the effect of rapid palatal expander appliances on speech
TRANSCRIPT
The Effect of Rapid Palatal ExpanderAppliances On Speech
A thesis submitted in conformity with the requirements for the degree of Master of Science, Graduate Department of Dentistry,
University of Toronto
Kyle Stevens
Copyright 2010
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The effect of rapid palatal expander appliances on speechMaster of Science (Orthodontics), November 2010Kyle Stanley Hillman StevensGraduate Orthodontics, Faculty of DentistryUniversity of Toronto
ABSTRACT
Background: Rapid palatal expanders have a screw that covers the palate and may
affect speech.
Methods: RPEs were treatment planned for 22 patients. Speech recordings were
completed at 6 different time points. Analysis for speech acceptability, /i/ vowel
formants, and /s/ and /∫/ fricative spectra were analyzed.
Results: When the appliance was inserted, speech acceptability deteriorated but
improved over time. For vowel /i/, the first formant increased and second formant
decreased. For fricatives (/s/, /∫/), low to high frequency ratios indicated that the
sounds were distorted when the appliance was inserted. The formants and ratios
returned to normal levels over time. Examination of the four spectral moments found
the spectral mean decreased, standard deviation increased, skewness became more
positive, and kurtosis decreased at appliance insertion. Repeated measures ANOVAs
found significant effects for time for all acoustic measures.
Conclusions: Speech was altered when the appliance was inserted, but improved over
time.
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ACKNOWLEDGEMENTSSincere thanks for all those who have supported me over the past three years. Special mention of a few particular individuals, for without their guidance and assistance, the completion of my project would have been impossible:
Dr. Tim Bressmann, University of Toronto, Department of Speech and Language Pathology, for helping me learn a completely new area of research and always being available to answer my numerous questions. Without his creativity and knowledge, this study would never have come into existence.
Dr. Bryan Tompson, University of Toronto, Department of Graduate Orthodontics, for being a wonderful Department Head over the past three years and for helping to ensure that this project and each school term were as stress-free as possible.
Dr. Siew-Ging Gong, University of Toronto, Department of Graduate Orthodontics, for consistently providing her input and helping me write a thesis that would allow readers not trained in speech pathology understand the topic.
Janette Quintero, University of Toronto, Department of Speech and Language Pathology, for helping me set-up experiments, analyze results, and always being available to answer speech-related questions.
Christina Khaouli, University of Toronto, Department of Speech and Language Pathology for helping me analyze the never-ending recordings.
Geoffrey Metz, for spending many hours helping me edit and make this thesis readable.
My parents, Chris and Debbie, for their love and support, emotionally and financiallythroughout my education.
Daniel Fabiano, who was always there when I needed encouragement and someone to talk to at the end of a hard day.
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TABLE OF CONTENTS Page
1. ABSTRACT .............................................................................................................. ii
2. ACKNOWLEDGEMENTS ...................................................................................... iii
3. TABLE OF CONTENTS ......................................................................................... iv
4. LIST OF FIGURES .................................................................................................. v
5. LIST OF TABLES ................................................................................................... vi
6. LIST OF APPENDICES ......................................................................................... vii
7. INTRODUCTION, STATEMENT & SIGNIFICANCE OF THE PROBLEM ........... 1
8. REVIEW OF THE LITERATURE ........................................................................... 3
9. PURPOSE OF THE STUDY ...................................................................................16
10. HYPOTHESES .......................................................................................................17
11. MATERIALS AND METHODS .............................................................................18
12. RESULTS ................................................................................................................25
13. DISCUSSION .........................................................................................................69
14. CONCLUSIONS .....................................................................................................84
15. LIMITATIONS .......................................................................................................85
16. APPENDIX .............................................................................................................87
17. REFERENCES .........................................................................................................97
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LIST OF FIGURES
Page
1. Constricted and expanded maxilla ........................................................................... 5
2. Banded and bonded RPE.......................................................................................... 6
3. Acceptability average rating ..................................................................................26
4. Vowel /i/-Second formant frequency .....................................................................30
5. Vowel /i/-First formant frequency..........................................................................32
6. Vowel /i/-Ratio of formant distances......................................................................35
7. Fricative /∫/-Frequency band-volume ratios...........................................................38
8. Fricative /s/-Frequency band-volume ratios ...........................................................42
9. Fricative /∫/-Spectral mean .....................................................................................47
10. Fricative /∫/-Standard deviation..............................................................................49
11. Fricative /∫/-Skewness.............................................................................................51
12. Fricative /∫/-Kurtosis...............................................................................................53
13. Fricative /s/-Spectral mean .....................................................................................55
14. Fricative /s/-Standard deviation..............................................................................58
15. Fricative /s/-Skewness.............................................................................................60
16. Fricative /s/-Kurtosis...............................................................................................62
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LIST OF TABLES
Page
1. Acceptability t-tests ................................................................................................27
2. Vowel /i/-Second formant frequency t-tests...........................................................31
3. Vowel /i/-First formant frequency t-tests...............................................................33
4. Vowel /i/-Ratio of formant distances t-tests ...........................................................36
5. Fricative /∫/-Frequency band-volume ratios t-tests ................................................39
6. Fricative /s/-Frequency band-volume ratios t-tests ................................................44
7. Fricative /∫/-Spectral mean t-tests...........................................................................47
8. Fricative /∫/-Skewness t-tests..................................................................................51
9. Fricative /∫/-Kurtosis t-tests ....................................................................................53
10. Fricative /s/-Spectral mean .....................................................................................56
11. Fricative /s/-Standard deviation..............................................................................58
12. Fricative /s/-Skewness.............................................................................................60
13. Fricative /s/-Kurtosis...............................................................................................62
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LIST OF APPENDICES
Page
A. Interactions .............................................................................................................87
i. Acceptability Data................................................................................................87
ii. Vowel /i/ First Formant Frequency......................................................................88
iii. Vowel /i/ Ratio of Difference between First and Second Formants at eachtime period and this Difference at Time Period 1.............................................89
iv. Fricative /∫/ Frequency band-volume ratio..........................................................90
v. Fricative /s/ Frequency band-volume ratio..........................................................91
vi. Fricative /∫/ Spectral Mean (1) .............................................................................92
vii. Fricative /∫/ Spectral Mean (2) .............................................................................93
viii. Fricative /s/ Spectral Mean...................................................................................94
B. Sentence articulation test ........................................................................................95
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INTRODUCTION, STATEMENT & SIGNIFICANCE OF THE PROBLEM
When speech is produced, the lungs create pulmonary pressure that forces air
through the glottis. The vibrations of the vocal folds create a sound, which resonates
in the pharyngeal, oral, and nasal cavities. Speech sounds are produced by
adjustments of the articulating organs, namely the mandible, lips, tongue and soft
palate. Modifications of the resonating cavities’ size, shape, type of opening, or
thickness of surface can alter the quality of speech sounds. It can therefore be
expected that when an object is placed in the pharyngeal-oral space, speech sound
characteristics may be altered.
One class of foreign objects inserted into the oral cavity are dental appliances.
Dental appliances are used over a wide span of ages from young children who wear
appliances to tip individual teeth, to the older population to replace missing teeth.
The insertion of these appliances has the potential to affect the oral space, and
therefore may distort speech sounds. Previous studies on speech and dental
appliances have examined the acoustic changes and negative effects caused by
removable retainers, bite blocks, dentures, and orthopaedic functional appliances.
Rapid palatal expanders (RPEs) are a common dental appliance utilized in orthodontic
practice, yet little is known about the potential perceptual and acoustic alterations
caused by the appliance and the duration of the effects. Although the use of the RPE
is temporary, the duration of use can extend over 6 months, which means that
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children may have to speak with the appliance over a long period of time. The
present study was undertaken to investigate how speech is affected by the insertion of
an RPE and how well an individual is able to adapt to the appliance over time.
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REVIEW OF THE LITERATURE
Speech articulators
The oral cavity is formed by the maxillary, mandibular, and palatine bones,
which are covered with mucosa. The oral cavity contains the tongue, soft palate and
teeth. The tongue is an essential organ involved in deglutition, gustation, jaw growth
and development, tooth alignment, and speech. Most of the speech sounds are
formed by the tongue. The tongue moves in a number of directions throughout
speech and contacts different areas during the pronunciation of various phonemes.
Phonemes are the basic distinctive units of speech sounds from which words are
formed, for example consonants and vowels. For instance, the tip of the tongue
contacts the upper teeth when /θ/ ('th') is pronounced, or the alveolar ridge with
sounds like /t/ or /s/. The dorsum of the tongue touches the soft palate for the /k/
sound. The acoustic theory of speech explains how modifications of the vocal tract
shape cause acoustic output alterations (Fant 1960).
Along with the tongue, the lips, teeth, alveolar ridge, and hard and soft palates
are speech articulators. The shape of the throat, nose, and mouth influence the
speech sound quality (Haydar et al. 1996). Defective speech can occur when there is
any osseous, muscular, soft tissue, or dental deformity that impairs these articulators
(Runte et al. 2002). A main area of research interest for speech misarticulations has
been with anterior open bite and the /s/-distortions that it may cause (Subtelny and
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Subtelny 1962, Fletcher et al 1961). Phoneme distortions, particularly of the /s/
sound, have been associated with a narrower palate, increased palatal height, and
occlusal anomalies which decrease the posterior intermaxillary space (Laine 1986 and
1987). The speech articulators adapt to changes in the oral cavity within certain
physiological and functional limits. When speech has been distorted over a period of
time, psychological or physical factors may hamper further adaptation (Warren et al
1980). Speech typically is more difficult with the insertion of a physical obstruction
in the oral cavity, such as a dental appliance, which can influence the normal
function of the articulators.
Rapid palatal expanders
Epidemiological studies have estimated that as many as 60% of children and
teenagers in industrialized nations could benefit from orthodontic treatment. In a
representative American sample of children and teenagers, it was found that 20% had,
or were having, orthodontic treatment (Proffit et al., 1998). Orthodontists use intra-
oral appliances to move teeth, to correct tooth-jaw relationships, and to improve
function, esthetics, and oral health. There are many different types of appliances used
to perform various actions to help achieve these goals, including those used to change
skeletal characteristics, such as a constricted maxillary arch.
The maxillary arch may be constricted due to genetic or environmental
influences. This constriction can lead to dental problems such as crowding, crossbites
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and/or speech problems (Fig. 1). In order to help correct the transverse relationship
between the maxilla and mandible, maxillary arch expansion is frequently necessary.
Palatal expanders are used to expand the arch by applying a force across the maxillary
midpalatal suture, by turning a screw that connects both halves of the appliance (Fig.
2).
Figure 1. Examples of constricted (left) and expanded maxillary arch (right). Note the V-shaped arch of a constricted maxilla, with incisors that are blocked out and out of alignment. In comparison, an expanded arch is U-shaped.
There are many different types of palatal expanders. An expander can be fixed
(cemented to the teeth) or removable, as well as tooth-borne (Hyrax ) or tooth- and
tissue-borne (Haas ). In addition, the method of expansion can be slow (1-2 turns per
week) or rapid (1-2 turns per day). There are two types of fixed expanders, banded
and bonded. Bonded expanders have acrylic, which covers the buccal, lingual, and
occlusal surfaces of the premolars and molars (Fig. 2, right), whereas banded
expanders are fixed to the first bicuspids and first molars with the use of dental bands
(Fig. 2, left). In orthodontics, the banded or bonded Hyrax rapid palatal expander
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(RPE) is frequently used. This RPE has been recommended for unilateral or bilateral
crossbite correction, increasing arch length and width of the maxilla, mobilization of
maxillary sutures to facilitate correction of a Class III midface deficiency, increasing
apical base width to facilitate buccal root torque of posterior teeth, and reducing nasal
resistance and providing normal breathing pattern (Sarver and Johnston 1989, Sarver
1995). The expander’s central jackscrew and other attachments stretch across the
palate (Fig. 2), which can impede normal movement of oral structures. This can limit
the tongue’s contact with the palate and alter certain speech sounds.
Figure 2. Example of banded RPE (left) and bonded RPE (right). Both appliances share the same central jackscrew apparatus, but the method of dental attachment differs. The banded RPE attaches via dental bands whereas the bonded RPE attaches via acrylic.
