Original article

The influence of vertical dimension of occlusionchanges on the electroencephalograms of completedenture wearers

Risa Matsuda DMD*, Yoshikazu Yoneyama DMD, PhD,Masakazu Morokuma DMD, PhD, Chikahiro Ohkubo DMD, PhD

Department of Removable Prosthodontics, Tsurumi University of Dental Medicine, 2-1-3 Tsurumi, Tsurumi-ku,

Yokohama, Kanagawa 230-8501, Japan

j o u r n a l o f p r o s t h o d o n t i c r e s e a r c h 5 8 ( 2 0 1 4 ) 1 2 1 – 1 2 6

a r t i c l e i n f o

Article history:

Received 14 November 2013

Received in revised form

21 January 2014

Accepted 25 January 2014

Available online 16 April 2014

Keywords:

Vertical dimension of occlusion

Complete denture

Edentulous

Electroencephalogram

a b s t r a c t

Purpose: The present study was conducted to identify how changes in the vertical dimen-

sion of occlusion (VDO) affect the sensory perception and activity of the brain in complete

denture wearers using an electroencephalogram (EEG).

Methods: Subjects were 21 individuals wearing complete dentures who regularly visited the

Division of Prosthodontics at Tsurumi University Dental Hospital for checkups (12 males

and 9 females, average age: 76.6). Based on their original dentures, two duplicate dentures

with different VDO (�3 mm and +5 mm) were fabricated. EEG activity and occlusal force

were measured before and after gum chewing with each denture in all subjects. Negative

indicator scores for psychological conditions and stable neuronal activity (Da) were calcu-

lated using EEG data. Statistical analysis was performed using the Wilcoxon test to compare

changes in the sensory perception, activity of the brain, and occlusal force (a = 0.05).

Results: After gum chewing with the +5-mm denture, a significant increase was observed in

the negative indicator score ( p < 0.05). No significant difference was found in the Da values

before and after gum chewing with any of the dentures ( p > 0.05). A significant decrease was

observed in the occlusal force between the original denture and the �3-mm denture

( p < 0.05).

Conclusion: Psychological condition and occlusal force were influenced by immediate

changes in the VDO of the complete denture.

# 2014 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.

Available online at www.sciencedirect.com

ScienceDirect

journal homepage: www.elsevier.com/locate/jpor

1. Introduction

Long-term use of a complete denture can result in jaw

displacement due to abrasion of the artificial teeth. This can

not only lead to aesthetic impairment but can also cause

* Corresponding author. Tel.: +81 45 580 8421; fax: +81 45 573 9599.E-mail address: matsuda-risa@tsurumi-u.ac.jp (R. Matsuda).

1883-1958/$ – see front matter # 2014 Japan Prosthodontic Society. Phttp://dx.doi.org/10.1016/j.jpor.2014.01.003

reduced masticatory performance and create abnormal

stresses during chewing and biting. The vertical dimension

of occlusion (VDO) affects the occlusal force, which may

influence the stimulation of the central nervous system via

the trigeminal nerve [1]. Also, previous studies have shown

that occlusal disharmony caused by reduced masticatory

ublished by Elsevier Ireland. All rights reserved.

Table 1 – Subjects’ characteristics.

No. Age Gender Type of denture base Type of artificial teeth Duration of denture use Occlusal force (N)

Original �3 mm +5 mm

1 76 M Resin Hard resin 2 M 311 307 416

2 80 M Metal Hard resin 6 Y 7 M 224 230 273

3 77 F Metal Hard resin 6 Y 5 M 154 171 255

4 85 F Resin Hard resin 9 Y 7 M 119 102 427

5 76 M Resin Hard resin 1 Y 7 M 305 286 334

6 84 F Metal Metal 4 Y 11 M 368 225 249

7 84 M Resin Hard resin 2 M 299 191 135

8 83 F Metal Metal (upper)

Hard resin (lower)

5 Y 174 161 216

9 86 F Metal Metal (upper)

Hard resin (lower)

