The influence of maxillary central incisor position in complete dentures on /s/ sound production

Transcription

1 The influence of maxillary central incisor position in complete dentures on /s/ sound production Christoph Runte, Dr med dent, a Michael Lawerino, Dr med dent, b Dieter Dirksen, c Dr rer nat, Friedhelm Bollmann, Prof Dr med, Dr med dent, d Antoinette Lamprecht-Dinnesen, Prof Dr med, e and Eberhard Seifert, PD Dr med f Center for Dental Medicine, University of Muenster, Meunster, Germany, and University of Berne, Berne, Switzerland Statement of problem. The insertion of prosthodontic restorations often leads to speech defects, most of which are transient but nevertheless a source of concern to the patient. For the dental practitioner, there are few guidelines on designing a prosthetic restoration with maximum phonetic success. Purpose. This study investigated the effect of different maxillary central incisor positions on phonetic patterns. Material and methods. The inclination angle of central incisor blocks in duplicate complete maxillary dentures was changed in a range of 30 degrees to +30 degrees from the original position (0 degrees). Test words and sentences were acoustically analyzed. Spectral parameters such as first peak, noise band (defined by upper and lower limits of the most intensively blackened frequency area), Fast Fourier Transformation power spectrum, energy spectrum, and time were investigated. Influences of oral stereognosis, hearing, and age as cofactors on /s/ articulation were also taken into account. Results. The change of incisor block angle in both directions usually caused a poorer execution of the /s/ sound. The labial angulation seemed to have a greater effect than the palatal angulation. The most significant changes were those in the noise band and energy spectrum. Conclusion. Immediate phonetic adaptation of prosthetic restorations in the maxillary incisor region can be achieved only if the original position of the natural teeth is transferred to the denture. Although these misarticulations are, in most cases, likely to disappear within a few weeks, they may persist and even lead to psychosocial problems. A better understanding of the causes of misarticulation and the limits of adaptation according to certain morphologic parameters of dentures is important. (J Prosthet Dent 2001;85: ) CLINICAL IMPLICATIONS The insertion of prosthodontic restorations often leads to speech defects. This study on the effect of different maxillary central incisor positions on phonetic patterns indicated that immediate phonetic adaptation of restorations in the maxillary incisor region can be achieved only if the original position of the natural teeth is transferred to the denture. a Senior Registrar, Department of Prosthodontics, University of Muenster. bresearch Associate, Department of Prosthodontics, University of Muenster. c Research Associate, Biophysics Laboratory, University of Muenster. dprofessor and Head, Department of Prosthodontics, University of Muenster. e Professor and Head, Department of Phoniatrics and Pedaudiology, University of Muenster. f Associate Professor, Department of Phoniatrics, Inselspital, University of Berne. It is claimed that the incisors may influence pronunciation. 1 Bankson and Byrne, 2 who examined the effect of missing incisors on the consonant phonation of children, reported that among the examined consonants, only the /s/ sound was affected. About half of the patients experienced no disturbances at all. It is well known that insertion of a prosthodontic restoration may lead to disturbed pronunciation 3-5 and, in certain patients, even involve the parameters of the vocal fold. 6 The sounds formed in the labiodental, linguodental, and linguoalveolar regions therefore are of special interest to the dentist. Studies on speech sound production may have a clinical impact because many patients attach great importance to undisturbed speech sound production after dental treatment. Heyink et al 7 found that 28 (21%) of 131 denturewearing individuals from an elderly Dutch population had speech problems. Among the sounds formed in the anterior maxillary MAY

2 RUNTE ET AL Fig. 1. Spectral analysis. On left: 2 spectra of word Platz. On right: FFT power spectrum for each /s/ sound. Upper spectra were recorded while maxillary central incisors were displaced 30 degrees in palatal direction; lower spectra show speech sounds with same teeth displaced 30 degrees in labial direction. region, the /s/ sound is most frequently distorted, possibly because the /s/ sound formation needs particularly fine adjustment of the tongue and depends on special neuromuscular and psychoauditive abilities. The /s/ sound is common in most languages throughout the world. The inability to pronounce sibilant sounds correctly is referred to as sigmatism. 