Dental appliances and Speech
Dental appliances can cause articulation disorders with the linguodental,
labiodental, or linguoalveolar consonants and high front vowels (Bloomer 1957).
When an appliance is inserted in the mouth, it will obstruct different areas depending
Dental Bands
CentralJackscrew
Acrylic
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on the type and shape of the appliance. These obstructions can result in various
speech sound distortions depending on which articulators are blocked.
Orthodontic appliances, though effective in correcting skeletal or
dentoalveolar imbalances, have been known to have detrimental effects on speech
(Feldman 1956). The introduction of a dental appliance can interfere with the
movements of the speech articulators. These appliances have been shown to have
significant effects on consonant and vowel production (McFarland et al 1996).
Although many individuals will learn to adapt to the new intra-oral appliance, others
will find it much more difficult. It has been found that there is a significant variation
between an individual’s use of compensatory mechanisms to aid in overcoming these
obstructions (Baum and McFarland 2000).
The impact of orthodontic appliances on speech is a complex matter to
investigate, as there are numerous types of appliances with varying sizes and shapes.
In order to facilitate comparison, research has focused on appliance subclasses, such as
different functional appliances with a similar mode of action, and patient preferences,
when examining speech. An inverse relationship between patient acceptance and
appliance size was found for maxillary activators (Sergl et al 1998).
Speech Analysis
The most common speech research technique is spectral analysis (Agnello and
Wictorin 1972, Ritchie and Ariffin 1982), which examines the recorded speech as a
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function of frequency (Hz) and volume (dB) over time (ms). Spectral analysis allows
for objective acoustic assessment, revealing the sound energy's frequency distribution.
However, it is equally important to determine whether or not listeners are sensitive
to any spectral changes. Recent research tends to incorporate both perceptual and
acoustic analyses to investigate speech perturbations due to the insertion of an
appliance (McFarland et al. 1996, Baum and McFarland 2000). Other techniques,
such as electropalatography and ultrasound, have also been used in speech research.
(Bernhardt et al. 2005, Hiiemae and Palmer 2003).
In order to investigate the effect dental appliances have on speech, most
researchers will select particular phonemes to examine and compare. The choice of
phoneme is based on what particular consonants and/or vowels are likely to be
affected by appliance insertion. Vowels are sounds produced with an open vocal tract
with low intraoral pressure. Constrictions of the vocal tract along the path from
glottis to lips determine the resulting formant frequency pattern. Formants are an
amplitude peak in the frequency spectrum of sound. Typically, vowels in which the
tongue is positioned high, close to or contacting the palate, such as /i/, are more likely
to be affected by modifications of the vocal tract by a dental appliance (McFarland
and Baum 1995, McFarland et al. 1996). Fricatives, like /s/ and /∫/, are frequently
examined in dental appliance speech research due to their tongue-palate contact and
their additional required precision for production (Baum and McFarland 1997,
McFarland and Baum 1995, Hamlet et al. 1979). The fricative consonants /s/ and /∫/
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are characterized by the approximation of the anterior tongue and the alveolar ridge
or palate. A narrow groove in the tongue creates a small passage and the resulting
turbulences produce a wide frequency band noise (Shadle and Mair 1985). Some
research has shown that disturbances in the oral cavity have greater effects on
consonant production, as precise tongue positioning relative to the palate is required
for accurate production of consonants compared to vowels (Flege et al. 1988,
McFarland et al. 1996). Certain consonants like /s/ or /z/ require additional precision
for proper pronunciation (Baum and McFarland 1997, Hamlet et al. 1979).
Adaptation to Intraoral Appliances
The mechanism of speech adaptation to intraoral appliances is not completely
understood, though a number of theories have been proposed. Speech production and
adaptation rely on both auditory and somatosensory feedback, yet there is some
debate on the dominant sensory modality (Houde and Jordan 1998, Tremblay et al.
2003, Jones and Munhall 2005). In the absence of any articulatory compensation,
perturbations would cause changes to the vocal tract resonant characteristics and
speech articulator behaviour, producing articulation and/or resonance disorders
(Bloomer 1971). The system of speech production, however, is adaptable, and speech
may sound relatively normal even if the articulatory system is structurally or
functionally perturbed.
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Adaptation to dental appliances has been the main focus of a number of
studies. Many of these investigations have concentrated on determining whether or
not complete adaptation occurs, and if so, how long it takes to occur (McFarland et al.
1996, Hamlet and Stone 1978, Hamlet et al. 1979). Speech adaptation was found to be
faster for vowels than consonants (McFarland and Baum 1995), and vowel adaptation
was found to be more complete than consonant adaptation (Heydecke et al. 2004).
Speech adaptation studies have shown that patients reach a physiologic limit in
adaptation. Speech tends to improve during the first few days, but then will plateau
without further improvement (Stewart et al 1997). Other studies have shown that
these compensatory mechanisms could potentially be counterproductive, making the
speech distortions worse (Warren et al 1980).
Most of the speech research examining the effects of dental appliances assessed
the palatal perturbation caused by appliances modifying palatal shapes (especially
augmentation of the palatal ridge), or the consequence of an increased vertical
dimension caused by a bite block. Both of these perturbations have been shown to
provoke an incomplete immediate adaptive response from the articulators, and both
required a relatively long period of compensation before there was accommodation to
the mechanical obstacle (Hamlet and Stone 1978, Hamlet et al. 1979). Similar results
were found in other studies that attempted to improve compensation by requiring the
participants to read texts aloud between recordings (McFarland and Baum 1995,
McFarland et al. 1996, Baum and McFarland 1997). Even with such intensive speech
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practice, limitations were still observed in articulatory compensation. This lack of
complete appliance adaptation was examined in an electropalatographic study, in
which the linguopalatal contact was assessed using an artificial palate appliance with
excess palatal acrylic (Hamlet 1988). It was found that patients' original linguopalatal
contact pattern was maintained even after a week of practice, particularly for the /s/
sound.
The focus of most research has been on normal speakers, and their inability to
completely adapt to the temporary insertion of an appliance in the oral cavity. It is
even more important to understand how patients who have or have had pre-existing
articulation disorders are able to handle an intrusive dental appliance that drastically
alters the shape of the oral cavity. For example, patients who had childhood lisps and
other articulation disorders were found to take longer to adapt to a maxillary denture
(Hamlet and Stone 1982, Hamlet 1985). These patients adopted unusual tongue and
jaw postures when the appliance was inserted, and retained these positions over a two
week period even though these positions did not facilitate normal speech.
Consequently, the compensatory mechanisms of patients with previous articulation
disorders were different and less effective than those of patients with no previous
speech problems.
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Speech and Rapid Palatal Expanders
A recent publication investigated the influence of palatal expanders on speech,
oral comfort, swallowing, and mastication (De Felippe et al. 2010). This was the first
study that looked at rapid palatal expanders and their potential impact on speech. A
questionnaire was given to patients who had received a palatal expander three-to-
twelve months prior to the survey. Expanders in the study included Hyrax-banded,
Hyrax-bonded, Haas, and quad-helix. It should be noted that a quad-helix is usually
considered a slow palatal expander. This appliance does not have a central jackscrew
but four active helical springs on the lingual side of the maxillary alveolar ridge. The
questionnaire found that approximately 90% of patients stated that the expander
affected their speech. Alveolar sounds like /s/, /z/, /t/, and /d/ were the major
phonemes reported as being most challenging. Based on this retrospective
questionnaire, patients reported that by the end of the first week after appliance
insertion their speech problems resolved. It was also found that there were no
significant correlations between speech, type of appliance, sex or age.
Cooperation and Compliance
Orthodontic appliances can have both direct and indirect effects on speech.
The direct consequences include the structural and functional difficulties imposed on
the patient, which results in articulatory perturbations. The indirect consequences
may not always be as apparent, yet may have just as great an impact on the patient.
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The speech disorder may take a toll on the physical and mental health of the patient.
This must be considered, as these indirect consequences can alter treatment
cooperation and compliance. If cooperation and compliance are negatively affected,
ultimately orthodontic treatment will be a more unpleasant experience for everyone
involved.
The cooperation of the patient and parent plays an important role in
orthodontic treatment for obtaining an ideal result in an efficient manner. The
orthodontist relies on the patient and/or parent for regularly attended appointments,
appropriately followed appliance instructions and diet, and maintenance of oral
hygiene. The patient's acceptance of the orthodontic appliance can influence
compliance and thereby contribute to a successful outcome. Although it may be
difficult to avoid speech disorders caused by an orthodontic appliance, methods of
improving cooperation and compliance should be investigated (Sergl et al 2000).
It would be helpful if one was able to predict compliant patients to anticipate
and alleviate relevant issues before they interfere with treatment. Most research has
found that the best predictor is age because younger patients are more compliant
(Allan and Hodgson 1968, Weiss and Eiser 1977). Compliance and speed of
adaptation to the appliance were also improved when patients were aware of their
malocclusion (Lewit and Virolainen 1968). Sergl et al. (2000) found that compliance
and treatment success were improved when patients were made aware of potential
difficulties with the appliance, and when the individual believed in his or her ability
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to function competently with the appliance in place (Sergl et al. 2000). The initial
physical and functional discomfort associated with an appliance, particularly if
unexpected, affects acceptance and adaptation to the appliance and overall treatment
(Sergl et al. 1998). These observations are germane to the present study because an
RPE is typically one of the first appliances inserted at the beginning of treatment. If
the patient's initial experience is not ideal, this may negatively influence the
remainder of the orthodontic treatment, which could carry on for years.
With the insertion of an RPE, patients can experience unpleasant tactile
sensations, soreness of the teeth, feelings of oral cavity constraint, and altered
appearance, particularly during appliance activation when a diastema opens between
the maxillary central incisors. The RPE will also displace the tongue and affect
speech. Parents and patients can become concerned when there is a change in
speech, as speech and language difficulties have been associated with behavioural
problems, poor academic performance, and personal and social difficulties (Glascoe
2000, Beitchman et al. 2001). When speech is altered, it can also negatively affect a
patient's self-esteem (Zentner et al 1996). Unsuccessful speech adaptation to dental
appliances is a persistent and important problem that may be a major barrier to
successful treatment (Zentner et al 1996).
In order to enhance compliance, cooperation, and appliance adaptation and to
reduce unpleasant experiences, the patient and parent should be informed of all
potential appliance consequences prior to commencing treatment (Sergl et al. 2000).
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This discussion should not only include what can happen, but specifically in the case
of RPEs, should ideally include how long speech is likely to be affected and which
sounds are more likely to be a problem. It has been argued that an honest and
complete transfer of information strengthens the orthodontist-patient relationship,
improving long-term patient management and treatment results (Sinha et al. 1996).
The literature demonstrates that unsuccessful speech adaptation to dental
appliances is a persistent and important problem that may be a significant factor in
treatment success. In clinical practice, orthodontists using RPEs will tend to tell their
patients they may sound different initially but that they will sound better with time.
This information is typically grounded in clinical intuition and experience using the
appliance. However, such patient counseling is not based on research evidence. The
present study aims to provide first insights into the typical pattern of speech
adaptation in patients wearing an RPE.
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PURPOSE
The aim of this investigation was to perform a more accurate and detailed
analysis of speech changes over time after RPE insertion.
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HYPOTHESIS
The speech of patients will be adversely affected by the rapid palatal expander
appliance. In particular, we expect to see the following findings:
Patients will sound worst directly after the RPE insertion.
Over time, patients will adapt to the appliance. However, speech
acceptability will not return to pre-appliance levels until after the
appliance is removed.
The appliance will affect the patients’ vowel space. For the vowel /i/, vowel
centralization is expected, resulting in increased first formants and
decreased second formants.
The fricatives /s/ and /∫/ will be distorted as a result of the appliance
insertion. The spectral peaks of the fricatives will be lowered and
attenuated. The spectral mean will decreasing, the standard deviation will
increase, the skewness will become more positive and the kurtosis will
decrease.
NULL HYPOTHESIS
The rapid palatal expander appliance will not affect the speech of the patients,
and patients will be able to fully adapt to the appliance over the course of the
treatment.
