This chapter discusses chronic Occluso-Muscle Disorder, which is a myogenous subset of Temporomandibular Disorder symptoms resultant from occlusally activated muscle hyperactivity. Published T-Scan-based research since 1991 has determined that a significant etiologic component of Occluso-Muscle Disorder is prolonged (in time) occlusal surface friction that occurs between opposing posterior teeth during mandibular excursions. This friction results in prolonged compressions of the Periodontal Ligament fibers of the involved teeth, which triggers excess muscle contractions within the masticatory muscles. This chapter describes the neuroanatomy of how the excursive friction induces masticatory muscle hyperactivity and illustrates the patient occlusal factors that promote prolonged occlusal surface friction. It explains the patient section criteria for determining if an Occluso-Muscle Disorder patient is a candidate for occlusal intervention, details the computer-guided Occluso-Muscle Disorder treatment known as Disclusion Time Reduction, and supports this measured occlusal treatment with the research studies that validate using this highly effective Occluso-Muscle Disorder therapy.
Chronic Occluso-muscle Disorder (Dawson, 1989a) is a myogenous subset of Temporomandibular Disorder symptoms that afflicts the masticatory musculature with chronic pain, headaches and dysfunction. The associated muscle hyperactivity is a primary source of the frequently observed and highly similar group of symptoms that suffering patients commonly describe (Glickman, 1979a; Dawson, 1989a):
Chronic facial pain, chronic temporal headaches, frequent clenching and grinding of the teeth, morning jaw pain, eye strain, earaches, chewing fatigue, chewing muscle and tooth pain, temperature sensitive teeth, and mild clicking and popping of the Temporomandibular Joints.
Muscle hyperactivity etiologies previously cited within the literature are Bruxism (Clayton, Kotowicz, & Zahler, 1971; Dawson, 1989b), clenching habits (Bertram, Rudisch, Bodner, & Emshoff, 2002), malocclusion (Mohlin, et. al., 2004), Trigeminal Neuralgia (Zakrzewska & McMillan, 2011), and occlusal interferences (Glickman, 1979b; Baba, Yugami, Yaka, & Ai, 2001).
Longstanding advocated treatments for chronic masticatory muscle hyperactivity have attempted to treat the symptomotology (Herman, Schiffman, Look, & Rindal, 2002) without addressing an underlying non-physiologic occlusal surface friction problem, that has been shown to be etiologic for the hyperactivity (Williamson and Lundquist 1983; Kerstein &Wight, 1991; Kerstein, 1995; Kerstein, Chapman, &Klein, 1997; Kerstein &Radke 2006; Kerstein & Radke, 2012). Despite the number of studies that have demonstrated an occlusal surface friction/masticatory muscle hyperactivity relationship to symptom appearance and frequency, an occlusal etiology as being causative for chronic Occluso-muscle Disorder symptoms, has not yet been widely accepted within the differing disciplines of Dental Medicine. In the traditional approaches to treating Occluso-muscle Disorder symptoms, the occlusion has been considered a limited component of the etiology, in favor of emotional and psychological factors, where it has been suggested that treatments be reversible and non-invasive to the teeth and oral structures.
Appliance therapy (Bertram, Rudisch, Bodner, & Emshoff, 2002) is the most frequently employed treatment. The main effects an intraoral appliance creates that can improve Occluso-muscle Disorder symptomotology are:
Key Terms in this Chapter
Maximum Intercuspal Position (MIP): MIP is the patient’s maxillomandibular relationship where the teeth are in maximum occlusal contact irrespective of the position of the condyle-disk assemblies. MIP is where the patient’s teeth habitually fit when they self-close into complete tooth intercuspation. ICAGD is performed in the MIP, which simplifies treatment for the patient by maintaining the habitual occlusal contact pattern. Since the patient is not moved to a different occlusal position there is no need for them to adapt to an appliance, a new vertical dimension, or a newly established closure occlusal contact pattern. Additionally, treating an Occluso-muscle Disorder patient in MIP is easier for the clinician because the patient stays in their stable base occlusal contact pattern during treatment.
Disclusion Time Reduction: Reducing the time-duration that posterior occlusal surfaces frictionally engage during right, left, and protrusive excursive movements to be less than 0.5 seconds per excursion. It is routinely accomplished by reshaping the opposing occlusal surfaces that frictionally engage using the ICAGD coronoplasty, with or without adding in steeper anterior guidance contacts that will more rapidly lift apart the posterior teeth.
Working Side Group Function: Working side group function describes an occlusal scheme where the 1 st molar, both premolar teeth, and the canine, all together share the lateral excursive guidance on the side toward which an excursion is made. The posterior teeth stay in contact initially, and then progressively disengage as the anterior guidance lifts the posterior teeth apart. Since the 1980’s working side group has been advocated as an acceptable occlusal scheme. However, modern research has shown that working side group function with molar and premolar shared guidance contact is problematic neurophysiologically, because it activates excess masticatory muscle contractions during excursive movements.
