The Role Of Bioelectronic Instruments In The Management Of TMD
BARRY C. COOPER, D.D.S.
Temporomandibular Disorders (TMD) comprise a group of conditions that can affect changes in the form and function of the TMJ, masticatory muscles and dental apparatus. Proper management of TMD by the dentist requires accurate appraisal of the status of the patient's dentition, TMJ and the associated neuromuscular apparatus. Certain predefined standards or parameters of function/dysfunction are accepted by the profession. Electronic instrumentation provides objective measurement of many of these biological phenomena, and thus can be used throughout treatment to provide critical analyses that monitor and enhance treatment efficacy. A treatment protocol for TMD is presented utilizing electronic instrumentation to establish a neuromuscular occlusion.
In order to understand how TMD treatment can be improved by the use of electronic quantification of masticatory function, one must first understand the essential pathophysiology of TMD. Temporomandibular Disorders (TMD) comprise a group of disorders involving many hard and soft tissues associated with mandibular and masticatory function. Commonly, TMD's co-exist with other musculoskeletal disorders within the head and neck area. The total management of these composite, multifaceted and multicausal conditions often requires the diagnostic and therapeutic intervention of a multidisciplinary team of health care providers.
The specific TMD problem of this complex illness which necessitates involvement of the dentist also defines a necessity to objectively measure and quantify masticatory function. TMD is a musculoskeletal disorder which affects alterations in the structure and/or function of the temporomandibular joints, the masticatory muscles, the dentition and its supporting structures and the complex neuromuscular system attached to these structures.
Each TMD patient possesses a unique set of symptoms, clinical presentation and history. A patient may have primarily a disorder within the temporomandibular joints, primarily one involving the masticatory muscle function, or both. It is commonly agreed that conservative reversible therapies should be employed whenever possible in the initial treatment of TMD's. The therapies most often found successful clinically involve alteration in the function of the mandible and TMJ which is accomplished through the use of intraoral orthotic appliances of various types.
Some appliances are specifically designed to alter dental occlusion, others to relax hyperactive muscles and still others to change the condylar position within the TMJ by repositioning the mandible. Additionally, dentists frequently utilize therapeutic modalities to improve the function of the masticatory muscles, by lowering resting activity and improving functioning activity. It is, therefore, because of their intimate knowledge of the structure and function of the mandible, dental occlusion and masticatory muscles that dentists have rightfully assumed the role of primary TMD therapists.
Proper diagnosis of TMD must therefore begin with an objective evaluation of the status of the components of each patient's illness. It has been acknowledged by many in the field that a need for objective data in decision making is necessary to reduce reliance on subjective improvement and clinically observed data. [2-4]
The primary components of TMD's and the treatments modalities employed involve mandibular movement, dental occlusion, masticatory muscle and TMJ function. With objective data, the patient's condition before treatment can be assessed, a therapeutic plan created to affect the needed changes and the results of treatment analyzed for efficacy. Electronic instrumentation provides the reproducible objective data needed for this task. It is used to quantify what function/dysfunction the patient started with and what improvement was obtained through treatment.
A. ELECTRONIC JAW TRACKING
The Computerized Mandibular Scan (CMS) K6-I (Myo-Tronics, Inc. Tukwila, WA) and the BioEGN (BioResearch, Inc. Milwaukee, WI) are instruments which record the position and movements of the mandible by monitoring the position of a small magnet affixed to the gingiva beneath the mandibular incisors. This small object can, without adding a significant artifact to the jaw, precisely record in three dimensions the following: [5-7]
- Range of mandibular motion maximum opening, lateral and protrusive movements.
- Characteristics of movement velocity, fluidity and direction of movement during opening and closing.
- The position of the mandible at rest relative to the maximum intercuspal position (ICP).
- The trajectory (arc) of mandibular movement from rest position to occlusion.
- The position and movement of the mandible during swallowing.
All recorded data described above and below are displayed on the computer screen of this instrument.
B. ELECTROMYOGRAPH (EMG)
Surface electromyography measures muscle function during two activity states, rest and function. Four groups of muscles can be simultaneously recorded bilaterally. As applied to clinical practice it can be used measure mandibular elevator or closing muscles (anterior/ posterior temporalis, masseter) and depressor or opening muscles (anterior digastric) to record the following: [8-17]
- Resting activity at initial presentation and following muscle relaxation with TENS therapy.
