The Effect of Rapid Palatal Expander Appliances On Speech · between the maxilla and mandible, maxillary arch expansion is frequently necessary. Palatal expanders are used to expand

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

v

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.

3

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

11

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.

13

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

14

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).

15

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.

19

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):

20

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/,

21

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

22

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


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


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


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 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


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).


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 the SA low and SA high pre-appliance speech groups (p=0.009, 1−β =0.758,


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.


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


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 the SA low and SA high pre-appliance speech groups (p=0.003, 1−β =0.870,


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.


"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


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 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



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


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


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-


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


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



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



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


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 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



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


Table 11. Paired t-tests for the standard deviations of the fricative /s/

59






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-


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


Table 12. Paired t-tests for the skewness of the fricative /s/

61






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-


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


Table 13. Paired t-tests for the kurtosis of the fricative /s/

63




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


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


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


66

D. Fricative spectral moments


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


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


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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The Effect of Rapid Palatal Expander Appliances On Speech · between the maxilla and mandible, maxillary arch expansion is frequently necessary. Palatal expanders are used to expand