W.D. McCall

Functional occlusal forces: An investigation by telemetry

In normal chewing the forces exerted on the occlusal surface seldom exceeded 10 to 15 pounds, as recorded by an eight-channel force transmitter in a removable fixed partial denture. Ninety-five percent of forces were less than 3.5 pounds for subject A, 2.0 pounds for subject B, and 10.0 pounds for subject C. The chewing frequency and the places of maximal force on the occlusal surface were relatively constant. The electromyographic chewing patterns could be considered normal in all circumstances. There was a remarkable statistically significant day-to-day variation in force values. The forces also changed for different kinds of food. The differences between maximum and minimum force values were highest in voluntary, nonfunctional movements.

FORMALIN INDUCES BIPHASIC ACTIVITY IN C-FIBERS IN THE RAT

While the formalin test is a widely used behavioral model of tonic chemogenic pain, little is known about the responses of primary afferent nociceptors to formalin. Formalin (2.5%, 50 microliters) was injected either directly in or adjacent to the mechanical receptive fields of single C-fibers isolated from the saphenous nerve of pentobarbital-anesthetized rats. The average formalin-evoked response in C-fibers (n = 29) over time was biphasic. This biphasic time course of the C-fiber response to formalin is similar to that of the behavioral response in the awake animal and is compatible with the hypothesis that increased C-fiber activity contributes to the behavioral response in phase 2, as well as in phase 1 of the formalin test.

Effect of gum hardness on chewing pattern

Chewing rhythms are set by a putative central pattern generator whose output is influenced by sensory feedback. In this study we assessed how an altered feedback imposed by changing the hardness of a gum bolus modifies the timing of chewing, the maximal gape, and the activity in the masseter muscle on the chewing side. Ten adult subjects with no orofacial dysfunction chewed a standard piece of soft or hard gum for at least 3 min in random order. Vertical jaw movements were recorded with a kinesiograph and activity of the masseter muscle was recorded and integrated from surface EMG electrodes. The subjects sat in a dental chair and viewed a video lecture to distract their attention from chewing; they were instructed to chew on the right molars. Cycle-by-cycle analysis showed that 9 of the 10 subjects chewed the hard gum more slowly than the soft with no significant change in gape. The increases in cycle duration were due to changes in the duration of the opening and occlusal phases. The duration of closing was not significantly changed even though the duration and level of masseter activity were both significantly increased. We conclude that gum hardness by altering proprioceptive feedback modifies the output of the masticatory central pattern generator in such a way that the temporal aspects of chewing and the output of the masseteric motor pool are affected.

A Numerical Model of Temporomandibular Joint Loading

A numerical model of the mandible, its articulating surfaces, and the forces exerted by the primary masticatory muscles has been developed for the purpose of investigating loading of the temporomandibular joint. Evidence is presented which shows that the temporomandibular joint is a load-bearing joint over the normal functional range of bite-force positions and angles. In this investigation, temporomandibular joint loads were found to vary from a maximum appositional force of 60% of the bite force (when bite forces were applied to the incisors) to a distracting force of about 5% of the bite force (when applied to the distal surfaces of the third molars). TMJ loads tended to reach a minimum as a result of vertically directed bite forces positioned at the second molars. A range of conditions in which bite forces were directed parallel to or within approximately 20° of the mid-sagittal plane was found to be conducive to stability of the temporomandibular joint. This stability included symmetry in the direction and in the magnitude of condylar loads as well as the presence of small forces tending to appose the condyle and articular eminence. TMJ loads tended to reach a maximum in response to mediolaterally directed bite forces. This result is consistent with the fact that no muscle of mastication exhibits a spatial orientation in which the muscle fibers are predominantly mediolateral in direction.

Devices for the diagnosis and treatment of temporomandibular disorders. Part II: Electromyography and sonography

This second article in the three-part series on temporomandibular disorder (TMD) devices compares the claimed diagnostic usefulness of electromyography and sonography with the present scientific evidence. This review concludes that there is no evidence to support the use of either surface electromyography or silent period duration for the evaluation or diagnosis of TMD. Furthermore, in view of the available evidence, sonography and Doppler ultrasound have no particular advantage over a conventional stethoscope or direct auscultation.

Effect of botulinum toxin injection on nocturnal bruxism: a randomized controlled trial.

