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
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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: [email protected] (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.
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 6126
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.
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