Open Journal of Stomatology, 2013, 3, 365-369 OJST
http://dx.doi.org/10.4236/ojst.2013.37062 Published Online October 2013 (http://www.scirp.org/journal/ojst/)
Automatic evaluation of speech impairment caused by
wearing a dental appliance
Mariko Hattori1, Yuka I. Sumita2, Hisashi Taniguchi2
1Clinics for Oral and Maxillofacial Rehabilitation, Tokyo Medical and Dental University, Tokyo, Japan
2Department of Maxillofacial Prosthetics, Tokyo Medical and Dental University, Tokyo, Japan
Email: sasamfp@tmd.ac.jp
Received 4 August 2013; revised 4 September 2013; accepted 21 September 2013
Copyright © 2013 Mariko Hattori et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
In dentistry, speech evaluation is important for ap-
propriate orofacial dysfunction rehabilitation. The
speech intelligibility test is often used to assess pa-
tients’ speech, and it involves an evaluation by human
listeners. However, the test has certain shortcomings,
and an alternative method, without a listening pro-
cedure, is needed. The purpose of this study was to
test the applicability of an automatic speech intelligi-
bility test system using a computerized speech recog-
nition technique. Speech of 10 normal subjects, when
wearing a dental appliance, was evaluated using an
automatic speech intelligibility test system that was
developed using computerized speech recognition
software. The results of the automatic test were re-
ferred to as the speech recognition scores. The Wil-
coxon signed rank test was used to analyze differ-
ences in the results of the test between the following 2
conditions: with the palatal plate in place and with
the palatal plate removed. Spearman correlation co-
efficients were used to evaluate whether the speech
recognition score correlated with the result of con-
ventional intelligibility test. The speech recognition
score was significantly decreased when wearing the
plate (z = 2.807, P = 0.0050). The automatic evalua-
tion results positively correlated with that of conven-
tional evaluation when wearing the appliance (r =
0.729, P = 0.017). The automatic speech testing system
may be useful for evaluating speech intelligibility in
denture wearers.
Keywords: Prosthodontics; Maxillofacial Prosthodontics;
Speech; Automatic Speech Recognition
1. INTRODUCTION
The orofacial region is a complex of organs, most of
which play a role in speech production. In the field of
dentistry, speech evaluation is important for the appro-
priate orofacial dysfunction rehabilitation. Because the
teeth and alveolar ridge are speech articulators, speech
ability can be impaired by dental disorders such as miss-
ing teeth or by maxillofacial disorders caused by surgical
treatment affecting orofacial structures such as resection
of tumors in bone and soft tissue like the palate or tongue.
Prosthetic treatment can often be useful for speech reha-
bilitation in such patients [1]. However, placement of
dental appliances can sometimes compromise speech
when the appliances interfere with articulation. For ex-
ample, consonants are often affected by placing a new
denture, and the patient needs time to compensate for
this change [2]. Therefore, the speech of patients reha-
bilitated with prosthesis should be carefully assessed and
monitored.
In dentistry, the speech intelligibility test is often used
to assess speech and involves evaluation of the patient’s
speech by human listeners [3-6]. The procedure is simple;
only a recording device is needed to record the patient’s
speech and play it back to the listeners for evaluation.
However, the test is associated with time costs because
listeners must provide their time to complete the evalua-
tion. Moreover, the result is also dependent on the lis-
tener’s ability [7]. Consequently, speech evaluation
methods that do not require subjective listening evalua-
tions have been sought, and an automatic speech intelli-
gibility testing system using a computerized speech rec-
ognition technique was previously developed [8,9].
These new systems have been used to evaluate speech
in maxillectomy patients, which enable patients to self-
record utterances and the examiners to obtain test results
without requiring the inputs from human listeners.
Significant correlations were found between the re-
sults of the automatic tests and that of the conventional
test involving human listeners. These findings suggested
that the systems used in the present study, which involve
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M. Hattori et al. / Open Journal of Stomatology 3 (2013) 365-369
366
no listening procedure, may effectively identify speech
disorders in patients with maxillofacial defects.
In this study, the applicability of one of the new sys-
tems was tested to evaluate speech in normal subjects
when wearing a dental appliance—in this instance—a
palatal plate [9]. If the system detected slight differences
in articulation caused by wearing the plate, it suggested
that the system can be used not only for detecting severe
speech disorders in patients with maxillofacial defects
but also for minor speech problems in those wearing
dentures. Two null hypotheses were proposed: 1) no dif-
ferences in the result of the automatic test between 2
conditions will be observed; with the palatal plate in
place and with the palatal plate removed; and 2) the
speech recognition score will not correlate with the result
of the conventional intelligibility test.
