Otsuka et al.

Asian Pac J Dent 2019; 19: 45-50

Real time measurement of stress by electroencephalogram duringcontentious mouth opening
Ryoko Otsuka, DMD, PhD (1), Yoshiaki Nomura, DDS, PhD (1), Ayako Okada, DDS,
PhD (2), Masahide Uraguchi, DDS, PhD (1,3), Hisanori Tadokoro, DDS (4), Tetsuya
Nagai, DDS (5), Yoshihito Fujii, DDS (6), Masahiro Miura, DDS (7), Ryo Kawachi, DDS(4), Masashi Yamamoto, BCom (3), Taketoshi Wakana, BIC (8), and Nobuhiro Hanada,
DDS, PhD (1)(1) Department of Translational Research, (2) Department of Operative Dentistry, Tsurumi University
School of Dental Medicine, Yokohama, (3) Medical Group Seiwa, Tama, (4) Private Practice, Machida,(5) Private Practice, Tama, (6) Private Practice, Sagamihara, (7) Private Practice, Akishima, and (8)Futek Electronics Co., Ltd., Yokohama, Japan
Purpose: Dental treatment is a stressful event. The aim of this study was to evaluate the feasibility ofelectroencephalography (EEG) for the measurement of stress the stress of the patient’s ongoing dental treatment.
Materials and Methods: Real-time brain activity was measured for five healthy subjects (three males and two
females) under contentious opening mouth conditions and compared with the relaxed conditions for 18 minutes.
Brain activities were measured under the conditions that subjects were sited on the dental chair in horizontal
situation. Electroencephalograph (EEG) were used to measure the five type of brain waves: θ, α1, α2, α3, and β.
Results: In θ wave, α3 wave and β wave, widening gap between opening mouth condition and closing mouth
conditions were observed with over the time course. This tendency was confirmed by autoregressive moving
average (ARMA) model and mixed effect modeling. All of the coefficients of opening mouths were statisticallysignificant, when closing mouth used as reference. EEG may be useful tool to measure the stress during dental
treatment. Stress by sitting on dental chair in horizontal situation was depended on personality traits.
Conclusion: Contentious opening mouth may be stressful; however, the amount of stress may be small. Thechanges can be seen within 18 min. Prolonged chair time for the dental treatment may not be recommended.
(Asian Pac J Dent 2019; 19: 45-50.)
Key Words: dental treatment, electroencephalograph, stress

Introduction
Dental treatment is a stressful event. Multiple factors that induce anxiety were summarized in previous review
paper [1,2]: previous negative or traumatic experience, vicarious learning from anxious family members or peers,vulnerable position of lying back in a dental chair [3-5], sights of needles and air-turbine drills, sounds ofdrilling and screaming, the smell of eugenol and cut dentin, sensations of high-frequency vibrations in the dental
setting [6-8], fear of pain, blood-injury fears, lack of trust or fear of betrayal, fear of being ridiculed, fear of theunknown, fear of detached treatment by a dentist or a sense of depersonalization, fear of mercury poisoning, fearof radiation exposure, fear of choking and/or gagging, a sense of helplessness on the dental chair, and lack ofcontrol during dental treatment [1,9]. These are all negative images of dental treatment. These images induce
dental anxiety or phobia. The patients with dental anxiety or phobia refused the dental treatment. To recommend
the dental treatment for these patients, information about stress levels ongoing dental treatment is necessary.
However, there is little information about the stress levels of the patients. To measure the stress of the patient’s
ongoing dental treatment, non-invasive and real time monitoring system for measuring stress is necessary.
Electroencephalography (EEG) is an electrophysiological monitoring method to record electrical activity ofthe brain. It is typically noninvasive. EEG measures voltage fluctuations resulting from ionic current within theneurons of the brain [10]. In clinical contexts, EEG refers to the recording of the brain's spontaneous electricalactivity over a period of time [10]. EEG is generally used to diagnose epilepsy, sleep disorders, depth ofanesthesia, coma, encephalopathies, and brain death, tumors, and stroke [11,12]. It can applicable for the45

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Asian Pac J Dent 2019; 19: 45-50

response for visual, somatosensory, or auditory stimulus. Therefore, it can applicable for cognitive science,cognitive psychology, and psychophysiological research. Therefore, EEG may be feasibility to measure thestress of the patient’s ongoing dental treatment.
The aim of this study was to evaluate the feasibility of EEG for the measurement of stress the stress of thepatient’s ongoing dental treatment. To simplify this aim, this study evaluated the real-time brain activity bycontentious opening mouth conditions and compared with the relaxed conditions.

