Alteration of masticatory muscle EMG activities during chewing after a reversible bite-raising in guinea pigs

doi:10.1016/j.archoralbio.2011.01.009

Archives of Oral Biology

Volume 56, Issue 8, August 2011, Pages 793-798

https://doi.org/10.1016/j.archoralbio.2011.01.009 Get rights and content

Abstract

Previous studies have investigated the effects of increasing the occlusal vertical dimension (OVD) with an oral appliance on masticatory muscle EMG activity during oral behaviours in humans and animals. The present study investigated whether a short-term and reversible increase in OVD, followed by a reduction in OVD to the normal level, resulted in a time-correlated change in the EMG activities of the masseter and digastric muscles during chewing. To do this, a guinea pig model in which an increased OVD was established with natural tooth contacts was used. In the control group, in which no bite-raising treatment was applied, OVD gradually increased with a natural growth during the experimental period whilst the masseter and digastric EMG activities, burst duration, and chewing rhythm were unchanged. When the increase in OVD was established in the bite-raised group, the EMG activities of the masseter and digastric muscles were significantly increased by 88.6 and 55.2% from those before bite-raising treatment, respectively. However, during the following 11 days, the increased EMG activities of both muscles did not show changes associated with the subsequent decrease in the OVD to a normal level. The burst durations of both muscles and chewing rhythm were not significantly affected by the change in OVD during the experimental period. Within the limited recording period of the study, the return of OVD from increased to normal levels did not reverse the increased chewing-related masticatory muscle EMG activity that was induced by the bite-raising treatment.

Introduction

Previous studies have investigated the effects of increasing the occlusal vertical dimension (OVD) on masticatory muscle EMG activity during chewing or various oral behaviours in humans1, 2 and animals.3, 4, 5, 6 As an acute response to an increased OVD produced by an oral appliance, the EMG activity of the masseter muscle during chewing was decreased whilst that of the digastric muscle was increased.2, 3, 4 When an oral appliance was fixed in place for a few weeks, the duration of muscle activation was increased in both the masseter and digastric muscles although the oral behaviours involved were not specified.3, 5, 6 These studies suggested that the neuromuscular activities of jaw muscles during oral behaviours are able to respond to an experimentally increased OVD depending on the time frame after the oral appliance has been fixed to the teeth.

When using guinea pigs to investigate the effects of changes in OVD, although their neuromuscular functions can adapt to experimental bite-raising, the OVD should be strictly controlled and maintained at a level appropriate for guinea pigs.7, 8 In an animal model in which animals were subjected to a reversible increase in OVD with natural molar tooth contact using an oral appliance, the increased OVD had returned to the same level as that of age-matched naïve controls within 4–5 days after the oral appliance had been removed.7, 8, 9 This model allows the bite-raised animals to contact their opposing natural teeth after the removal of appliance. The changes in chewing movements induced by an increase in OVD were found to be exclusively associated with the reduced gape and no alterations in chewing rhythm or pattern were seen.⁹ However, these changes in chewing jaw movements disappeared as the OVD returned to the normal level. These findings suggest that chewing movements can be modified by a temporal change in OVD although the intrinsic programme for chewing is maintained.

Since jaw movements reflect the neuromuscular activities of masticatory muscles, we hypothesized that EMG activities in jaw-closing and opening muscles during chewing may be associated with the changes in OVD as the increased OVD decreases to a normal physiological level. Therefore, the purpose of the present study is to evaluate masseter and digastric EMG activity during chewing according to the OVD before and after reversible bite-raising was applied to guinea pigs.

Section snippets

Materials and methods

All experimental procedures were approved by the Committee on Animal Research of the Matsumoto Dental University. Eighteen male Hartley guinea pigs (4–5 post-natal weeks old) were used.

