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Incisal relationships during speech
RESEARCH SI:~-l-IoK
LOUIS
AND
EDUCATION
r:I~rToII
J. BOUCHER
Incisal relationships P. G. T. Howell, I’nited
Medical
during
speech
B.Sc., B.D.S. Ph.D.*
and Dental
Schools of Guy’s
and St. Thomas’s Hospital,
London,
England
N
iswonger’ indicated the importance of the rest position of the mandible in the treatment of patients with complete dentures and said that it should be related to the measurement of the occlusal vertical dimension. The difference between the measurements of the occlusal vertical dimension and resting vertical dimension provides the interocclusal distance.’ From clinical studies, Silverman2-4 considered that the resting vertical dimension was insufficiently dynamic to represent the position of the mandible during its normal functional movements. He therefore proposed an alternative measurement procedure to provide a definition for the occlusal vertical dimension, in place of the static method described. He used phonetics in the assessment of the mandibular position for the occlusal vertical dimension and proposed that the smallest separation of the maxillae from the mandible during speech be adopted as the major criterion. Silverman defined the distance between the closest speaking position and the teeth in centric occlusion as the closest speaking space. He called the most protrusive position of the mandible the anterior speaking space.4 The importance of phonetics in complete denture construction was also emphasised by Mehringer’ and Pound,“,’ who studied mandibular movements during speech by direct observation of the teeth. Detailed measurement of the mandibular movements during function has been examined by numerous workers and notably reviewed by Hildebrand” and later by Bates et al9 These studies, however, have been predominantly limited to investigations of mastication or forced border movements instead of speech. A study of 246 adolescents was undertaken by Benediktsson,1° who used radiographic techniques to examine the position of the tongue and mandible at rest and in the production of the /s/ sound. The sample was subdivided on the basis of the degree of horizontal and vertical overlap of the incisor teeth. The results indicated a trend between increased closest speaking space and increased vertical overlap of the teeth and a similar tendency for increased anterior speaking space with increased horizontal overlap of the teeth. Prtsrnted hefore the Academy of Denture Prosthetics, Hilton Head, S.C *I,rcturer, Department of Prosthetic Dentistry. THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
Fig. 1. Articulated diagnostic casts have a thin acrylic resin slip formed to buccal sulcus and teeth from lower canine to lower canine. Small bar magnet of Kinesiograph is held in place across midline in acrylic resin. The Case Gnathic Replicator was developed to enable the three dimensional movements of the mandible to be accurately measured and reproduced on articulated artificial stone casts of the subject.” Its role in the study of speech was apparently restricted to monitoring the position of the mandible during the production of the letter “m” to assessits relation to the rest position of the mandible and hence the interocclusal distance. This undoubtedly was a result of the weight of the measuring device and the passage of wires through the commissure of the mouth inhibiting natural speech by the subject. Geissler’* examined the mandidular movement during speech by using an arrangement of synchronized transmitters. The speech of 54 subjects was monitored in this way while they recited two short sentences, but minimal results were published. Jankelson et al.13described equipment suitable for the examination and measurement of mandibular movement-the Mandibular Kinesiograph (Myotronics Research Inc., Seattle, Wash.). The transponder is a small bar magnet cemented to the labial surface of the lower incisor teeth. The position of the magnet is determined by an array of magnetometers. The accuracy of this instrument has been demonstrated as has its ability to be interfaced with a computer for linearization of the output and off-line analysis of jaw movement.14.‘* Other systems that provide accurate measurements of 93
HOWELL
SIRIUS 1 COMPUTER
ANALOCUE TO DIGITAL CONVERTOR
KINESIOCRAPH
Fig. 2. Diagrammatic representation of computer-Kinesiograph arrangement showing its connection to microcomputer by way of analogue to digital convertor.
