Journal of Oral Science
Online ISSN : 1880-4926
Print ISSN : 1343-4934
ISSN-L : 1343-4934
Original Article
Differences in the effectiveness of stabilization splints between the categories of sleep bruxism
Yasushi OnoguchiKyosuke Oki Yoshihiro TsukiymaYasunori AyukawaKiyoshi Koyano
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2025 Volume 67 Issue 2 Pages 101-105

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Abstract

Purpose: The present study investigated the effects of stabilization splints on two categories of sleep bruxism using a portable electromyographic recording system.

Methods: Twenty-six individuals confirmed as mild to severe bruxers by nocturnal masseter electromyographic episodes were enrolled in the study. Participants wore a stabilization splint during sleep for 30 nights, and masseter muscle activity was measured at baseline, immediately after, and 1 and 4 weeks after insertion of the splint. Bursts in masseter electromyographic episodes were separated into phasic bursts or tonic bursts, then each burst was analyzed in terms of duration, frequency, and magnitude of bursts.

Results: The frequency of phasic bursts significantly decreased immediately after insertion of the splint compared with the baseline. The geometric mean magnitude of tonic bursts decreased when wearing the splint compared with the baseline.

Conclusion: These findings suggest that stabilization splints reduce jaw-muscle activity during sleep in patients suffering from sleep bruxism by reducing the frequency of phasic bursts in the short term and reducing the magnitude of tonic bursts over a longer period.

Introduction

Bruxism is defined as a repetitive jaw-muscle activity characterized by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible. It is divided into two categories: sleep bruxism (SB) and awake bruxism [1]. Because of the individual’s awareness of awake bruxism, it is presumed that excessive force that causes structural damage is unlikely to occur. SB, however, can create extremely strong forces because of the individual’s state of unconsciousness, and is thought to cause excessive tooth wear, aggravation of periodontal disease, failure of dental restorations and implants [2,3,4], hypertrophy of masticatory muscles and temporomandibular disorders (TMD) [5,6].

Stabilization splints have been widely used for managing SB because of their non-invasiveness and resilience [7]. Stabilization splints protect the teeth [8] and balance the allocation of force, such as occlusal force to the dentition [9,10] and force loaded on the temporomandibular joint [11,12,13]. However, their effectiveness in reducing SB activity [14,15,16] remains questionable. Some studies have reported that stabilization splints reduced SB activity for only a short period of time [17], whereas others reported that it had no effects [18,19]. It is necessary to establish a consensus on the effect of stabilization splints in reducing SB activity.

A previous clinical study reported differences in the effect of oral devices on nocturnal masseter electromyographic (EMG) activity between the components of sleep bruxism [1]. Intraoral device use, including stabilization splints, for 1 week reduced the frequency of phasic bursts but did not reduce tonic bursts [20]. Effects of oral devices over a longer period, however, have not been studied in terms of duration, frequency, and magnitude of phasic bursts and tonic bursts.

Therefore, the purpose of the present study was to examine the effect of stabilization splints on the components of SB, using a portable EMG recording system over a longer period. Bursts in nocturnal masseter EMG activity were separated into phasic bursts or tonic bursts, then each EMG burst was analyzed in terms of duration, frequency and magnitude. The null hypothesis examined in the present study was that there was no difference in the effect of stabilization splints on EMG bursts between phasic bursts and tonic bursts regarding masseter EMG activity.

Materials and Methods

Study participants

Twenty-six bruxers (7 men, 19 women; median age 38.6 years; range 24-71 years) who were recruited from students and staff at Kyushu University, and outpatients at Kyushu University Hospital between April 2010 and March 2014 participated in the present study. Inclusion criteria were: (i) patients must meet the clinical diagnostic criteria for SB of the American Academy of Sleep Medicine (AASM) (2005) [21]; and (ii) be in good general health.

Exclusion criteria were: (i) more than two missing posterior teeth excluding third molars; (ii) use of removable partial dentures; (iii) TMD problems based on the research diagnostic criteria for TMD (RDC/TMD) [22]; (iv) under medication that may have an effect on sleep dynamics; (v) dependence on alcohol or drugs; (vi) ongoing medical or dental care; (vii) diagnosis of major neurological or psychiatric disorders; and (viii) diagnosis of sleep disorders.

All participants were assessed by one dentist in charge to ensure that they met these criteria. Each participant gave informed consent before participation in this study.