12 Y 177 116 144

10 70 M Resin Hard resin 2 M 299 134 253

11 76 F Resin Hard resin 1 Y 9 M 88 90 97

12 84 F Resin Hard resin 2 M 197 200 267

13 67 M Resin Hard resin 3 Y 4 M 480 467 348

14 83 M Resin Hard resin 2 M 221 106 332

15 69 F Resin Hard resin 7 Y 469 276 493

16 67 M Resin Hard resin 16 Y 230 357 667

17 76 M Resin Hard resin 5 M 338 227 193

18 67 M Resin Hard resin 7 Y 69 126 153

19 58 M Resin Hard resin 6 M 172 220 225

20 82 M Resin Hard resin 1 Y 3 M 465 358 671

21 66 F Metal Hard resin 4 M 208 121 242

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performance produces chronic stress, which, if prolonged, can

cause a decrease in learning ability [2]. Animal experiments

have shown that changes in the VDO or presence of occlusal

interference can cause changes in the serum corticosterone

levels as well as an increase in the amount of dopamine

released into the brain. Indeed, previous research has shown

that occlusal interference and occlusal disharmony can cause

stress on higher brain functions as well as on the whole body,

and that occlusal disharmony can have a serious effect on the

immune system and the nervous system [3].

Rhythmic masticatory muscle activity is coordinated by

voluntary as well as reflexive control exerted by the upper

central nervous system, including the motor area of the

cerebral cortex and the hypothalamic-amygdala pathway, as

well as by the reflex arc whose central connections are located

in the midbrain, the pons, the medulla oblongata, and the

upper cervical segments of the spinal cord [4]. In addition to

receiving input from the upper central nervous system, the

masticatory function processes peripheral sensory feedback

from the teeth, jaws, masticatory muscles, and temporoman-

dibular joints, whereas the central nervous system issues

motor commands to muscles. The act of mastication is known

to promote and maintain certain cognitive functions such as

learning and memory [5]. Previous research has demonstrated

that loss of the periodontal membrane due to the loss of teeth

causes decreased stimulation to the hippocampus, which

increases the risk of Alzheimer’s disease [6]. According to a

previous animal experiment, a partial loss of trigeminal

mesencephalic neurons regulating periodontal mechanore-

ceptors occurs in guinea pigs that had had their teeth

removed, which triggers remodeling of the central neural

circuits that control masticatory muscle activity [7,8].

However, there is no existing evidence as to how changes

in the VDO can affect the sensory perception and activity of

the brain in complete denture wearers. In view of this, the

present study was conducted to discover how changes in

the VDO affect the sensory perception and activity of the

brain as measured by an electroencephalogram (EEG) in

patients with complete dentures. Occlusal force was also

measured because it also has the potential to affect brain

activity.

2. Materials and methods

2.1. Subjects

Subjects were 21 individuals wearing maxillary and man-

dibular complete dentures who regularly visited the Division

of Prosthodontics at Tsurumi University Dental Hospital

for checkups (12 males and 9 females, aged 58–86 years

with the average age being 76.6 � 7.8 years) (Table 1). There

was wide variation in the duration of denture use, but all of

the dentures had been maintained by prosthodontic spe-

cialists. Severe abrasion of the artificial teeth was never

observed, and the VDO of all the dentures was appropriate.

No subjects had histories of brain disease, such as cerebral

infarction, or had been diagnosed with dementia, such as

Alzheimer’s disease. All subjects were fully informed of and

consented to the research methods, which had been

approved by the ethics committee of Tsurumi University

School of Dental Medicine (approval number: 305, August

31, 2005).

2.2. Fabrication of duplicate dentures

To observe the brain response to the alteration of the vertical

dimension of occlusion, the 2 types of duplicate dentures for

Fig. 1 – EEG measurements were performed while the

subjects were seated in a resting position with their eyes

closed.

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each subject were fabricated. To fabricate the duplicate

dentures, an impression of the original denture was taken

using a silicon impression material. Autopolymerized

denture base resin (PalaXpress, Heraeus Kulzer, Germany)

was then poured into the impression according to the

manufacturer’s instructions, and was then pressurized to 2

atmospheres at 608 for 30 min. Each subject was asked to try

on the duplicate dentures for adjustments. Because we had

to ensure that the duplicate dentures used in the present

study were identical in all aspects except for the VDO, we

used a semi-adjustable articulator (Pro Arch IIIEG, SHOFU,

Kyoto) with a face-bow transfer to recreate a 3-dimensional

orientation of the maxillary dental arch relative to a

subject’s skull. The occlusion of contact balance of the

duplicate denture was adjusted according to Nakazawa’s

measurements [9]. Two types of duplicate dentures were

fabricated with different VDO: a denture adjusted to occlude

with the incisal guide pin lowered by 3 mm (hereafter the

�3-mm denture) and a denture adjusted to occlude with the

incisal guide pin raised by 5 mm (hereafter the +5-mm

denture).

