Determination of Applicable Multiple Thresholds of EMGBiofeedback Training for Daytime Clenching Behavior

Akira WATANABE1, Masanori FUJISAWA1§, Tomoaki IIZUKA1,Masayuki SATO1, Naoki IWASE1, Kiyotaka KANEMURA2,

Norimasa TANABE2 and Kanji ISHIBASHI2

1Division of Fixed Prosthodontics, Department of Restorative & Biomaterials Sciences, Meikai University School of Dentistry,2Division of Fixed Prosthodontics, Department of Prosthodontics, School of Dentistry, Iwate Medical University

Abstract

Purpose : Although a daytime clenching is thought to be one of the oral parafunctions that leads to dental problems, a treatment

strategy has not yet been devised. Electromyogram (EMG) biofeedback training thresholds were determined to ascertain effective

regulation of daytime clenching behavior.

Materials and Methods : Twenty subjects (10 males and 10 females ; mean age, 30.9±5.6 years) who had mild to moderate

masseter muscle pain with daytime clenching behavior were recruited. Subjects were fitted with a hearing-aid-shaped EMG record-

ing and biofeedback apparatus, which was used to continuously record EMG data from the temporal muscle on the side of habitual

mastication under natural conditions for five hours. Recorded EMG data were analyzed to pick up clenching events by EMG

thresholds that combined activity (10, 20, and 30% of maximum voluntary contraction ; MVC) and duration (1−9 seconds).

Results : Eighteen of the 20 subjects exhibited two effective thresholds, while two subjects had only a single effective threshold.

None of the subjects demonstrated more than two effective thresholds. Clenching events that could not be detected by the primary

threshold but were detected by the secondary threshold comprised 25.8%.

Conclusion : Within the limitations of this study design, multiple thresholds of EMG biofeedback for daytime clenching were ef-

fective in reducing parafunctional oral habit. Further research is needed to confirm an enduring effect.

Key words : bruxism, oral parafunctions, temporomandibular disorders

日中のクレンチング習癖者に対する咀嚼筋筋電図バイオフィードバック訓練の複数閾値の適用に関する検討

渡邉 明1 藤澤 政紀1§ 飯塚 知明1 佐藤 雅介1

岩瀬 直樹1 金村 清孝2 田邉 憲昌2 石橋 寛二2

1明海大学歯学部機能保存回復学講座歯科補綴学分野2岩手医科大学歯学部歯科補綴学講座冠橋義歯補綴学分野

要旨目的：日中クレンチングの抑制を目的とした咀嚼筋筋電図バイオフィードバック（EMG-BF）訓練を，より効果的なものとするため，訓練閾値を複数設定することの妥当性について検討した．方法：日中のクレンチングを自覚し，咀嚼筋痛を有するクレンチング習癖者 20名（女性 10名，男性 10名，30.9±5.6

歳）を被験者とした．EMG は側頭筋前部筋束より導出し，昼食を含む 5時間の EMG 記録を行った．解析ソフト上で筋活動量（10％，20％，30％ MVC）と筋活動持続時間（1～9 sec）を組み合わせた閾値を設定し，クレンチングなどの非機能運動時にのみ検出する訓練閾値およびイベント数について検討した．

明海歯学（J Meikai Dent Med）41（1）, 1−5, 2012 1

Introduction

Bruxism as one of the undesirable oral parafunc-tions is considered to lead to dental problems such astemporomandibular disorders (TMD), tooth attrition,abfraction, broken and cracked teeth, gingival reces-sion, sensitive teeth, occlusal trauma, and limitationsfor dental implants1−4). While nocturnal bruxism hasbeen focused on, daytime clenching, even weak con-traction, is also recognized as a contributing factor toTMD. Electromyogram (EMG) biofeedback duringboth diurnal and nocturnal bruxism would be useful toregulate excessive muscle activity5, 6). To regulate un-conscious bruxism, some devices have been used dur-ing sleep7−9), with favorable results. From a practicalperspective, it is easier for patients to recognize theEMG biofeedback signal when they are awake ratherthan asleep. We have developed a portable EMG re-cording and biofeedback system10) which is muchsmaller (width : 21 mm, height : 64 mm, thickness :12.5 mm) than the devices reported previously11, 12) and,therefore, is less noticeable during ambulatory record-ing under natural daily-life circumstances. Further-more, EMG biofeedback training as a reminder ofdaytime clenching reduced parafunctional behavior,even through no feedback signal was provided aftertwo consecutive training days10).