Stabilization splints

Stabilization splints to cover the occlusal surfaces of the upper dental arch were fabricated with light-cured acrylic resin (Splint-Resin LC; GC Corp., Tokyo, Japan). The splint had a smooth surface and occlusal contact with the mandibular buccal cusps in the intercuspal position, and cuspid guidance. In the second molar, it was 1-2 mm thick, covered one-third of the buccal crown, and extended 10 mm from the cervical line of the tooth toward the palate. The final splint adjustment was performed in the participant’s oral cavity.

EMG recording of masseter muscle

The activity of EMG was recorded from one side of the masseter muscles using a portable EMG recording system (ProComp Infiniti; Thought Technology, Montreal, Canada) and disposable Ag/AgCl surface electrodes (T3402M – Triode electrode; Thought Technology) (Fig. 1). Measurements were taken by the participant in the daily sleep environment after careful instruction. After the skin was cleaned with ethanol, bipolar electrodes were placed on the masseter muscle parallel to muscle fibers with a 20-mm inter-electrode distance. The EMG signals sampling frequency was 2,048 Hz. Participants were trained to place electrodes in the same positions with an instructional leaflet which included illustrations to explain the step-by-step procedure. Recording commenced after the participant’s skill in placing the electrodes was confirmed. At the beginning and end of measurements, participants were instructed to perform three sessions of maximum voluntary clenching lasting 2 seconds. The mean EMG activity of the first maximal clenching session was submitted for data analysis as the maximal voluntary contraction (MVC). The onset of sleep duration was defined as 20 min after the first maximal clenching session or when stable EMG signals were subsequently observed. The reliability of EMG data was verified by monitoring the raw signals. In cases where technical problems were reported or observed, additional instruction was given and extra recordings were made after baseline measurements.

Fig. 1 Disposable Ag/AgCl surface electrodes; T3402M – Triode electrode, Thought Technology

Experimental procedures

Participants wore the stabilization splint during sleep for 30 nights, and were instructed to record the masseter EMG activity for 2 consecutive nights at baseline, immediately after, and 1 and 4 weeks after wearing the splint (Fig. 2). At the first visit, participants were instructed on how to use the equipment, which they took home. The masseter EMG data were validated at the second visit (baseline). Any technical problems reported or observed were followed by appropriate instruction and additional documentation. This countermeasure was also implemented at visits at 0, 1 and 4 weeks. The data obtained at baseline (second night), immediately after (first night), 1 week after (first night) and 4 weeks after (first night) wearing the splint were submitted for data analysis. The purpose of the first night recoding at baseline was to allow the participant to become familiar with the portable electromyography device and sleeping environment; therefore, the first night data was discarded, and data from the second night were used as baseline. The first night data were used for other time-points. The data obtained from the second night were used if technical errors were observed in the first-night data.

Fig. 2 Study design

Participants wore a stabilization splint during sleep for 30 nights. EMG data were recorded for 2 consecutive nights at each time-point.

Data analysis

Data analysis was performed with the RMS data using a software program (Biograph Infiniti version 5.1.2, Thought Technology). To minimize the effect of recorded data artifacts on the results, all EMG data were carefully examined with unaided eyes, and the data in which the artifacts were recognized were then excluded.

The threshold of nocturnal masseter EMG events was set above 10% MVC. The algorithm for EMG analysis was based on the work of Lavigne et al. [23,24]. An EMG burst lasting longer than 0.25 s but less than 2.0 s was defined as a phasic burst, and one lasting longer than 2.0 s was defined as a tonic burst. When the interval of EMG bursts was less than 2.0 s, these bursts were regarded as one episode. An episode with more than three phasic bursts was classified as phasic. An episode with a tonic burst was classified as tonic. The episode with a combination of phasic and tonic bursts was classified as a mixed episode. Phasic and tonic bursts in these three types of episodes were submitted for analysis.

The mean duration of the burst (duration), the mean number of bursts per hour of sleep at night (frequency), and the geometric mean of maximum %MVC of the burst (level) were calculated for phasic bursts and tonic bursts.

All procedures except treatment were performed by one person, and blinding was maintained until completion of data analysis.

Statistical analysis

Mann-Whitney U test was performed to compare the parameters (duration, frequency, level) at baseline between phasic bursts and tonic bursts. The parameters for each time-point were compared using Friedman’s test Bonferroni correction. A value of P < 0.05 was considered statistically significant. All statistics were conducted using IBM SPSS Statistics 22 for Windows (IBM SPSS Statistics 22 for Windows; IBM Corp., Armonk NY, USA).