Materials and Methods
Subjects
Five healthy subjects were participated in this study. They were three males and two female, and their ages were45, 28, 40, 38, and 33, respectively. As study design was cross over design, brain activities were measured twice
for every subject. The order to measure the stress conditions were randomly allocated. This study was approvedby the Ethical Committee of Tsurumi University School of Dental Medicine (Approval Number: 1627). Written
approval was obtained from the institution where the study was carried out. The participants were informed
about the study, and written consent was obtained.
Stress measurement conditions
Brain activities were measured under the conditions that subjects were sited on the dental chair in horizontal
situation. The operators advised the subjects to be relax and eyes should be closed. For the opening mouth
conditions, Multiple Mouth Opener (Takasago Medical Industry Co., Ltd., Tokyo, Japan) were set in the rightmolar and opening distance were set as 4 mm. For the closing mouth conditions, operators advised the subjects
to close the mouth. Brain activities were measured by Brain Pro FM-929 (Futek Electronics Co., Ltd.,
Yokohama, Japan). Sensor bands (2 electrodes) were attached to the forehead, and electroencephalograms wererecorded for 3 min through ear grounding [13-15].
Stress measurement
Electroencephalograph (EEG) were used to measure the five type of brain waves: θ, α1, α2, α3, and β. These fivebrain waves are denoted that: θ, 4-6 Hz, idling, sleepy [16,17]; α1, 7-8 Hz, relax [18]; α2, 9-11 Hz, relax andconcentrated [18], α3, 12-13 Hz, drowsy [18]; β, 14-23 Hz, active thinking, focus, high alert, anxious so-called
stress wave [19,20]. These five were recorded every second. It is generally known that observed values of brain
waves varies between subjects, data is commonly expressed as the percentage of each waves. In this study, data
were expressed by the percentage of each wave in the total of five waves.
Statistical analysis
Data of recorded brain wave every second were transformed into moving average for 3 min. Time series analysis
were carried out to construct autoregressive moving average (ARMA) model. As the recorded data were nested
in subjects, and time, mixed effect modeling was carried out to find out the effect of stress under opening mouth.
Then, average value of every 3 min of five waves described above was used for the outcome variable. These
analyses were carried out by IBM SPSS Statistics ver 24.0 (IBM, Tokyo, Japan).

Results
Five brain waves obtained by the average five subjects were graphically illustrated in Fig. 1. Red line denoted
opening mouth and blue line denoted closing mouth conditions. Solid line denoted the observed values of 346

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Asian Pac J Dent 2019; 19: 45-50

minutes’ moving average of each brain wave. In θ wave, α3 wave, and β wave, widening gap between opening
mouth condition and closing mouth conditions were observed with over the time course.

A

B

C

D

Fig. 1
Transition of brain waves obtained by the average of fivesubjects
Three minutes’ moving average of each brain wave wasillustrated.
A, θ wave; B, α1 wave; C, α2 wave; D, α3 wave; E, β wave
Red line denoted opening mouth and blue line denoted
closing mouth.
In θ wave, α3 wave, and β wave, the difference of thewidening gap between opening mouth condition andclosing mouth conditions with over the time course
Solid line, observed values; Brake line: predictive values;
Dot line: confidence intervals of predictive values

E

These time series data were applied for the time series analysis model to calculate the predictive values of thetransition of brain waves. Autoregressive moving average (ARMA) model, which consisted of the combinationof autoregressive and moving average, was applied in this study. The results of the fitness index were shown in
Table 1. All of the data were significantly fitted for the models, and the p-values were all less than 0.01.
Predictive values by the results of ARMA models were overwritten on Fig. 1. Broken lines and dot lines denoted
the predictive values and their upper and lower limit of the confidence intervals. Predictive values were also
indicated that widening gap between opening mouth condition and closing mouth conditions were observed withover the time course in θ wave, α3 wave, and β wave.

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Table 1 Estimated parameters and fitness indexes for the transition of brain waves byautoregressive moving average model (ARMA model)
Model fit
SRSquareParameter of ARMA modelParameter
Estimate
SD
Intercept
0.08
0.001
Close
0.573
<0.001Time
3.50×10-5
1.17×10-6
θIntercept
0.09
0.001
Open
0.891
<0.001Time
1.90×10-4
2.64×10-6
Intercept
0.15
0.001
Close
0.283
<0.001Time−1.90×10-5
1.15×10-6α1Intercept
0.15
0.001
Open
0.27
<0.001Time−2.40×10-5
1.52×10-6
Intercept
0.3
0.001
Close
0.95
<0.001Time−1.30×10-4
1.13×10-6α2Intercept
0.24
0.001
Open
0.371
<0.001Time−4.70×10-5
2.41×10-6
Intercept
0.2
0.001
Close
0.27
<0.001Time−1.60×10-5
9.99×10-7α3Intercept
0.19
0
Open
0.889
<0.001Time
4.80×10-5
6.66×10-7
Intercept
0.31
0.001
Close
0.641
<0.001-5
Time−6.10×10
1.78×10-6βIntercept
0.3
0.001
Open
0.069
<0.001Time
1.60×10-5
2.26×10-6
Data were significantly fitted for the models, and all p-values were less than 0.01.
p-valuep-value<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001