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MATERIALS AND METHODS
A. Subjects
Ethics approval was given by the Health Sciences Research Ethics Board at the
University of Toronto. Twenty-two patients treatment planned for a rapid palatal
expander in conjunction with their orthodontic treatment in the Graduate
Orthodontic Clinic at the University of Toronto were recruited to the study. The
need for a rapid palatal expander as a part of the patient's treatment was determined
by the treating orthodontic residents and their orthodontic supervisors. Prior to the
initiation of the study, consent forms were reviewed and signed by the patient and if
under 16 years old, his or her parent. Of the twenty-two patients, thirteen were
females and nine males with ages ranging from nine to nineteen, with the mean age
of fourteen. This study did not alter or interfere with the overall orthodontic
treatment and did not add any extra visits to the orthodontic clinic for the
participants. All orthodontic treatment procedures e.g., maxillary and mandibular
alginate impressions for RPE fabrication, cementation and removal of the appliances
at beginning and end of treatment, respectively, were performed by the orthodontic
resident assigned to each patient. An additional step for patients recruited to the study
was a speech recording of approximately five minute duration conducted six times
throughout the treatment (see section C for the time points). All recordings were
performed by the investigator.
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B. Appliance fabrication
All twenty-two RPEs were made by the same lab technician in the Graduate
Laboratory at the Faculty of Dentistry, University of Toronto. RPEs were fabricated
with a central jackscrew. The expander mechanism was attached to four extensions
from the bands or acrylic arising from the lingual surfaces of the first premolars and
molars. Although there was no standard distance from the palate to the screw and the
extension arms, this distance was never less than 5mm. The screw was not flush to
palate to avoid trauma to the palatal mucosa during expansion. For the bonded RPEs,
the acrylic that was attached to the teeth was approximately 2mm thick on the
occlusal, buccal, and lingual surfaces.
C. Stimuli and procedures
The 15 sentences from the Fisher-Logemann Test of Articulation (FLTA;
Fisher and Logemann 1971) and the 20 sentences from the Great Ormond Street
Speech Assessment (GOSSPASS '98; Sell et al. 1999) were used for the recordings.
These sentences encompass all sounds of Canadian English and allow a detailed
assessment of particular individual phonemes. All speech samples were collected
using a laptop computer with a high quality microphone and the recording software
Audacity. All samples were recorded in a quiet room directly onto the hard disk
drive using a microphone that was placed 1-2 inches below the patient's chin. Each
patient read all thirty-five sentences at six different time periods (TP):
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Time period 1 (TP1)
Just prior to RPE insertion/cementation
Same day at TP2
Time period 2 (TP2)
Right after the RPE was inserted/cemented
Same day at TP1
Time period 3 (TP3)
During the RPE activation phase
Typically 2-4 weeks after TP1/TP2
Time period 4 (TP4)
During the RPE retention phase
Typically 1-2 months after TP3, or 2-3 months after TP1/TP2
Time period 5 (TP5)
After RPE was removed from patient's mouth
Typically 2-3 months after TP4, or 5-6 months after TP1/TP2
Time period 6 (TP6)
1-2 months after RPE was removed
From these thirty-five sentences, three sentences were selected for analysis in
the present study. Because the appliance lies across the palate, it was suspected that
alveolar and palatal phonemes would be affected the most. Therefore the vowel /i/,
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and fricatives /s/ and /∫/ were selected for analysis.The sentence "Let me keep a little
of this wedding cake to eat later" was selected to assess the impact of the appliance on
the vowel /i/. The sentence "Suzie sewed zippers on two new dresses at Bessie's house"
was used for the assessment of /s/, and the sentence "Sean is washing a dirty dish" for
the analysis of /∫/.
D. Analysis
Acceptability data:
Speech acceptability was assessed by ten naïve listeners, five male and five
female, who evaluated the three sentences of all twenty-two patients at all six time
periods. The participants were members of the public who were unaware of the
purposes of the investigation and had no prior training in phonetics, linguistics or
dentistry. The recordings were randomized and the participants listened via
headphones to all 396 recordings at a comfortable loudness and graded the patient's
speech on a numerical scale:
0 = normal speech acceptability
1 = speech acceptability mildly affected
2 = speech acceptability moderately affected
3 = speech acceptability severely affected
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Vowel /i/:
Using the WaveSurfer software, acoustic analyses were completed for the /i/
sentence. For the vowel /i/, two tokens were segmented for speech analysis. Long
term linear predictive coding (LPC) using 512 points and Hamming window, was used
to measure the first (F1) and second formants (F2) at each time period for each
patient. Formants are regions of high acoustic energy and are measured as an
amplitude peak in the frequency spectrum. The sentence had two words containing
an /i/ phoneme, "keep" and "eat", so two F1 and two F2 were measured. For any
missing data, the average formant for that particular phoneme at that time period was
calculated and replaced the missing data for the patient. Since the patients were all
different ages and genders, factors known to influence formant measurements, a
relative measure to define the distance between these two formants was calculated.
The distance between F1 and F2 was measured and a ratio was calculated by dividing
this F1-F2 distance for each time period by the F1-F2 distance from time period 1
(before the appliance was inserted).
Fricatives /s/ and /∫/:
Using the WaveSurfer software, acoustic analyses were also completed for the
/s/ and /∫/ sentences. For the fricatives /s/ and /∫/, target phonemes in the sentences
were isolated for speech analysis (three in /s/ sentence: "dress", "Bessie", "house", and
two in /∫/ sentence: "wash", "dish"), but both /s/ and /∫/ were analyzed separately.
23
Long term Fast Fourier Transforms (FFT) technique using 64 points and a Hamming
window setting, was used to evaluate each fricative. The output for each phoneme
consisted of uncalibrated amplitude values in decibels for 32 frequency bands. In
order to reduce the data and to decide which frequency bands should be used in the
analysis, factor analysis was employed. Because the amplitude values were not
calibrated, a ratio was used. A ratio of the amplitude associated with a low frequency
band and the amplitude associated with a higher frequency band was calculated for
each phoneme for each time period for each patient. Both the low and high
frequency band were chosen from the frequency bands identified by a factor analysis.
This ratio described the ‘crispness’ of the higher frequency band. Depending on
which sound was analyzed, the higher frequency band was selected to be close to the
average centroid frequency of either the /s/ or /∫/.
For the fricatives /s/ and /∫/, spectral moments were calculated. Using KAY-
Multi-Speech Model 3700, the recordings were low-pass filtered to 11.025 kHz,
following the procedure used for spectral moment analysis by Forrest et al. 1988), and
Jongman et al. (2000). Fast Fourier transforms (FFTs) were calculated using Hamming
windows with 98% pre-emphasis. Spectral moments for each individual fricative
were calculated with a 40 msec Hamming window at the central 40 ms location. For
each individual phoneme in the sentence, the spectral mean, standard deviation,
skewness, and kurtosis were measured.
24
For the acoustic data for each sound at each time period, histograms were
created to examine the data distributions. The data sets were all normally distributed.
For the acceptability data, a non-continuous ordinal rating system as used. However
by calculating an average of the 10 listeners for each recording, a continuous,
normally distributed data set was produced.
Statistical analysis
Perceptual and acoustic data were analyzed statistically using repeated
measures Analysis of Variance (ANOVA) with post-hoc paired t-tests or independent
t-tests. Boxplots were also used to examine interactions between variables. Missing
data for individual patients were replaced with the group mean for that time period.
Strict significant cut offs (ie. p<0.05) were not employed in the study due to the small
sample size and to attempt to avoid type II errors. Significance values that were close
to being significant (ie p<0.1) were still examined for trends in the data.
25
RESULTS
A. Acceptability data
In a first step, the naïve listeners’ average ratings of the three sentences for
each of the six time periods were graphed using boxplots. The boxplots followed a
clear pattern. Higher average ratings indicated that the speech sounded more
distorted to the listeners. When the appliance was first inserted and cemented in the
patients’ mouth, the average rating increased, indicating a poorer speech
acceptability. The average ratings improved over time, eventually returning to the
pre-appliance level when the appliance was removed. The final time period (1-2
months post-appliance removal) had a lower average rating compared to pre-
appliance values.
In order to investigate whether patients with pre-existing speech difficulties
had additional issues adapting to the RPE, the pre-appliance average ratings (TP1) for
the 22 patients were examined. The 22 participants were placed into two groups, low
speech acceptability ratings (SA low) and high speech acceptability ratings (SA high).
In order to place patients in the two groups, the 11 patients with the lowest average
ratings (least speech distortion) were the SA low group and the 11 patients with the
highest average ratings (greatest speech distortion) were the SA high group.
However, this division was not possible as both the 11th and 12th patients had the
same average rating of 0.65. Unequal groups of SA low (12 patients) and SA high (10
26
patients) were created by dividing the groups between the 12th and 13th patient. The
average rating for the SA low group ranged from 0 to 0.65, and the SA high group
from 0.7 to 2.2. This SA low - SA high variable was used when analyzing the
acceptability data, but also for each of the three phonemes examined in this study.
Figure 3. The average rating of the 10 naïve listeners for the 22 patients at 6 time periods
A repeated measures analysis of variance (ANOVA) was performed to examine
the average ratings with respect to time period and whether appliance type (banded
or bonded RPE) or pre-appliance speech rating (SA low or SA high) influenced the
results. Mauchly's test of sphericity (Mauchly 1940) was not found to be significant
(p=0.149) so sphericity was assumed and used to determine within-subject effects.
The effect of time period was found to be significant (p<0.001, 1−β =1, ηp2=0.633,
27
dF=5, F=84.372). Post-hoc analysis of time period using 15 paired t-tests revealed
that, as the initial boxplots displayed, the mean scores increased from time period 1
(TP1; pre-appliance) to TP2 (after appliance cementation). The average scores
decreased as time elapsed, still remaining greater than TP1, at TP3 and TP4 (during
activation of the appliance and during the appliance retention phase, respectively),
but the scores at TP5 and TP6 (when appliance was first removed and 1-2 months
post-appliance removal, respectively) were lower than those at TP1. All t-tests were
found to be significant (p<0.05) except TP1-TP5 (p=0.092).
Time Pair SignificanceTP1-TP2 0.000TP1-TP3 0.000TP1-TP4 0.006TP1-TP5 0.092TP1-TP6 0.000TP2-TP3 0.000TP2-TP4 0.000TP2-TP5 0.000TP2-TP6 0.000TP3-TP4 0.001TP3-TP5 0.000TP3-TP6 0.000TP4-TP5 0.000TP4-TP6 0.000TP5-TP6 0.000
Table 1. Paired t-tests for the acceptability data
No interaction was found between time and appliance type, time and pre-
appliance speech rating, nor the interaction between all three (p=0.262, p=0.268 and
p=0.259 respectively).
28
Between-subject effects of the ANOVA identified a significant difference
between the SA low and SA high pre-appliance speech groups (p<0.001, 1−β =1,
ηp2=0.435, dF= 1, F=37.729). Six separate independent t-tests were performed to
examine the difference between these two groups at each time period. Significant
differences (p<0.001) were found between SA low and SA high speech groups at each
time period. Although these groups were perceptually different at each time period
(the SA high group sounded more distorted), the SA high group did not fare worse
with the appliance inserted. In order to examine if the SA high group sounded worse
with the appliance at any time period, the difference between the speech rating
initially (TP1) and a subsequent time period (TP2 to TP6) was calculated and a
repeated measures ANOVA was performed on these differences. When looking at the
between-subject effects for the pre-appliance speech rating groups, there was no
significant difference (p=0.807). Although there was always a significant difference
between the SA low and SA high groups at any point, perceptually, all patients
appeared to cope with the RPE in a similar way.
The difference between the two appliance groups was close to being
statistically significant (p=0.085, 1−β=0.406, ηp2=0.059, dF= 1, F=3.085). Due to this
close significance, six separate independent t-tests were performed to examine the
difference between these two groups at each time period. However, there was no
time period that showed a significant difference between the group, nor was close to
being significant.