8 With removable dentures, the cause of disturbed pronunciation may well be the design of the alveolar area. Rothman 9 pointed out that the tongue contacts a specific part of the teeth, alveolar ridge, or hard palate during the production of each consonant. As these structures are covered or replaced by the denture, an appropriate restoration is necessary for undisturbed sound production. Disturbed pronunciation may result as a direct influence of the artificial teeth and palate on air flow but also may be caused by a different tongue position or movement (due, for example, to a changed perception). Tanaka 10 found that the artificial palatal vaults of maxillary dentures often have a concave shape. In contrast, natural palatal vaults are of convex shape in the alveolar region. His conclusion was that the palatal vaults of maxillary dentures should be shaped like natural ones to faciliate correct pronunciation. He also reported that the quality of speech sound production improved within the first week after insertion of new dentures. Ritchie and Ariffin 11 reported speech defects caused by different incisor positions in maxillary dentures irrespective of the shape of the palatal vault and found that a displacement of the maxillary incisors in a labial direction was most likely to cause speech problems. Speech defects were also observed after the insertion of fixed partial dentures. According to Ödman and Karlsson, 12 7 (7%) of 100 adult patients with at least 5 fixed partial denture units stated that their speech was affected. The most important instruments for the investigation of speech sound production are the trained hearing of a speech and language professional, spectral analysis, and palatographics. Spectral analysis has long been used to examine the effects of dental prostheses on speech sound production. 13,14 With the use of spectral analysis, a sound event can be split into 3 dimensions: frequency, amplitude, and chronologic sequence. The data obtained can be visualized in 2-dimensional Cartesian coordinates with the color or grey shade as the third dimension (Fig. 1). Although less common, a 3-dimensional profile representation can be used instead. The spectrum of a fricative sound is characterized by a distribution of sound energy over a wide frequency range. In contrast, a major part of the sound energy of vowels is concentrated on distinct frequency areas, the fundamental frequency of the glottis, and certain characteristic overtones (the formants). In fricatives, areas of high sound energy are also referred to as fricative formants. The first formant of a fricative is the area of very high sound energy of the lowest frequency. However, it does not necessarily have the maximum energy in the entire spectrum. The /s/ sound is characterized by a noise whose fre- 486 VOLUME 85 NUMBER 5

3 RUNTE ET AL Fig. 2. Age and sex of subjects and duration of complete denture wear. quency range is unclearly limited by a lower and a higher boundary. It is these boundaries that define the noise band range. 15 The physiologic /s/ sound is formed by adaptation of the lateral margins of the tongue to the palatal alveolar process from the lateral incisor region to its dorsal end. In the middle of the tongue, a channel remains for the current of air, which is guided over a predorsal groove. The contacts between tongue and palatal vault can be examined by palatography. Readily applied palatographic techniques have been described by Rothman, 9 Allen, 16 and Bloomer. 17 The /s/channel narrows continuously, reaching its narrowest point directly behind the central incisors, and causes turbulences and the characteristic noise. Therefore, the central incisors, which are directly adjacent to the air current, were the central topic of this investigation. The aim of this study was to examine the influence of maxillary central incisor position on /s/ sound production. MATERIAL AND METHODS Twenty edentulous subjects (12 women, 8 men) were recruited (Fig. 2). Their ages ranged from 43 to 87 years (mean age 69.5 years). The subjects had worn complete dentures for an average of 11.6 years. All subjects underwent an examination of their oral motor skills, mimic muscular activity, swallowing patterns, oral stereognosis, and hearing. Oral motor skills were investigated by observing the rest position of the tongue during slight opening and examining whether certain movements of the tongue (sticking out the tongue; movements to the left, right, up, and down; circular movements) and the lips were possible. The swallowing pattern was observed clinically by an experienced investigator (subjects had to swallow proceeding from their habitual occlusion position with and without their lips held open), and the lateral margin of the tongue was examined for any impressions of Fig. 3. Median section through duplicate denture, anterior area. Central incisors can be rotated around axis in palatal alveolar region. the teeth possibly caused by tongue thrust during swallowing. A 2-point discrimination test was used to examine the sensitivity of the tongue surface by means of an electronic caliper (Mitutoyo digimatic caliper, Mitutoyo Asia Pacific, Singapore). By gradually reducing the distance between the caliper tips and touching the anterior tongue surface, the shortest intertip distance at which the subjects could recognize both tips of the caliper as 2 distinct points was measured according to the procedure described by Ringel and Ewanowski. 18 In addition, the ability to recognize 4 small test objects (a cube, sphere, pyramid, and rectangular block, <1 cm 3, weight: mg) MAY