2.3. Measurement procedure

An EEG measured each subject at rest for 3 min so that the

measurement could be performed under stable conditions

(Fig. 1). With each subject, an EEG was performed for 3 min

immediately before and after a minute of chewing gum

(Xylitol, Lotte, Tokyo, Japan) wearing three types of dentures.

Our setting of EEG measurement is as follows:

- EEG A: EEG obtained before gum chewing with the subject

wearing the original denture

- EEG B: EEG obtained after gum chewing with the subject

wearing the original denture

- EEG C: EEG obtained before gum chewing with the subject

wearing �3-mm denture

- EEG D: EEG obtained after gum chewing with the subject

wearing �3-mm denture

- EEG E: EEG obtained before gum chewing with the subject

wearing +5-mm denture

- EEG F: EEG obtained after gum chewing with the subject

wearing +5-mm denture

A 30-min interval (30-min break) was allowed between

measurements with different dentures because a preliminary

study showed the effect of stimulation fades in 30 min.

Measurement of the occlusal force with each denture was

performed after the EEG recording to prevent the effects of

biting on the EEG readings (Fig. 2).

2.4. EEG recording

EEG measurements were performed inside a semi-anechoic

room using ESA-pro (Brain Functions Laboratory Inc., Kana-

gawa, Japan), with each subject wearing a helmet with

pasteless electrodes (Brain Functions Laboratory Inc.)

mounted on it, in accordance with the previous study [10].

2.4.1. ESAM analysisThe Emotion Spectrum Analysis Method (ESAM) was per-

formed to quantify changes in a subject’s psychological

condition over time based on the phase positions of brain

wave frequencies relative to one another. EEG measurement

bands were narrowed down from 5 Hz to 20 Hz. They were

divided into three frequency bands of 5–8 Hz (u wave), 8–13 Hz

(a wave), and 13–20 Hz (b wave). ESAM analysis was calculated

in the theta, alpha, and beta frequency bands every 5.12 s,

from which the four emotional states (i.e., stress, depression,

joy, and relaxation) were separated and their levels evaluated.

In the present study, a negative indicator score was calculated

to estimate the emotional change. The higher the negative

indicator score, the greater the discomfort [11].

2.4.2. DIMENSION analysisThe recorded EEG data was stored in a dedicated personal

computer, which was then transferred to the Electroencepha-

logram Analysis Center of Brain Functions Laboratory Inc.,

where the Diagnosis Method of Neuronal Dysfunction (DI-

MENSION) was performed. DIMENSION analysis quantitative-

ly estimates synaptic/neuronal dysfunction based on the

smoothness of the EEG frequency distribution. In general,

when neuronal activity in the cerebral cortex is stable, the

scalp potentials are distributed smoothly from high to low. In

DIMENSION analysis, an ideal potential distribution of an a

wave, which indicates stable neuronal activity, is defined as

Da = 1. The Da value decreases as cognitive function of the

brain deteriorates [12].

Fig. 2 – Flowchart of measurement.

Fig. 3 – Comparison of the negative indicator score before

and after gum chewing (n = 21).

Fig. 4 – Comparison of brain function index before and after

gum chewing (n = 21).

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2.5. Occlusal force

The occlusal forces of each subject were measured using an

Occluzer 709 (GC Corporation, Tokyo, Japan) and Dental Prescale

(without wax) (GC Corporation, Tokyo, Japan). The Frankfurt

plane of the subject’s head was first aligned parallel to the floor.

The operator pulled the subject’s lips away from the teeth and

had the subject bite down to check whether the subject could bite

with ease. The subject was subsequently instructed to bite as

hard as possible in central occlusion for 3 s [13].