Lee SJ, McCall WD, Jr., Kim YK, Chung SC, Chung JW: Effect of botulinum toxin injection on nocturnal bruxism: A randomized controlled trial. Objective:To evaluate the effect of botulinum toxin type A on nocturnal bruxism. Design:Twelve subjects reporting nocturnal bruxism were recruited for a double-blind, randomized clinical trial. Six bruxers were injected with botulinum toxin in both masseters, and six with saline. Nocturnal electromyographic activity was recorded in the subjects natural sleeping environment from masseter and temporalis muscles before injection, and 4, 8, and 12 wks after injection and then used to calculate bruxism events. Bruxism symptoms were investigated using questionnaires. Results:Bruxism events in the masseter muscle decreased significantly in the botulinum toxin injection group (P = 0.027). In the temporalis muscle, bruxism events did not differ between groups or among times. Subjective bruxism symptoms decreased in both groups after injection (P < 0.001). Conclusions:Our results suggest that botulinum toxin injection reduced the number of bruxism events, most likely mediated its effect through a decrease in muscle activity rather than the central nervous system. We controlled for placebo effects by randomizing the interventions between groups, obtaining subjective and objective outcome measures, using the temporalis muscle as a control, and collecting data at three postinjection times. Our controlled study supports the use of botulinum toxin injection as an effective treatment for nocturnal bruxism.

Electromyographic Silent Periods and Jaw Motion Parameters: Quantitative Measures of Temporomandibular Joint Dysfunction

The purpose of this research was to compare, in the subjects, the duration of the EMG silent period with jaw motion error. The results indicate that both jaw motion error and silent period duration are large in patients with TMJ-muscle-pain dysfunction, both are small in normal subjects, and both are small in successfully treated patients. There is a statistically significant correlation (r = 0.91; P < 0.01) between the two diagnostic parameters of TMJ-muscle-pain dysfunction.

Amitriptyline treatment of chronic pain in patients with temporomandibular disorders.

Randomized clinical trials of amitriptyline will require data from pilot studies to be used for sample size estimates, but such data are lacking. This study investigated the 6-week and 1-year effectiveness of low dose amitriptyline (10-30 mg) for the treatment of patients with chronic temporomandibular disorder (TMD) pain. Based on clinical examination, patients were divided into two groups: myofascial and mixed (myofascial and temporomandibular joint disorders). Baseline pain was assessed by a Visual Analogue Scale (VAS) for pain intensity and by the McGill Pain Questionnaire (MPQ). Depression was assessed by the Beck Depression Inventory (BDI) short form. Patient assessment of global treatment effectiveness was obtained after 6 weeks and 1 year of treatment by using a five-point ordinal scale: (1) worse, (2) unchanged, (3) minimally improved, (4) moderately improved, (5) markedly improved. The results showed a significant reduction for all pain scores after 6 weeks and 1 year post-treatment. The depression scores changed in depressed but not in non-depressed patients. Global treatment effectiveness showed significant improvement 6 weeks and 1 year post-treatment. However, pain and global treatment effectiveness were less improved at 1 year than at 6 weeks.

The influence of mechanical input parameters on the duration of the mandibular joint electromyographic silent period in man

Abstract The duration of the electromyographic silent period following a tap to the menton has been reported to be clinically useful in the diagnosis of mandibular joint dysfunction but not the influence of details of the tap. Using a solenoid-driven mechanical tapper, the following were investigated: in patients with joint dysfunction, effect on single muscles and position of the tap in a sequence of taps, in normal subjects, force of the tap, degree of opening of the jaw, angle of tap, and the biting force; all on the duration of the resulting silent period. No significant changes could be ascribed to any of these variables. The introduction between the teeth of wooden shims or a bite-force transducer were the only factors to change the duration. The dysfunction group had significantly longer silent periods than the normal group. It is concluded that, provided nothing is introduced between the teeth, the input parameters investigated do not influence the duration of the silent period.

Human Masticatory Muscle Forces during Static Biting

Muscle forces determine joint loads, but the objectives governing the mix of muscle forces involved are unknown. This study tested the hypothesis that masticatory muscle forces exerted during static biting are consistent with objectives of minimization of joint loads (MJL) or muscle effort (MME). To do this, we compared numerical model predictions with data measured from six subjects. Biting tasks which produced moments on molar and incisor teeth were modeled based on MJL or MME. The slope of predicted vs. electromyographic (EMG) data for an individual was compared with a perfect match slope of 1.00. Predictions based on MME matched best with EMG activity for molar biting (slopes, 0.89-1.16). Predictions from either or both models matched EMG results for incisor biting (best-match slopes, 0.95-1.07). Muscle forces during isometric biting appear to be consistent with objectives of MJL or MME, depending on the individual, biting location, and moment.