Charles H. Gibbs

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.

Biting strength and chewing forces in complete denture wearers

Most studies concur that denture wearers have only about one fifth to one fourth the bite strength and masticatory force of natural dentition subjects. There appears to be a wide range of acceptable chewing forces, as evidenced by the wide variation in bite strength of natural dentition subjects. However, bite strength and masticatory forces in denture wearers fall below the natural dentition range and therefore it is concluded that denture wearers are handicapped in bite force. The occlusal form of the posterior denture teeth did not significantly influence masticatory force.

An evaluation of mandibular border movements: Their character and significance

1. A comparison of protrusive and lateral condylar border movement pathways of 163 subjects revealed considerable similarity when the frequency of 80% of the pathways was compared with the average pathway. 2. A description of the pathways of posterior cusps during lateral contact gliding movement must consider three simultaneously acting guidance factors: (1) the nonworking condyle pathway, (2) the amount of Bennett movement or the working-side condyle displacement, and (3) the anterior guidance or working-side tooth contacts. 3. A Bennett movement of 2.5 to 3.5 mm caused a dramatic flattening of lateral movement pathways of the molar cusp as seen in the frontal plane. The steepness of neither the anterior guidance nor the nonworking condylar pathway had much influence on the molar cusp pathway in the presence of this excessive Bennett movement. 4. Viewed in the horizontal plane, excessive Bennett movement contributed to the greatest potential for collisions of molar cusps during lateral movements. This phenomenon was more pronounced on the nonworking side. 5. When the Bennett movement was 0.75 mm or less the tracing in the frontal plane showed that the 40-degree anterior guidance became the dominant influence over molar cusp lateral movement pathways.

Chewing Patterns in Normal Children

Chewing patterns are precisely plotted in deciduous, mixed and permanent dentitions. These show a progression from a large component in the opening movement with a more medial closing path in the deciduous dentition, to a more vertical overall pattern with the closing path lateral to the opening path in the early permanent dentition.

The nonsurgical treatment of a class II open bite malocclusion

This case was treated by residents in the postgraduate orthodontic program at the University of Florida under the supervision of Dr. Hocevar. A treatment regimen that he developed to increase the strength and endurance of the masticatory muscles was used. The patient performed prescribed daily clenching and chewing exercise with resilient posterior bite-blocks and wore a hard acrylic posterior biteplane the remainder of the time. It was hoped that this approach would increase the chances of treatment success and stability.