2. MATERIALS AND METHODS
The experimental palatal prosthesis was fabricated using
auto-curing methylmethacrylate resin (Palapress Vario
clear; Heraeus-Kulzer, Tokyo, Japan). An automatic
speech intelligibility test system and the convention me-
thod, involved human listening, were used to evaluate
speech in 10 subjects. The results of the 2 tests were
compared.
2.1. Subjects
Ten women (mean age, 26.5 years) who were native
Japanese speakers with normal speaking and hearing
abilities participated in this study. All possessed 28 or
more teeth in continuous dental arches. A power analysis
was conducted with α = 0.05 and power (β) = 0.80. On
the basis of the results of a pilot study, a sample size of
10 was found to be appropriate. Informed consent was
obtained from each subject, verbally and in writing. The
study protocol was approved by the Ethics Committee of
the Faculty of Dentistry, Tokyo Medical and Dental
University (Registration No. 576).
2.2. Fabrication of Experimental Palatal Plate
An impression of the upper jaw was acquired using a
ready-made impression tray and irreversible hydrocolloid
impression material (Algiace Z; DENTSPLY-Sankin K.
K., Tokyo, Japan), and an experimental palatal plate with
a thickness of 2.0 mm was then fabricated using auto-
curing methylmethacrylate resin (Palapress Vario clear;
Heraeus-Kulzer). Before the speech sample recording,
subjects tested their palatal plate to ensure adequate re-
tention and stability.
2.3. Automatic Speech Intelligibility Testing
The automatic conversation intelligibility test system [9]
was installed on a laptop (Vaio PCG-NV99E, Sony,
Tokyo, Japan) with Windows XP operating system (Mi-
crosoft, Tokyo, Japan). The automatic conversation in-
telligibility test system consists of the following 2 ap-
plications: a conversation intelligibility test recorder and
a conversation intelligibility test result viewer. Block
diagrams of applications are shown in Figures 1 and 2.
The conversation intelligibility test recorder consists
of a patient information input module, a control module,
a voice-input module, a test-text display module, a voice
data store processing module, and a test-data storage unit.
The conversation intelligibility test result viewer consists
of a test data file input module, a voice recognition mod-
ule, a test result display module, a unit sentence playback
module, and a continuous playback module. Voice data
are sent to the voice recognition module, where the
computerized speech recognition software ViaVoice®
(IBM ViaVoice for Windows, Pro V10 Japanese version,
ScanSoft, Tokyo, Japan) is used.
The test text to be read aloud was displayed on the
computer monitor test screen to create speech samples.
Recognition results and scores were displayed on the
results screen. The number of speech segments was cal-
culated and automatically shown as a percentage on the
upper right corner of the results screen. This percentage
Figure 1. The block diagram of the conversation intelligibility
test recorder.
Figure 2. The block diagram of the conversation intelligibility
test result viewer.
Copyright © 2013 SciRes. OPEN ACCESS
M. Hattori et al. / Open Journal of Stomatology 3 (2013) 365-369 367
constitutes the speech recognition score.
All 10 subjects were asked to speak the phrases shown
one by one on the test screen. A microphone (F-VX400,
Sony, Tokyo, Japan) was positioned 10 cm from the lips.
Phrases from “Jack and the Beanstalk” were used as the
test text. The utterances were recorded on the laptop
computer by means of a sound interface (Sound Blaster
Extigy, Creative Technology, Tokyo, Japan) in a sound-
proof room. The sampling rate was 11 kHz. The subjects’
speech was tested under the following 2 conditions: with
the palatal plate in place and with the palatal plate re-
moved.
2.4. Conventional Intelligibility Testing
In a quiet room, the recorded utterances were played
back on the computer to 5 linguistically-untrained adult
listeners with no hearing impairment. The listeners
evaluated each subject’s utterances on a scale of 1 to 5
according to Terai’s method for mild disorders as follows:
5, natural; 4, slightly unnatural; 3, sometimes unnatural;
2, slightly unintelligible; and 1, partially intelligible [6].
The mean of scores marked by the 5 listeners was used to
calculate the test result, namely conversational intelligi-
bility (Table 1).
2.5. Statistical Analysis
Normality was evaluated by normal distribution plots,
and histograms were used to depict the variability. Non-
parametric tests were applied to analyze the data. The
Wilcoxon signed rank test was used to analyze differ-
ences in the speech recognition score and conversational
intelligibility between the following 2 conditions: with
the palatal plate in place and with the palatal plate re-
moved. Conversational intelligibility and speech recog-
nition score of all 10 subjects when wearing the palatal
plate were plotted on a coordinate system. Spearman
correlation coefficients were used to evaluate whether
the speech recognition score correlated with conversa-
tional intelligibility. The analyses were conducted using
the program Statview-J Version 5.0 (SAS Institute Inc.,
Cary, NC).
