Paradigmatic shifts in occlusion and temporomandibular disorders.

There are several terms that identify proposed paradigms for the way things ought to be carried out in the health sciences: evidence-based, cause-and-effect, diagnostic gold-standard, patient-centred-outcomes, risk assessment, cost/benefit/risk, and efficacious/effective. Collectively these paradigms exhibit varying degrees of interdependence, and have the potential for changing the way dentistry is practiced. A paradigm can be thought of as a standard by which research and health science ought to be conducted and evaluated. In this sense scientists and clinicians try to figure out how to account for various observations and phenomena dictated by paradigms or models of health care; however, it may become necessary to shift to new paradigms that are more consistent with scientific and clinically reality. Some of the potential effects of these shifting paradigms on the practice and teaching of occlusion and temporomandibular disorders are considered.

Reflections on the Michigan splint and other intraocclusal devices.

It seems obvious in retrospect that the treatment of disorders by interocclusal devices followed two paths: stabilization splints and functional orthopedic appliances. The dividing line between them is not always clear. Both have some function related to the position of the mandible. They may not differ significantly in their control of occlusal stability (e.g., telescoping devices anchored to stabilization splints). The stabilization splint, as well as other conservative measures, will play an increasing role in accepted therapy for TMD. The use of anterior repositioning devices for TMD, including MPD syndrome, will decrease. Research may provide answers that allow them to be used more specifically and predictably. Perhaps there will be but little change in their use where there is an association of TMD and Class II malocclusion. There will be an increase in the use of interocclusal devices for the treatment of snoring and obstructive apnea. Some additional directions seem to have emerged in the late 1980s and early 1990s: In the absence of pain and significant debilitation, treatment for TMD, if any, is to be reversible. Prevention or aggravation of TMD should be practiced to the extent possible during dental procedures. One long-term, well-designed, prospective study indicated that the incidence and severity of TMD could be reduced by appropriate occlusal adjustment. There is a small, but nevertheless important minority of patients with TMD who progress to persistent pain and/or dysfunction. Initial management of the vast majority of patents with TMD should be use of noninvasive reversible therapies. Surgery is indicated in only a relatively small percentage of cases of TMD. Research on interocclusal devices should not terminate simply because they are in part dental devices (i.e., biomechanical forms of treatment). The diagnosis and treatment of TMD has been called a dilemma, especially for those patients with chronic pain for whom no treatment has been effective. However, it would be ill-advised to abandon what treatment is already known to be effective by allowing those few but psychosocially important patients with chronic pain to determine what should be done for the vast majority of patients with TMD: reversible forms of treatment, including physiotherapy, pharmacologicals, and the stabilization occlusal bite plane splint.

Philosophy of occlusion: past and present.

Controversy in a field usually stimulates research to find answers and to promote clinical excellence. Thus, differing ideas about occlusion relative to centrics, gnathology, TMD, occlusal adjustment, and periodontal therapy have led to a controversial body of literature; however, I think also it has led to better treatment for patients, regardless of whether, for example, the concept of point centric or freedom-in-centric is advocated. No one can practice dentistry without some concept of occlusion whether it is applied to one or two teeth or to complete mouth restoration. Although the work of committees to clarify terminology is quite appropriate, common usage, semantics, avoidance of confusion in the literature, and the ideological nature of the bias in science must be carefully considered. At times we learn from history that all ideologies need constant revisions; too often the need leads to changes by fiat rather than by virtue of research on problems that may actually exist in communication.

Reflections on the Michigan occlusal splint.

Specific features related to the development, design and use of the Michigan splint have been described. Additional benefits from the Michigan splint beyond what can be expected from conventional stabilization splints and bite planes have been suggested. Important aspects of corrections and maintenance care of the Michigan splint have been stressed.

Learning to reproduce a consistent functional jaw movement.

Several studies on the ability of a subject to perceive position and movement of the mandible have been done. Through the use of a computer pantograph and statistical analysis, it was determined that subjects were unable to learn to reproduce a consistent functional jaw movement.

Human jaw-opening muscle responses elicited by multiple-site electrical stimulation.

Electrical stimuli were applied to subjects' upper and/or lower gingivae around the right canines; (i) during maintained relaxation of masticatory muscles; (ii) at an active opening position; (iii) while clenching in an incisal edge-to-edge contact (IEC) position; and (iv) at the wide-open position. Reflex responses of the suprahyoid and jaw-closing muscles were obtained using surface electrodes. The electrical stimulation produced segmented reflex excitation(s) in the suprahyoid muscle and conventional reflex excitation and/or inhibition in the jaw-closing muscles when some background activity was maintained in the muscle(s). The excitatory reflex in the suprahyoid muscle responded to multiple site electrical stimulation which was delivered on both the upper and lower jaw simultaneously rather than to single site stimulation. Also, the responses depended on the intensity of the electrical stimulation. In particular, stronger intensities resulted in longer latencies. The results support the suggestions in our previous studies with mechanical stimuli, i.e. that the human jaw-opening reflex can be obtained only when some background activity is maintained in the jaw openers, perhaps due to low threshold afferent input, and that spatial summation may be effective for the reflex.

Method for identification and classification of single motor unit potentials in diagnostic electromyography.

It is important to have an objective method for recording jaw muscle capacity such as EMG before, during and after treatment of muscle dysfunction and also for oral rehabilitation with dentures, implants or other types of restorations. Because measurements of motor unit potentials (MUPs) are needed in several areas of EMG analysis, algorithms have been developed in our laboratory for use in a small computer-aided system for semi-automatic detection and pattern recognition of MUPs. Based upon the test recordings it is suggested that a characteristic 'maximal voltage increase per microsecond during the spike-phase' can be used as a supplement to the more generally used parameter 'rise-time'. Examples are given of how the programs can be useful in the study of the functional anatomy of jaw muscles by recording normative values for MUPs and their recruitment patterns.

