Coordinated features in jaw and neck muscle activities induced by chewing of soft and hard gum in healthy subjects

Abstract

Backgrounds: Jaw and neck muscles may be activated by chewing load using a hard food. However, it remains unclear how effects the gum hardness to the coordinated features in jaw and neck muscle activities during chewing performance.

Objectives: This study was conducted to quantitatively elucidate the effects of the hardness of the gum on coordinated features in jaw and neck muscle activities using intermuscular EMG-EMG transfer function and EMG-EMG coherence function analyses in 18 healthy subjects.

Methods: Jaw and neck muscle activities were aggregated into the first peak frequency of the power spectrum, and power, gain, phase, and coherence parameters between jaw and neck muscle activities were examined in the first peak frequencies during soft and hard gum chewing.

Results: The first peak frequency was not significantly different between soft and hard gum chewing. In contrast, power values of the jaw and neck muscles were significantly increased by chewing of hard gum as compared with soft gum, whereas gain, phase, and coherence were not significantly changed by gum hardness.

Conclusions: The chewing rhythm, the quantitative and temporal coordination, and the functional coordination in jaw and neck muscle activities were not changed during soft and hard gum chewing, as well as increased jaw and neck muscles activities. It is therefore concluded that the chewing rhythmicity and jaw and neck muscles coordination accompanied with the increased jaw and neck muscle activities are maintained under the condition of the chewing load using gum hardness in the healthy individuals.

Keywords: chewing gum; masticatory muscles; masticatory systems; neck muscles; surface electromyography.

FIGURE 1

Raw and rectified EMG activities and power spectrum, as well as representative power phase and coherence in jaw and neck muscle activities with soft and hard gum chewing. Raw EMG activities (a, b) and full wave rectification of muscle activity (c, d) in jaw and neck muscles during chewing of soft (a, c) and hard (b, d) gum for 80s in a representative subject. Area between vertical lines indicates analyzing phase (61.5 s). The power spectrum for jaw and neck muscle activities by FFT from 0 to 20 Hz (e, f), and arrows indicate the first peak frequency in the power spectrum. Gain (g, h) and phase (i, j) were analyzed using transfer function analysis, while coherence (k, l) was analyzed using coherence function analysis. The 95% confidence level (0.19) for the coherence spectrum shown in (k) and (l) is presented as a horizontal line. C and NC represent chewing side and non‐chewing side, respectively. Mm, ta, AD, and SCM represent masseter muscle, anterior temporal muscle, anterior digastric muscle, and sternocleidomastoid muscle, respectively

FIGURE 2

Gain for jaw and neck muscle activities. Mean and standard deviation of gain values for the first peak frequency of jaw closing (NC‐mm, C‐/NC‐ta), jaw opening (C‐/NC‐AD), and neck (C‐/NC‐SCM) muscle activities are shown. No significant differences were seen for gain between soft and hard gum chewing (Wilcoxon signed‐rank test, paired t‐test). The prefixes of ‘C’ (open circle) and ‘NC’ (black circle) denote the chewing side and non‐chewing side muscles, respectively. Mm, ta, AD, and SCM represent masseter muscle, anterior temporal muscle, anterior digastric muscle, and sternocleidomastoid muscle, respectively

FIGURE 3

Phase for jaw and neck muscle activities. Mean and standard deviation of phase values for first peak frequency of jaw closing (NC‐mm, C‐/NC‐ta), jaw opening (C‐/NC‐AD), and neck (C‐/NC‐SCM) muscle activities are shown. No significant differences were seen for phase between soft and hard gum (Wilcoxon signed‐rank test, paired t‐test). The prefixes of ‘C’ (open circle) and ‘NC’ (black circle) denote the chewing side and non‐chewing side muscles, respectively. Mm, ta, AD, and SCM represent masseter muscle, anterior temporal muscle, anterior digastric muscle, and sternocleidomastoid muscle, respectively

FIGURE 4

Coherence for jaw and neck muscle activities. Mean and standard deviation of coherence values for the first peak frequency of jaw closing (NC‐mm, C‐/NC‐ta), jaw opening (C‐/NC‐AD), and neck (C‐/NC‐SCM) muscle activities are shown. No significant differences were seen for coherence between soft and hard gum (Wilcoxon signed‐rank test, paired t test). The 95% confidence level (0.19) for the coherence spectrum is shown by a horizontal line. The prefixes of ‘C’ (open circle) and ‘NC’ (black circle) denote the chewing side and non‐chewing side muscles, respectively. Mm, ta, AD, and SCM represent masseter muscle, anterior temporal muscle, anterior digastric muscle, and sternocleidomastoid muscle, respectively