4 a a RUNTE ET AL Table Ia. FFT power spectrum analysis showing the highest peak and its relation to the sound level of the whole /s/ sound FFT power spectrum analysis (test word: Floss ) 0 degrees 30 degrees labial 30 degrees palatal Subject no. Highest peak (Hz) Ranking number Highest peak (Hz) Ranking number Highest peak (Hz) Ranking number Mean intraorally was tested for the assessment of oral stereognostic ability. Hearing was also tested by recording audiograms with a Madsen OB-822 instrument (Madsen Electronics, Buffalo, N.Y.) for all subjects. Examination of the /s/ sound duplicates of all maxillary dentures were performed. A plaster cast impression of the incisal edges of the incisors and canines was made for each denture to preserve the original position of the anterior teeth. Central incisors were sectioned from the duplicate, and the block was slightly reduced in the anterior cervical region and then remounted in its original position with a transversal axis, using the plaster cast. The central incisors could then be rotated from 30 degrees to the palate to 30 degrees to the lip (Fig. 3). During the experiments, the central incisor block was fixed in each position with wax (Periphery wax, Enda Lactona B. V., Bergen op Zoom, The Netherlands). Under standardized recording conditions (DAT- Recorder Sony TCD-D3, Sony Corp, Tokoyo, Japan; 50 cm speaker-microphone distance), the subjects were asked to speak the German words "Platz" [plats], "verpassen" [fεr'pas n], and "Floss" [flo:s] and the sentences "Fischer's Fritze fischt frische Fische" ['fi s 'frıts fi t 'frı 'fı ] and "da knisterts und flisterts und pisperts" [da: 'knist ts und 'pısp ts und 'flıst ts]. e e e e All texts were spoken and recorded 3 times, the first time with the central incisors in original position (0- a a degree angulation), the second with 30-degree angulation in a palatal direction, and the third with 30-degree angulation in a labial direction. From the recordings, the following sounds were examined: /s/ from the words Floss and verpassen (equivalent to the English voiceless /s/ in miss ), /ts/ from the words Platz and Fritze (equivalent to the English /ts/ in pizzicato ), and /st/ from the word knisterts (equivalent to the /st/ sound in thirsty ). For spectral analysis, a Speech-Lab CSL 4300B instrument (Kay Elemetrics Corp, Pine Brooks, N.J.) was used. The following parameters were examined: first fricative formant, Fast Fourier Transformation (FFT) power spectrum, noise band range, duration of /s/ sounds and the whole words, and energy spectrum. The frequency with the absolute maximum energy level was taken from the FFT power spectrum. Because the subjects spoke with varying loudness levels, this highest peak of amplitude was related to the volume of the whole /s/ sound. By this means, a relative value suitable for interindividual comparison was obtained. The energy spectrum is defined as sound volume over a period of time. As in the process performed with the highest peak of the FFT power spectrum, the level of the /s/ sound was related to that of the preceding vowel. To account for differences in the absolute values of the investigated parameters (FFT power spectrum, measuring duration, and energy spectrum), a comparison was performed with the Friedman test VOLUME 85 NUMBER 5

5 RUNTE ET AL Fig. 4. Frequency of maximum energy peak of /s/ sound in test word Floss. Table Ib. FFT power spectrum analysis showing the highest peak and its relation to the sound level of the whole /s/ sound FFT power spectrum analysis (test word: Floss ) 0 degrees 30 degrees labial 30 degrees palatal Subject Amplitude relative to Amplitude relative to Amplitude relative to no. /s/ sound (=1) Ranking number /s/ sound (=1) Ranking number /s/ sound (=1) Ranking number Mean The absolute values of the test results with different incisor positions were allocated with ranking numbers. The mean average values of the ranks of the respective central incisor positions were investigated. The correlation between the examined parameters of the /s/ sounds and the age of the subjects, the 2-point discrimination, and the time the complete denture had been in use was analyzed with the Spearman correlation test. A simplified summary presenting only the significance levels of all correlation data is given in the Results section. Calculations were performed with the statistical MAY