In a previous study10), a fixed single threshold wasapplied for training sessions only to remind of clench-ing events without interruption of functional mandibu-lar movement such as eating, speaking, and laughing.To provide more effective ways of providing feedback

signals, multiple thresholds were determined for day-time clenching regulation.

Materials and Methods

SubjectsTwenty subjects (10 males, 10 females ; mean age :

30.9±6.8 years) with masticatory muscle pain wererecruited. Inclusion criteria were : age between 20 and35 years, awareness of pain or stiffness in the mastica-tory muscles, and subjective awareness of daytimeteeth clenching. Furthermore, two or more items de-scribed below were required : tooth indentation insidethe cheek and/or on the tongue, masticatory musclehypertrophy, bone torus, jaw opening range less than40 mm between upper and lower incisal edges, or ten-derness of the masticatory muscles on palpation, mild-moderate pain intensity (2−4 out of 10 in NumericalRating Scale). Exclusion criteria were : wearing a re-movable partial denture, lack of any occlusal support-ing zone due to teeth loss in the molar region, currentuse of muscle relaxants or anti-inflammatory medi-cine, or advanced periodontal disease and psychiatricor neurologic disorders.

This research was approved by the Human ResearchEthics Committee of Iwate Medical University DentalSchool, and a signed informed consent form was ob-tained from each subject after they had received a de-tailed explanation of the research protocol.

EMG recordingA hearing-aid-shaped EMG recording apparatus withauditory biofeedback system was placed behind theear of each subject (Fig 1). This portable device wascomposed of three components－an electromyographyunit, a data-logger, and an auditory feedback unit.

結果：被験者 20名中 18名に於いて効果的な第二閾値まで設定可能であったのに対し，2名では第一閾値のみ設定可能であった．また，3個以上設定可能な被験者はいなかった．第一閾値で検出されず，第二閾値でのみ検出されたイベントの割合は，検出されたイベント総数の 25.8％であった．考察：今回の限られた条件の中ではあるが，日中のクレンチングに対する EMG-BF 訓練時に訓練閾値を複数設定することは，口腔悪習癖を減少させるのに効果的であると考えられた．

索引用語：ブラキシズム，口腔パラファンクション，顎機能障害（顎関節症）

─────────────────────────────§Correspondence : Masanori Fujisawa, Division of Fixed Prosthodon-

tics, Meikai University School of Dentistry, 1-1 Keyakidai, Sakado,Saitama 350-0283, Japan

2 WATANABE A, FUJISAWA M, IIZUKA T, et al J Meikai Dent Med 41, 2012

EMGs were recorded from the anterior part of thetemporal muscle on the habitual side of masticationunder natural conditions, continuously for five hours,including lunchtime. Subjects were instructed to be-have normally, with the exception of washing theirfaces, avoid touching the electrode unit or cable inten-sively, and avoid any actions that might create unde-sirable noise interference of the EMG signals. To cali-brate the EMG signal levels, a maximum voluntarycontraction (100% MVC) lasting 3 seconds was re-peated three times with a 30-second interval betweenthe tasks both at the beginning and end of the dailyrecording period.

Data analysis procedureThe fully rectified EMG data were transformed into

root mean square values with a sampling rate of 4 Hz.Voice recording (Memory Recorder DMR-1800 S,Toshiba, Tokyo, Japan) and a self-administered chartwere used to identify the parafunctional activities cor-responding to the EMG signals. The voice recordingdevice and self-administered chart did not aim tocheck all the parafunctional activities, merely help dis-criminate functional (talking, eating lunch) from para-functional activities. The threshold which discrimi-nated parafunctional mandibular movements such asclenching or grinding from the functional ones (Fig 2)such as eating, speaking, and laughing was calculated.The proper threshold for each subject was assignedusing a combination of the intensity and duration ofeach EMG activity (Fig 3). Those thresholds wouldalert to parafunctional mandibular movements withoutdisturbing functional mandibular movements, where

by 27 recording points including combinations of du-rations (1～9 seconds) and intensities (10, 20, and30% MVC) are set (Fig 4). The threshold which does

Fig 1 The portable EMG recording and biofeedback system.Left panel : at completion of the apparatus set-up. Right panel :the apparatus is covered by the subject’s hair.