- Resting activity at presentation following a course of therapy before and after TENS therapy.
- Functioning electrical activity during normal closure and during maximum clench.
- Comparative clenching activity (force) in various occlusal materials and positions
- Function can be tested with natural occlusion, cotton rolls, a therapeutic position in a bite registration as well as in an orthotic appliance, denture or crowns.
- Location of the rest position of the mandible.
- Sequential muscle firing during closure to analyze occlusion to determine the presence of bilateral occlusal balance or unilateral prematurity.
C. TM JOINT SOUND RECORDING
Electrosonography or Joint Vibration Analysis are terms used to denote the recording of sound emanating from the temporomandibular joints during the opening and closing movements of the jaw.  This technique is valuable as it records the following:
- Precise sound or vibrations emanating from each joint simultaneously. (It does so far more accurately and objectively than does stethoscopic auscultation.)
- Exact locations in open/close at which sound is produced and recorded.
- Sounds at stages of therapy for comparison.
D. TENS THERAPY
Transcutaneous Electrical Neural Stimulation (TENS) is used to relax hyperactive muscles. It is a neuromuscular stimulator. The term TENS is also used to describe another type of instrument which is a pain suppresser. In the later case its effect is one of competitive stimulation in order to close the "gate" which allows pain stimuli to ascend to the higher centers of the central nervous system.
TENS as used in the TMD management protocol described in this article is for neuromuscular stimulation. It is a low amplitude, low frequency intermittent stimulation which causes muscles to alternately contract and then relax in a pumping manner, similar to a massage. Applied bilaterally to an area over the notch between the TMJ and the coronoid process, the stimulus reaches the mandibular division of the trigeminal nerve (V) deep to the mandible as well as the superficial facial (VII) nerve.
Significantly, the stimulation is delivered bilaterally via neural pathways to all masticatory muscles innervated by the mandibular division of the trigeminal nerve. This includes the medial (internal) pterygoid, lateral (external) pterygoid, masseter, temporalis and anterior digastric muscles. This type of TENS therapy is applicable to reduce muscle hyperactivity in the muscles of mastication, which is a frequent component of TMD.  With the musculature relaxed, the mandible can assume a position with minimal postural activity in the antagonistic muscles (elevators and depressors). It is, therefore, a more accurate "rest position of the mandible," than the assumed or accommodative pseudo-rest position with which patients present.
The rest position achieved in this manner can be used as a reference point for the selection by the doctor of a therapeutic treatment position. TENS stimulation can cause an arc-like movement of the mandible beginning at rest position. This is referred to a neuromuscular trajectory.
All of the measurement instruments, most of which have been in clinical usage for almost two decades, have been granted the American Dental Association Council on Scientific Affair's Seal of Acceptance as aids in the diagnosis of temporomandibular disorders TMD (1994/1995).
The decision to treat a patient for TMD is based entirely on the patient's history, symptoms and clinical presentation and the professional judgment of the clinician. Following screening, actual treatment begins after selection of a treatment position and the gathering of objective masticatory function data to support the use of that position. This data is serially obtained throughout treatment to assess whether the desired improvement in masticatory function has been achieved with that treatment strategy.
Thus the ability to measure ultimately aids the trained clinician in deciding on a treatment plan and a therapeutic jaw position.[22-24]
The protocol that will be described below is designed to incorporate quantification of those parameters of mandibular function that can be measured as they relate to a neuromuscular treatment strategy.
A combination of electronic jaw tracking , EMG and Sonography is utilized at the outset of the study to document the resting and functioning activity of the masticatory muscles, mandibular position at rest compared to occlusion and the type of mandibular movement that is possible, and the presence of joint sounds at presentation. TENS therapy is used during the test protocol to relax the masticatory muscles.
Following at least 60 minutes of TENS, EMG monitoring aids the clinician in determining whether the elevator muscles (anterior temporalis and masseter) and depressor muscles (digastric) have achieved a balanced, reduced resting activity level.
At that point, jaw tracking recordings are made to compare pre-TENS and post-TENS resting mandibular positions, freeway space in three dimensions, range of motion, closure and swallowing patterns as well as the velocity and fluidity of mandibular movement.