6 RUNTE ET AL Table IIa. Noise band range. Results are for the /s/ sound in the test word Floss Noise band range: Floss Lower boundary frequency (Hz) Upper boundary frequency (Hz) Subject no. 0 degrees 30 degrees labial 30 degrees palatal 0 degrees 30 degrees labial 30 degrees palatal software SPSS/PC + V2.0 (SPSS Inc, Chicago, Ill.). RESULTS Primary speech parameters First fricative format: There were changes in the frequency of the first fricative formant with the different incisor positions (0 degrees, 30-degrees labial, and 30-degrees palatal), but they were not significant according to the Friedman analysis. FFT power spectrum: There was a significant correlation between the frequency of the maximum energy level and the incisor position with the word Floss. The frequency of the maximum energy peak was lowered in both palatal and labial angulation (P=.0456; absolute values, Tables Ia and Ib; mean average values of ranks, Fig. 4). Noise band range: The noise band of the /s/ sound was generally located in an area between approximately 4 and 11 khz. When the incisors were moved labially or palatally, a significant decrease in the upper boundary frequency was observed for the /s/ sounds in the words Floss (P=.0393; absolute values, Table IIa), verpassen (P=.0174), and Platz (P=.0020). In contrast, significant changes in the lower boundary of the noise band were observed with the word verpassen. A palatal position caused an increase in frequency, and a labial position a decrease in frequency (P=.0020; Table IIb; mean average values of ranks, Fig. 5). This means that changes of incisor position, especially in a palatal direction, led to a smaller noise band range for some words. Duration of the /s/ sound: The duration of the /s/ sounds within the test words was shortened when the incisors were placed palatally (mean reduction: seconds) or labially compared with the original position. The only exception was the word Fritze, with which the mean duration of the /s/ sound became seconds longer. The time taken for the whole word was usually shortened when the central incisors were displaced (in either a labial or palatal direction). The effect reached significance level with the following test words: Floss (P=.0002) and verpassen (P=.0235). In both instances, the incisors were displaced in a palatal direction. Energy spectrum: In the original position, the mean relation between the energy of the vowels and the energy of the /s/ sounds was 1.13:1. The mean value was 1.16:1 when the incisors were placed in a labial position and 1.15:1 when the incisors were fixed in a palatal position. This indicates that the /s/ sounds were spoken with less energy in relation to the preceding vowels when the teeth were displaced. However, this effect reached a statistically significant level only with the test word Fritze (P=.0351). 490 VOLUME 85 NUMBER 5

7 RUNTE ET AL Table IIb. Noise band range. Results are for the /s/ sound in the test word verpassen Noise band range: verpassen Lower boundary frequency (Hz) Upper boundary frequency (Hz) 0 degrees 30 degrees labial 30 degrees palatal 0 degrees 30 degrees labial 30 degrees palatal Subject no. av r av r av r av r av r av r Mean r av = Absolute value; r = ranking number. Age related to speech parameters Significant relations between age, oral abilities, and the length of time complete dentures were worn were examined with the Spearman correlation test. No significant correlation between age of the subjects and the first fricative formants was found. With the words Floss and Platz, all incisor positions (0 degrees, 30 degrees labially, and 30 degrees palatally displaced) showed a significant correlation between age and noise band range (upper and lower boundary frequency). Further significant values were found with the test words verpassen (0 degrees and 30 degrees labially, upper boundary frequency only); Fritze (30 degrees labially, upper boundary frequency only); Platz (30 degrees palatally, lower boundary frequency only); and knisterts (0 degrees, lower boundary frequency only). These significant values (P<.05, Table IIIa) indicate a reduction of the upper and a rising of the lower boundary frequency with increasing age, meaning that the noise band range became smaller. With the frequencies of the maximum energy level from the FFT power spectrum and the age of the subjects, significant values were found with the test words verpassen, Fritze, knisterts (all 0 degrees only), and Floss (30 degrees palatally). These significant values (Table IIIb) suggest a reduction of the frequency and amplitude of the maximum energy level with increasing age. No significant correlation was found between the age of the subjects and duration of the /s/ sound. However, with the words Floss (all incisor positions), verpassen, and Platz (both 0 degrees only), significant values were found between the duration of the whole word and the age of the subjects (Table IIIc). These values indicate a reduction of the time taken to speak the whole word. Significant correlations between the energy spectrum and age of the subjects could be found only for the words Floss (30 degrees palatally displaced only), verpassen (30 degrees labially only), and Platz (both 0 degrees and 30 degrees labially, Table IIId), indicating that increasing age led to a reduction of the energy of the /s/ sound in relation to the preceding vowel. Oral abilities related to speech parameters Intraoral form discrimination and swallowing patterns were examined as described in the Material and Methods section. All subjects were capable of intraoral form discrimination, and none showed pathologic swallowing patterns. Consequently, no significant relations between swallowing patterns, form discrimination, and MAY