Results

All participants uneventfully completed the required measurements.

The mean nocturnal masseter EMG episodes per hour of sleep at baseline was 6.6 (4.4-11.7) times/h. For the severity assessment of sleep bruxism, the classification of Lavigne et al. and Romper et al. according to the frequency of episodes can be used. The participants in this study were widely distributed, from mild to severe.

The parameters at the baseline and the statistical results of the comparison between phasic and tonic bursts are shown in Table 1. The frequency of phasic bursts was significantly higher than that of tonic bursts (Mann-Whitney U test, P < 0.001) The duration and level (Mann-Whitney U test, P < 0.001) of phasic bursts were significantly lower than those of tonic bursts. Figure 3 shows the results of comparisons of the parameters at each time-point for phasic bursts and tonic bursts. The duration of tonic bursts revealed a significant decrease only at 1 week compared with the baseline (P = 0.013, Friedman’s test Bonferroni correction). The frequency of phasic bursts revealed a significant decrease at 0 and 1 weeks compared with the baseline (P < 0.01, Friedman’s test Bonferroni correction), and tonic bursts revealed a significant decrease at all time-points compared with the baseline (P = 0.042 [0 week], P = 0.048 [1 week], P = 0.037 [4 week], Friedman’s test Bonferroni correction). The level of phasic bursts revealed a significant decrease at only 0 week compared with the baseline (P = 0.013, Friedman’s test Bonferroni correction), and tonic bursts revealed a significant decrease at 1 week compared with the (P = 0.042, Friedman’s test Bonferroni correction).

Table 1 Parameters at baseline and comparison between phasic burst and tonic bursts

Phasic burst Tonic burst P-value
Duration (s) 0.67 (0.59-0.73) 3.66 (2.88-4.10) <0.001
Frequency (times/h) 24.95 (15.32-57.69) 3.93 (1.57-7.28) <0.001
Level (%MVC) 28.41 (25.39-35.24) 56.32 (40.23-73.85) <0.001

Values given are median (IQR); Mann-Whitney U test, n = 26

 

Fig. 3 Mean masseter electromyographic activity

a) Duration: the mean duration of the burst. b) Frequency: the mean number of bursts per hour of sleep at night. c) Level: the geometric mean of maximum %MVC of the burst. Error bar: one standard deviation. Friedman’s test Bonferroni correction, *P < 0.05; **P < 0.01; n = 26

Discussion

The diagnostic criteria for SB from the AASM [21] were used to select participants, and nocturnal masseter EMG activities were then confirmed by actual recordings in the previous study [1]. The mean number of nocturnal masseter EMG episodes at baseline for the 26 participants was 9.2 ± 8.2, with a range of 2.3-36.6 times/h, indicating that the degree of SB ranged from mild to severe based on the research diagnostic criteria for SB [23] and subsequent studies [7].

A portable EMG recording system was used to evaluate the effect of stabilization splints on nocturnal masseter EMG activities for a longer period with multiple measurements, as in previous studies [17,25,26]. Although possible countermeasures to avoid recording failure were implemented, some errors were anticipated. Hence, masseter EMG recordings were conducted for 2 consecutive nights at each time-point. If an error was observed in the data from 1 night, data from the other night were submitted for analysis. Accordingly, there were no missing values for masseter EMG data. A portable EMG measuring device was loaned to each participant so that the measurement could be conducted in a natural sleep environment. Measurements were conducted at home when the participants went to bed, so the influence of the sleep environment on the data was minimal [27].

The results from the present study indicated that stabilization splints decreased nocturnal masseter EMG activity when analyzed in the ‘burst’; that is, the stabilization splint reduced the frequency of phasic bursts immediately after wearing it, but the effect diminished after 1 week, whereas the magnitude of tonic bursts was reduced for a longer period (4 weeks). As a consequence, the null hypothesis that “there was no difference in the effect of stabilization splints on EMG bursts between phasic bursts and tonic bursts regarding masseter EMG activity” was rejected.

The frequency of phasic bursts decreased significantly in the short term after the insertion of the splint compared with the baseline. The short-lasting effect of the stabilization splint on nocturnal masseter EMG activity as reported in previous studies [17,25] was again confirmed in this study. Although central mechanisms are predominant [28], changes in the input from peripheral receptors might have had an effect, resulting in a temporary reduction of EMG activity [16,29,30].

