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A. Right masseter muscle, control group, showing the polygonal aspect of the fibers (X 250 of original magnification). B. Left masseter muscle, control group, showing the polygonal aspect of the fibers (X 250 of original magnification). C. Polygonal muscle fibers in the fascicule of the right masseter muscle, control group (X 125 of original magnification). D. Polygonal muscle fibers in the fascicule of the right masseter muscle, occlusal altered group (X 500 of original magnification). E. Altered fibers with central nucleus on the left side of the occlusal altered group (X 125 of original magnification). F. High magnification of anterior view showing these characteristics (X 500 of original magnification).
Source publication
The aim of this study was to evaluate alterations in the masseter muscle of 30 male guinea-pigs submitted to occlusal alteration. The animals were divided into 2 equal groups, the control group (C) only submitted to surgical stress, and the occlusal altered group (T) submitted to teeth extraction. Each group was subdivided into 3 groups, with 5 ani...
Contexts in source publication
Context 1
... masseter muscle of the control animals showed polygonal muscle fibers comprising fasciculi in the su- perficial region of the muscle ( Fig. 2A) and an endomy- sium rich in blood vessels. No difference was observed between the right ( Fig. 2A) and the left side (Fig. ...
Context 2
... masseter muscle of the control animals showed polygonal muscle fibers comprising fasciculi in the su- perficial region of the muscle ( Fig. 2A) and an endomy- sium rich in blood vessels. No difference was observed between the right ( Fig. 2A) and the left side (Fig. ...
Context 3
... masseter muscle of the control animals showed polygonal muscle fibers comprising fasciculi in the su- perficial region of the muscle ( Fig. 2A) and an endomy- sium rich in blood vessels. No difference was observed between the right ( Fig. 2A) and the left side (Fig. ...
Similar publications
The functional requirements in muscle use are related to the fiber type composition of the muscles and the crosssectional area of the individual fibers. We investigated the heterogeneity in the fiber type composition and fiber cross-sectional area in two muscles with an opposing function, namely the digastric and masseter muscles (n
= 5 for each mu...
Citations
... Por otra parte, el aparato mandibular de estos roedores ha sido capaz de promover una diversificación evolutiva equivalente. Muchos estudios publicados en Caviomorpha sustentan nuestros hallazgos, especialmente describiendo la diversificación morfológica del cráneo, la mandíbula y los rasgos Capítulo 1 dentarios (e.g., el tamaño del proceso angular, el ancho cigomático, la procumbencia dentaria, la microestructura de los molariformes), y vinculándolos a sus diferentes nichos ecológicos, dietas, habilidades sociales y locomotoras, y potencialidades funcionales, por ejemplo, para la vida subterránea (ver, por ejemplo, Vassallo, 1998;Fernández et al., 2000;Bacigalupe et al., 2002;Verzi, 2002;Mora et al., 2003;Mardegan Issa et al., 2007;Vieytes et al., 2007;Lessa et al., 2008;Álvarez et al., 2011). Entonces, los cambios en el desempeño de la fuerza de mordida le permitirían al aparato mandibular involucrarse en otros comportamientos (e.g., excavación) más allá del estrictamente trófico, lo que en el caso de Ctenomys está estrechamente vinculado a la ocupación de un nicho ecológico distintivo. ...
... Resumiendo, la importante radiación observada en los roedores caviomorfos tanto en lo geográfico como en lo ecológico, ha producido un importante abanico de modificaciones cráneomandibulares y dentarias dependiendo de las adaptaciones particulares a las demandas mecánicas asociadas a determinadas dietas, usos de nicho, modos de locomoción y relaciones sociales interespecíficas, más allá del efecto alométrico del tamaño corporal. Entonces, más allá de las descripciones eco-morfológicas hechas de estos roedores (ver por ejemplo Vassallo, 1998;Fernández et al., 2000;Bacigalupe et al., 2002;Verzi, 2002;Mora et al., 2003;Mardegan Issa et al., 2007;Vieytes et al., 2007;Lessa et al., 2008;Álvarez et al., 2011;Álvarez et al., 2013), este análisis integrativo morfo-funcional nos permitió concluir que las especies andino-patagónicas tienden a presentar dientes más robustos, mejor anclados y más resistentes a la flexión y la torsión, y molares más efectivos ante una dieta abrasiva, así como una musculatura aductora mandibular mucho más desarrollada, lo que en conjunto les permite producir mayores fuerzas de mordida relativas que otros representantes del infraorden provenientes del casco amazónico y, consecuentemente, les habría permitido adquirir el modo de vida que las caracteriza así como conquistar ambientes mucho más áridos. ...