8 RUNTE ET AL Table IIIb. Age related to FFT power spectrum Hypothesis: Increasing age correlates to reduced frequency of highest peak in FFT power spectrum Verpassen 0 degrees Hypothesis: Increasing age correlates to lower amplitude of highest peak in relation to amplitude of whole /s/ sound Floss 30 degrees palatal Fritze 0 degrees Knisterts 0 degrees Table IIIc. Age related to duration of whole word Hypothesis: Increasing age correlates to shorter time for duration of whole test word Floss 0 degrees Floss 30 degrees labial Floss 30 degrees palatal Verpassen 0 degrees Platz 0 degrees Fig. 5. Upper and lower boundary frequency of /s/ sound in test word verpassen. Table IIIa. Age related to noise band range Test Boundary Significance words frequency Incisor position factor Hypothesis: Increasing age correlates to reduction of upper or rise of lower boundary frequency Floss Upper 0 degrees Floss Upper 30 degrees labial Floss Upper 30 degrees palatal Platz Upper 0 degrees Platz Upper 30 degrees labial Platz Upper 30 degrees palatal Verpassen Upper 0 degrees Verpassen Upper 30 degrees labial Fritze Upper 30 degrees labial Platz Lower 30 degrees palatal Knisterts Lower 0 degrees speech parameters could be found with the data material. Significant relations between 2-point discrimination and the first fricative formant were found with the words Floss (30 degrees labially only), verpassen (30 degrees labially only), Fritze (0 degrees), and knisterts (30 degrees labially and 30 degrees palatally) (Table IVa). The poorer the 2-point discrimination abilities (the greater the distance between 2 points on the tongue had to be for the subject to be able to recognize them as distinct points), the higher the frequency of the first fricative formant median. No significant correlations were found between 2-point discrimination and the upper boundary frequency. The lower boundary frequency showed a significant correlation to the 2-point discrimination ability with the test words Floss (all incisor positions), Platz (30 degrees labially only), Fritze (0 degrees only), and knisterts (0 degrees only) (Table IVb). The significant values indicated a rising of this boundary frequency with poor 2-point discrimination abilities. No correlation between the FFT power spectrum and 2-point discrimination abilities was registered at a significance level of P<.05. Only for the words Floss (all incisor positions) and knisterts (30 degrees labially) could a significant correlation between 2-point discrimination abilities and the duration of the /s/ sound be found. This indicated that a poor 2-point discrimination ability was 492 VOLUME 85 NUMBER 5

9 RUNTE ET AL Table IIId. Age related to energy spectrum Hypothesis: Increasing age correlates to reduced /s/ sound energy compared with preceding vowel Floss 30 degrees palatal Verpassen 30 degrees labial Platz 0 degrees Platz 30 degrees labial Table IVa. Two-point discrimination related to first fricative formant Hypothesis: Poor 2-point discrimination abilities correlate to rise of first fricative formant frequency median Floss 30 degrees labial Verpassen 30 degrees labial Fritze 0 degrees Knisterts 30 degrees labial Knisterts 30 degrees palatal Table IVc. Two-point discrimination related to duration of /s/ sound Hypothesis: Poor 2-point discrimination abilities correlate to prolonged /s/ sound Floss 0 degrees Floss 30 degrees labial Floss 30 degrees palatal Knisterts 30 degrees labial Table IVd. Two-point discrimination related to duration of whole word Hypothesis: Poor 2-point discrimination abilities correlate to prolonged test word Platz 30 degrees labial Fritze 0 degrees Fritze 30 degrees palatal Knisterts 30 degrees palatal Table IVb. Two-point discrimination related to lower boundary frequency of noise band range Hypothesis: Poor 2-point discrimination abilities correlate to rise of lower boundary frequency Floss 0 degrees Floss 30 degrees labial Floss 30 degrees palatal Platz 30 degrees labial Fritze 0 degrees Knisterts 0 degrees correlated with a prolongation of the /s/ sound (Table IVc). This is also true for the duration of the whole word with the test words Platz (30 degrees labially only), Fritze (0 degrees and 30 degrees palatally), and knisterts (30 degrees palatally only) (Table IVd). No significant correlation was recorded between 2- point discrimination and the energy spectrum. Duration of complete denture wear related to speech parameters A significant correlation between the duration of