Although the frequency and level of phasic bursts significantly decreased immediately after the insertion of the splint, no significant difference in the duration and level of tonic bursts was noted. These findings are in line with those of a previous study by Arima et al. [20]. The reason is unknown, but it is assumed that these findings are related to a difference in the mechanisms between phasic burst and tonic burst.

The present study revealed that the geometric mean magnitude of tonic bursts decreased significantly by wearing a stabilization splint. Moreover, the trend of the effect was recognized throughout the intervention period; that is, up to 4 weeks. A previous study reported that the ratio of tonic bursts to phasic bursts in SB was larger [31]. Therefore, wearing splints in patients with SB is considered to be effective. Although this study has limitations, the results are considered to be relevant because the reduction in tonic bursts reduces the risk of adverse effects on stomatognathic structures and prosthetic devices including dental implants. Wearing a stabilization splint has several effects, including increasing the vertical dimension of the occlusion, distributing occlusal forces, and changing sensory inputs from the stomatognathic system [8], but the exact mechanisms are uncertain at present. These effects could be partly due to a protection mechanism for stomatognathic structures in the form of an inhibitory reflex to masticatory muscles in response to mechanosensory inputs from the periodontal mechanoreceptors [32,33,34,35]. Tonic masticatory muscle contractions with a higher magnitude of activity might trigger an inhibitory reflex when a stabilization splint is worn, but this would not stop the activity completely. On the contrary, phasic bursts might not be strong enough to reach the threshold that triggers an inhibitory reflex, because the magnitude of tonic bursts was higher than those of phasic bursts.

The frequency of tonic burst showed significant differences among all of the time-points. Nevertheless, tonic bursts may not have a significant effect because their frequency values are significantly lower than those of phasic bursts.

The duration of phasic bursts showed no differences among the time-points. There was a difference in the duration of tonic bursts up to a week. These results suggest that wearing a stabilization splint does not have a long-term effect on the duration of nocturnal masseter EMG activity in patients suffering from sleep bruxism, and that the exact mechanism is also unknown.

This study demonstrated that stabilization splints reduce jaw-muscle activity during sleep in patients suffering from sleep bruxism by reducing the frequency of phasic bursts in the short term and reducing the magnitude of tonic bursts over a longer period. However, the results should be interpreted with caution, because it is not possible to explain how SB is affected by various peripheral impulses and sensory impact from periodontal membranes, muscle spindle, and oral tissue.

Abbreviations

AASM: American Academy of Sleep Medicine; DC/ TMD: diagnostic criteria for temporomandibular disorders; EMG: electromyographic; MVC: maximal voluntary contraction; RMS: root mean square; SB: sleep bruxism; TMD: temporomandibular disorders

Ethical Statements

This study was approved by the Ethical Committees for Observational Research of Kyushu University Hospital and Medical Institutions (No. 25084) and was conducted in accordance with the 1975 Declaration of Helsinki (revised 2013). Signed consent forms were obtained from all participants after all aspects of the study were fully explained.

Conflicts of Interest

The authors declare that they have no conflicts of interest to report. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. One of the authors (K.K.) belongs to the Division of Advanced Dental Devices and Therapeutics, Faculty of Dental Science, Kyushu University. This division is endowed by GC Corp, Tokyo, Japan. However, GC Corp did not play any role in this study and no funds from GC Corp were received as stated above.

Funding

This study was institutionally funded by the Section of Implant and Rehabilitative Dentistry, Division of Oral Rehabilitation, Faculty of Dental Science, Kyushu University, Fukuoka, Japan

Author Contributions

YO: recruitment, data collection, data analysis and writing - original draft, KO: data analysis and writing - original draft, YT: writing - review and editing curation, YA: writing - review, editing and supervision, KK: writing - review, editing and supervision. All authors have given final approval for this version to be published.

ORCID iD

1)YO: jinono0821@gmail.com, https://orcid.org/0009-0003-8111-5255

2)KO*: o-ki@dent.kyushu-u.ac.jp, https://orcid.org/0009-0006-7031-8462

3)YT: tsuki@dent.kyushu-u.ac.jp, https://orcid.org/0009-0009-9279-4621

1)YA: ayukawa@dent.kyushu-u.ac.jp, https://orcid.org/0000-0003-0039-716X

3)KK: koyano@dent.kyushu-u.ac.jp, https://orcid.org/0000-0001-7459-0101

Acknowledgments

The authors would like to thank the Department of Fixed Prosthetics, Kyushu University Hospital for their support.

Data Availability Statements

The experimental data obtained in this study are published in this article.


References
 
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