Fig. 3. Arrangement of equipment in surgery for analysis of mandibular movement. Computer and Kinesiograph screen are out of subject’s line of sight to avoid bias from this direction. the movement of the mandible have been described,‘9-2’ but only George” used one of these to measure some aspects of speech. METHOD Ninety-seven dental students agreed to take part in a study of mandibular movement during function. The data from 95 subjects are presented in this report: 39 women and 56 men from 18 to 29 years of age with an age mean of 20 years and 9 months. They each read a short standard passage of text during which their incisal movements were monitored with the Kinesiograph (Myotronics Research Inc.). Before the experiment, impressions of the teeth and 94
surrounding soft tissues were made and the diagnostic casts were articulated with the use of a face-bow record. An acrylic resin slip was made to fit the mandibular cast and to lie in the labial sulcus to hold the small bar magnet of the kinesiograph close to the labial aspect of the mandibular incisor teeth (Fig. 1). The mandibular cast and articulator ring were placed on a leveled surveyor table and the orientation of the magnet was adjusted to lie horizontally across the midline with its outer face parallel to the surveyor’s pencil. The horizontal (overjet) and vertical overlap (overbite) of the central incisor teeth was measured directly from each subject at the time of the experiment. The acrylic resin slip with the magnet was positioned in the subject’s mouth so that it neither interferred with the occlusion nor was displaced by prominent frenae. The slip was then cemented to the labial surfaces of the mandibular anterior teeth with Peripheral Seal (De Trey Division, Dentsply Ltd., Weybridge, Surrey, England). The occlusion was rechecked and the subject was then seated in the chair of a dental operatory. The Kinesiograph sensor array was aligned with its vertical set of sensors lying perpendicular to the Frankfort plane and thus perpendicular to the magnet when the teeth were in centric occlusion. Minor adjustments were made to the angulation and vertical position of the sensor array so that the oscilloscope spot representing the magnet’s position was centered on the screen during a high degree of amplification. Opening and closing movements of the mandible were observed and further small adjustments made where necessary to produce a vertical frontal trace on the Kinesiograph oscilloscope. The rest position of the mandible was assessedand measured directly from the oscilloscope of the Kinesiograph while the subject was unaware of the measurement procedure. The trace usually remained unstable for a period of time before it stabilized into a reasonably constant position. When any doubt was present the JULY 1986
VOLUME
56
NUMBER
1
INCISAL
RELATIONSHIPS
DURING
SPEECH
Fig. 4. Screen of computer showing high-resolution display of speech envelope for one individual. Graticule is graduated in 1 mm intervals and lateral and protrusive border movements are displayed to show relationships of opposing teeth. subjects were asked to lick their lips, say “mm,” swallow, and relax before the reading was reassessed. The subjects were asked to read aloud the following short passage of text, often called “The Rainbow Passage.“22 When the sunlight strikes raindrops in the air they act like a prism and form a rainbow. The rainbow is a division of white light into many beautiful colors. These take the shape of a long round arch with its path high above and its ends apparently beyond the horizon. There is, according to legend, a boiling pot of gold at one end. People look but no one ever finds it. When a man looks for something beyond his reach, his friends say that he is looking for the pot of gold at the end of the rainbow. The position of the mandibular incisor teeth during the reading of “The Rainbow Passage” was monitored by the Kinesiograph and displayed on its oscilloscope screen. However, as has been indicated elsewhere, this output is nonlinear.‘4~1s To correct the nonlinearity and permit the recall and analysis of mandibular movement in three dimensions, the signals were sampled at the rear of the instrument by an analogue to a digital convertor at a rate of 100 Hz under the control of the ACT Sirius 1 microcomputer (ACT (UK) Ltd, Halesowen, West Midlands, United Kingdom). The data were stored on the system’s integral hard disk. Lateral and protrusive border movements were recorded separately. The original experimental arrangement’8 has been updated to take account of the recent advances in computer technology, and the modified experimental setup is shown in Figs. 2 and 3. The stored data were analyzed off-line by a computer THE JOURNAL
OF PROSTHETIC
DENTISTRY
program that made correction for the nonlinearity of response of the Kinesiograph and provided the real three-dimensional coordinates of the magnet. The individual points of movement were displayed on the highresolution monitor of the computer. A linear interpolation between each successive point enabled a display of the cumulative speech pattern or envelope from both a frontal and a lateral view (Fig. 4). The lateral and protrusive border movements are included to show the relation of the maxillary teeth. A 1 mm scale was superimposed on the screen display to permit direct measurement. The computer monitor was photographed with the use of color slide film (Kodak 64, Kodak Ltd, Hemel Hempstead, Herts, UK.), which was projected at 25 times enlargement. This image was measured and used to provide the data presented here. RESULTS The subjects who had measurements of their speech envelope and other parameters recorded included three groups of students, each group representing half an academic year. No restriction on the basis of skeletal or mandibular relation was placed on entry into this study for the volunteers, other than their presence within the department. A wide variety of occlusal and skeletal relationships was present within the sample group as demonstrated by the scatter diagram of the measurements of the horizontal and vertical overlap of their incisor teeth (Fig. 5). The ranges of movement of the mandible during the reading of “The Rainbow Passage” in the anteroposterior, vertical, and lateral directions are shown in Table I. 95
HOWELL
A , 1*
2,
3
4
5
6
7
8
N=
HORIZONTAL OUERLAP (MM) Fig.
Anteroposterior range Vertical range Lateral range Valuesexpressed
Mean
SEM
SD
Range
4.17 8.31 1.61
20.14 kO.26 50.07
1.41 2.51 0.67
0.4- 7.5 3.6-16.0 0.4- 4.0
in mm.