2.6. Statistical analysis

Statistical analysis was performed using the Wilcoxon test

(SPSS software version 17.0J, SPSS Inc., Tokyo, Japan) to

evaluate changes in the sensory perception and activity of the

brain before and after gum chewing with the original denture,

the �3-mm denture, and the +5-mm denture (a = 0.05). The

occlusal forces of the �3-mm denture and the +5-mm denture

were compared to the original denture using the Wilcoxon test

(a = 0.05).

3. Results

3.1. ESAM analysis

Sensory evaluation revealed no significant difference in the

negative indicator score before and after gum chewing with

the original denture and the �3-mm denture ( p > 0.05, EEG A

and EEG B: p = 0.848; EEG C and EEG D: p = 0.063). After gum

chewing with the +5-mm denture (EEG E and EEG F), a

significant increase was observed in the negative indicator

score ( p < 0.05, p = 0.009) (Fig. 3).

3.2. DIMENSION analysis

The Da values of 11 subjects were confirmed at the baseline to

be lower than 0.952, which means the subject possibly

suffered from Alzheimer’s dementia [14]. No significant

difference was found in the Da values before and after gum

chewing with any of the dentures (EEG A and EEG B: p = 0.835;

EEG C and EEG D: p = 0.509; EEG E and EEG F: p = 0.085) (Fig. 4).

3.3. Occlusal force

The average occlusal force for the original dentures was

255 � 120 N, that for the �3-mm denture was 213 � 100 N, and

that for the +5-mm denture was 304 � 157 N. A significant

difference was observed in the occlusal force between the

original dentures and the �3-mm denture ( p < 0.05, p = 0.034)

(Fig. 5). There was no significant difference between the

original and the +5-mm dentures.

4. Discussion

The present study used an EEG to examine how VDO can affect

brain function in complete denture wearers. In edentulous

individuals, periodontal mechanoreceptors are lost due to the

loss of teeth. Sensory and motor information related to dental

Fig. 5 – Comparison of the occlusal force (n = 21).

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occlusion is, therefore, believed to be transmitted to the brain

via receptors in the periosteum, temporomandibular joint,

masticatory muscles, and oral mucosa [15]. The problem with

a complete denture is that, over time, abrasion of the artificial

teeth leads to decreased VDO, reduced masticatory efficiency,

alteration of the pathways that drive mastication, fatigue in

the masticatory muscles, mandibular displacement, and

aesthetic impairment [16,17]. The highlight of the present

study is that, because subjects were wearers of complete

dentures, it was possible to specify an arbitrary VDO, which

allowed us to examine how changes in the VDO could

influence brain function.

Generally, altering a VDO by using a bite-elevating

appliance, such as an occlusal splint, is known to increase

occlusal force in healthy dentulous individuals. In the present

study, however, although patients wearing the +5-mm

denture tended to exert increased occlusal force, this differ-

ence was not statistically significant. This may be due to the

fact that, even though the +5-mm denture was carefully

adjusted to occlude with the VDO raised 5 mm above the

proper vertical position, some patients found it much easier to

bite by using their original dentures. On the other hand, a

significant reduction in the occlusal force was observed with

the �3-mm denture that was adjusted to occlude with the VDO

lowered 3 mm below the proper vertical position. This finding

is in line with the general notion that a decreased VDO leads to

a reduced occlusal force [18]. Discomfort associated with the

alteration of the VDO might have also influenced the occlusal

force in �3-mm denture wearers.

In the previous study, it was suggested that objective

assessment of dental therapy is possible based on physiologi-

cal indicators using EEG [10,19,20]. According to a previous

study, experimental occlusal interference causes discomfort,

and the resulting emotional change is reflected in an EEG,

which allows us to detect the impairment of masticatory

ability through EEG analysis [21]. Kikuchi demonstrated

through EEG measurements that discomfort in subjects with

palatal dentures increased due to a change in the oral

environment [22]. Nishiyama et al. examined gum chewing

with and without an occlusal interference device that

stimulated a negative change in the oral sensation in four

subjects using EEG and ESAM [11]. Furthermore, a previous

animal experiment showed that occlusal disharmony in rats

and monkeys that underwent the bite-raising procedure

induced a stress reaction caused by increased plasma

corticosterone and urine cortisol levels [23,24]. Koshino

et al. claimed that complete denture wearers’ satisfaction

with the dentures and ease of mastication can influence their

physiological and psychological aspects of Quality of life [25].

