Muscle Fiber Type Composition, Fiber Diameter, Capillary Density in Temporalis and Masseter Muscles and Correlation with Bite Force

Abstract

SUMMARY:The jaw muscles are essential components in the stomatognatic system. Their complex architecture allows them to execute several motor tasks. One of the structural peculiarities is the presence of hybrid and neonatal fibers.We studied the differences of the fiber-type in masseter and temporalis muscles along the first to nineth decades in both genders. Seventy-four (74) samples were analyzed by immunohistochemistry. Slow and fast muscle fibers distribution was similar in both muscles in both genders. Hybrid fiber was observed in all decades, and its frequency decreased significantly (p<0.001) with aging in masseter. Neonatal myosin expression was observed in all decades, its expression was more frequent in masseter (p=0.01), and males in temporalis (p=0.025). Decrease of the cross sectional area of fast and slow fibers, and decrease of capillary density were detected with aging. These morpho-immunohistochemical alterations on masseter and temporalis muscles correlated to the decrease in bite force with aging.

Insertion Area in the Mandible Masticatory Muscles for use in Finite Element Analyses

“…The masseter muscle showed the highest insertion area, followed by the temporal muscle. These results are according to the report by Guimarães et al (2013), which observed the highest number of fibers inserted in the mandible's ramus and body, and coronoid process, respectively, for the same muscles.…”

Differences in muscle mechanics underlie divergent optimality criteria between feeding and locomotor systems

“…However, as the goal of this study was to directly compare muscles of the feeding TA B L E 2 Interspecific (n = one individual per species) summary statistics (mean ± standard deviation) for the mechanical variables across the range of joint excursion for each of the representative muscles Specifically, we treat all muscles as if they have similar contractile properties, internal architecture, physiological cross-sectional area, fiber types, and activity patterns. Some of these variables are known to vary between the feeding and locomotor systems (e.g., Hoh, 2002;Österlund et al, 2011;Anderson and Roberts, 2020) and have effects on an individual muscle's ability to generate force or speed (Narici et al, 1992;Morse et al, 2005;Knudson, 2007;Eng et al, 2009;Taylor and Vinyard, 2009;Guimarães et al, 2013). Furthermore, this study ignores length-tension properties of muscles (Dumont and Herrel, 2003;Eng et al, 2009;Gidmark et al, 2013) and muscle architecture dynamics (Laird et al, 2020).…”

Measuring Selection on Physiology in the Wild and Manipulating Phenotypes (in Terrestrial Nonhuman Vertebrates)

“…Maximal bite force capacity has been correlated with linear morphometric measures of head size and head shape, such as head length, head depth, and head width (143,148,178,232,336), as well as geometric morphometric measures of multidimensional shape (101,146,178,201). Bite force is also determined by mechanical properties of the jaw apparatus, such as the inlever-outlever proportions of the jaw, the size, insertion points and orientation of the jaw musculature, and the microstructure of muscle fibers (141,142,147), as well as physiological properties, such as physiological crosssectional area and fiber length (88,134,144,335) and muscle fiber types (127). Although bite force is repeatable (6), we know essentially nothing about its heritability.…”