29
An interaction between the appliance type and the pre-appliance speech rating
was found to be significant by the ANOVA (p=0.011, 1−β=0.733, ηp2=0.124, dF= 1,
F=6.931). To examine this interaction, a multiple line graph with banded/bonded
appliance and SA low/SA high speakers was produced for all six time periods. At each
time period, the line pattern appeared similar. At TP2, when the appliance was
inserted, SA low speakers with a bonded appliance had increased average rating
scores.
B. Vowel - /i/
For the vowel sentence "Let me keep a little of this wedding cake to eat later",
two /i/ phonemes were analyzed, using "keep" and "eat". The second formants (F2)
were measured and examined over time. Boxplots were used to visualize the F2
change at each time period. These boxplots showed the F2 decreasing at TP2, then at
each subsequent time period the F2 increased, finally returning to the TP1 level at
TP6. A repeated measures ANOVA was performed to assess the F2 change at each
time period and to determine whether or not type of appliance or pre-appliance
speech rating influenced the F2. Mauchly's test of sphericity was found to be
significant (p=0.003) so sphericity was not assumed. Greenhouse-Geisser (p=0.520)
was used to determine within-subject effects (Greenhouse and Geisser 1959). The
effect of time period on F2 was found to be significant (p<0.001, 1−β =1, ηp2=0.828,
dF=2.60, F=67.222). There were no significant findings with the time/appliance
30
interaction, time/pre-appliance rating interaction, or time/appliance/pre-appliance
rating interaction (p=0.477, p=0.403 and p=0.180 respectively). Post-hoc analysis of
time period using 15 paired t-tests revealed that, as the initial boxplots displayed, the
F2 decreased when the appliance was inserted (TP2). The F2 continued to increase at
TP3, TP4, TP5 and eventually returned very close to the pre-appliance level at TP6.
All t-tests were found to be significant (p<0.05) except TP1-TP6 (p=0.152).
Figure 4. Second formant frequency for the vowel /i/ at each time period
31
Time Pair SignificanceTP1-TP2 0.000TP1-TP3 0.000TP1-TP4 0.000TP1-TP5 0.017TP1-TP6 0.152TP2-TP3 0.008TP2-TP4 0.000TP2-TP5 0.000TP2-TP6 0.000TP3-TP4 0.007TP3-TP5 0.000TP3-TP6 0.000TP4-TP5 0.000TP4-TP6 0.000TP5-TP6 0.035
Table 2. Paired t-tests for the vowel /i/ second formants
Between-subjects effects of the ANOVA found no significant differences
between type of appliance, pre-appliance speech rating, nor their interaction
(p=0.300, p=0.924, p=0.205 respectively).
The first formants (F1) were also measured and examined over time. Boxplots
were used to visualize the F1 change at each time period. These boxplots showed the
F1 increased at TP2 and TP3. F1 then began to decrease at TP4, and at TP5 and TP6,
F1 decreased below TP1. A repeated measures ANOVA was performed to assess the
F1 change at each time period and to determine whether or not the type of appliance
or the pre-appliance speech rating influenced the F1. Mauchly's test of sphericity was
not found to be significant (p=0.466) so sphericity was assumed and used to determine
within-subject effects. The effect of time period on F1 was found to be significant
32
(p<0.001, 1−β =0.999, ηp2=0.350, dF=5, F=7.533). There were no significant findings
with the time/appliance interaction, time/pre-appliance rating interaction, or
time/appliance/pre-appliance rating interaction (p=0.788, p=0.739 and p=0.591
respectively). Post-hoc analysis of time period using 15 paired t-tests revealed that, as
the initial boxplots displayed, the F1 increased when the appliance was inserted and
remained at approximately the same frequency at TP3. F1 then began to decrease at
TP4, still being greater than TP1. At TP5 and TP6, F1 continued to decrease, but was
less than TP1. All t-tests were found to be significant (p≤0.01) except TP1-TP4
(p=0.059), TP1-TP5 (p=0.368), TP1-TP6 (p=0.092), TP2-TP3 (p=0.672), TP2-TP4
(p=0.376), and TP5-TP6 (p=0.803).
Figure 5. First formant frequency for the vowel /i/ at each time period
33
Time Pair SignificanceTP1-TP2 0.000TP1-TP3 0.004TP1-TP4 0.059TP1-TP5 0.368TP1-TP6 0.092TP2-TP3 0.672TP2-TP4 0.376TP2-TP5 0.002TP2-TP6 0.000TP3-TP4 0.011TP3-TP5 0.000TP3-TP6 0.000TP4-TP5 0.011TP4-TP6 0.002TP5-TP6 0.803
Table 3. Paired t-tests for the vowel /i/ first formants
The test for between-subjects effects of the ANOVA found no significant
differences between type of appliance and pre-appliance speech rating (p=0.823 and
p=0.107 respectively). The interaction between appliance type and pre-appliance
speech rating was close to being significant (p=0.073, 1−β =0.440, ηp2=0.212, dF=1,
F=3.769) so a multiple line graph with banded/bonded appliance and SA low/SA high
speakers was produced at all six time periods to examine this interaction. The F1 for
the patients with the banded RPE appeared to have a consistent relationship between
SA low and SA high speakers, with SA high speakers having a greater F1 than the SA
low. For the patients with the bonded RPE, the relationship between SA low and SA
high speakers was more variable. When the bonded appliance was inserted at TP2,
the SA high speakers’ F1 increased more than the other three groups. However, with
34
each subsequent time period, the SA high/bonded speakers' F1 decreased, ending up
at TP6 lower than pre-appliance level and lower than the SA low/bonded speakers.
The SA low speakers at TP6 returned to TP1 F1 level, but the SA high speakers
decreased compared to TP1 level, with the SA high/bonded decreasing the most.
The patients in this study comprised both males and females, and patients of
different ages, variables shown to influence formant measurements (Perry et al 2001).
It was therefore necessary to calculate a relative measure to define the distance
between the two formants. The ratio of the distance between F1 and F2 divided by
the pre-appliance (TP1) F1-F2 distance was examined over time. Boxplots were used
to display this change in the distance ratio. From TP1 to TP2, the ratio decreased.
The ratio then increased with each subsequent time period (TP3-TP5), eventually
reaching pre-appliance TP1 levels at TP6. A repeated measures ANOVA was
performed to assess the ratio change at each time period and to determine whether or
not type of appliance or pre-appliance speech rating influenced the ratio. Sphericity
was not assumed as Mauchly's test of sphericity was found to be significant (p=0.017).
Greenhouse-Geisser (p=0.570) was used to determine within-subject effects. The
effect of time period was found to be significant (p<0.001, 1−β =1, ηp2=0.867, dF=2.851,
F=91.382). There were no significant findings with the time/appliance interaction or
time/pre-appliance rating interaction (p=0.543 and p=0.431 respectively). A
time/appliance/pre-appliance rating interaction was found to be significant (p=0.008,
1−β =0.745, ηp2=0.208 dF=2.274, F=4.285). Post-hoc analysis of time period using 15
35
paired t-tests revealed that, as the initial boxplots displayed, the ratio decreased when
the appliance was inserted, but then increased over each time period, reaching TP1
level at TP6. All t-tests were found to be significant (p≤0.05) except TP1-TP5 which
was close to being significant (p=0.063), and TP1-TP6 (p=0.609).
Figure 6. For vowel /i/, the difference between the first and second formants at each time period divided by the difference between the first and second formants at time period 1
36
Time Pair SignificanceTP1-TP2 0.000TP1-TP3 0.000TP1-TP4 0.000TP1-TP5 0.063TP1-TP6 0.609TP2-TP3 0.018TP2-TP4 0.000TP2-TP5 0.000TP2-TP6 0.000TP3-TP4 0.001TP3-TP5 0.000TP3-TP6 0.000TP4-TP5 0.000TP4-TP6 0.000TP5-TP6 0.033
Table 4. Paired t-tests for vowel /i/; the difference between the first and second formants at each time period divided by the difference between the first and second formants at time period 1
The interaction between time, appliance type and pre-appliance speech rating
was significant (p<0.001, 1−β =0.745, ηp2=0.208, dF=2.851, F=3.670) so a multiple line
graph with banded/bonded appliance and SA low/SA high speakers was produced at
all six time periods to examine this interaction. At TP2 when the appliance was
inserted, the F1-F2 with pre-appliance F1-F2 ratio decreased, more so for the SA
high/bonded group. Over time, at TP3 this ratio increased. The values for the SA
high/bonded group were lower than for the other three groups. By TP4, the SA low
and SA high speakers were similar in each group, with the banded group having a
slightly greater ratio compared to the bonded group. At TP5 and TP6, the ratios
returned to TP1 levels and all groups were similar.
37
Between-subjects effects of the ANOVA found no significant differences
between type of appliance, nor the interaction of appliance type and pre-appliance
speech rating (p=0.976 and p=0.557 respectively). However, a close to significant
result was found for the SA low and the SA high pre-appliance groups (p=0.089, 1−β
=0.400, ηp2=0.0.193, dF=1, F=3.351). Six separate independent t-tests were performed
to examine the difference between these two groups at each time period. No
significant differences were found between SA low and SA high speakers at any time
period.
C. Frequency band-volume ratios
i) Fricative - /∫/
For the fricative /∫/ in the sentence "Sean is washing a dirty dish", two /∫/
phonemes were analyzed, using "wash" and "dish". Long-term FFT for each phoneme
consisted of 32 fixed frequency bands in Hertz (Hz) and the associated variable
volume measured in decibels (dB) for each patient at each time period. In order to
reduce this large amount of data and to decide which frequency bands should be used
in the statistical analysis, factor analysis was used. This analysis produced four
frequency bands: 875Hz, 1875Hz, 3125Hz, and 4625Hz. The volume associated with
each frequency band is variable and can be affected by day-to–day variation in vocal
loudness. In order to control for this variability, a ratio was calculated using two of
the four frequency bands identified using factor analysis. The dB ratio of the
38
frequency bands at 875Hz and 3125Hz was used in the statistical analysis. The 875Hz
band represented a frequency band that was far enough away from the peak /∫/
frequency. The 3125 Hz band represented a frequency band that was close to the /∫/
major frequency peak. The associated volume of the peak was expected to be
attenuated with the insertion of the RPE. The 3125Hz band was assumed to be close
to this peak as Behrens and Blumstein (1988) found the major frequency peak for /∫/
within the 2500 to 3500 Hz range.
Figure 7. The ratio of the volumes associated with the frequency bands 875Hz and 3125Hz at each time period for the fricative /∫/
A repeated measures ANOVA was performed to assess the fricative /∫/ volume
ratio change at each time period and to determine whether or not the type of
appliance or the pre-appliance speech rating influenced the ratio. Mauchly's test of
sphericity was found to be significant (p=0.003) so sphericity was not assumed.
39
Greenhouse-Geisser (p=0.745) was used to determine within-subject effects. The
effect of time period on the volume ratios was found to be significant (p<0.001, 1−β
=1, ηp2=0.299, dF=3.726, F=17.076). Post-hoc analysis of time period using 15 paired t-
tests revealed that when the appliance was inserted, the ratio decreased (TP1-TP2).
This decreased ratio was associated with a decrease in volume of the fricative. At
TP3, the ratio increased from TP2, but was still decreased compared to TP1. At TP4,
the ratio remained approximately the same, but just slightly decreased compared to
TP3. TP5 and TP6 both increased, but TP6 just slightly decreased compared to TP1.
All t-tests were found to be significant (p<0.05) except TP1-TP6 (p=0.287), TP3-TP4
(p=0.573), TP3-TP5 (p=0.289), TP3-TP6 (p=0.071), TP4-TP5 (p=0.073), and TP5-TP6
(p=0.346).
