Parker E. Mahan

Occlusal forces during chewing and swallowing as measured by sound transmission

Forces during the phase of occlusal contact during chewing and swallowing are surprisingly high (36.2% and 41%), about 40% of the subjects maximum biting force. Previous studies using transducers in fixed partial dentures measured only a portion of the total force and have given the impression that chewing forces are much less than the data reported in this study. The importance of occlusal stability in the intercuspal position is of utmost clinical significance. Steep anterior guidance does not appear to expose the teeth to extreme lateral forces. The gliding contacts of the teeth while entering and leaving the intercuspal position have been shown to be of short duration and low magnitude when compared with the forces generated in the intercuspal position. During chewing, the peak occlusal force occurred well after the peak EMG activity. EMG activity by itself does not directly correlate with the force generated during chewing. The sound transmission method for measuring interjaw force during chewing, which was developed as part of this project, proved to be practical for research purposes. No intraoral devices are required, and the time relationship to force is accurate to within 15 ms.

Limits of human bite strength

lhe greatest human bite strength in the early literature was reported more than 300 years ago by Borelli of Rome, Italy, in 1681.’ He attached weights to a cord, which passed over the molar teeth of the open mandible, and with closing of the jaw, up to 440 lbs (200 kg) were raised.’ In recent times, the greatest reported bite strength was 348 lbs (158 kg) in the Alaskan Eskimo.2 Bite strength records have been limited by instrumentation. Black,3 for example, reported that at least one of his subjects could have exceeded the 275 lb (125 kg) limit of his gnathodynamometer. Furthermore, his subjects were biting unilaterally and, as in many other studies, did not have the advantage of bilateral support. An improved gnathodynamometer was needed if increased bite strengths were to be measured. Today’s soft diet cannot compare with the hard, frozen diet of the Eskimos for strengthening the mandibular muscles.4 However, many people today undergo jaw muscle-strengthening through clenching and bruxing habits that may be considerably more rigorous than even the chewing demands of the Eskimo. Our hypothesis was that human bite strength of the bruxer-clencher has been underestimated, and some individuals can exceed the bite strength of the Eskimo.

Superior and inferior bellies of the lateral pterygoid muscle EMG activity at basic jaw positions

I n 1961 Kamiyama’ reported reciprocal activity of the superior (SLP) and inferior (ILP) bellies of the lateral pterygoid muscle in 12 human subjects. He found that the SLP was active during closing, retraction, and lateral movement in the ipsilateral direction while the ILP was active during opening, protrusion, and lateral movement in the contralateral direction. McNamara2 demonstrated in monkeys that the ILP acts synergistically with the suprahyoid muscles in mouth opening while the SLP is active during mouth closing. Lipke et a1.3 reported in 1977 that electromyographic (EMG) studies in 10 human subjects revealed independent activity of the two bellies of the lateral pterygoid muscle. However, recent reports by Lehr and Owens4 and Auf der Mau? have claimed that separate roles for the ILP and SLP in humans could not be supported electromyographically. Miller and Vargervik” and Mahan et al.’ reported three different EMG patterns from the right lateral pterygoid muscle. The objective of the present study was to record simultaneous EMG activity in the right SLP and ILP and to determine the response of each belly of the muscle during clenching of the teeth and at basic mandibular positions. Fig. 1. Parasagittal section through left TMJ bisecting superior belly of lateral pterygoid muscle. A = Mandibular condyle; B = articular eminence; C = inferior belly of lateral pterygoid muscle (ILP); D = superior belly of lateral pterygoid muscle (SLP); E = fascia and fat lateral to ILP; F = temporal muscle fibers; G = buccal fat pad; and H = maxillary antrum.

EMG activity of the superior belly of the lateral pterygoid muscle in relation to other jaw muscles

A lthough there have been a number of studies that involved the function of jaw muscles, due to its deep placement, the action of the superior belly of the lateral pterygoid (SLP) muscle has not been studied widely. The electromyographic (EMG) activities of the superior and inferior bellies of the lateral pterygoid muscles have been shown to be reciprocal in humans’-‘,+ and rhesus monkeys. *-lo The SLP muscle is of particular interest because it attaches to the anterior border of the mandibular disk anterior to the point where it inserts at from the pterygoid fovea. Activity of this muscle in relation to the function of other jaw muscles seems to be important in mandibular condyle-disk discoordination and in temporomandibular joint (TMJ) and muscle pain. A previous article from our laboratory’ described the EMG activities of the superior and inferior bellies of the lateral pterygoid muscles during basic jaw positions and clenching the teeth. The present article describes the activities of SLP and the inferior belly of the lateral pterygoid (ILP) in relation to masseter, temporal, anterior belly of the digastric, and medial pterygoid muscles during some basic jaw positions and movements. Understanding the relationship of muscle functions during basic jaw movements is an important step in understanding muscle function during preconscious chewing, swallowing, and speech.

Temporomandibular joint forces measured at the condyle of Macaca arctoides.

