title: Changes in jaw muscle activity and the physical properties of foods with different textures during chewing behaviors.
abstract: This study aimed to investigate how the activity of the masseter (Mas) and suprahyoid (Hyoid) muscles is influenced by the physical properties of food, how changes in the rheological properties of food differ between different foods during the process of food reduction, and how different salivary flow rates affect bolus-making capability during masticatory behavior in healthy humans. Ten healthy adults participated in this study. Electromyographic (EMG) recordings were obtained from the Mas and Hyoid muscles, and 15 g of steamed rice and rice cake was prepared as test foods. In the ingestion test, the subjects were asked to eat each food in their usual manner. The chewing duration, number of chewing cycles before the first swallow, Mas and Hyoid EMG activity, and chewing cycle time were compared between the foods. Total chewing duration was divided into three substages: early, middle, and late; chewing cycle time and EMG activity per chewing cycle of each substage were compared between the foods and among the substages. In the spitting test, the rheological properties of the bolus at the end of each substage were compared between the foods and among the substages. Finally, stimulated salivary flow rates were measured and the relationships between salivary flow rate and chewing duration, EMG activity, and changes in physical food characteristics were investigated. There were significant differences in total chewing duration and the number of chewing cycles, but not in chewing cycle time, between the foods, which had similar hardness values. The EMG activity levels of the Mas and Hyoid per chewing cycle for the rice cake were significantly greater than for the steamed rice throughout the recording periods. While Mas activity did not change among the substages during chewing, Hyoid EMG activity decreased as chewing progressed. Chewing cycle time also gradually decreased as chewing progressed. The hardness of both foods initially increased, then gradually decreased back to baseline. The adhesiveness of the rice cake initially increased, and did not fall throughout the recording period; the adhesiveness of the steamed rice did not significantly change. Cohesiveness barely changed in either of the two foods during chewing, but was significantly greater for the rice cake than for the steamed rice. Finally, a correlation between the stimulated salivary flow rate and chewing performance was evident only in a change in Mas EMG activity. The current results demonstrate that the activities of the Mas and Hyoid muscles changed as chewing progressed, and were affected by hardness, adhesiveness, and cohesiveness. Salivary flow rate may affect the changes in Mas activity during the process of bolus formation.
authors.affiliation: Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Chuo-ku, Niigata 951-8514, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Iguchi
authors.affiliation: Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Chuo-ku, Niigata 951-8514, Japan.
authors.forename: Jin
authors.initials: J
authors.lastname: Magara
authors.affiliation: Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Chuo-ku, Niigata 951-8514, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakamura
authors.affiliation: Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Chuo-ku, Niigata 951-8514, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Tsujimura
authors.affiliation: Oral Rehabilitation, Niigata University Medical and Dental Hospital, 1-754 Asahimachi-dori, Chuo-ku, Niigata 951-8520, Japan.
authors.forename: Kayoko
authors.initials: K
authors.lastname: Ito
authors.affiliation: Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Chuo-ku, Niigata 951-8514, Japan. Electronic address: inoue@dent.niigata-u.ac.jp.
authors.forename: Makoto
authors.initials: M
authors.lastname: Inoue
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D005502:Food; D006801:Humans; D007568:Jaw / Q000502:physiology*; D008409:Mastication / Q000502:physiology*; D008410:Masticatory Muscles / Q000502:physiology*; D012212:Rheology; D012463:Saliva / Q000378:metabolism; D013997:Time Factors; D055815:Young Adult
keywords: Electromyography; Masseter muscle; Mastication; Physical property; Salivary flow rate; Suprahyoid muscles