These movements demonstrated a wide range for all directions of the speech envelope. The maximum and minimum movement values of the teeth during speech in the anteroposterior and vertical directions are shown in Table II. The mean value for the closest vertical position of the teeth to centric relation was 3.1 mm and the mean maximum vertical separation to the open position was 11.4 mm. In 8 of the 95 subjects it was not possible to distinguish any departure from centric relation as the most superior position of speech (the closest speaking space). The most anterior position of the teeth was 1.5 mm, but this had a range from 5 mm anteriorly to nearly 2 mm posteriorly! The width of the speech envelope was narrow at 1.7 mm, ranging only from 0.4 to 4 mm. The closest position of the mandibular incisor teeth to the anterior guidance formed by the palatal aspect of the maxillary incisor teeth was measured for 58 of the 95 subjects and found to have a mean value of 0.68 mm, with a range of 0 to 5.2 mm. The expected variation in the resting vertical dimension was found. It had a mean of 2.3 mm and a range of 0.4 to 7 mm and is included in 96
R = 0.33
5. Scatter diagram showing incisor horizontal and vertical overlaps.
Table I. Range of movement for the lower incisor teeth during the reading of a standard passage of text forming an envelope of speech for 95 subjects. Parameter
95
Table II for comparison with the values of the closest speaking space. A plot of the values of the closest speaking space versus the vertical overlap of the teeth for this group of subjects is shown in Fig. 6. There was a considerable scatter of the points but a regression coefficient (r = 0.61) indicated a positive correlation that was statistically significant at the 0.1% level. A plot of the values of the anterior speaking position and the horizontal overlap of the incisor teeth yielded a regression coefficient (r = 0.29) that showed only a weak correlation between these two parameters (Fig. 7).
DISCUSSION In the few studies that have examined the movement of the incisor teeth during speech, most authors have examined the position of the incisor teeth in the vertical plane (a frontal view) using direct clinical observation, photography, or simple mechanical methods to provide their data.j- 5,6*‘2,23Only one study appears to have examined the movements in a sagittal plane (a lateral view) with the use of radiographic techniques.” In addition, one author used a more advanced apparatus to study speech.” These studies all observed the position of the teeth during the production of the /s/ sound, and have not examined the wider range of movements of the mandible found in the pronunciation of the full range of phonemes present in everyday speech. Furthermore it is hazardous to draw too great a conclusion from the enunciation of the single phoneme (word sound) inasmuch as it has been demonstrated that the vertical separation of the teeth even varies between succesive attempts at speaking JULY 1986
VOLUME
56
NUMBER
1
INCISAL
RELATIONSHIPS
DURING
SPEECH
UERTICAL OUERLAP ws
CLOSEST
SPEAKING
SPACE
10-l A 6:
A&A
A
A 6:
AA A
*
A
*
A
A
f
-AA AM A
amA.dMA A AAA
AAAA A*
a%.&*
4'
A A
A A
A A
1
A
AA
A A
A A
AA
A
AA
A
A A
*A
A A
0.
1
A
21A
3'
4'
5'
6'
7-T
-2; N=
Mrl
CLOSEST
SPEAKING SPACE
Fig. 6. Plot of closest speaking space versus vertical a single simple word. 23This finding was confirmed by George” who described two separate positions of the teeth during the /s/ sound, which he called the near and far /s/. The disparity between the two positions for apparently the same sound could be accounted for by its placement within the sentence and even the word being spoken. Indeed it is likely that there is a normal range of movement exhibited by a subject during production of the individual phonemes and that the incisor position is, at least partly, dependent on the preceding and succeeding phonemes. This study used a standard passage of text with a 76-syllable sample of the English language.22 The method used for measurement of the position of the lower incisor teeth has the advantage that it does not restrict the analysis to a single viewing point. The plane of choice in which measurements are to be made is entirely under software control after the raw data have been acquired. The range of movements of the mandible during the reading of the standard text, describing a speech envelope, has not been previously reported. It appears that this envelope is fairly constant for an individual when a standard passage is read at a normal rate and volume. The ranges of movement in the anteroposterior, lateral, and vertical directions provide a description of the speech envelope (Table I). The lateral width of the speech envelope is narrow and is, in general, less than 1 mm either side of the midline. The values of the mean closest speaking space (Table II) is greater than the values published by George” (1.8 mm with a range of 1.1 mm) and his anterior speaking space of 0.5 mm is smaller than the figure obtained here. However it should THE JOURNAL
OF PROSTHETIC
DENTISTRY
95
R = 0.61 overlap
of incisor teeth.
Table II. Selected measurements in anteroposterior and vertical directions --Parameter
Mean
SEM
SD
Anterior speaking space Closest speaking space Rest vertical dimension Closest tooth contact
1.51
eO.14
1.30
3.10
20.18
l.Th
O-R.0
2.31
to.14
I .3
0.4-7.0
0.68
11-0.15
1.16
--
Renne 5.0-1.8(ret)
o-5.2
---.-. _-.. -.