Time Pair SignificanceTP1-TP2 0.000TP1-TP3 0.010TP1-TP4 0.004TP1-TP5 0.034TP1-TP6 0.287TP2-TP3 0.000TP2-TP4 0.000TP2-TP5 0.000TP2-TP6 0.000TP3-TP4 0.573TP3-TP5 0.289TP3-TP6 0.071TP4-TP5 0.073TP4-TP6 0.005TP5-TP6 0.346
Table 5. Paired t-tests for the ratio of the volumes associated with the frequency bands 875Hz and 3125Hz at each time period for the fricative /∫/
40
An interaction between time and pre-appliance speech rating was also found
to be significant (p=0.026, 1−β =0.719, ηp2=0.064, dF=3.726, F=2.720). Boxplots at each
time period for SA low and SA high pre-appliance speech rating were created. By
examining the boxplots from TP1 to TP6, the SA high speakers always had a reduced
ratio compared to the SA low speakers, but at TP2, when the appliance was inserted,
the SA low speakers had a decreased ratio, similar to the SA high group. However, by
TP3 the TP1, pre-appliance ratio relationship between SA low and SA high was
restored and remained consistent in TP4 and TP5. At TP6, the SA low speakers
remained at TP1 levels, however the SA high speakers had an increased ratio.
No significant time/appliance, nor time/appliance type/pre-appliance rating
interactions were found (p=0.300 and p=0.357 respectively). Between-subject effects
of the ANOVA did not find a significant difference between appliance type nor the
interaction between appliance type and pre-appliance speech rating (p=0.235 and
p=0.801 respectively).
Between-subject effects of the ANOVA identified a significant difference
between the SA low and SA high pre-appliance speech groups (p=0.009, 1−β =0.758,
ηp2=0.157, dF= 1, F=7.425). Six separate independent t-tests were performed to
examine the difference between these two groups at each time period. A significant
difference between SA low and SA high group was found at TP1 (p=0.002, t=3.320,
df=42), where the ratio was smaller for the SA high group, indicating a decreased
fricative volume. No significant difference was found at TP2 (p=0.972). At TP3, the
41
SA high speakers had decreased volumes, but only a tendency towards significance
was found (p=0.072). At TP4, there was a significant difference between the groups,
with lower volumes in the SA high group (p=0.02, t=2.422, dF=42). At TP5, again the
SA high speakers had decreased volumes and the difference between the groups was
found to be significant (p=0.010, t=2.717, dF=42). At TP6, there was no significant
difference between the groups, although the SA high speakers had decreased volumes
(p=0.280).
ii) Fricative - /s/
For the fricative sentence "Suzie sewed two zippers on two new dresses at
Bessie's house", three /s/ phonemes were analyzed, using "dress", "Bessie", and "house".
As with the /∫/ fricative, the long-term FFT for each phoneme consisted of 32 fixed
frequency bands in Hertz (Hz) and the associated variable volume measured in
decibels (dB) for each patient at each time period. Again, factor analysis was used to
reduce this large amount of data and aid in our selection of frequency bands used in
the statistical analysis. Factor analysis identified six frequency bands: 375Hz,
1625Hz, 2375Hz, 4125Hz, 6125Hz, and 7125Hz. A ratio was calculated to account for
variability in microphone position and speaking volume. The ratio consisted of two
of the six frequency bands. The volume ratio expressed the relationship of a less
variable lower frequency band to a more variable higher frequency band. The dB
ratio of the associated 1625Hz/4125Hz was used in the statistical analysis to account
42
for voice level changes. The 1625Hz band was the low band chosen, representing a
frequency band that was far enough away from the peak /s/ frequency and therefore
its associated volume was less likely to be affected by the insertion of an RPE. The
4125Hz band was the high band chosen, representing a frequency band that was close
to the /s/ major frequency peak, whose associated volume was expected to be
attenuated with the insertion of the RPE. The 4125Hz band was assumed to be close
to this peak as Behrens and Blumstein (1988) found the /s/ major frequency peak
within the 3500 to 5000 Hz range.
Figure 8. The ratio of the volumes associated with the frequency bands 1625Hz and 4125Hz at each time period for the fricative /s/
A repeated measures ANOVA was performed to assess the fricative /s/ volume
ratio change at each time period and to determine whether or not the type of
43
appliance or the pre-appliance speech rating influenced the ratio. Mauchly's test of
sphericity was found to be significant (p=0.003) so sphericity was not assumed.
Greenhouse-Geisser (p=0.425) was used to determine within-subject effects. The
effect of time period on the volume ratios was found to be significant (p=0.001, 1−β
=0.935, ηp2=0.102, dF=2.123, F=7.072). Post-hoc analysis of time period using 15
paired t-tests revealed that when the appliance was inserted, the ratio decreased (TP1-
TP2). This decreased ratio was associated with a decrease in volume of the fricative.
At TP3, the ratio was slightly decreased from TP2. At TP4, the ratio increased above
TP1, and at TP5 the ratio decreased compared to TP4 but was close to and slightly
greater than TP1. The ratio increased and has greater than any other time period at
TP6. All t-tests were found to be significant except TP1-TP4 (p=0.414), TP1-TP5
(p=0.777), TP1-TP6 (p=0.153), TP2-TP3 (p=0.535), TP4-TP5 (p=0.329), and TP4-TP6
(p=0.104).
44
Time Pair SignificanceTP1-TP2 0.005TP1-TP3 0.023TP1-TP4 0.414TP1-TP5 0.777TP1-TP6 0.153TP2-TP3 0.535TP2-TP4 0.003TP2-TP5 0.025TP2-TP6 0.001TP3-TP4 0.000TP3-TP5 0.000TP3-TP6 0.000TP4-TP5 0.329TP4-TP6 0.104TP5-TP6 0.008
Table 6. Paired t-test for ratio of the volumes associated with the frequency bands 1625Hz and 4125Hz at each time period for the fricative /s/
No significant time/appliance type interaction, nor time/appliance type/pre-
appliance rating interaction was found (p=0.725 and p=0.379 respectively). The
interaction of time with pre-appliance speech rating was close to being statistically
significant (p=0.059, 1−β =0.564, ηp2=0.044, dF=2.123, F=2.829). Boxplots at each time
period for SA low and SA high pre-appliance speech rating were created. By
examining the boxplots, from TP1 to TP6, the SA high speakers had similar ratios to
the SA low speakers. At TP2, the both ratios decreased similarly. However,
beginning at TP3 to TP5, the SA high group then began to have a decreased ratio
compared to the SA low group. By TP6, the groups were back to having similar ratios
again.
45
Between-subject effects of the ANOVA identified a significant difference
between the SA low and SA high pre-appliance speech groups (p=0.003, 1−β =0.870,
ηp2=0.137, dF= 1, F=9.825). Six separate independent t-tests were performed to
examine the difference between these two groups at each time period. No significant
difference between SA low and SA high groups was found at TP1 (p=0.260) or TP2
(p=0.893). A significant difference between these groups was found at TP3 (p=0.020,
t=2.288, df=64), where the ratio was smaller for the SA high group, indicating a
decreased fricative volume. At TP4, the SA high speakers had decreased volumes, but
no significant difference was found, though there was a tendency towards
significance (p=0.079). At TP5, again the SA high speakers had decreased volumes
and was found to be significant (p<0.001, t=3.689, dF=64). At TP6, there was no
significant difference between the groups, though the SA high speakers did have
decreased volumes and it was close to being significant (p=0.078).
Between-subject effects of the ANOVA did not find a significant difference
between banded and bonded appliances, nor an interaction between type of appliance
and pre-appliance rating (p=0.567 and p=0.924).
D. Spectral moments
Spectral moments were used as an additional method to quantitatively classify
the fricative data. Studies have found these moments provide critical information as
to the place of articulation of these fricatives (Forrest et al. 1988, Jongman et al. 2000).
46
The four moments summarize the concentration, variance, tilt and peakedness of the
energy distributions.
i) Fricative - /∫/
"Sean is washing a dirty dish" had two /∫/ phonemes that were analyzed,
"wash" and "dish". For both phonemes, spectral mean (Hz), standard deviation (Hz),
skewness, and kurtosis were measured. For each of these four measurements a
repeated measures ANOVA was completed with appropriate post-hoc tests.
a) Spectral Mean - Using a repeated measures ANOVA, Mauchly's test of
sphericity was found to be significant (p<0.001) so sphericity was not assumed.
Greenhouse-Geisser (p=0.538) was then used to determine significance of the various
ANOVA measurements. The effect of time period on spectral mean was found to be
significant (p<0.001, 1−β =0.973, ηp2=0.156, dF=2.688, F=7.391). Post-hoc analysis of
time period using 15 paired t-tests revealed that when the appliance was inserted, the
spectral mean decreased. With each subsequent time period the spectral mean
increased (TP2-TP3-TP4), eventually reaching pre-appliance TP1 levels when the
appliance was removed (TP5) and remained at this level, slightly greater than TP1,
after the appliance had been off for 1-2 months (TP6). Significant paired t-tests were
found for TP1-TP2 (p<0.001) , TP2-TP3 (p=0.01), TP2-TP4 (p=0.001), TP2-TP5
(p=0.001), TP2-TP6 (p<0.001), and TP3-TP6 (p=0.044).
47
Figure 9. Spectral mean for the fricative /∫/ at each time period
Time Pair SignificanceTP1-TP2 0.000TP1-TP3 0.137TP1-TP4 0.999TP1-TP5 0.485TP1-TP6 0.235TP2-TP3 0.010TP2-TP4 0.001TP2-TP5 0.001TP2-TP6 0.000TP3-TP4 0.113TP3-TP5 0.131TP3-TP6 0.044TP4-TP5 0.457TP4-TP6 0.223TP5-TP6 0.577
Table 7. Paired t-tests for the spectral means of the fricative /∫/
48
No time/pre-appliance speech rating interaction was found (p=0.369), however
a time/appliance type interaction was found to be significant (p=0.026, 1−β =0.714,
ηp2=0.026, dF=2.688, F=3.359). Boxplots were created for the banded versus bonded
appliance type at each time period. Before the appliance was inserted, patients who
were to get a bonded appliance had higher spectral means. When the appliance was
inserted at TP2, the patients with a bonded appliance had a greater decrease in
spectral mean, but then returned to having a similar pre-appliance relationship from
TP3 to TP6.
The interaction between time/appliance type/pre-appliance speech rating was
close to being significant (p=0.085, 1−β =0.540, ηp2=0.055, dF=2.688, F=2.328). A
multiple line graph with banded/bonded appliance and SA low/SA high speakers was
produced at all six time periods to examine this interaction. When the appliance was
inserted at TP2 there was a decrease in spectral mean frequency for all groups, but
more so for the SA high/bonded and SA low/bonded group. This mean frequency for
each group increased at TP3, TP4 and TP5. At TP6 the frequency remained stable
and had returned to pre-appliance (TP1) levels with the SA high/banded having an
increased mean frequency than at TP1.
Between-subjects effects of the ANOVA found no significant differences
between type of appliance, pre-appliance speech rating nor their interaction (p=0.299,
p=0.459 and p=0.845 respectively).
49
b) Standard Deviation - Using a repeated measures ANOVA, Mauchly's test of
sphericity was found to be significant (p<0.001) so sphericity was not assumed.
Greenhouse-Geisser (p=0.293) was then used to determine significance of the various
ANOVA measurements. The effect of time period on standard deviation was not
found to be significant (p=0.108, 1−β =0.409, ηp2=0.058, dF=2.688, F=2.328). No post-
hoc tests were completed for standard deviation.
Figure 10. Standard deviation for the fricative /∫/ at each time period
No interaction of time with appliance type, pre-appliance speech rating nor
the combination of all three was found to be significant (p=0.734, p=0.429, and
p=0.194 respectively). Between-subjects effects of the ANOVA found no significant
differences between type of appliance, nor the interaction of appliance type with pre-
50
appliance speech rating (p=0.177 and p=0.220 respectively). However, a significant
difference was found between the pre-appliance speech rating (SA low/SA high)
group (p=0.042, 1−β =0.535, ηp2=0.099, dF=1, F=4.401). Six independent t-tests were
completed, evaluating the difference between SA low and SA high groups at each
time period. At each time period the SA high group had a greater standard deviation.