In the present study, sensory evaluation revealed that the

usage of the +5-mm denture caused a significant increase in

the negative indicator score, indicating that increasing a VDO

by 5 mm can induce stress. This finding is in line with a

previous study’s report that an increase in VDO often leads to

psychological distress [26].

Removal of pain and a considerable improvement in

masticatory capabilities, including the attainment of a normal

molar occlusion, brought about by denture treatment posi-

tively affect brain function [10]. In the present study, the

effects of both increased and decreased of VDO on Da values

were not significant.

On the other hand, this study found that there were 11

patients with low Da values (Da < 0.952). Musha et al. reported

that a person whose Da was lower than 0.952 had a higher

possibility of suffering from Alzheimer’s dementia [14]. Consid-

ering that we intended to include subjects with no history of

brain disease confirmed by clinical interview and examination,

this finding might suggests heterogeneity of edentulous patient

in terms of brain function as measured by Da value.

This study experimentally changed the vertical dimension

of the complete dentures in 21 edentulous patients and

measured the EEGs of these patients. To the best of our

knowledge, this is the first study that evaluated the brain

function in such a large number of edentulous patients under

conditions where 3 different occlusal dimensions were

precisely simulated. However, one of the limitations of this

study was that we only tested the immediate effects of the

change in the vertical dimension, while a long-term effect is

more clinically relevant. Another limitation was that, al-

though the brain function may potentially be affected by many

factors and highly variable and therefore the effects of

potential confounding factors and the reproducibility of the

measurements should be taken into considerations, we

conducted only a single measurement of a limited number

of variables. Actually, while a significant change in the

negative indicator scores before and after gum chewing with

the increased VDO was found, no significant difference was

found for scores with and without the VDO change after gum

chewing, which suggests that the study result is not conclu-

sive and further studies are warranted. We selected this study

design because of its technical complexity and mainly ethical

considerations; our study should clearly be considered an

exploratory investigation into whether change in the vertical

dimension is related to brain function. Confirmatory studies

that investigate carefully selected variables for a longer term

should be done only after several studies like ours find and

suggest a significant relationship. Given this general caution-

ary note and based on the data collected, we suggest that

psychological conditions and occlusal force might be influ-

enced by changes in the VDO of complete dentures.

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5. Conclusion

This study changed the vertical dimension of the experimen-

tal complete dentures in 21 edentulous patients and measured

the occlusal forces and the EEGs of these patients. Within the

limitations of this study, the following conclusions were

obtained: (1) The occlusal force was significantly decreased by

the denture with a lower vertical dimension; (2) ESAM analysis

revealed a significant increase in psychological distress after

gum chewing with the denture with a higher vertical

dimension; and (3) DIMENSION analysis found no consistent

effect of the vertical dimension, and half of the subjects

indicated low Da values.

Acknowledgments

The authors thank Drs. Haruyama Matsuzaki, Yohei Kobaya-

shi, and Toshimitsu Musha (Brain Functions Lab., Inc.,

Kanagawa, Japan) who provided support and advice in this

study.

r e f e r e n c e s

[1] Williams WN, Levin AC, LaPointe LL, Comell CE. Bite forcediscrimination by individuals with complete dentures. JProsthet Dent 1985;54:146–50.

[2] Kim JJ, Diamond DM. The stressed hippocampus, synapticplasticity and lost memories. Nat Rev Neurosci 2002;3:453–62.

[3] Kubo KY, Yamada Y, Iinuma M, Iwaku F, Tamura Y,Watanabe K, et al. Occlusal disharmony induces spatialmemory impairment and hippocampal neurondegeneration via stress in SAMP8 mice. Neurosci Lett2007;414:188–91.

[4] Westberg KG, Kolta A. The trigeminal circuits responsiblefor chewing. Int Rev Neurobiol 2011;97:77–98.

[5] Ono Y, Yamamoto T, Kubo K, Onozuka M. Occlusion andbrain function: mastication as a prevention of cognitivedysfunction. J Oral Rehabil 2010;37:624–40.

[6] Okamoto N, Morikawa M, Okamoto K, Habu N, Hazaki K,Harano A, et al. Tooth loss is associated with mild memoryimpairment in the elderly: the Fujiwara-kyo study. BrainRes 2010;1349:68–75.