Table 1. The scale for the listening experiment of conversation
intelligibility.
criteria score
natural 5
slightly unnatural 4
sometimes unnatural 3
slightly unintelligible 2
partially intelligible 1
3. RESULTS
Conversational intelligibility and speech recognition
scores were not normally distributed with or without
placement of the palatal plate. Thus, nonparametric tests
were applied to analyze the data. The results of the auto-
matic tests are shown in Figure 3; those of the con-
ventional tests are shown in Figure 4.
The median and range of the speech recognition score
for the 10 subjects were 67.6 and 53.8 - 75.3 without the
palatal plate and 53.1 and 0.0 - 66.1 with the palatal plate,
respectively. Thus, the speech recognition score was sig-
nificantly decreased when wearing the plate (z = 2.807,
P = 0.0050; Figure 3).
All 10 subjects had a score of 5.0 in conversational
intelligibility when not wearing the palatal plate. Median
conversation intelligibility was 3.8 (range, 2.0 - 4.4)
when wearing the plate, indicating a significant decrease
in conversational intelligibility when wearing the palatal
plate (z = 2.814, P = 0.0049; Figure 4).
Speech recognition and conversational intelligibility
scores showed a positive correlation when wearing the
plate (correlation coefficient (r) = 0.729, P = 0.017; Fig-
ure 5).
Figure 3. The results of the automatic tests. The speech recog-
nition score was significantly decreased when wearing the pa-
latal plate (z = 2.807, P = 0.0050).
Figure 4. The results of the conventional tests. Conversational
intelligibility was significantly decreased when wearing the pa-
latal plate (z = 2.814, P = 0.0049).
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M. Hattori et al. / Open Journal of Stomatology 3 (2013) 365-369
368
Figure 5. Speech recognition score and conversational intelli-
gibility showed a positive correlation when wearing the plate
(correlation coefficient (r) = 0.729, P = 0.017).
4. DISCUSSION
The advantages of the automatic conversation intelligi-
bility test system, which employs computerized recogni-
tion software based on a fast Fourier transform-based
cepstrum analysis and hidden Markov model matching
technology, are its easy operation, objective evaluation,
and the lack of the need for human listeners [9]. In this
study, the system was able to detect significant decreases
in the speech recognition score when subjects were wear-
ing the palatal plate, indicating that the system can detect
slight differences in articulation caused by the plate.
Wearing the plate not only blocked sensory feedback
from the palate but it also changed the positional rela-
tionship of the tongue and the articulators because of the
plate’s thickness. This affected consonant synthesis and
resulted in an unnatural-sounding speech. Such an im-
pairment created sufficient acoustic differences in some
instances that the computerized speech recognition soft-
ware recognized words that were different from the ac-
tual test words. This explains why the low conversational
intelligibility scores given by human subjects in the tra-
ditional testing method correlated positively with the
speech recognition score given by the automatic test sys-
tem. In future, the automatic testing system may prove
useful for evaluating the effects of different denture de-
signs or of denture adjustment on speech.
The present study compared the speech recognition
scores with and without wearing a dental appliance.
Based on these results, the null hypotheses-there is no
difference in the result of the automatic test between the
following 2 conditions: with the palatal plate placed and
with the palatal plate removed and speech recognition
score is not correlated with the result of conventional
intelligibility test—were rejected.
Future studies should examine the score using dental
appliances of different designs. The results of computer-
ized speech recognition are reported to be affected by
variability in speaker characteristics such as age, sex, and
accent [10,11]. Accordingly, the subjects in the present
study were limited to same sex, had a small age distribu-
tion, and spoke 1 language in the same regional accent.
Further study is warranted with a larger number of sub-
jects of both sexes, in different age groups, and speaking
with different accents. In addition, because utterances
were recorded immediately after placing the palatal plate
in this study, it will be interesting to examine changes in
the speech recognition score over time as the subject gets
habituated to the denture placement.
5. CONCLUSION
The automatic test system detected a significant differ-
ence in speech intelligibility, using the speech recogni-
tion score, in normal subjects with and without place-
ment of a palatal plate. The results of the automatic test
system and the conventional evaluation method by hu-
man listeners were positively correlated. These findings
suggest that the system can be used to evaluate speech
intelligibility of denture wearers.
6. ACKNOWLEDGEMENTS
This research was supported by the Japan Society for the Promotion of
Science Grants-in-Aid for Scientific Research (KAKENHI; KAKENHI
[Grant No. 23792207]).
This work was supported by a support program for women research-
ers from the Tokyo Medical and Dental University.
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