A significant difference was found between these groups at TP1 (p=0.019), TP4
(p=0.008), and TP5 (p=0.005).
c) Skewness - Using a repeated measures ANOVA, Mauchly's test of sphericity
was found to be significant (p=0.014) so sphericity was not assumed. Greenhouse-
Geisser (p=0.765) was then used to determine significance of the various ANOVA
measurements. The effect of time period on skewness was found to be significant
(p=0.018, 1−β =0.793, ηp2=0.072, dF=3.824, F=3.124). Post-hoc analysis of time period
using 15 paired t-tests revealed that prior to appliance insertion, there was a negative
skew to the data. When the appliance was inserted, the skewness became more
positive. At TP3 and TP4, the skewness returned to pre-appliance levels, being
slightly more negative than TP1. This skewness returned to being more positive at
TP5 and TP6. The t-tests only found significance for TP4-TP5 (p=0.007) and TP4-
TP6 (p=0.014).
51
Figure 11. Skewness for the fricative /∫/ at each time period
Time Pair SignificanceTP1-TP2 0.340TP1-TP3 0.724TP1-TP4 0.277TP1-TP5 0.060TP1-TP6 0.078TP2-TP3 0.272TP2-TP4 0.093TP2-TP5 0.268TP2-TP6 0.466TP3-TP4 0.395TP3-TP5 0.075TP3-TP6 0.083TP4-TP5 0.007TP4-TP6 0.014TP5-TP6 0.641
Table 8. Paired t-tests for the skewness of the fricative /∫/
52
No interaction of time with appliance type, pre-appliance speech rating nor
the combination of all three was found to be significant (p=0.160, p=0.178 and
p=0.278 respectively). Between-subjects effects of the ANOVA found no significant
differences between type of appliance, pre-appliance speech rating nor their
interaction (p=0.162, p=0.434 and p=0.218 respectively).
d) Kurtosis - Using a repeated measures ANOVA, Mauchly's test of sphericity
was found to be significant (p<0.001) so sphericity was not assumed. Greenhouse-
Geisser (p=0.579) was then used to determine significance of the various ANOVA
measurements. The effect of time period on kurtosis was close to being significant
(p=0.073, 1−β =0.578, ηp2=0.057, dF=2.895, F=2.406). Because of this tendency towards
significance, post-hoc analysis of time period using 15 paired t-tests revealed that
when the appliance was inserted the kurtosis value decreased, but returned to pre-
appliance range from TP3 to TP6. Significant t-tests were found for TP1-TP2
(p=0.003) , TP2-TP3 (p=0.001), TP2-TP4 (p=0.001) and TP2-TP5 (p=0.004), with TP2-
TP6 close to being significant (p=0.061).
53
Figure 12. Kurtosis for the fricative /∫/ at each time period
Time Pair SignificanceTP1-TP2 0.003TP1-TP3 0.404TP1-TP4 0.763TP1-TP5 0.324TP1-TP6 0.812TP2-TP3 0.001TP2-TP4 0.001TP2-TP5 0.004TP2-TP6 0.061TP3-TP4 0.620TP3-TP5 0.768TP3-TP6 0.437TP4-TP5 0.435TP4-TP6 0.643TP5-TP6 0.113
Table 9. Paired t-tests for the kurtosis of the fricative /∫/
54
No significant interaction of time and appliance type, time and pre-appliance
speech rating nor the combination of all three was found (p=0.467, p=0.793 and
p=0.182 respectively). Between-subjects effects of the ANOVA found no significant
differences between type of appliance, pre-appliance speech rating nor their
interaction (p=0.295, p=0.558 and p=0.353).
ii) Fricative - /s/
"Suzie sewed two zippers on two new dresses at Bessie's house" had three /s/
phonemes that were analyzed, "dress", "Bessie" and "house". For each phoneme,
spectral mean (Hz), standard deviation (Hz), skewness, and kurtosis were measured.
For each of these four measurements a repeated measures ANOVA was completed
with appropriate post-hoc tests.
a) Spectral Mean - Using a repeated measures ANOVA, Mauchly's test of
sphericity was found to be significant (p<0.001) so sphericity was not assumed.
Greenhouse-Geisser (p=0.694) was then used to determine significance of the various
ANOVA measurements. The effect of time period on spectral mean was found to be
significant (p<0.001, 1−β =0.964, ηp2=0.084, dF=3.468, F=5.659). Post-hoc analysis of
time period using 15 paired t-tests revealed that when the appliance was inserted, the
spectral mean decreased. With each subsequent time period the spectral mean
increased (TP2-TP3-TP4), eventually reaching pre-appliance TP1 levels when the
55
appliance was removed (TP5), and remained at this level after the appliance had been
off for 1-2 months (TP6). Significant paired t-tests were found for TP1-TP2 (p=0.005)
, TP2-TP3 (p=0.002), TP2-TP4 (p=0.009), TP2-TP5 (p<0.001), TP2-TP6 (p<0.001),
TP3-TP5 (p=0.032) and TP4-TP5 (p=0.03).
Figure 13. Spectral mean for the fricative /s/ at each time period
56
Time Pair SignificanceTP1-TP2 0.005TP1-TP3 0.276TP1-TP4 0.327TP1-TP5 0.478TP1-TP6 0.811TP2-TP3 0.002TP2-TP4 0.009TP2-TP5 0.000TP2-TP6 0.000TP3-TP4 0.662TP3-TP5 0.032TP3-TP6 0.088TP4-TP5 0.030TP4-TP6 0.083TP5-TP6 0.467
Table 10. Paired t-tests for the spectral means of the fricative /s/
No significant interaction of time and appliance type, and time and pre-
appliance speech rating was found to be significant (p=0.604 and p=0.492
respectively). The interaction of time, appliance type and pre-appliance speech rating
was close to being significant (p=0.066, 1−β =0.624, ηp2=0.036, dF=3.468, F=2.328).
When the appliance was inserted at TP2 there was a decrease in spectral mean
frequency for all groups, but more so for the SA low/bonded group. By TP3, all groups
returned to pre-appliance (TP1) levels except the SA high/banded group. The SA
high/banded group over time returned to TP1 level.
Between-subjects effects of the ANOVA found no significant differences
between type of appliance, nor the interaction of appliance type with pre-appliance
speech rating (p=0.839 and p=0.996 respectively). However a close to significant
57
result was found between the pre-appliance speech rating group (p=0.092, 1−β =0.391,
ηp2=0.045, dF=1, F=2.923). Six independent t-tests were completed, evaluating the
difference between SA low and SA high groups at each time period. A significant
difference was found between these groups at TP4 (p=0.028) and was close to being
significant at TP3 (p=0.073), and TP5 (p=0.057). The spectral mean of the SA high
group was decreased compared to the SA low group.
b) Standard Deviation - Using a repeated measures ANOVA, Mauchly's test of
sphericity was found to be significant (p<0.001) so sphericity was not assumed.
Greenhouse-Geisser (p=0.783) was then used to determine significance of the various
ANOVA measurements. The effect of time period on standard deviation was found to
be significant (p=0.018, 1−β =0.795, ηp2=0.047, dF=3.915, F=3.051). Post-hoc analysis
of time period using 15 paired t-tests revealed that when the appliance was inserted
(TP2), the standard deviation increased. The standard deviation remained increased
at TP3 and TP4, but decreased to pre-appliance levels at TP5, and decreased even
more at TP6. Significant paired t-tests were found for TP2-TP6 (p=0.003), TP3-TP5
(p= 0.024), TP3-TP6 (p=0.001), TP4-TP5 (p=0.004) and TP4-TP6 (p<0.001).
58
Figure 14. Standard deviation for the fricative /s/ at each time period
Time Pair SignificanceTP1-TP2 0.663TP1-TP3 0.375TP1-TP4 0.340TP1-TP5 0.341TP1-TP6 0.098TP2-TP3 0.564TP2-TP4 0.548TP2-TP5 0.066TP2-TP6 0.003TP3-TP4 0.934TP3-TP5 0.024TP3-TP6 0.001TP4-TP5 0.004TP4-TP6 0.000TP5-TP6 0.247
Table 11. Paired t-tests for the standard deviations of the fricative /s/
59
No significant interaction of time and appliance type, time and pre-appliance
speech rating nor the combination of all three was found (p=0.935, p=0.904 and
p=0.631 respectively). Between-subjects effects of the ANOVA found no significant
differences between type of appliance, pre-appliance speech rating nor their
interaction (p=0.641, p=0.190 and p=0.110 respectively).
c) Skewness - Using a repeated measures ANOVA, Mauchly's test of sphericity
was found to be significant (p=0.002) so sphericity was not assumed. Greenhouse-
Geisser (p=0.814) was then used to determine significance of the various ANOVA
measurements. The effect of time period on skewness was found to be significant
(p<0.001, 1−β =0.973, ηp2=0.079, dF=3.824, F=4.071). Post-hoc analysis of time period
using 15 paired t-tests revealed that prior to appliance insertion, there was a negative
skew to the data. When the appliance was inserted, the skewness became more
positive. The data became more negative at TP3 and TP4, but still remained more
positive compared to pre-appliance (TP1) levels. By TP5 and TP6, the skewness
eventually returned close to TP1 values. The t-tests found significance for TP1-TP2
(p=0.001), TP2-TP3 (p=0.001), TP2-TP4 (p=0.004), TP2-TP5 (p<0.001), and TP2-TP6
(p=0.001).
60
Figure 15. Skewness for the fricative /s/ at each time period
Time Pair SignificanceTP1-TP2 0.001TP1-TP3 0.270TP1-TP4 0.211TP1-TP5 0.911TP1-TP6 0.716TP2-TP3 0.001TP2-TP4 0.004TP2-TP5 0.000TP2-TP6 0.001TP3-TP4 0.977TP3-TP5 0.247TP3-TP6 0.332TP4-TP5 0.203TP4-TP6 0.315TP5-TP6 0.750
Table 12. Paired t-tests for the skewness of the fricative /s/
61
No significant interaction of time and appliance type, time and pre-appliance
speech rating nor the combination of all three was found (p=0.942, p=0.227 and
p=0.214 respectively). Between-subjects effects of the ANOVA found no significant
differences between type of appliance, pre-appliance speech rating nor their
interaction (p=0.313, p=0.151 and p=0.896 respectively).
d) Kurtosis - Using a repeated measures ANOVA, Mauchly's test of sphericity
was found to be significant (p<0.001) so sphericity was not assumed. Greenhouse-
Geisser (p=0.668) was then used to determine significance of the various ANOVA
measurements. The effect of time period on kurtosis was not found to be significant
(p=0.133, 1−β =0.504, ηp2=0.029, dF=3.339, F=1.849). No post-hoc tests were
completed for kurtosis.
62
Figure 16. Kurtosis for the fricative /s/ at each time period
Time Pair SignificanceTP1-TP2 0.069TP1-TP3 0.123TP1-TP4 0.054TP1-TP5 0.225TP1-TP6 0.535TP2-TP3 0.506TP2-TP4 0.810TP2-TP5 0.225TP2-TP6 0.037TP3-TP4 0.573TP3-TP5 0.711TP3-TP6 0.157TP4-TP5 0.369TP4-TP6 0.086TP5-TP6 0.364
Table 13. Paired t-tests for the kurtosis of the fricative /s/
63
No significant interaction of time and appliance type, time and pre-appliance
speech rating nor the combination of all three was found (p=0.213, p=0.941 and
p=0.682 respectively). Between-subjects effects of the ANOVA found no significant
differences between type of appliance, nor the interaction of appliance type with pre-
appliance speech rating (p=0.401 and p=0.845 respectively). However a close to
significant difference was found between the pre-appliance speech rating group
(p=0.056, 1−β =0.482, ηp2=0.057, dF=1, F=3.776). Six independent t-tests were
completed, evaluating the difference between SA low and SA high groups at each
time period. At each time period the SA high group had a decreased kurtosis value.
A significant difference was found between these groups at TP3 (p=0.03) and TP4
(p=0.039), with close significance at TP5 (p=0.056).
64
SUMMARY OF RESULTS
A. Acceptability data
When the RPE was inserted (TP2), the patients' speech acceptability scores
increased (speech acceptability deteriorated). Over time, the acceptability scores
decreased (speech acceptability improved), only returning to pre-appliance levels
when the appliance was removed (TP5). At 1-2 months post-removal (TP6) the scores
were decreased compared to pre-appliance levels (speech acceptability improved). No
significant differences were found between the SA low and SA high patients, nor the
banded and bonded appliance types.