Values expreswd in mm.
be noted that George restricted himself to subjects whose skeletal and occlusal relationships were Class I. Geissler12 found that the range of movement from the closest speaking position to the widest opening was 4.1 mm, compared to the vertical range of 8.3 mm in this study. He gave a range for the closest speaking distance itself between 0 and 5.5 mm. No other data were published. Benediktsson’s data’” are not readily grouped for total figures but the values of 2.23 mm closest speaking space and 1.77 mm anterior speaking space are intermediate between the values presented here and those of George. Benediktsson also indicated that during the /s/ sound a trend was noticed between an increased vertical overlap and closest speaking space and an increased protrusion and increased horizontal overlap. Silverman3 and Pound’ have long expounded the role of phonetics in the construction of complete dentures, using the /s/ sound as major criterion in the assessment 97
HOWELL
ANTERIOR SPEAKING SPACE HORIZONTAL
OVERLAP
N-
HORIZONT?
Fig. 7. Anterior
speaking
space plotted
of the occlusal vertical dimension and in the positioning of the maxillary and mandibular labial segments. This vertical dimension, is selected so that the teeth do not contact during speech, and there is a separation of the occlusal rims of about 2 mm. The horizontal overlap of the teeth are assessedby the degree of protrusion of the mandible during speech to its anterior speaking position. The implication of these methods is that there is a universal relationship between the horizontal and vertical overlap of the incisor teeth and the position adopted by the mandible as its most forward and upper position during speech. In the group of young dentate subjects included in this study, the correlation between the vertical overlap of the teeth and the closest speaking space yielded a regression coefficient (r = 0.6) that shows a degree of dependence statistically significant but without a strong correlation. This is illustrated by the wide scatter of points in Fig. 6. The relationship between the anterior speaking space and the horizontal overlap of the teeth shows only a weak correlation (r = 0.3) that is barely significant. SUMMARY 1. The dimensions of movement of the mandible during the reading of a standard passage of text have been measured and enable a speech envelope to be described. 2. The relationship between closest speaking space and the vertical overlap of the incisor teeth shows that there is a trend in this direction, but it is not as definitive a correlation as has been previously assumed. 3. The relationship between the anterior speaking space and the horizontal overlap of the incisor teeth 98
OUERLAP
95
R = 0.28
against horizontal
overlap
of incisor teeth.
shows a similar trend but with a much reduced correlation. 4. There was often a small space of approximately 0.2 mm between the mandibular incisor teeth and the palatal aspects of the maxillary incisor teeth that, although a common finding in this study, was by no means a constant feature for all subjects. REFERENCES 1. Niswonger ME: Rest position of the mandible and centric relation. J Am Dent Assoc 21:1572, 1934. 2. Silverman MM: Determination of vertical dimension by phonetics. J PROSTHE.T DENT 6~465, 1956. 3. Silverman MM: The speaking method in measuring vertical dimension. J PROSTHET DENT 3:193, 1953. 4. Silverman MM: Occlusion in Prosthodontics and in the Natural Dentition. Washington DC, 1962, Mutual Publishing Co. EJ: The use of speech patterns as an aid in 5. Mehringer prosthodontic reconstruction. J PROSTHE.~ DENT 13S2.5, 1963. 6. Pound E: The mandibular movements of speech and their seven related values. J PR~STHET DENT l&835, 1966. 7. Pound E: Controlling vertical dimension and speech. J PROSTHET DENT 36~125, 1976. 8. 9. 10.
11. 12.
Hildebrand GY: Studies in the masticatory movements of the human lower jaw. Skand Arch Physiol Suppl 61, 1931, Bates JF, Stafford GD, Harrison A: Masticatory function-a review of the literature. J Oral Rehabil 2~281, 1975. Benediktsson Is: Variation in tongue and jaw position in 3” sound production in relation to front teem occlusion. Acta Odontol Stand 15:275, 1958. Gibbs CH, Messerman T, Reswick JB, Dreda HJ: Functional movements of the mandible. J PROSTHKT DENT 26~604, 1971. Geissler PR: Studies of mandibular movement in speech. J Dent 3:256,
1975.
13.
Jankelson 0. Swain CW, Crane PF, Radke ,JC: Kinesiographic instrumentation: A new technology. J Am Dent Assoc 9Oz8.14,
14.
Hannam AG, Scott JD, De Cou RE: A computer-based system
1975.
for the simultaneous measurement of muscle activity and jaw JULY 1986
VOLUME
56
NUMBER
I
INCISAL
15.
16. 17.
18.
19. 20.
