Incisal bite force direction in humans and the functional significance of mammalian mandibular translation

Hylander, William L.

doi:10.1002/ajpa.1330480102

Cited by 96 publications

(30 citation statements)

References 14 publications

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“…The asymmetry of retractive and protrusive shear forces predicted by this model appears to be a contrary result to that reported by Koolstra et al (1988) and thus might tend to agree with Hylander's (1978) finding for incisal bite force direction. Greater protrusive shear would be the result expected from the anatomy of the masticatory muscles, since the muscle mass capable of exerting a retractive pull on the mandible is much less than that which can exert a protrusive pull.…”

Section: Discussioncontrasting

confidence: 61%

Using sensitivity analysis to validate the predictions of a biomechanical model of bite forces

Sellers

Crompton

2004

Annals of Anatomy - Anatomischer Anzeiger

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Section: Discussioncontrasting

confidence: 61%

Using sensitivity analysis to validate the predictions of a biomechanical model of bite forces

Sellers

Crompton

2004

Annals of Anatomy - Anatomischer Anzeiger

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“…Assuming that the working-side corpus and condyle in an anisognathic individual must translate mediolaterally and/or rotate about a vertical axis to bring the molars into functional occlusion, it is likely that, relative to more vertically oriented adductors, the balancing-side deep masseter is stretched beyond its resting length prior to the masticatory power stroke. This passive stretching of the sarcomeres beyond their resting length will result in reduced muscle-force production, as the amount of force a muscle can generate is inversely proportional to the distance it is stretched beyond its resting length (Carlson, 1977;Hylander, 1978Hylander, , 1992Weijs et al, 1989). Thus, given the increased relative activity of balancing-side deep masseter during mastication (Hylander et al, 1987(Hylander et al, , 1998(Hylander et al, , 2000Hylander and Johnson, 1994), and given a likely increase in the amount and duration of the transverse component of crushing force during the power stroke (Kay and Hiiemae, 1974;Hiiemae, 1978), isognathic jaws in anthropoids may enhance force generation in more transversely oriented balancing-side jaw muscles during the power stroke (vs. the primitive, more anisognathic masticatory apparatus of strepsirhines and, presumably, basal primates).…”

Section: Evolution Of Anthropoid Masticatory Adaptationsmentioning

confidence: 95%

Evolution of anthropoid jaw loading and kinematic patterns

Ravosa

Vinyard

Gagnon

et al. 2000

Am. J. Phys. Anthropol.

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Major transformations in the skull and masticatory system characterized the evolution of crown anthropoids. To offer further insight into the phylogenetic and arguably adaptive significance of specific primate mandibular loading and kinematic patterns, allometric analyses of metric parameters linked to masticatory function are performed within and between 47 strepsirhine and 45 recent anthropoid species. When possible, basal anthropoids are considered. These results are subsequently integrated with prior experimental and morphological work on primate skull form. As compared to strepsirhines, crown anthropoids have a vertically longer ascending ramus linked to a glenoid and condyle positioned relatively higher above the occlusal plane. Interestingly, anthropoids and strepsirhines do not exhibit different mean ratios of condylar to glenoid height, which suggests that both clades are similar in their ability to evenly distribute occlusal contacts and perhaps forces along the postcanine teeth. Thus, given the considerable suborder differences in the scaling of both glenoid and condylar height, we argue that much of this variation in jaw-joint height is linked to suborder differences in relative facial height due in turn to increased encephalization, basicranial flexion, and facial kyphosis in anthropoids. Due to a more elongate ascending ramus, anthropoids evince more vertically oriented masseters than like-sized strepsirhines. Having a relatively longer ramus and a more medially displaced lateral pterygoid plate, crown anthropoids exhibit medial pterygoids oriented similar to those of strepsirhines, but with a variably longer lever arm. As anthropoid masseters are less advantageously placed to effect transverse movements/forces, we argue that balancing-side deep-masseter activity underlying a wishboning loading regime serves to increase, or at least maintain, transverse levels of jaw movement and occlusal force at the end of the masticatory power stroke. Crown anthropoids are also more isognathic and isodontic than strepsirhines. A consideration of early anthropoids suggests that the crown anthropoid masticatory pattern, i.e., more vertical masseters due to a high condyle as well as greater isognathy and isodonty, occurred stepwise during stem anthropoid evolution. This appears to correspond to a more transverse, and perhaps progressively larger, power stroke across oligopithecids, parapithecids, and propliopithecids.