Fig 2 An example of a fully rectified EMG signal of functional(left arrow) and parafunctional (right arrow) events.

Fig 3 Schematic configuration of a valid threshold. A 2-secondor longer duration with 10% MVC allows the differentiation ofevents because the duration of the functional and parafunctionalmovement EMG waveforms crossing the break line (10% MVC)was 1 and 5 seconds, respectively.

Fig 4 The number of functional and parafunctional events ofvarious durations detected on the EMG exceeding 10, 20, and30% of the maximum voluntary contraction (MVC) in Subject 1.

Applicable Multiple Thresholds of EMG-BF 3

not detect an event at the time of functional activities,but detects an event only at the time of parafunctionalactivities, was determined. In the threshold valuewhich fulfills this condition, that with the highest de-tection rate of events was set up as the primarythreshold. Moreover, in addition to the primary thresh-old, the thresholds which fulfill the conditions de-scribed above were then set as the secondary and sub-ordinate (Fig 5).

Finally, the possible rate of eligible subordinatethresholds were determined.

Results

The effective primary thresholds were assigned forall of the 20 subjects. Eighteen of the 20 subjects ex-hibited the secondary eligible threshold, while the sub-ordinate threshold was not applicable for the remain-ing two subjects. The third threshold, however, wasnot applicable to any subjects (Fig 6).

Although 18 subjects had two different combina-tions of thresholds, all the events were completelyidentical in 13 subjects (Fig 7).

Total numbers of clenching events determined byprimary and secondary thresholds were 23 and 13, re-spectively, in the remaining five subjects who exhib-ited two different effective thresholds to pick up dis-tinct events. However, five events were found to beidentical. Taking these five events into account, thesecondary threshold comprised 25.8% clenchingevents in those five subjects (Fig 8).

Discussion

In recent dental practice, new strategies have beendeveloped to expand the dental treatment options,such as dental implants and all-ceramic restorations.On the other hand, bruxism inhibits such promisingdental practice. Moreover, oral parafunction plays animportant role as a contributing factor to TMD. SinceTMD patients with masticatory muscle pain habitually

Fig 6 Number of subjects who exhibited primary and subordi-nate thresholds.

Fig 5 An example of a different event picked up with twothresholds.

Fig 7 Detailed description of the detected events with the secon-dary threshold.

Fig 8 Detailed description of the clenching events in the fivesubjects who had different thresholds to pick up distinctiveevents.

4 WATANABE A, FUJISAWA M, IIZUKA T, et al J Meikai Dent Med 41, 2012

keep their teeth in contact to some extent13−15), cogni-tive biobehavioral therapy could be expected to be asuitable strategy for pain management.

EMG biofeedback training is expected to help re-duce overload to stomatognathic components includingthe tooth structure, which could lead to the idea notonly to treat TMD, but also to enhance the indicationsof dental implants and all-ceramic restorations.

Our previous report10) showed EMG biofeedbacktraining with an effective single threshold on two con-secutive days decreased daytime clenching. Further-more, a long- lasting learned effect was also found insome cases16).

In this study, multiple effective thresholds were de-termined in the same subjects as in the previous re-port. Five subjects exhibited two different thresholdsto pick up distinctive clenching events, leading to adetection rate of 25.8%. On the other hand, using thesecondary threshold made it difficult to detect extraparafunctional events in 75% of them. In this study,multiple thresholds would work better in some sub-jects ; however, it is difficult to confirm what is anintrinsic factor for those who showed effective results.Since this study was designed to determine the ration-ale of using multiple thresholds of EMG biofeedbackfor clenching patients, a practical study is needed inthe following step. The stress level and other physi-ological parameters also need to be recorded simulta-neously in the future.

Conclusion

Within the limitations of this study design, multiplethresholds of EMG biofeedback for daytime clenchingcould be effective in reducing parafunctional oralhabit. Further research is needed to confirm an endur-ing effect.

This research was supported by Grant-in-Aid for ScientificResearch (No.16390561, No. 20592276 and No.23390447)from the Japan Society for the Promotion of Science, and Miy-ata Research Grant-in-Aid (A) 2010.

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(Received November 4, 2011 ; Accepted December 2, 2011)

Applicable Multiple Thresholds of EMG-BF 5