ICAGD Coronoplasty: ICAGD is a measurement driven, computer-guided, occlusal adjustment procedure that shortens prolonged excursive movement occlusal surface contact frictional durations. It is an excursively focused occlusal adjustment procedure that is performed from MIP. It is commenced with excursive movement occlusal adjustments, which differs from all other advocated occlusal adjustment and Equilibration procedures that commence with closure movement occlusal corrections. The main objective of ICAGD is to shorten the posterior Disclusion Time to < 0.5 seconds in all three excursions, to compress the excursively engaged teeth and their respective Periodontal Ligament fibers, for far less time than in the pretreatment condition. Shortening the Disclusion Time equally shortens the excursive masticatory muscle contraction durations and lessens the volume of excursive muscle contractions, by markedly lessening the time Periodontal Ligament mechanoreceptors are compressed during excursive movements. A post treatment Disclusion Time per excursion of < 0.5 seconds establishes a statistically significant, hyperactive muscular relaxation effect from within the patient’s own neurophysiology.
T-Scan/BioEMG: The T-Scan III/BioEMG synchronization records simultaneously, both occlusal contact force and timing data, and its corresponding muscle activity levels. The two integrated systems capture real-time occlusal contact data and masticatory muscle electrical potentials that during playback, are analyzed by the clinician in a dynamic “Movie”, where both technologies play side-by-side on the computer desktop. In this way, transitory occlusal contact force and timing variances can be time-correlated to specific changes in masticatory muscle activity levels. Both the T-Scan data and the EMG data can be played together forwards and backwards continuously, in 0.003 second frames, or in stop-action, to be able to view small time-increments that relate occlusal function to muscle function.
Excursive Occlusal Surface Friction: Opposing posterior tooth occlusal surface “milling” engagement that occurs early in an excursive movement, in and around the central fossa prior to when the anterior guidance lifts the posterior teeth apart. The duration of the excursive frictional engagement is equal to the time duration that the involved teeth compress their respective Periodontal Ligament mechanoreceptors. The PDL mechanoreceptor compressions in turn, hyperactivate the masticatory musculature.
Open Canine Contact: When a space exists between opposing maxillary and mandibular canines in the Maximum Intercuspal Position. A lack of canine contact predisposes the occlusal function to prolonged posterior Disclusion Time and prolonged occlusal surface excursive friction, which can lead to the development of hyperactive masticatory musculature. Open canine contact is such an important factor in creating excursive masticatory muscle hyperactivity, that when treating Occluso-muscle Disorder patients who present with open canine contact, it must be addressed before any other clinical step can be successfully undertaken.
Lingual-to-Lingual Working Excursive Contacts: Masticatory muscular hypercontraction is a PDL mechanoreceptor compression mediated process. Lingual-to-lingual excursive interfering contacts compress the PDL mechanoreceptors similarly to how buccal-to-buccal working side interfering contacts do, but the lingual-to-lingual contacts cannot be visualized intraorally. Tooth compressions and PDL compressions occur in all directions such that lingual-to-lingual contacts are often a significant component of a prolonged working side group function that creates hyperactivity in the masticatory musculature. Lingual-to-lingual working side contacts can be clearly observed in T-Scan data when they exist in an excursive movement.
Unique Molar Periodontal Ligament Mechanoreceptor Neuroanatomy: The molar Periodontal Ligament mechanoreceptors are part of the Peripheral Nervous System (PNS). Peripheral Nerves lie outside of the brain and spinal column, such that they usually make their initial synapse outside of the Central Nervous System (CNS). However, the molar Periodontal Ligament (PDL) mechanoreceptors are unique in that despite being Peripheral Nerve afferents, they are the sole human peripheral nerves that enter the CNS directly (into the Mesencephalic Nucleus) and travel further within the CNS to the Trigeminal Motor Nucleus, where they make their first synapse with the efferent motor fibers to the four muscles of mastication, the tensor tympani, the tensor veli palatini, the mylohyoid, and the anterior belly of the digastric muscles.
Unmeasured Occlusal Adjustments: Unmeasured occlusal adjustments involve subjectively interpreting the size, color, and shape characteristics of articulating paper markings to determine occlusal contact force content. Current research indicates that clinicians guess (< 15% accuracy) at which contacts they believe are forceful contacts, whereby this method does not guide a clinician to select correct contacts for treatment. Unmeasured occlusal adjustments have yielded mixed results in the treatment of Occluso-muscle Disorder. This random, subjective contact selection that is based upon paper mark appearance has led to unpredictable therapeutic effects that have been reported in unmeasured occlusal adjustment studies.
Factors that Promote Long Disclusion Time: Prolonged Disclusion Time and occlusal surface excursive friction are present within an occlusal scheme resultant from many contributory factors. These eight factors predispose the occlusion to excursive movement friction: the Angle’s Classification, an anterior Open Occlusion, the presence of occluding 3 rd molars, poor vertical tooth orientation, a lack of canine contact in MIP, shallow anterior guidance surfaces, an exaggerated Curve of Spee, tipped-up mesiodistal molar orientation, and lingual-to-lingual working side excursive contacts.