B. Vowel - /i/
When the RPE was inserted (TP2), the second formant decreased and the first
formant increased. Over time both formants began returning to the pre-appliance
level (second formant increased and first formant decreased). By the retention phase
(TP4), the first formant reached its pre-appliance level, whereas the second formant
only returned to pre-appliance levels 1-2 months post-removal (TP6).
When the ratio of the distance between the first and second formants at each
time period during and after the treatment was compared to the pre-treatment ratio
(TP1), the ratio decreased at RPE insertion (TP2) and slowly increased over time
returning to pre-appliance levels at RPE removal (TP5).
65
No significant differences were found between the SA low and SA high
patients, nor the banded and bonded appliance types.
C. Fricative frequency band-volume ratios
i) Fricative - /∫/
Upon RPE insertion (TP2), the 875Hz/3125Hz volume ratio decreased. Over
the course of the treatment, this volume ratio increased but only returned to pre-
appliance levels 1-2 months post-removal (TP6). Differences were found between the
SA low and SA high patients were the SA high patients had decreased volume ratios
compared to the SA low group at TP1, TP3, TP4 and TP5. No significant differences
were found between the banded and bonded appliance types.
ii) Fricative - /s/
Upon RPE insertion (TP2), the 1625Hz/4125Hz volume ratio decreased. Over
time, this volume ratio increased, and returned to pre-appliance levels by the
retention phase (TP4). Differences were found between the SA low and SA high
patients where the SA high patients had decreased volume ratios compared to the SA
low group at TP3 and TP5. No significant differences were found between the
banded and bonded appliance types.
66
D. Fricative spectral moments
i) Fricative - /∫/
Spectral Mean
When the RPE was inserted (TP2) the spectral mean decreased, but returned
to pre-appliance levels by the activation phase (TP3). No significant differences were
found between the SA low and SA high patients, nor the banded and bonded
appliance types.
Standard Deviation
No significant effect was found for the standard deviation with the insertion of
the appliance. No significant differences were found between the banded and bonded
appliance types. Significant differences were found between the SA low and SA high
patients where the SA high patients had greater standard deviation at TP1, TP4 and
TP5.
Skewness
Minimal significant effects on skewness were found with appliance insertion.
No significant differences were found between the SA low and SA high patients, nor
the banded and bonded appliance types.
Kurtosis
When the appliance was inserted (TP2) the kurtosis value decreased, but
returned to pre-appliance levels by the activation phase (TP3). No significant
67
differences were found between the SA low and SA high patients, nor the banded and
bonded appliance types.
i) Fricative - /s/
Spectral Mean
When the appliance was inserted (TP2) the spectral mean decreased, but
returned to pre-appliance levels by the activation phase (TP3). Differences were
found the SA low and SA high patients were the SA high patients had a greater
decrease in spectral mean at TP3, TP4 and TP5. No significant differences were found
between the banded and bonded appliance types.
Standard Deviation
The effect of the RPE on standard deviation was found post appliance removal
(TP6), where the standard deviation was less at TP6 compared to other time points.
No significant differences were found between the SA low and SA high patients, nor
the banded and bonded appliance types.
Skewness
When the appliance was inserted (TP2) the skewness became positive but
returned to pre-appliance levels (more negative) at the activation phase (TP3). No
significant differences were found between the SA low and SA high patients, nor the
banded and bonded appliance types.
68
Kurtosis
When the appliance was inserted (TP2) the kurtosis value decreased, but
returned to pre-appliance levels by the activation phase (TP3). No significant
differences were found between the SA low and SA high patients, nor the banded and
bonded appliance types.
69
DISCUSSION
A. Acceptability data
It is important to note as a caveat that speech acceptability is a global measure
of the listener’s social response to a speaker. Such a judgment may potentially be
influenced by factors such as regional accent, voice quality or nasality, none of which
were systematically assessed in this study. The acceptability measure also does not
replace a detailed phonetic profile of the patient’s speech.
The naïve listeners’ scores demonstrated that the RPE clearly had a negative effect on
the patients' speech. When the appliance was first cemented in the mouth, the
patients' speech sounded the most distorted. The appliance's screw obstructed the
tongue and blocked the alveolar process and palate. Over time, patients adapted to the
appliance. During the weeks between the recordings, the patients had many
opportunities to practice speaking with the appliance during normal daily activities.
With this practice, they were able to improve over time, despite the considerable
speech perturbation. When the appliance was removed from the mouth, patients
sounded as they previously had, before the appliance was cemented. However, after
the appliance was removed for 1-2 months, patients sounded better than they did
initially. This could be due to an increased palatal width, which may have
contributed to improving phoneme production. Laine (1986) found that patients with
a narrower palate had increased more /s/ sound distortions than controls. Similar
70
perceptual results were found in studies that looked at other appliances such as bite
blocks and artificial palates with increased alveolar acrylic (Baum et al 1996,
McFarland et al 1996, Baum and McFarland 1997, 2000). Although the investigators
used different methods, all demonstrated increased speech distortions. The studies
used removable appliances that were used solely for the study and not for clinical
treatment. The appliances were only left in the mouth for short periods of time (15
min to 60 min). Perceptual analysis after these short periods did find some adaptation
and improved ratings, but adaptation was rarely complete. It was interesting to see in
this study how the initial adaptation will continue to refine and improve over the
duration of an actual course of orthodontic treatment.
In order to investigate whether patients with pre-existing speech difficulties
had additional issues adapting to the RPE, the pre-appliance average ratings (TP1) for
the 22 patients were examined. The group of 22 was arbitrarily divided into twelve
SA low and 10 SA high patients. The cutoff score was 0.7. If a threshold of 1.0 or
greater had been chosen to divide the groups, the ‘bad’ group would have shown more
consistent speech distortions. We acknowledge that the close-to-equal group division
may not have been the most precise way of separating pre-existing speech difficulties.
It was expected that the bonded appliance would cause worse speech
distortions than the banded appliance because of the additional bite-block effect of
the acrylic coverings of the teeth. This, however, was not found to be the case, and
there were no differences between the two groups. The bonded RPE is fabricated
71
with minimal acrylic on the occlusal surface. Past studies examining the effect of bite
blocks on speech used a small bite block (2.5mm to 5mm interincisal distance) versus
a large bite block (10mm to 22.5mm interincisal distance) and found fast adaptation to
the small bite-block (McFarland and Baum 1995, Baum et al 1996). The bonded RPE
in this study would be closer to the small bite block design, so the additional
perturbation was probably negligible.
The interaction between the appliance type and the pre-appliance speech
rating demonstrated that the SA low/bonded speakers sounded worse when the
appliance was first inserted, but returned to the pre-appliance pattern by the
activation phase (TP3). However, this finding is based on a small number of patients.
The twenty-two patients were divided into four groups (SA low/banded, SA
low/bonded, SA high/banded, SA high/bonded), resulting in five or six patients per
group. With such small groups, it is difficult to draw definite conclusions.
B. Vowel - /i/
To examine the effect that RPEs have on the articulation of the vowel /i/, the
first and second formant frequencies were examined. Stevens and House (1955)
found that the main acoustic effects of tongue height changes were on the first
formant. As the tongue's height increased, the first formant decreased. This was
more distinct for front vowels. The same study determined that tongue advancement
72
was the main acoustic effect on the second formant. As the constriction moved from
back to front, the second formant increased. The vowel /i/ is a high, front vowel, and
therefore altering tongue height and advancement can alter first and second formants
considerably.
The decrease in second formant and increase in first formant upon RPE
insertion was likely related to the change in tongue height and advancement. When
the appliance was inserted, the tongue was unable to access the typical /i/ "high-front"
location in the anterior oral cavity and the /i/ sound was centralized. Over time the
patient's adaptation to the appliance improved, resulting in an increase in the second
formant. These second formants increased more slowly than the decreasing first
formants. The second formants only returned to pre-appliance levels when the
appliance had been out of the mouth for 1-2 months, whereas the first formants
reached this level by the retention phase. The patients were never able to completely
adapt to the appliance in the mouth.
This study's result of slow adaptation is dissimilar to previous studies that
examined the vowel /i/'s first and second formants with the insertion of a dental
appliance. As discussed earlier, Baum and McFarland (1995) examined large and
small bite blocks. They observed only a formant change in the large bite block
immediately upon insertion, but no significant formant differences after 15 min of
conversation. McFarland et al (1996) investigated /i/ formant changes when an
artificial palate with additional alveolar acrylic was inserted and found no significant
73
effects immediately upon insertion nor after conversation. Both studies found that
vowel compensatory strategies were faster than consonants. This immediate and
complete compensation did not occur with an RPE. The formants for /i/ only returned
to pre-appliance levels when the appliance was removed. The RPE screw apparatus is
more obstructive and limits the tongue's movements more than a bite block or an
artificial palate.
As previously discussed, a relative measure was used to account for gender and
age differences. This measure was achieved by calculating a ratio comprised of the
distance between the first and second formants at each time period with this formant
difference before the appliance was inserted (TP1). The relative formant distance
slowly increased as the tongue adapted to the appliance, but still remained
significantly smaller during the activation and retention phase. The formant ratio
only returned close to pre-appliance levels once the appliance was removed.
For the formant ratio, an interaction between time, appliance type, and pre-
appliance speech rating demonstrated SA high/bonded speakers had the greatest ratio
change, with the F1-F2 distance decreasing the most in this group. However, by the
retention phase, this group was similar to the other groups and returned to pre-
appliance levels when the appliance was removed. This demonstrated that speakers
with potential pre-existing speech difficulties had problems adapting to the bonded
RPE when it was inserted and when the oral environment was changing. Again it
must be noted that this interaction was based on a small sample size.
74
No significant differences were found between the banded and bonded RPE
groups. This result is perhaps not unexpected as the Baum and McFarland (1995)
study only found that formants were affected when the large (22.5mm interincisal
opening) bite block was inserted, which is far larger than the bite block of the RPE.
A Fowler and Turvey (1980) study also found minimal vowel formant change with
the insertion of a standard dental bite block.
C. Fricative - /∫/
The 875Hz/3125Hz volume ratio data demonstrated, that when the appliance
was inserted, there was a significant attenuation of the higher, 3125Hz, frequency
band's volume. Over time, this higher band's volume still remained significantly
attenuated, but improved over time turning to pre-appliance levels 1-2 months post-
removal. The insertion of the RPE obstructed the anterior oral cavity and likely
changed the airflow properties of the passive articulation zones resulting in a /∫/
sound that was less crisp.
There were differences between the pre-appliance speech rating groups over
time. The SA low group was better able to adapt to the oral environment changes of
the RPE over time. The SA high group had more difficulty in achieving this result.
After 1-2 months post-removal, the SA low group returned to normal, but the SA
high group showed improvement in the /∫/ sound. This improvement possibly is due
75
to an increase in arch width, which has been shown to improve fricative production
(Laine 1986).
The four spectral moments summarized the concentration, variance, tilt and
peakedness of the energy distributions.
a) Spectral Mean
When examining the mean centroid frequencies for the fricative /∫/, there was
a significant reduction in the spectral mean when the RPE was inserted, however by
the time of the activation phase this mean returned to the pre-appliance level. This
demonstrates a quick articulator adaptation to the appliance once the patient was able
to practice speaking at home. This result is different from the frequency band-
volume ratio result which found a slower adaptation time, only returning to pre-
appliance levels once the appliance had been removed for 1-2 months.
The interaction between time/appliance type/pre-appliance speech rating
demonstrated that the SA low/bonded group and SA high/bonded group had greater
difficulty with the RPE when it was inserted, resulting in a greater spectral mean
decrease. Both groups did improve over time, with the SA high/bonded group
eventually having a greater spectral mean than pre-appliance, once the RPE had been
removed for 1-2 months. This could possibly show the SA high/bonded group
improving after treatment with the appliance. This was similar to the result of the /∫/
frequency band-volume ratio, where the SA high speakers had improved ratios at 1-2
76
months post-removal compared to pre-appliance values. However, this interaction
was only close to being significant and only based on a small sample size of five.
b) Standard Deviation
Of the four spectral moments, the standard deviation gives the least amount of
information regarding a fricative. Standard deviation gives an indication of how
much variation or scatter there is in the data. Fricatives will require at least some
scatter to produce their signal. The SA high speakers tended to have more scatter and
therefore a less defined signal when compared with the SA low group.
c) Skewness
Skewness is a measure of asymmetry in the distribution of the data. Before the
appliance was inserted there was a negative skewness to the data which indicates that
there is a higher concentration of high frequencies in the data. When the appliance
was inserted the skewness became more positive, indicating an increase in lower
frequencies. This also was seen in the decreased spectral mean of the data. Skewness
returned to pre-appliance levels by the activation phase.
d) Kurtosis
Kurtosis is a measure of "peakedness" of the distribution curve. When the
appliance was inserted the kurtosis value decreased which indicates a less distinct
77
peak and flatter data. The more distinct peak did however return by the activation
phase.