The South American histrichomorph, or caviomorph, rodents have radiated and evolved isolated in the subcontinent achieving a broad range of body sizes, inhabited habitats, locomotor modes, ecological habits, social relationships, etc., by differentially using their masticatory apparatus at all of those aspects. Then, this clade represents an excellent model for the morpho-functional analysis of the cranio-madibular system (e.g., live performance, biomechanical properties, structural resistances). Therefore, in vivo bite forces were recorded, the jaw adductor musculature was dissected (paying attention at both inner muscle and biomechanical properties) and CT scans were performed on the skull and mandible of diverse species, coming from most of the families of the infraorder. Likewise, the morphological properties associated to the teeth structural resistance were studied at both gnawing (incisors) and grinding (molariforms) processes. Primarily, we observed that the bite force troughout the mammalian class presents a negative allometry against the body mass. Particularly, caviomorph diggers (specially chisel-tooth diggers) or animals with highly aggressive social interactions bit relatively harder than ground-dwellers and highly social species, showing also stiffer (for both bending and torsional stress) and more robust incisors with larger roots. The
molar occlusal surface area, by contrast, had a higher affinity with mechanical nutritional and environmental properties. The cranio-mandibular system outstandingly exhibited that differences in bite force would be mainly due to the muscle development either than the mechanical relationships of the lever arms in rodents (i.e., the skull morphology). Finally, the structural condition of the zygomatic arch and the mandible would seem to show a certain degree of association with the muscle action and biting directions.
... On the other hand, the mandibular apparatus of these rodents has been able to promote an equivalent evolutionary diversification as well. Many published analyzes on Caviomorpha support our findings, especially, by describing the morphological diversification of cranial, mandibular, and dental traits (e.g., angular process' size, zygomatic width, dental procumbency, molariforms' microstructure), and linking them to their different ecological niches, diets, social and locomotor skills, and functional potentialities, for example, for the subterranean lifestyle (see, e.g., Vassallo, '98;Fernández et al., 2000;Bacigalupe et al., 2002;Verzi, 2002;Mora et al., 2003;Mardegan Issa et al., 2007;Vieytes et al., 2007;Lessa et al., 2008;Álvarez et al., 2011). So, changes in the performance of biting force would allow the mandibular apparatus to be involved in some other behaviors (e.g., digging) beyond the strictly trophic one, which in the case of Ctenomys is closely linked to the occupation of a distinctive ecological niche. ...
Mammals have developed sophisticated strategies adapting to particular locomotor modes, feeding habits, and social interactions. Many rodent species have acquired a fossorial, semi-fossorial, or even subterranean life-style, converging on morphological, anatomical, and ecological features but diverging in the final arrangement. These ecological variations partially depend on the functional morphology of their digging tools. Muscular and mechanical features (e.g., lever arms relationship) of the bite force were analyzed in three caviomorph rodents with similar body size but different habits and ecological demands of the jaws. In vivo forces were measured at incisors' tip using a strain gauge load cell force transducer whereas theoretical maximal performance values, mechanical advantages, and particular contribution of each adductor muscle were estimated from dissections in specimens of Ctenomys australis (subterranean, solitary), Octodon degus (semi-fossorial, social), and Chinchilla laniger (ground-dweller, colonial). Our results showed that C. australis bites stronger than expected given its small size and C. laniger exhibited the opposite outcome, while O. degus is close to the expected value based on mammalian bite force versus body mass regressions; what might be associated to the chisel-tooth digging behavior and social interactions. Our key finding was that no matter how diverse these rodents' skulls were, no difference was found in the mechanical advantage of the main adductor muscles. Therefore, interspecific differences in the bite force might be primarily due to differences in the muscular development and force, as shown for the subterranean, solitary and territorial C. australis versus the more gracile, ground-dweller, and colonial C. laniger. J. Exp. Zool. 9999A: XX-XX, 2014. © 2014 Wiley Periodicals, Inc.