complete denture wear and the first fricative formant was found only with the words verpassen and Fritze (both 0 degrees). With these words, the longer a complete denture had been worn, the Table Va. Duration of complete denture wear related to first fricative formant Hypothesis: Long experience with denture correlates to rise in first fricative formant frequency median Verpassen 0 degrees Fritze 0 degrees higher was the first fricative formant median (Table Va). The upper boundary frequency revealed no significant correlation to the duration of complete denture wear. The longer a complete denture had been worn, the higher was the lower boundary frequency. This correlation was found for the test words verpassen (all incisor positions), Platz (30 degrees palatally), and knisterts (0 degrees) (Table Vb). A significant correlation was registered between the time a complete denture had been worn and the frequency of the highest peak of the FFT power spectrum only with the test words verpassen and Platz (both 30 degrees palatally). The longer a denture had been worn, the higher the frequency of the highest peak in the FFT power spectrum (Table Vc). A significant reduction of the amplitude of the highest peak in the FFT power spectrum in relation to the whole /s/ sound with increasing experience with the denture was found only for the test word Floss in the 30-degree palatal position (Table Vc). MAY

10 RUNTE ET AL Table Vb. Duration of complete denture wear related to lower boundary frequency of noise band range Hypothesis: Long experience with denture correlates to rise of lower boundary frequency Verpassen 0 degrees Verpassen 30 degrees labial Verpassen 30 degrees palatal Platz 30 degrees palatal Knisterts 30 degrees labial Table Vc. Duration of complete denture wear related to FFT power specturm Hypothesis: Long experience with denture correlates to higher frequency of highest peak in FFT power spectrum Verpassen 30 degrees palatal Platz 30 degrees palatal Hypothesis: Long experience with denture correlates to lower amplitude of highest peak in relation to amplitude of whole /s/ sound Floss 30 degrees palatal Table VI. Overview of the results of speech sound analysis Parameter First fricative formant Upper boundary frequency of noise band Lower boundary frequency of noise band Frequency of the maximum energy level in the FFT power spectrum Amplitude of the maximum energy level in the FFT power spectrum Duration of /s/ sound Energy spectrum Result Not significant In labial position: Reduction In palatal position: Reduction In labial position: Rise In palatal position: Reduction In labial position: Reduction In palatal position: Reduction Not significant In labial position: Reduction In palatal position: Reduction In labial position: Rise In palatal position: Rise No significant correlation was found between the time a complete denture had been worn and the duration of /s/ sounds, the duration of whole test words, and their energy spectrum. Not surprisingly, a significant correlation was found between the age of the subjects and duration of complete denture wear (Spearman correlation coefficient r 2 = 0.878) (Fig. 2). DISCUSSION Although Bond and Lawson 3 claimed that most speech sound disturbances were due to denture volume and that the position of the teeth and shape of the denture surface were less important, the results of this study show a significant influence of tooth position on the /s/ sound. The effect seems to be dependent on the word in which the /s/ sound is spoken. Some parameters changed irrespective of the direction of displacement, so that disorientation may be an important factor in addition to aerodynamic effects. As sigmatism is much more frequent than /f/ sound disturbances, we did not examine the influence of the central incisor position on the /f/ sound. This sound is, however, highly dependent on the maxillary central incisors. Another method for investigation of sound production, one easily performed by a dentist, is palatography. However, this technique fails to distinguish between 2 different sounds in some situations. Allen 16 found that the patterns for the T, D, N, and L sounds were not distinct. Moreover, some sounds require no palatolingual contact at all. For example, according to Bloomer, 17 during /m/ and /b/ sound production, the bilabial valve is closed. If not only single sounds but also complex speech signals (sequences of speech sounds with different palatolingual contact areas) are examined, the only possible palatographic method available is electropalatography, which can show dynamic progress. However, as the number of sensors placed on the palatal vault is limited, so is the resolution. Spectral analysis indicated that displacement of the maxillary central incisors led to misarticulation of the /s/ sound, with slightly more disturbances when the teeth were moved into a labial position than into a palatal position. Ritchie and Ariffin 11 came to a similar conclusion when examining the effects of dentures with different incisor positions. The subjects in their study had to wear 6 different dentures, each for 30 minutes; thus, their study also covered adaptation effects to a certain degree. 494 VOLUME 85 NUMBER 5