From a mandibular position established as the "rest position," the TENS stimulus is used to cause the jaw to swing on an arc-like trajectory. A mandibular position along that arc, which is usually 1 mm above rest position, is selected to be the therapeutic or treatment occlusal position It is referred to as the neuromuscular or myocentric occlusal position.
The treatment position is then recorded intraorally in a bite registration material. Ideally, it is a material which is passive on insertion and ultimately achieves a non-elastic hard final set. An ethyl methacrylate acrylic material (blue sapphire, H. Bosworth, Skokie Ill) is ideal for this procedure.
The bite registration is removed from the mouth in a partially cured rubbery state and achieves its final cure (polymerization) between lubricated study casts.
Multiple bite registrations can be obtained, which can then be compared using EMG for maximum bilaterally symmetrical activity during maximum voluntary clench. The bite registration producing the maximal, most balanced EMG muscle function is selected for use in the fabrication of a "Neuromuscular" orthosis.
A mandibular orthotic appliance is fabricated and delivered to the patient. Its occluding surface is anatomically formed to interdigitate with the maxillary teeth, providing a stable occlusion synchronized with balanced muscle function. Before insertion of the orthosis, the patient receives TENS therapy for 60 minutes to relax the masticatory muscles. This re-establishes the rest position of the mandible as a "point of reference" before adjustment of the therapeutic occlusion. TENS then is used to swing the jaw involuntarily to locate premature occlusal contacts.
Once adjusted, voluntary chewing is used to locate functional interferences along inclined planes. After adjustment, EMG testing of maximum voluntary clenching aids in determining the bilateral symmetry and functional effectiveness of the therapeutic occlusion. This precision appliance is worn 24 hours a day, including during eating.
The patient returns for usually three adjustment visits. At each visit TENS is used to relax muscles preceding any necessary occlusal adjustment. TENS is utilized during the adjustment as described in the insertion process.
After three months of full-time orthotic use, the patient returns for a complete electronic study. This is a duplicate of the initial study. It enables the clinician to record and evaluate, with precise measurable data, the improvements achieved by therapy. This includes mandibular range and quality (velocity and fluidity) of motion, changes in joint sound, and muscle resting and functioning activity.
The doctor can also compare the therapeutic occlusion provided by the orthosis with the original acrylic "bite" by EMG analysis, jaw tracking and examination of the articulated casts. This is a valuable aid in determining whether the mandibular rest and the therapeutic treatment positions have changed and whether the appliance has undergone occlusal attrition.
Each patient must be treated uniquely relative to the need for a form of long term maintenance of a therapeutic occlusion. Some patients can resume satisfactory function in their pre-treatment occlusal position with the improved mandibular and muscle function achieved by initial therapy. Other patients require some form of part-time augmentation to provide improvement in mandibular position through orthotic use. Still others require long term perpetuation of a new maxillo-mandibular occlusal position on an ongoing basis.
For the later group, the form of long term treatment is patient specific.
It is up to the treating doctor and patient, sometimes in consultation with other dental specialists, to create a treatment plan. It may involve restorative dentistry, orthodontics or oral surgical procedures (TMJ or orthognathic), or the ongoing use of a removable orthosis made of durable materials. The ongoing use of electronic instruments described here is a valuable adjunct in the treatment planning/ decision-making process, as it provides objective measurements of mandibular position and masticatory muscle function.
The use of electronic measurement instrumentation can be valuable in almost all forms of dental practice. Wherever occlusion and mandibular function are being monitored, modified or restored, quantitative measurement aids the skilled clinician by providing better observation, measurement and analysis.
In this discussion, I have described how electronic measurement can be used as an objective milestone in planning and implementing a treatment plan for the TMD patient. While the treatment protocol described reflects a specific neuromuscular treatment philosophy, different protocols can be tailored to provide relevant data for other treatment strategies. However, that said, the clinician must develop a protocol in which each specific test adds or refines the treatment plan.
Without a rationale driving the protocol, the measurements and data generated are without purpose. Thus, objective measurement of mandibular and masticatory muscle function provides information essential in establishing the status of patients before TMD therapy is instituted, by providing quantification and documentation of elements or parameters of their illness. The same instruments are also valuable in reviewing treatment outcome and in re-evaluating the treatment plans in patients who don't have immediate improvement. If a patient has slight improvement with early treatment and correlative data suggesting better masticatory function is obtained, a decision to continue treatment can be justified. If the data does not show this, alternate treatments can be implemented.
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