RELATIONSHIPS
DURING
SPEECH
movement during mastication in man. Arch Oral Biol 22:17, 1977. ,Jankelson B: Measurement accuracy of the mandibular kinesiograph-A computerized study. J PROSTHET DENT 44~656, 1980. Neil1 DJ: Masticatory function. J Dent Assoc SA 37:631, 1982. George JP: IJsing the Kinesiograph to measure mandibular movement during speech: A pilot study. J PROSTHET DENT 49:263, 1983. Neil1 DJ, Howell PGT: Kinesiograph studies of jaw movement using the Commodore Pet microcomputer for data storage and analysis. J Dent 12:53, 1984. Lemmer J, Lewin A, van Rensburg LB: The measurement of jaw movement: Part 1. J PROSTHETDENT 36:211, 1976. Jemt T. Positions of the mandible during chewing and swallowing recorded by light-emitting diodes. J PROSTHETDENT 48~206, 1982.
21.
22. 23.
Hobo S. Mochizuki S: A kinematic inves:tgation (11mandibular border movements by means of an electronic nleasuring system. Part I: Development of the measuring svstem J PKOSTWETI DENT 50:368, 1983. Fairbanks G: Voice and articulation drillboos ed 2. Nrw York 1940, Harper & B.os. Publishers, Inc. p 127 Dombrady L: Knvestigation into the transient notability of the rest position. J PROSTHET DEN-F 16:479, 1966
Refmnt request, to: DR. P. G. T. HOWELL. GUY’S Hos~r.4~ DENTAL SCHOOL LONDON SE1 9RT ENGLAND
Shear strength of lingual rest seats prepared in bonded composite Richard W. Toth, D.D.S., M.S.,* Guy E. Fiebiger, D.M.D.,*+ J. Rodway Mackert, Jr., D.M.D., Ph.D.,*** and Barry M. Goldman, D.D.S., M.S.**** Medical College of Georgia, School of Dentistry, Augusta, Ga.
A
ccurate rest seats are essential to the design of removable partial dentures to prevent gingival displacement and for the transmission of forces along the long axes of abutment teeth.‘,* The commonly accepted designs of rest seats prepared in the enamel of anterior teeth are the lingual (cingulum) rest and the incisal rest. Lingual rest seats are preferred because of their more favorable proximity to the abutment tooth’s center of rotation and for their superior esthetics. Most anterior teeth, especially in the mandible, do not present suitable contours or depth of enamel for adequate preparation. As a result, the dentist resorts to incisal rest seats with their disadvantages of poor esthetics, potential occlusal interference, and unfavorable torquing because of their
The opinions or assertions contained in this article are those of the authors and are not to be construed as official or as reflecting the views of the Department of the Navy. *Former Resident in Prosthodontics; currently Lieutenant Commander (DC) USN, Dental Officer, USS Nimitz. **Associate Professor, Prosthodontic Department. ***Associate Professor, Dental Materials Division. ****Professor and Director, Postgraduate Program in Prosthodontics. THE JOURNAL
OF PROSTHETIC
DENTISTRY
location farther from the tooth’s center of rotation. Cast restorations have been advocated even though they necessitate increased reduction of tooth structure and greater cost to the patient.* The use of bonded composites in abutment tooth preparation for removable partial dentures is a provocative concept. There are several desirable aspects to the use of lingual rest seats prepared in a bonded composite: (1) torquing forces are minimized by placing the rest seat closer to the tooth’s center of rotation, (2) the preparation is esthetic, (3) the technique conserves intact tooth structure, (4) the procedure is economical in terms of monetary cost to the dentist and patient and in terms of chair time, (5) no laboratory procedures are involved, and (6) the preparation of the abutment teeth after material placement is no more complicated than routine mouth preparation for any removable partial denture. Using these materials to create retentive undercuts, Hebel et a1.3reported favorable wear patterns of both the composite and the retentive clasp tip in an in vitro simulation of 3 years in function. Wong et a1.4proposed the clinical feasibility of cast lingual rest seats with the use of an orthodontic resin bonding system. In the dental clinics at the Medical
College of Georgia,
lingual
rest 99
LOUIS
AND
EDUCATION
r:I~rToII
J. BOUCHER
Incisal relationships P. G. T. Howell, I’nited
Medical
during
speech
B.Sc., B.D.S. Ph.D.*
and Dental
Schools of Guy’s
and St. Thomas’s Hospital,
London,
England
N
iswonger’ indicated the importance of the rest position of the mandible in the treatment of patients with complete dentures and said that it should be related to the measurement of the occlusal vertical dimension. The difference between the measurements of the occlusal vertical dimension and resting vertical dimension provides the interocclusal distance.’ From clinical studies, Silverman2-4 considered that the resting vertical dimension was insufficiently dynamic to represent the position of the mandible during its normal functional movements. He therefore proposed an alternative measurement procedure to provide a definition for the occlusal vertical dimension, in place of the static method described. He used phonetics in the assessment of the mandibular position for the occlusal vertical dimension and proposed that the smallest separation of the maxillae from the mandible during speech be adopted as the major criterion. Silverman defined the distance between the closest speaking position and the teeth in centric occlusion as the closest speaking space. He called the most protrusive position of the mandible the anterior speaking space.4 The importance of phonetics in complete denture construction was also emphasised by Mehringer’ and Pound,“,’ who studied mandibular movements during speech by direct observation of the teeth. Detailed measurement of the mandibular movements during function has been examined by numerous workers and notably reviewed by Hildebrand” and later by Bates et al9 These studies, however, have been predominantly limited to investigations of mastication or forced border movements instead of speech. A study of 246 adolescents was undertaken by Benediktsson,1° who used radiographic techniques to examine the position of the tongue and mandible at rest and in the production of the /s/ sound. The sample was subdivided on the basis of the degree of horizontal and vertical overlap of the incisor teeth. The results indicated a trend between increased closest speaking space and increased vertical overlap of the teeth and a similar tendency for increased anterior speaking space with increased horizontal overlap of the teeth. Prtsrnted hefore the Academy of Denture Prosthetics, Hilton Head, S.C *I,rcturer, Department of Prosthetic Dentistry. THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
Fig. 1. Articulated diagnostic casts have a thin acrylic resin slip formed to buccal sulcus and teeth from lower canine to lower canine. Small bar magnet of Kinesiograph is held in place across midline in acrylic resin. The Case Gnathic Replicator was developed to enable the three dimensional movements of the mandible to be accurately measured and reproduced on articulated artificial stone casts of the subject.” Its role in the study of speech was apparently restricted to monitoring the position of the mandible during the production of the letter “m” to assessits relation to the rest position of the mandible and hence the interocclusal distance. This undoubtedly was a result of the weight of the measuring device and the passage of wires through the commissure of the mouth inhibiting natural speech by the subject. Geissler’* examined the mandidular movement during speech by using an arrangement of synchronized transmitters. The speech of 54 subjects was monitored in this way while they recited two short sentences, but minimal results were published. Jankelson et al.13described equipment suitable for the examination and measurement of mandibular movement-the Mandibular Kinesiograph (Myotronics Research Inc., Seattle, Wash.). The transponder is a small bar magnet cemented to the labial surface of the lower incisor teeth. The position of the magnet is determined by an array of magnetometers. The accuracy of this instrument has been demonstrated as has its ability to be interfaced with a computer for linearization of the output and off-line analysis of jaw movement.14.‘* Other systems that provide accurate measurements of 93
HOWELL
SIRIUS 1 COMPUTER
ANALOCUE TO DIGITAL CONVERTOR
KINESIOCRAPH
Fig. 2. Diagrammatic representation of computer-Kinesiograph arrangement showing its connection to microcomputer by way of analogue to digital convertor.
Fig. 3. Arrangement of equipment in surgery for analysis of mandibular movement. Computer and Kinesiograph screen are out of subject’s line of sight to avoid bias from this direction. the movement of the mandible have been described,‘9-2’ but only George” used one of these to measure some aspects of speech. METHOD Ninety-seven dental students agreed to take part in a study of mandibular movement during function. The data from 95 subjects are presented in this report: 39 women and 56 men from 18 to 29 years of age with an age mean of 20 years and 9 months. They each read a short standard passage of text during which their incisal movements were monitored with the Kinesiograph (Myotronics Research Inc.). Before the experiment, impressions of the teeth and 94
surrounding soft tissues were made and the diagnostic casts were articulated with the use of a face-bow record. An acrylic resin slip was made to fit the mandibular cast and to lie in the labial sulcus to hold the small bar magnet of the kinesiograph close to the labial aspect of the mandibular incisor teeth (Fig. 1). The mandibular cast and articulator ring were placed on a leveled surveyor table and the orientation of the magnet was adjusted to lie horizontally across the midline with its outer face parallel to the surveyor’s pencil. The horizontal (overjet) and vertical overlap (overbite) of the central incisor teeth was measured directly from each subject at the time of the experiment. The acrylic resin slip with the magnet was positioned in the subject’s mouth so that it neither interferred with the occlusion nor was displaced by prominent frenae. The slip was then cemented to the labial surfaces of the mandibular anterior teeth with Peripheral Seal (De Trey Division, Dentsply Ltd., Weybridge, Surrey, England). The occlusion was rechecked and the subject was then seated in the chair of a dental operatory. The Kinesiograph sensor array was aligned with its vertical set of sensors lying perpendicular to the Frankfort plane and thus perpendicular to the magnet when the teeth were in centric occlusion. Minor adjustments were made to the angulation and vertical position of the sensor array so that the oscilloscope spot representing the magnet’s position was centered on the screen during a high degree of amplification. Opening and closing movements of the mandible were observed and further small adjustments made where necessary to produce a vertical frontal trace on the Kinesiograph oscilloscope. The rest position of the mandible was assessedand measured directly from the oscilloscope of the Kinesiograph while the subject was unaware of the measurement procedure. The trace usually remained unstable for a period of time before it stabilized into a reasonably constant position. When any doubt was present the JULY 1986