D) Fricative - /s/
The 1625Hz/4125Hz volume ratio data demonstrated, that when the appliance
was inserted, there was a significant attenuation of the higher, 4125Hz, frequency
band's volume. However, after the completion of the appliance activation, no
attenuation was found. As with the fricative /∫/, the RPE obstructed the anterior oral
cavity and changed the airflow properties of the passive articulation zones, resulting
in a less crisp /s/ sound. The tongue was able to adapt producing a /s/ sound that had a
similar low to high ratio as pre-appliance, once the RPE stopped being turned and the
oral environment was stable.
As with the fricative /∫/, there were differences between the pre-appliance
speech rating groups. The SA low group was better able to adapt to the oral
environment changes of the RPE over time. The SA high group had more difficulty
in achieving this result. Once patients were able to adjust to no longer having the
appliance in the mouth, the SA high speakers’ /s/ sounds were restored. Unlike the /∫/
sound, the SA high group /s/ sound did not show improvement from pre-appliance to
1-2months post removal.
There were no significant differences between the banded and bonded
appliances for the fricatives /∫/ and /s/. The spectral moments were also examined.
78
a) Spectral Mean
When examining the mean centroid frequencies for the fricative /s/, there was
a significant reduction in the spectral mean when the RPE was inserted, however by
the activation phase this mean returned to the pre-appliance level. This demonstrates
a quick articulator adaptation to the appliance once the patient was able to practice
speaking at home. This result is slightly different from the frequency band-volume
ratio, which found that adaptation took slightly longer, occurring once the appliance
stopped moving during the retention phase.
The interaction between time/appliance type/pre-appliance speech rating
demonstrated that the SA low/bonded group had the greatest decrease in spectral
mean when compared to the other three groups when the appliance was first inserted.
All groups adapted similarly, improving over time and returning to pre-appliance
levels, though the SA high/banded group did take slightly longer. This again was
based on a small sample.
The differences between the pre-appliance speech rating groups demonstrated
that the SA low group was better able to adapt and the SA high group appeared to
have greater difficulty adapting to the RPE when producing the /s/ sound. This is a
similar finding to the /s/ frequency band-volume ratio result.
79
b) Standard Deviation
When the appliance was inserted there was increased scatter of the fricative
sound, but returned to pre-appliance levels once the RPE was removed.
c) Skewness
As with the fricative /∫/, when the appliance was inserted the data became
more positive indicating that there was an increase in lower frequencies. This also
helps explain the decreased spectral mean of the data. This returned to pre-appliance
levels by the activation phase.
d) Kurtosis
Similar results to the fricative /∫/ were found with decreased kurtosis values
when the appliance was inserted, indicating a less distinct peak and flatter data. The
more distinct peak did however return by the activation phase.
A similar trend was found where the SA low group was better able to adapt to
the appliance, with the SA high group having decreased kurtosis values. Both groups
returned to pre-appliance kurtosis values by the 1-2 month post-RPE removal period.
E. Fricatives - /∫/ and /s/
All the fricative data showed that when the RPE was inserted, there were
significant effects on the /∫/ and /s/ phoneme production. The volume-ratios
80
demonstrated a greater effect of the RPE. The spectral moments of both /∫/ and /s/
typically had significant effects upon RPE insertion but returned to pre-appliance
levels by the activation phase.
In this study, decreased frequency band-volume ratios and spectral moments
could be the result of the patients moving the point of fricative constriction in the
oral cavity more posteriorly due to the presence of the RPE screw apparatus. Another
possibility is that these results are demonstrating modification of the nature of the
constriction and change in the airflow direction (Baum and McFarland 1997). It is
difficult to determine each patient's specific articulatory compensations and the
length of the adaptation process (McFarland et al. 1996).
Previous studies have found that oral cavity perturbations affect consonant
production more than vowels (McFarland et al. 1996, McFarland and Baum 1995).
This result however is not consistent with this study. The fricative spectral moments
displayed appliance effect only immediately after insertion and no significant effect
by the activation phase. The frequency band-volume ratios of the fricatives
demonstrated greater appliance effects, for the /s/ until after the activation phase and
for the /∫/ until 1-2 months after the appliance was removed. The formant frequency
measurements for the vowel /i/, however, only returned to pre-appliance levels once
the appliance had been removed for 1-2 months. These results indicate that the
patients in this study were incomplete in the articulatory adaptations for /i/. This
81
could be due to the differing appliances used in the studies, as previous research
examined bite blocks and artificial palates.
Adaptation to dental appliances has been the focus of a number of studies.
Intensive practice between recordings has been a common method to attempt to
modulate this adaptation period (McFarland et al. 1996, Baum and McFarland 2000).
Other studies had the participants wear the appliance over a two week period during
awake hours. From these studies, appliance adaptation (artificial palate with excess
alveolar acrylic) typically took 2 to 4 weeks (Hamlet et al 1976, 1978, 1979). It was
around this time that adaptation occurred in the present study.
Past investigations have found that some participants have better adaptation to
a dental appliance after one hour of practice than others (Baum and McFarland 1997,
2000). It has been suggested that individual speakers can differ in overall articulatory
skill and capacity to alter articulatory dimensions in response to modification in the
configuration of the vocal tract (Savariaux et al 1995, 1999, Munhall et al 1994).
Because of these variations among individuals, the patient group was divided into SA
low and SA high speakers. This group division did appear to have more of an effect on
the fricatives /s/ and /∫/ in both ratio and spectral moment evaluation. Both groups
tended to sound worse when the appliance was inserted, but the SA low were more
likely to do significantly better. The pre-existing speech difficulty (SA high) group
may have had a greater challenge producing a constriction for fricative production,
and were slow to develop the necessary compensatory mechanisms.
82
F. Summary
In order to improve the relationship between clinician and patient, and to
potentially improve the ability of the patient to adapt to the appliance, the patient
and parent should be made aware of potential appliance consequences prior to
treatment initiation (Sergl et al. 2000). In a typical counseling session, the concepts
discussed are usually limited to direct physical consequences, such as unpleasant
tactile sensations, soreness of the teeth, feelings of oral cavity constraint, and altered
appearance. Speech, however, is hardly mentioned. Prior to appliance insertion
clinicians usually will tell their patients that they will sound better over time and will
sound like their normal selves in a day or two. These statements provided are quite
vague, don't prepare the patient for the specifics of the appliance-caused speech
distortion, and may not be entirely accurate. It would be ideal if the clinician could
give the patient an idea of what sounds are likely to be altered and for how long this
effect is likely to last. Based on the speech acceptability results of this study, the
patients did improve over time, though they sounded distorted throughout treatment,
only sounding like their pre-appliance selves once the appliance was removed. These
results were based on /i/, /∫/ and /s/-laden sentences, which were expected to have a
greater alteration after RPE insertion. Patients could be told that they will likely
have no trouble pronouncing many sounds, but others may prove to be a greater
challenge. The pronunciation of certain phonemes like /i/, /∫/ and /s/ may be more
difficult than the others, and although they will sound better over time, these sounds
83
may not sound normal until the appliance is removed. This information will allow
the patient to better prepare for and manage use of the RPE, strengthen the
orthodontist-patient relationship, potentially improve long-term treatment
compliance, and likely improve the results of orthodontic treatment.
84
CONCLUSIONS
The results of this study found that:
Rapid palatal expanders have a negative effect on speech
Adaptation to the new appliance is difficult when it is first inserted, but
patients slowly adapt to the appliance over time
Based on the perceptual data, the naïve listeners found that after expansion,
and after the patients were able to adapt to the lack of appliance in the mouth
(1-2 months post-removal) the patients sounded better than they did originally
Consultation with the patient and parent prior to insertion of the appliance is
desirable to inform them of what speech effects are likely to occur and the
expected duration.
85
LIMITATIONS
There were a few of limitations to the present study. Although the appliance
was made by the same technician, the placement of the screw apparatus in relation to
the oral cavity was likely different between patients and difficult to standardize.
Some patients have a high palatal arch whereas some patients’ palates are quite flat.
The screw apparatus is fabricated in such a way that it does not lay flat against the
palate, nor is it in line with the tooth attachments. The screw apparatus is offset
towards the palate approximately 5-10mm from the tooth attachments, so the
distance between the screw and the palate was variable. A screw that was far away
from the palate and farther into the oral cavity, as in a patient with a high palatal
arch, could potentially have greater difficulties as if would be expected to be more
obstructive.
The discrepancy between the maxilla and mandible was different in each
patient. This means that the amount of expansion was different in each patient.
Some patients required only a few millimetres, whereas other patients’ were quite
constricted and possibly needed more. The amount of expansion in each patient was
not measured and it is not know whether the amount of expansion could alter the
speech in these patients.
The study was limited to only 22 patients. A larger sample would be better to
achieve improved power and effect size. An increase in the number of subjects would
86
also be helpful when dividing the groups among the different variables, for example
appliance type and pre-appliance speech rating.
The quality of life of these patients was not assessed in this study. Though
there were significant speech effects found both acoustically and perceptually, it is
not known whether these patients felt that their speech was affected and if so, if it
resulted in any decreased quality of life consequences.
87
APPENDIX-Interactions
Note for Appendix: good=SAlow, bad=SAhigh
Acceptability Data: appliance type*pre-appliance speech rating
88
Volume /i/ - First Formant Frequency: appliance type*pre-appliance speech rating
89
Volume /i/ - F2-F1 ratio: time*appliance type*pre-appliance speech rating
90
Fricative /∫/ - Frequency band - Volume Ratio: time* pre-appliance speech rating
91
Fricative /s/ - Frequency band - Volume Ratio: time*pre-appliance speech rating
92
Fricative /∫/ - Spectral Mean: time*appliance type*pre-appliance speech rating
93
Fricative /∫/ - Spectral Mean: time*appliance type
94
Fricative /s/ - Spectral Mean: time*appliance type*pre-appliance speech rating
95
APPENDIX-Sentence Articulation Test
1. Pete’s job was to keep the baby happy
2. Today Dick told Patty about it
3. The girls were baking the biggest cake for Mr. Tag
4. Their brother wouldn’t bathe because he thought a bath would make his toothache worse
5. In a half day, he repaired five television sets, two telephones, and a very old stove
6. Suzie sewed zippers on two new dresses at Bessie’s house
7. She usually rushes to push the garage door closed
8. George is at the church watching a magic show
9. We rode with Lucy around the tall tower in her new yellow car
10. Why haven’t you looked anywhere behind the house or beyond the hill yet?
11. Nancy found some fine hangers among the many things at the sale
12. Let me keep a little of this wedding cake to eat later
13. Father asked how much money Tom had saved to buy a bird cage
14. Ruth caught a cold because she wouldn’t wear her new warm wool coat
15. I found a huge toy music box outside Roy’s house
16. Mom came home
17. The puppy is playing with a rope
18. Bob is a baby boy
19. The phone fell off the shelf
20. Dave is driving a van
21. Neil saw a robin in a nest
22. A ball is like a balloon
96
23. Tim is putting a hat on
24. Daddy mended a door
25. I saw Sam sitting on a bus
26. The zebra was at the zoo
27. Sean is washing a dirty dish
28. Charlie’s watching a football match
29. John’s got a magic badge
30. The bell’s ringing
31. Karen is making a cake
32. Gary’s got a bag of lego
33. Hannah hurt her hand
34. This hand is cleaner than the other
35. The hamster scrambled up Stuart’s sleeve
97
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