[7] Kimoto A, Enomoto S, Kobayashi S, Ohashi I, Nakamura Y.Responses of trigeminal mesencephalic neurons to teethextraction in the guinea pig. In: Morimoto T, Matsuya T,Takada K, editors. Brain and oral functions – oral motorfunction and dysfunction. Amsterdam: Elsevier; 1995. p. 49–58.

[8] Hu JM, Dostrovsky JO, Lenz GJ, Sessle BJ. Tooth pulpdeafferentation is associated with functional alterations inthe properties of neurons in the trigeminal spinal tractnucleus. J Neurophysiol 1986;56:1650–68.

[9] Nakazawa I. Zenbusyougishigaku. 8th ed. Tokyo:Nagasuesyoten; 1979: 137–8 [article in Japanese].

[10] Morokuma M. Influence of the functional improvement ofcomplete dentures on brain activity. J Jpn Prosthodont Soc2008;52:194–9.

[11] Nishiyama Y, Ohnuki M, Kikuchi S, Suzuki K, Ohkubo C.Evaluation of psychological effect of prosthetic treatmentusing Emotion Spectrum Analysis Method (ESAM). JProsthodont Res 2011;55:82–8.

[12] Hara J, Shankle WR, Musha T. Cortical atrophy inAlzheimer’s disease unmasks electrically silent sulci andlowers EEG dipolarity. IEEE Trans Biomed Eng 1999;46:905–10.

[13] Suzuki T, Kumagai H, Watanabe T, Uchida T, Nagao M.Clinical evaluation of measuring system of occlusal force.Kokubyo Gakkai Zasshi 1994;61:437–45 [article in Japanese].

[14] Musha T, Asada T, Yamashita F, Kinoshita T, Chen Z,Matsuda H, et al. A new EEG method for estimating corticalneuronal impairment that is sensitive to early stageAlzheimer’s disease. Clin Neurophysiol 2002;113:1052–8.

[15] George AZ. Biomechanics of the edentulous state. In:George AZ, Charles LB, editors. Prosthodontic treatment foredentulous patients: complete dentures and implant-supported prostheses. 12th ed. Philadelphia: Elsevier; 2004.p. 6–23.

[16] Hirano S, May KB, Wagner WC, Hacker CH. In vitro wear ofresin denture teeth. J Prosthet Dent 1998;79:152–5.

[17] Ekfeldt A, Karlsson S. Changes of masticatory movementcharacteristics after prosthodontics rehabilitation ofindividuals with extensive tooth wear. Int J Prosthodont1996;9:539–46.

[18] Prombonas A, Vlissidis D, Molyvdas P. The effect of alteringthe vertical dimension of occlusion on biting force. JProsthet Dent 1994;71:139–43.

[19] Okamoto N. Effect of occlusal support by implantprostheses on brain function. J Prothodont Res 2011;55:206–13.

[20] Shibuya N. Influence of dentures in partial denture wearerson brain function. Ann Jpn Prothodont Soc 2009;1:148–56[article in Japanese].

[21] Ichikawa D. The effect of experimental occlusalinterference on electroencephalograms by comparingpsychophysiological response and masticatory muscleactivity. J Jpn Prosthodont Soc 2001;45:305–14 [article inJapanese].

[22] Kikuchi S. Evaluation of the psychological effect of changesin the oral environment. Prosthodont Res Pract 2005;4:84–93.

[23] Yoshihara T, Taneichi R, Yawaka Y. Occlusal disharmonyincreases stress response in rats. Neurosci Lett2009;452:181–4.

[24] Budtz-Jørgensen E. Occlusal dysfunction and stress. Anexperimental study in macaque monkeys. J Oral Rehabil1981;8:1–9.

[25] Koshino H, Hirai T, Ishijima T, Tsukagoshi H, Ishigami T,Tanaka Y. Quality of life and masticatory function indenture wearers. Oral Rehabil 2006;33:323–9.

[26] Otsuka T, Watanabe K, Hirano Y, Kubo K, Miyake S, Sato S,et al. Effects of mandibular deviation on brain activationduring clenching: an fMRI preliminary study. Cranio2009;27:88–93.