Changes in OVD

The change in OVD during the course of the experiment in the control and bite-raised groups is shown in Fig. 1. The OVD of the control animals gradually increased by 2.4 ± 2.1% (0.3 ± 0.3 mm) during the experimental period due to normal developmental growth. At the 0th day, the OVD in the bite-raised group had increased by 17.5 ± 4.7% (2.2 ± 0.6 mm) compared with that before bite-raising (at the −10th day) (p < 0.05). Compared to the control group, the OVD was significantly higher in bite-raised group on

Discussion

The present study indicated that a short-term and reversible increase in OVD resulted in an increase in the EMG activities of the Mass and Dig muscles during chewing. However, the increased EMG activities in both muscles did not decrease as the OVD returned to the normal level. These results suggest that, within the limited recording period of the study, the return of the OVD from increased to normal levels does not simply reverse the increases in chewing-related masticatory muscle EMG activity

Acknowledgement

This study was supported by Matsumoto Dental University intramural research funding and by a Grant-in-Aid for Scientific Research (B) (No. 18390526) from the Japan Society for the Promotion of Science (JSPS).

Funding: This study was supported by Matsumoto Dental University intramural research funding and by the Grant-in-Aids for Scientific Research (B) (No. 18390526) from the Japan Society for the Promotion of Science (JSPS).

Competing interests: None declared.

Ethical approval: The study

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Cited by (6)