11 RUNTE ET AL The changes in /s/ sound production registered in the current study mostly affected the noise band range and the power spectrum patterns. For the dental practitioner, problems may result if a more labial or palatal tooth position is required for mechanical reasons in partial denture design. The time taken for the complete spoken words was shortened in this study, whereas Tobey and Finger 4 observed a generalized slowing of speech when new dentures were worn in comparison with no dentures worn. This may be a result of the more discrete change in the dentures in this study. Because the age of the subjects and the period a complete denture had been worn showed a significant correlation as expected, it is hardly surprising that a correlation was also found between age and changes in noise band range and between the period a complete denture had been worn and changes in noise band range (Tables IIIa and Vb). However, this effect was more likely due to age and therefore to reduced adaptability of the subject than to the time a complete denture had been worn. Bankson and Byrne 2 showed that even missing incisors do not necessarily affect the speech sound production of children. Although subjective observations were used instead of spectral analysis and a missing incisor has greater consequences for the morphology, it may be concluded in connection with this study that children who are undergoing speech development have a greater potential for adaptation than adults. As Palmer 5 stated, it is not possible to produce a cookbook approach to the analysis of speech sound production for prosthodontic practice. Speech sound disturbances may occur after prosthodontic treatment. More emphasis should be placed on reconstruction of the dental arch and of the palatal ridge in its original position and shape. SUMMARY Spectral analysis revealed a significant correlation between incisor position and /s/ sound production. The most important effect was on noise band range and power spectrum. There seems to be a dependence on the sound context in which the /s/ sound is spoken. Table VI summarizes the examined speech parameters and the effect of changes in incisor position on these parameters. REFERENCES 1. Haitas GP, Wolfaardt JF, Carr L. Speech defects in prosthetic dentistry. Part I The mechanism of speech production. J Dent Assoc S Afr 1985;40: Bankson NW, Byrne MC. The relationship between missing teeth and selected consonant sounds. J Speech Hear Disord 1962;27: Bond EK, Lawson WA. Speech and its relation to dentistry. I. Speech and speech defects. Dent Pract Dent Rec 1968;19: Tobey EA, Finger IM. Active versus passive adaptation: an acoustic study of vowels produced with and without dentures. J Prosthet Dent 1983;49: Palmer JM. Analysis of speech in prosthodontic practice. J Prosthet Dent 1974;31: Seifert E, Runte C, Riebandt M, Lamprecht-Dinnesen A, Bollmann F. Can dental prostheses influence vocal parameters? J Prosthet Dent 1999;81: Heyink J, Heezen J, Schaub R. Dentist and patient appraisal of complete dentures in a Dutch elderly population. Community Dent Oral Epidemiol 1986;14: Dox I. Melloni s illustrated medical dictionary. Baltimore (MD): Williams and Wilkins; p Rothman R. Phonetic considerations in denture prosthesis. J Prosthet Dent 1961;11: Tanaka H. Speech patterns of edentulous patients and morphology of the palate in relation to phonetics. J Prosthet Dent 1973;29: Ritchie GM, Ariffin YT. Sonographic analysis of speech sounds with varying positions of the upper anterior teeth. J Dent 1982;10: Ödman PA, Karsson S. Follow-up study of patients with bridge constructions performed by private dental surgeons and at a university clinic, 8 years following insertion. J Oral Rehabil 1988;15: Spangenberg HD Jr. The effects of a dental prosthetic appliance on the quality of the voice: an experimental study. Proc Staff Meet Mayo Clinic 1937;12: Petrovic A. The use of spectrograms for speech analysis in full denture wearers. A preliminary report. J Oral Rehabil 1974;1: Neppert J, Petursson M. Elements of acoustic phonetics [in German]. Hamburg: Buske; p Allen LR. Improved phonetics in denture construction. J Prosthet Dent 1958;8: Bloomer H. Speech defects associated with dental malocclusions and related abnormalities. In: Travis LE, editor. Handbook of speech pathology and audiology. New York (NY): Meredith; p Ringel RL, Ewanowski SJ. Oral Perception: 1. Two-point discrimination. J Speech Hear Res 1965;8: Miller RG Jr. Simultaneous statistical inference. 2nd ed. New York (NY): Springer; p Reprint requests to: DR CHRISTOPH RUNTE DEPARTMENT OF PROSTHODONTICS UNIVERSITY OF MUENSTER WALDEYER STRASSE 30 D MUENSTER GERMANY FAX: (49) crunte@uni-muenster.de Copyright 2001 by The Editorial Council of The Journal of Prosthetic Dentistry /2001/$ /1/ doi: /mpr MAY