Automatic evaluation of speech impairment caused by wearing a dental appliance

doi:10.4236/ojst.2013.37062

Paper Menu >>

Journal Menu >>

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: [email protected]

Received 4 August 2013; revised 4 September 2013; accepted 21 September 2013

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

OPEN ACCESS

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.

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).

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.

REFERENCES

[1] Chierici, G. and Lawson, L. (1973) Clinical speech con-

siderations in prosthodontics: Perspectives of the prost-

hodontist and speech pathologist. Journal of Prosthetic

Dentistry, 29, 29-39.

http://dx.doi.org/10.1016/0022-3913(73)90136-4

[2] Kong, H.J. and Hansen, C.A. (2008) Customizing palatal

contours of a denture to improve speech intelligibility.

Journal of Prosthetic Dentistry, 99, 243-248.

http://dx.doi.org/10.1016/S0022-3913(08)60049-9

[3] Umino, S., Masuda, G..G., Ono, S. and Fujita, K. (1998)

Speech intelligibility following maxillectomy with and

without a prosthesis: An analysis of 54 cases. Journal of

Oral Rehabilitation, 25, 153-158.

http://dx.doi.org/10.1046/j.1365-2842.1998.00238.x

[4] Rieger, J., Wolfaardt, J., Seikaly, H. and Jha, N. (2002)

Speech outcomes in patients rehabilitated with maxillary

obturator prostheses after maxillectomy: A prospective

study. The International Journal of Prosthodontics, 15,

139-144.

[5] Sullivan, M., Gaebler, C., Beukelman, D., Mahanna, G.,

Marshall, J., et al. (2002) Impact of palatal prosthodontic

intervention on communication performance of patients’

maxillectomy defects: A multilevel outcome study. Head

Neck, 15, 530-538. http://dx.doi.org/10.1002/hed.10095

[6] Terai, H. and Shimahara, M. (2001) Speech intelligibility

M. Hattori et al. / Open Journal of Stomatology 3 (2013) 365-369

369

OPEN ACCESS

in conversation of patients with mild articulatory disor-

ders. Journal of the Japanese Stomatological Society, 50,

104-108.

[7] Imai, S., Yamashita, Y., Ohno, K., Suzuki, N. and Michi,

K. (1994) Speech intelligibility in conversation of post-

surgical oral cancer patients—Comparison with syllable

intelligibility and patient’s own assessment. The Japan

Journal of Logopedics and Phoniatrics, 35, 29-38.

http://dx.doi.org/10.5112/jjlp.35.29

[8] Hattori, M., Sumita, Y.I., Kimura, S., Mukohyama, H.

and Taniguchi, H. (2005) Development of an automatic

speech intelligibility test system using a computerized

speech recognition technique. Maxillofacial Prosthetics,

28, 36-48.

[9] Hattori, M., Sumita, Y.I., Kimura, S. and Taniguchi, H.

(2010) Application of an automatic conversation intelli-

gibility test system using computerized speech recogni-

tion technique. Journal of Prosthodontic Research, 54,

7-13. http://dx.doi.org/10.1016/j.jpor.2009.07.004

[10] Benzeghiba, M., De Mori, R., Deroo, O., Dupont, S.,

Erbes, T., et al. (2007) Automatic speech recognition and

speech variability: A review. Speech Communication, 49,

763-86. http://dx.doi.org/10.1016/j.specom.2007.02.006

[11] Rebman, C., Aiken, M. and Cegielski, C. (2003) Speech

recognition in the human-computer interface. Information

& Management, 40, 509-519.

http://dx.doi.org/10.1016/S0378-7206(02)00067-8