VOLUME
56
NUMBER
1
INCISAL
RELATIONSHIPS
DURING
SPEECH
Fig. 4. Screen of computer showing high-resolution display of speech envelope for one individual. Graticule is graduated in 1 mm intervals and lateral and protrusive border movements are displayed to show relationships of opposing teeth. subjects were asked to lick their lips, say “mm,” swallow, and relax before the reading was reassessed. The subjects were asked to read aloud the following short passage of text, often called “The Rainbow Passage.“22 When the sunlight strikes raindrops in the air they act like a prism and form a rainbow. The rainbow is a division of white light into many beautiful colors. These take the shape of a long round arch with its path high above and its ends apparently beyond the horizon. There is, according to legend, a boiling pot of gold at one end. People look but no one ever finds it. When a man looks for something beyond his reach, his friends say that he is looking for the pot of gold at the end of the rainbow. The position of the mandibular incisor teeth during the reading of “The Rainbow Passage” was monitored by the Kinesiograph and displayed on its oscilloscope screen. However, as has been indicated elsewhere, this output is nonlinear.‘4~1s To correct the nonlinearity and permit the recall and analysis of mandibular movement in three dimensions, the signals were sampled at the rear of the instrument by an analogue to a digital convertor at a rate of 100 Hz under the control of the ACT Sirius 1 microcomputer (ACT (UK) Ltd, Halesowen, West Midlands, United Kingdom). The data were stored on the system’s integral hard disk. Lateral and protrusive border movements were recorded separately. The original experimental arrangement’8 has been updated to take account of the recent advances in computer technology, and the modified experimental setup is shown in Figs. 2 and 3. The stored data were analyzed off-line by a computer THE JOURNAL
OF PROSTHETIC
DENTISTRY
program that made correction for the nonlinearity of response of the Kinesiograph and provided the real three-dimensional coordinates of the magnet. The individual points of movement were displayed on the highresolution monitor of the computer. A linear interpolation between each successive point enabled a display of the cumulative speech pattern or envelope from both a frontal and a lateral view (Fig. 4). The lateral and protrusive border movements are included to show the relation of the maxillary teeth. A 1 mm scale was superimposed on the screen display to permit direct measurement. The computer monitor was photographed with the use of color slide film (Kodak 64, Kodak Ltd, Hemel Hempstead, Herts, UK.), which was projected at 25 times enlargement. This image was measured and used to provide the data presented here. RESULTS The subjects who had measurements of their speech envelope and other parameters recorded included three groups of students, each group representing half an academic year. No restriction on the basis of skeletal or mandibular relation was placed on entry into this study for the volunteers, other than their presence within the department. A wide variety of occlusal and skeletal relationships was present within the sample group as demonstrated by the scatter diagram of the measurements of the horizontal and vertical overlap of their incisor teeth (Fig. 5). The ranges of movement of the mandible during the reading of “The Rainbow Passage” in the anteroposterior, vertical, and lateral directions are shown in Table I. 95
HOWELL
A , 1*
2,
3
4
5
6
7
8
N=
HORIZONTAL OUERLAP (MM) Fig.
Anteroposterior range Vertical range Lateral range Valuesexpressed
Mean
SEM
SD
Range
4.17 8.31 1.61
20.14 kO.26 50.07
1.41 2.51 0.67
0.4- 7.5 3.6-16.0 0.4- 4.0
in mm.
These movements demonstrated a wide range for all directions of the speech envelope. The maximum and minimum movement values of the teeth during speech in the anteroposterior and vertical directions are shown in Table II. The mean value for the closest vertical position of the teeth to centric relation was 3.1 mm and the mean maximum vertical separation to the open position was 11.4 mm. In 8 of the 95 subjects it was not possible to distinguish any departure from centric relation as the most superior position of speech (the closest speaking space). The most anterior position of the teeth was 1.5 mm, but this had a range from 5 mm anteriorly to nearly 2 mm posteriorly! The width of the speech envelope was narrow at 1.7 mm, ranging only from 0.4 to 4 mm. The closest position of the mandibular incisor teeth to the anterior guidance formed by the palatal aspect of the maxillary incisor teeth was measured for 58 of the 95 subjects and found to have a mean value of 0.68 mm, with a range of 0 to 5.2 mm. The expected variation in the resting vertical dimension was found. It had a mean of 2.3 mm and a range of 0.4 to 7 mm and is included in 96