Table 2 Results of mixed effect modeling
Fixed effect model
Random effect model
Coefficient
95% CI
p-value Coefficient
95% CI
p-value
Intercept
0.15
0.143 - 0.156<0.001 0.15
0.066 - 0.233
0.008
θ Opening mouth −0.087−0.012<0.001 −0.087−0.008<0.001Time
1.0×10-4
1.0×10-4 -1.0×10-4<0.001 1.0×10-4−2.0×10-4 - 4.0×10-4 0.359
Intercept
0.142
0.138 - 0.146<0.001 0.142
0.031 - 0.253
0.024
α1 Opening mouth 0.002−0.0080.329
0.002
0.001 - 0.003<0.001Time−2.0×10-5−3.0×10-5 - −1.0×10-4<0.001 −2.0×10-5−9.0×10-5 - 4.0×10-5 0.419
Intercept
0.245
0.241 -0.249<0.001 0.245
0.207 - 0.283<0.001
α2 Opening mouth 0.015
0.012 -0.019<0.001 0.015
0.013 - 0.018<0.001Time−9.0×10-5−1.0×10-4 - −8.0×10-5<0.001 −9.0×10-5−2.0×10-4 - 5.0×10-5 0.155
Intercept
0.205
0.202 - 0.208<0.001 0.205
0.156 - 0.254<0.001
α3 Opening mouth −0.017−0.006<0.001 −0.017−0.003<0.001
-5
-6
-5
-5
-5
-4
Time
2.0×109.0×10 - 2.0×10<0.001 2.0×10−9.0×10 - 1.0×10
0.68Intercept
0.314
0.308 - 0.320<0.001 0.314
0.145 - 0.483
0.007
β Opening mouth −0.024−0.01<0.001 −0.024−0.004<0.001Time−2.0×10-5−4.0×10-5 - −9.0×10-6
0.001−2.0×10-5−2.0×10-4 - 1.0×10-4 0.648
For opening mouth, closing mouth was used as reference. The coefficients of brain waves were statistically significant.

The results described above were depended on time series analysis. By the time series analysis, factors that
affected on the transitions could not be statistically evaluated. Therefore, multilevel modeling was applied to
calculate the effect of opening mouth for the transitions of brain waves. The results were shown in Table 2. For
fixed effect models, coefficients of opening mouth of all of the brain waves were statistically significant. Then,random effect models were constructed by using time for random variable. The coefficients of opening mouth of
all of the brain waves were also statistically significant.

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Discussion
In this study, opening mouth clearly affected the brain waves. Dental anxiety and phobia are a frequently
encountered problem in dental offices. These patients need to be identified and their concerns should be
addressed. The etiologies of dental anxiety and phobia are consisted of multiple factors: previous negative
traumatic experience or lack of understanding, and the vulnerable position of lying back in a dental chair etc.
[1-6]. Stress during the dental treatment can be the trigger of dental anxiety or phobia, the stress under the dental
treatment should be minimized. The objective assessment of stress has been developed. Blood pressure, pulse
rate, pulse oximetry, finger temperature, and galvanic skin response can greatly enhance the diagnosis andenable categorization of these individuals as mildly, moderately, or highly anxious or dental phobic [1,21].
These devices take advantage of measuring the subtle changes vital reactions. Among them, galvanic skin
response has been validated as an accurate method in measuring dental anxiety. In addition to these devices,Electroencephalography (EEG) are also available to measure the stress [22-24]. The advantage of EEG is that it
can measure and monitor real time changes of the stress during dental treatment. And it can measure
simultaneously stress and relaxation.
As shown in Fig. 1, α1 and α2 waves, which denote the relaxation status, were decrease in accordance with thelaps of time when compared with the baseline. However, ranges of changes of these waves were small. For θ
wave, which also denote the relax conditions, changes of opening mouth conditions were almost stable. In
contrast, changes of closing mouth condition were clearly increased. These results indicated that sitting on dental
chair in horizontal situation were not so stressful. Previous report had shown that the vulnerable position of lying
back in a dental chair was the etiology of dental anxiety [3]. The difference of the results may derive frompersonality traits. For α3 and β wave, even the ranges of changes were small, the difference between opening
mouth conditions and closing mouth conditions were clear. In addition to these graphical analyses, these results
were confirmed by statistical modeling. All of the coefficients were statistically significant. Therefore,
contentious opening mouth may be stressful, however, the amount of stress may be small.
Electroencephalography (EEG) may be useful tool to measure the stress during dental treatment. Stress by
sitting on dental chair in horizontal situation was depended on personality traits. Contentious opening mouth
may be stressful; however, the amount of stress may be small. The changes can be seen within 18 min.
Prolonged chair time for the dental treatment may not be recommended.
Acknowledgment
This study was supported by JSPS KAKENHI Grant Numbers 17K12030.
Conflict of Interest
The authors declare no conflict of interest exists.

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Correspondence to:
Dr. Yoshiaki Nomura
Department of Translational Research, Tsurumi University School of Dental Medicine,
2-1-3, Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan
Fax: +81-45-573-2473 E-mail: nomura-y@tsurumi-u.ac.jp
Accepted April 19, 2019.
Copyright ©2019 by the Asian Pacific Journal of Dentistry.
Online ISSN 2185-3487, Print ISSN 2185-3479

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