Functional Properties of Jaw and Tongue Muscles in Rats Fed a Liquid Diet after Being Weaned

Abstract

Decreased masticatory demands due to liquid or soft diets cause a reduction in the growth of craniofacial bones and in the development of feeding musculature, but the effects on masticatory function and jaw/tongue muscle activities are unclear. The present study was undertaken to test the hypotheses that a liquid diet feeding after weaning affects the critical-period programming of mastication and the motor performances of jaw and tongue muscles. Thirty-six male Wistar rats were divided into two equals groups at weaning and fed either a solid (solid-diet group) or a liquid (liquid-diet group) diet until they reached 50 days of age. Electromyograms (EMG) of the masseter, medial pterygoid, temporalis, anterior digastric, styloglossus, and genioglossus were recorded while animals were naturally ingesting ordinary pellets, apple cubes, and a liquid diet. It was found that: (1) a more irregular chewing rhythm, a shorter chewing sequence, and a longer chewing cycle were found in the liquid-diet group, but there were no differences observed during lapping/licking between the two groups; (2) during the chewing cycles, the EMG onset of each muscle in relation to that of the masseter in the liquid-diet group was similar to that in the lapping/licking cycles in both groups; (3) the activities of jaw elevators (masseter, medial pterygoid, and temporalis) during the chewing cycles were significantly higher in the liquid-diet group; and (4) the increase in the EMG activities of jaw elevators during pellet chewing compared with apple cube chewing was significantly weaker in the liquid-diet group, whereas such an enhancement was found simultaneously in the styloglossus in the solid-diet group, and in the anterior digastric in the liquid-diet group. These findings verify that: (1) the motor output of jaw and tongue muscles may be altered in rats fed a liquid diet after being weaned; (2) the feeding of a liquid diet to rats after being weaned may obstruct the functional transition from suckling to mastication; and (3) jaw elevators that develop without motor learning of mastication are inefficiency when performing functionally.

Sexual dimorphism of murine masticatory muscle function

“…In humans, the masseter, temporalis and medial pterygoid muscles are the primary jaw closers, which develop the most force and are the site of pain after chewing. In rodents, it is the masseter that is the major force-producing jaw-closing muscle, which has been demonstrated by electromyographic monitoring of all muscles of mastication in rats (8). The masseter muscle fiber orientation is not uniform and can be parallel or perpendicular to the temporomandibular joint (TMJ).…”

Selection of reference foods for a scale of standards for use in assessing the transitional process from milk to solid food in infants and pre-school children

“…Chewing and swallowing problems of children at kindergarten age have been reported frequently (Yokomizo, 1992). These difficulties have long been suspected to be related to the too soft and too nutritious foods prevalent in the present diet, and the manner of nursing has also been put in question (Ito et al, 1982;Inoue et al, 1995;Sakashita et al, 1996, Liu et al, 1998.…”

“…Chewing and swallowing problems of children at kindergarten age have been reported frequently (Yokomizo, 1992). These difficulties have long been suspected to be related to the too soft and too nutritious foods prevalent in the present diet, and the manner of nursing has also been put in question (Ito et al, 1982;Inoue et al, 1995;Sakashita et al, 1996, Liu et al, 1998.There are three main methods for evaluating the growth and development of the masticatory system: morphological measurement of the dentition ; functional analysis of muscle activity (Nakano, 1993;Sakashita et al, 1998); and estimation of masticatory ability (Yurkstas & Manly, 1950). In the first, the size of the jaw and arch length deficiency cannot be measured before tooth eruption; in the second, although the functional record, such as electromyography (EMG) of the masseter muscle, may be available, it is not easy to apply for screening purposes because it requires expensive equipment and specially trained personnel.…”

The Effect of Masseter Activity Patterns during Chewing on Suprahyoid Activity in Subsequent Chewing Cycles

“…Neurons of either or both nucleus groups send action potentials, via the parvocellular reticular nucleus, to the jaw opening and closing motoneurons, innervating the muscles responsible for chewing movement [4]. Activity of the jaw opening muscles during fictive chewing affects the activity of the jaw closing muscles via action potentials from the sensory apparatus of the muscle spindles and periodontal pressoreceptors, which are located in the orofacial region of animals [5][6][7][8] including humans [9][10][11]. Opening of the jaw stretches the muscle spindles of the jaw closing muscles, and the stretch reflex then contracts the muscles; conversely, closing of the jaw muscles during chewing is unlikely to affect jaw opening muscle activity [12], partly due to the lack of muscle spindles in the jaw opening muscles.…”

“…Opening of the jaw stretches the muscle spindles of the jaw closing muscles, and the stretch reflex then contracts the muscles; conversely, closing of the jaw muscles during chewing is unlikely to affect jaw opening muscle activity [12], partly due to the lack of muscle spindles in the jaw opening muscles. Previous studies have exclusively considered the influence of jaw closing muscle activity on amplitudinal and/or durational parameters of jaw opening muscle activity, either in experimental animals [5][6][7][8] or in humans [9][10][11]. Few studies have examined the influence of jaw closing muscle activity patterns using specific parameters for assessment as opposed to visual observation.…”