Suppl , 2013