Anatomical and electromyographic studies of the digastric muscle.

The techniques and sites for EMG recordings from the digastric muscles are controversial. To re-evaluate old techniques for recording from the digastric muscles, especially the posterior bellies, the morphology of the muscles was studied by conventional dissections and by examination of specimens sectioned in the frontal and the horizontal planes. Based on these anatomical findings, recording sites and approaches to them were developed for the anterior and posterior bellies of the digastric muscles. EMG recordings from the two bellies of the muscle were obtained from five healthy subjects. The EMG recordings were ranked according to muscle activity level and the activity within single muscles and between muscles compared using the Wilcoxon signed rank test. The anterior and posterior bellies had synchronized activity in all mandibular movements but were silent or had negligible activity with the mandible in the rest position, when the head was rotated, and while clenching. Both bellies had marked to very marked activity during jaw opening, and moderate to marked activity during protrusion, retrusion and lateral movements. During swallowing the anterior and posterior bellies had patterns characterized by bursts of activity of high amplitude and short duration. The two bellies were not, however, always synchronously active.

Anatomical and electromyographic studies of the lateral pterygoid muscle.

The relationships of the lateral pterygoid muscle within the infratemporal fossa were observed by conventional dissections and by examination of specimens sectioned in the horizontal and frontal planes. The following less well-known features were noted. At the origins of the superior and inferior heads there are regions in which the fibres are interlaced or closely overlapped by fibres of either the temporalis muscle or the medial pterygoid muscle. Fibres of the superior head insert not only into the meniscus of the temporomandibular joint, but also into the pterygoid fovea at the neck of the mandibular condyle. Specimens sectioned through the origin of the inferior head of the muscle show internal tendon lamellae consistent with a pennate structure. Electromyographic (EMG) activity was recorded in five healthy subjects using concentric needle and fine-wire electrodes. Strong to very strong activity was consistently observed in the superior head during clenching and tooth gnashing. The inferior heads were silent or had negligible to slight activity most of the time during ipsilateral movements or clenching, but were co-activated bilaterally, with strong to very strong activity during jaw opening, protrusion, swallowing, tooth gnashing and during passive retrusion. They showed marked activity unilaterally during contralateral movements.

Follow-up study of silent periods in complete denture wearers.

Electromyographic silent periods in response to chin taps during clench were recorded from the anterior temporalis and masseter muscles. Ten complete denture wearers were observed up to the 1-year stage of denture wear and eight patients up to the 2-year stage. Silent periods were also recorded from patients clenching on paper rolls in place of the dentures. Regarding the patterns of the silent periods, similar observations of double silent periods were made as in our previous study up to the half-year stage of denture wear (McCall, Tallgren & Ash, 1979). The frequency of the double silent periods was 13.8% at the 1-year stage and 7.3% at the 2-year stage. The mean duration of the silent periods did not differ significantly at the 1-year and 2-year stages. The mean silent period duration when clenching on paper rolls without dentures in the mouth was significantly shorter than when clenching with the dentures.

Repair of periodontal angular bony defects evaluated by one- and two-dimensional radiographic analysis.

The healing of eighteen angular periodontal bony defects was evaluated radiographically 1 year after treatment. The pretreatment and posttreatment radiographs were exposed and processed in such a way that identical images were obtained. There was no correlation between one- and two-dimensional expressions of healing in such defects, and relative area changes were consistently larger than relative linear changes of the same defects. The area gain of bone was strongly correlated to the following morphologic variables: length of bone surface, original defect area, and height of the defect.

Concerns of patients seeking treatment for TMJ dysfunction.

One hundred fifty-seven patients, 126 women and 24 men, 10 to 75 years of age, completed a self-administered questionnaire. The questionnaire contained questions asking about the patients' chief complaint, treatment received before coming to the clinic, the patients' view of their problem, and who informed them of the possible end result of an untreated "TMJ problem." The results revealed that pain was the most commonly reported complaint (54%), discomfort and headache came second and third (52.2% and 46.5%, respectively). A significant correlation was found between inability to chew and pain, discomfort, tightness in the masticatory muscles, and locking and clicking of the joint. Most patients had received three or more types of treatment before coming to the University of Michigan, TMJ and Oral Facial pain Clinic. A significant correlation was found between an increased number of reported symptoms and an increase in the number of treatments. The most frequently used treatment methods were pain medication, mouth guard (appliances), and occlusal adjustment. Most patients (84.1%) were referred to the TMJ and Oral Facial Pain Clinic by dentists because of clicking, locking, and limitation of movement, with or without pain.

Excitatory response of jaw elevators associated with sudden discomfort during chewing.

Abnormalities associated with the chewing contraction of the masseteric and anterior temporal muscles were evaluated in patients who sensed pain in the area of the temporomandibular joint during mandibular movement. The patients were instructed in the use of an electronic switch to mark any event of discomfort/pain during natural chewing. Individual stimulus to response reaction-times were determined. The electromyographic pattern of the jaw elevators was quantified by root mean square (r.m.s.) peak voltage and contraction time. The statistical analysis of group data showed significantly prolonged contraction times and greater r.m.s. amplitudes for chewing cycles with, compared to cycles without, indication of pain. Also, individual data showed statistically significant differences between painful and non-painful cycles in some cases. It is concluded, that the conscious perception of nociception during the closing phase of chewing is associated with an excitatory response of jaw elevators.