Adverse effects of the bite-raised condition in animal studies: A systematic review
2019, Archives of Oral Biology
Citation Excerpt :
Interestingly, the EMG activity of the digastric, a jaw depressor muscle, has been shown to be significantly increased in the bite raised condition (Matsuka et al., 1998). On the other hand, a bite raising apparatus positioned on the lower incisors of guinea pigs induced a significant increase in the EMG activity of both the masseter and the digastric muscles (Kanayama et al., 2011). It must be noted, however, that rodent incisor teeth are quite different, both in structure and innervation, when compared to posterior teeth: it is possible that the different EMG alteration observed when rodent incisors are involved in the bite-raising procedure reflects these functional and anatomical characteristics (Piancino et al., 2017).
To provide a systematic review of the effects of the bite-raised condition in animal models, a widespread technique in modern orthodontics.
A systematic review of the literature was conducted. Original articles were searched through Pubmed, Cochrane Central database and Embase until December 2018.
242 articles were identified through database searching. After removing the duplicates, 198 articles were screened by reviewing the abstracts. 27 full text articles were assessed for eligibility and, after 7 exclusions, 20 articles were included in the review process. Studies selected by the review process concerned animal models. Histological, molecular, biochemical and electromyographical studies were evaluated. The results, with a high level of agreement in different animals, showed that the bite-raised condition is a source of stress, inducing increased plasma corticosterone, urinary cortisol and HPA axis alterations; it predisposes the organism to react to subsequent stressful stimulation with a significantly greater incretion of glucocorticoids, thus inducing hypersensitivity to novel forms of stress; it affects the structure of the hippocampus, reducing the number of neurons, increasing the number of glial cells and worsening memory and spatial orientation; it alters the electromyographical activity of masticatory muscles.
The results of research conducted on animal models do not necessarily apply directly to human beings. More clinical research, with special attention to adolescent patients, is necessary to clarify whether, in humans, the bite-raised condition is accompanied by adverse effects comparable to those observed in animals.
Effects of increased occlusal vertical dimension on the jaw-opening reflex in adult rats
2016, Archives of Oral Biology
Citation Excerpt :
Previous studies have reported that the jaw reflex is affected by changes in the stomatognathic area, including unilateral nasal obstruction (Funaki, Hiranuma, Shibata, Kokai, & Ono, 2014) and liquid-diet feeding (Changsiripun, Yabushita, & Soma, 2009; Changsiripun, Yabushita, & Soma, 2012). In addition, the nerve that controls the performance of appropriate chewing motions in the masticatory muscles may compensate for a change in occlusal dimension because the rhythm of mastication and jaw movement pattern do not change with iOVD (Kanayama et al., 2011). Therefore, the aim of this study was to investigate the effects of iOVD on the JOR in mature rats.
Malocclusion with deep overbite and facial esthetics improve when facial height is intentionally increased during orthodontic extrusion of the posterior teeth. Thus, a better understanding of post-treatment stability of increased occlusal vertical dimension (iOVD) in adult patients is important. We focused on the jaw-opening reflex (JOR), which plays an important role in the control of jaw movements during mastication, and investigated the effects of iOVD on the JOR in rats with an electrophysiological technique.
One hundred and twenty 13-week-old male Wistar rats were randomly divided into control and experimental groups. Rats in the experimental group received a 2-mm buildup of composite resin on the maxillary molars at 13 weeks of age. The JOR was induced by low-intensity electrical stimulation of the left inferior alveolar nerve. The electromyographic responses were recorded from the digastric muscle at 13, 14, 15, 17, 19, and 23 weeks of age. JOR properties including latency, duration, and peak-to-peak amplitude were measured and compared between the groups.
The latency of the JOR was significantly longer and the peak-to-peak amplitude was significantly smaller in the experimental group than in the control group from 14 to 19 weeks of age, while the reflex duration was not significantly different. Intra-group comparisons of the latency and peak-to-peak amplitudes among rats 14–19 weeks of age were significantly different between the experimental group and the control group.
iOVD affected the latency and amplitude of the JOR but not the duration. The JOR adapted after 10 weeks of iOVD.
Cortical area inducing chewing-like rhythmical jaw movements and its connections with thalamic nuclei in guinea pigs
2012, Neuroscience Research
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RJM can be induced by stimulating the CMA in guinea pigs (Lambert et al., 1985; Gerstner and Goldberg, 1991). However, the RJM induced in previous guinea pig studies were usually characterized by vertical open-close jaw movements and jaw-opening muscle activity (Goldberg et al., 1982; Lambert et al., 1985; Iriki et al., 1988; Chandler et al., 1990; Gerstner and Goldberg, 1991; Enomoto et al., 1995), that is, they did not resemble the typical jaw movement pattern observed during natural chewing (Byrd, 1981; Kanayama et al., 2010, 2011). In guinea pigs, it has not been clearly demonstrated whether electrical stimulation of the CMA induces chewing-like RJM.
Repetitive electrical stimulation to the cortical masticatory areas (CMA) evokes rhythmical jaw movements (RJM), whose patterns vary depending on the stimulation site, in various species. In guinea pigs, although alternating bilateral jaw movements are usually seen during natural chewing, it is still unclear which cortical areas are responsible for chewing-like RJM. To address this issue, we first defined the cortical areas inducing chewing-like RJM by intracortical microstimulation. Stimulation of the most lateral area of the CMA, the granular cortex, induced chewing-like RJM, but from the region medial to this area, simple vertical RJM were induced. Subsequently, to reveal the properties of these two areas in the CMA, the connections between the CMA and the dorsal thalamus were examined by neuronal tract-tracing techniques. The area inducing chewing-like RJM possessed strong reciprocal connections, mainly with the medial part of the ventral posteromedial nucleus, which is the sensory-relay thalamus. On the other hand, the simple vertical RJM-inducing area had reciprocal connections with the motor thalamus. The present study suggests that the CMA inducing chewing-like RJM is different from the CMA inducing simple vertical RJM, and plays a role in cortically induced chewing-like RJM under the influence of the sensory thalamus in guinea pigs.
Bite-raising splints to treat deep bite in pediatric patients: An electromyographic and kinesiographic assessment
2021, International Journal of Clinical Dentistry
Newly developed mastication activity reduction procedure rapidly induces abnormal atrophic change of the mandibular condyle in young and elder experimental animal models
2020, Journal of Oral Science
Temporal change in the occlusal vertical dimension and its involvement in modulation of jaw movement in bite-reduced animals
2018, Journal of Oral Science

^☆: This study was based on a thesis submitted to the Graduate School of Oral Medicine (HK), Matsumoto Dental University, in partial fulfilment of the requirements of a PhD degree.

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Alteration of masticatory muscle EMG activities during chewing after a reversible bite-raising in guinea pigs☆

Abstract

Introduction

Section snippets

Materials and methods

Changes in OVD

Discussion

Acknowledgement

J Prosthet Dent

Arch Oral Biol

Arch Oral Biol

Arch Oral Biol

The effect of vertical dimension change on mandibular movements and muscle activity

Int J Prosthodont

Effect of occlusal bite-raising splint on electromyogram, motor unit histochemistry and myoneuronal dimensions in rats

J Oral Rehabil

Effects of a bite-raising splint on the duration of the chewing cycle and the EMG activities of masticatory muscles during chewing in freely moving rabbits

J Oral Rehabil