Forces were measured at the articular surface of the temporomandibular joint (TMJ) condyle in two stump-tail monkeys (Macaca arctoides) during chewing, incisal biting, and drinking and also during aggressive behaviors. Force was measured with a thin piezoelectric foil transducer, which was cemented over the anterior and superior surfaces of the condyle. Wires from the upper and lower surfaces of the foil were insulated between two layers of Teflon tape and run subcutaneously to a telemetry unit, which was implanted in the upper back. Force applied across the foil by the condyle was detected by the telemetry unit and transmitted to an FM radio receiver outside the animal. The FM signals were received and demodulated, and a signal proportional to the force applied between the condyle and the TMJ fossa was displayed on a chart recorder. Data were collected over an 8-day period. The animals were not constrained. The TMJ was found to be load bearing. The greatest force of 39.0 lb (17.7 kg) was measured during feisty vocal aggression. Forces ranged as high as 34.5 lb (15.7 kg) during chewing and 28.5 lb (13.0 kg) during incisal biting. Forces were greater on the working (food) side than on the nonworking (balancing) side by average ratios of 1.4 to 2.6. A large unilateral interference at the most distal molar greatly disturbed chewing. It reduced TMJ forces by 50% or more, and the monkey refused to chew on the side opposite the interference.

Direct Measurement of Loads at the Temporomandibular Joint in Macaca arctoides

Loads at the articulating surface of the head of the condyle were recorded in one male adult Macaca arctoides. Following surgical implantation of the pressure-sensitive foil, the monkey was given hard and soft foods to chew. Loads were recorded during incisal biting and molar chewing. The bite data showed the following: The condylar head was loaded during molar chewing with a maximum load of 1-3 lb. The condylar head was loaded with a larger load of 3-4 lb during incisal biting.

Nerve entrapment in the lateral pterygoid muscle

The posterior trunk of the mandibular division of the trigeminal nerve normally descends deep to the lateral pterygoid muscle. In three of 52 dissections the three main branches of the posterior trunk (lingual, inferior alveolar, and auriculotemporal nerves) were observed to pass through the medial fibers of the lower belly of the lateral pterygoid muscle. The mylohyoid and anterior deep temporal nerves also were observed to pass through the lateral pterygoid muscle in other specimens. These nerve entrapments in the infratemporal fossa provide new information concerning the anatomic and clinical relationships between the mandibular nerve and the lateral pterygoid muscle. These findings support the hypothesis that a spastic condition of the lateral pterygoid muscle may be causally related to compression of an entrapped nerve that lead to numbness, pain, or both in the respective areas of nerve distribution.

Discomalleolar and anterior malleolar ligaments: Possible causes of middle ear damage during temporomandibular joint surgery

Damage to structures within the middle ear during surgical manipulation of the temporomandibular joint (TMJ) has been reported. Two structures are proposed as possible intermediaries in this trauma: the discomalleolar ligament (DML), which passes from the malleus to the medial retrodiscal tissue of the TMJ, and the anterior malleolar ligament (AML), which connects the malleus with the lingula of the mandible via the sphenomandibular ligament (SML). It has been hypothesized that when tension is applied to the DML and/or AML, the resulting movement of the malleus could cause damage to the tympanic membrane and associated structures. The objective of this study was to determine whether tension applied to the DML and/or the AML could cause movement of the malleus. With the use of a superior medial approach through the middle cranial fossa, the ligaments connecting the malleus with the mandible were examined in 52 adult/human cadaveric half-heads. Tension applied directly to the SML resulted in movement of the malleus in three specimens. Similar tension applied to the DML did not cause movement of the malleus. Histologic evidence showed a continuity of fibers between the SML and AML. When the mandibular condyle was distracted inferiorly, tension was demonstrated in the SML. The results indicate that the AML via the SML has the potential to cause middle ear damage and is more likely to do so than the DML.

Temporomandibular degenerative joint disease: Part I. Anatomy, pathophysiology, and clinical description

The anatomy and function of the temporomandibular joint (TMJ) are described in the detail needed to evaluate and treat temporomandibular degenerative joint disease (TDJD). Innervation of the joint and the mechanism of arthralgia are described and related to TDJD. The clinical course of TDJD, radiographic evaluation of it, histopathologic description, and etiology are presented.

Temporomandibular degenerative joint disease. Part II. Diagnostic procedure and comprehensive management.

The diagnostic procedure is given in the detail necessary to arrive at an accurate diagnosis of temporomandibular degenerative joint disease (TDJD). The differentiating clinical findings of degenerative joint disease (DJD) and rheumatoid arthritis of the temporomandibular joint (TMJ) are described. Principles and modalities of comprehensive management of TDJD are presented in the manner and sequence needed to allow practical clinical application. Methods of treatment are applied to the management of patients with acute and chronic TDJD. The surgical procedure for TDJD, intracapsular high condylectomy with a preauricular incision, is described in the detail required for individual application. Case reports are presented to illustrate the comprehensive management of TDJD.