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“…The bite force was assumed to act at the center of the biting tooth (M 1 for molar biting and I 2 for incisal biting), and its direction was taken perpendicular to the occlusal plane. Although some studies showed that maximum bite force does not necessarily occur perpendicular to the occlusal plane, especially in the incisal region (Hylander, 1978;Baragar and Osborn, 1987;Koolstra et al, 1988), this assumption was made to render the system statically determinate (see below). Once their direction and point of application were established, the lever arms of the bite force and the muscle forces relative to the condyle were calculated by taking the perpendicular distance between the line of action of a given force and the condylar axis (Figs.…”

Section: Estimation Of Model Inputsmentioning

confidence: 99%

Bite force production capability and efficiency in Neandertals and modern humans

O'Connor

Franciscus

Holton

2005

Am. J. Phys. Anthropol.

103

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Although there is consensus that Neandertal craniofacial morphology is unique in the genus Homo, debate continues regarding the precise anatomical basis for this uniqueness and the evolutionary mechanism that produced it. In recent years, biomechanical explanations have received the most attention. Some proponents of the "anterior dental loading hypothesis" (ADLH) maintain that Neandertal facial anatomy was an adaptive response to high-magnitude forces resulting from both masticatory and paramasticatory activity. However, while many have argued that Neandertal facial structure was well-adapted to dissipate heavy occlusal loads, few have considered, much less demonstrated, the ability of the Neandertal masticatory system to generate these presumably heavy loads. In fact, the Neandertal masticatory configuration has often been simultaneously interpreted as being disadvantageous for producing large bite forces. With rare exception, analyses that attempted to resolve this conflict were qualitative rather than quantitative. Using a three-dimensional digitizer, we recorded a sequence of points on the cranium and associated mandible of the Amud 1, La Chapelle-aux-Saints, and La Ferrassie 1 Neandertals, and a sample of early and recent modern humans (n = 29), including a subsample with heavy dental wear and documented paramasticatory behavior. From these points, we calculated measures of force-production capability (i.e., magnitudes of muscle force, bite force, and condylar reaction force), measures of force production efficiency (i.e., ratios of force magnitudes and muscle mechanical advantages), and a measure of overall size (i.e., the geometric mean of all linear craniofacial measurements taken). In contrast to the expectations set forth by the ADLH, the primary dichotomy in force-production capability was not between Neandertal and modern specimens, but rather between large (robust) and small (gracile) specimens overall. Our results further suggest that the masticatory system in the genus Homo scales such that a certain level of force-production efficiency is maintained across a considerable range of size and robusticity. Natural selection was probably not acting on Neandertal facial architecture in terms of peak bite force dissipation, but rather on large tooth size to better resist wear and abrasion from submaximal (but more frequent) biting and grinding forces. We conclude that masticatory biomechanical adaptation does not underlie variation in the facial skeleton of later Pleistocene Homo in general, and that continued exploration of alternative explanations for Neandertal facial architecture (e.g., climatic, respiratory, developmental, and/or stochastic mechanisms) seems warranted.

show abstract

Incisal bite force direction in humans and the functional significance of mammalian mandibular translation

Cited by 96 publications

References 14 publications

Using sensitivity analysis to validate the predictions of a biomechanical model of bite forces

Using sensitivity analysis to validate the predictions of a biomechanical model of bite forces

Evolution of anthropoid jaw loading and kinematic patterns

Bite force production capability and efficiency in Neandertals and modern humans

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