R = 0.33
5. Scatter diagram showing incisor horizontal and vertical overlaps.
Table I. Range of movement for the lower incisor teeth during the reading of a standard passage of text forming an envelope of speech for 95 subjects. Parameter
95
Table II for comparison with the values of the closest speaking space. A plot of the values of the closest speaking space versus the vertical overlap of the teeth for this group of subjects is shown in Fig. 6. There was a considerable scatter of the points but a regression coefficient (r = 0.61) indicated a positive correlation that was statistically significant at the 0.1% level. A plot of the values of the anterior speaking position and the horizontal overlap of the incisor teeth yielded a regression coefficient (r = 0.29) that showed only a weak correlation between these two parameters (Fig. 7).
DISCUSSION In the few studies that have examined the movement of the incisor teeth during speech, most authors have examined the position of the incisor teeth in the vertical plane (a frontal view) using direct clinical observation, photography, or simple mechanical methods to provide their data.j- 5,6*‘2,23Only one study appears to have examined the movements in a sagittal plane (a lateral view) with the use of radiographic techniques.” In addition, one author used a more advanced apparatus to study speech.” These studies all observed the position of the teeth during the production of the /s/ sound, and have not examined the wider range of movements of the mandible found in the pronunciation of the full range of phonemes present in everyday speech. Furthermore it is hazardous to draw too great a conclusion from the enunciation of the single phoneme (word sound) inasmuch as it has been demonstrated that the vertical separation of the teeth even varies between succesive attempts at speaking JULY 1986
VOLUME
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NUMBER
1
INCISAL
RELATIONSHIPS
DURING
SPEECH
UERTICAL OUERLAP ws
CLOSEST
SPEAKING
SPACE
10-l A 6:
A&A
A
A 6:
AA A
*
A
*
A
A
f
-AA AM A
amA.dMA A AAA
AAAA A*
a%.&*
4'
A A
A A
A A
1
A
AA
A A
A A
AA
A
AA
A
A A
*A
A A
0.
1
A
21A
3'
4'
5'
6'
7-T
-2; N=
Mrl
CLOSEST
SPEAKING SPACE
Fig. 6. Plot of closest speaking space versus vertical a single simple word. 23This finding was confirmed by George” who described two separate positions of the teeth during the /s/ sound, which he called the near and far /s/. The disparity between the two positions for apparently the same sound could be accounted for by its placement within the sentence and even the word being spoken. Indeed it is likely that there is a normal range of movement exhibited by a subject during production of the individual phonemes and that the incisor position is, at least partly, dependent on the preceding and succeeding phonemes. This study used a standard passage of text with a 76-syllable sample of the English language.22 The method used for measurement of the position of the lower incisor teeth has the advantage that it does not restrict the analysis to a single viewing point. The plane of choice in which measurements are to be made is entirely under software control after the raw data have been acquired. The range of movements of the mandible during the reading of the standard text, describing a speech envelope, has not been previously reported. It appears that this envelope is fairly constant for an individual when a standard passage is read at a normal rate and volume. The ranges of movement in the anteroposterior, lateral, and vertical directions provide a description of the speech envelope (Table I). The lateral width of the speech envelope is narrow and is, in general, less than 1 mm either side of the midline. The values of the mean closest speaking space (Table II) is greater than the values published by George” (1.8 mm with a range of 1.1 mm) and his anterior speaking space of 0.5 mm is smaller than the figure obtained here. However it should THE JOURNAL
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95
R = 0.61 overlap
of incisor teeth.
Table II. Selected measurements in anteroposterior and vertical directions --Parameter
Mean
SEM
SD
Anterior speaking space Closest speaking space Rest vertical dimension Closest tooth contact
1.51
eO.14
1.30
3.10
20.18
l.Th
O-R.0
2.31
to.14
I .3
0.4-7.0
0.68
11-0.15
1.16
--
Renne 5.0-1.8(ret)
o-5.2
---.-. _-.. -.
Values expreswd in mm.
be noted that George restricted himself to subjects whose skeletal and occlusal relationships were Class I. Geissler12 found that the range of movement from the closest speaking position to the widest opening was 4.1 mm, compared to the vertical range of 8.3 mm in this study. He gave a range for the closest speaking distance itself between 0 and 5.5 mm. No other data were published. Benediktsson’s data’” are not readily grouped for total figures but the values of 2.23 mm closest speaking space and 1.77 mm anterior speaking space are intermediate between the values presented here and those of George. Benediktsson also indicated that during the /s/ sound a trend was noticed between an increased vertical overlap and closest speaking space and an increased protrusion and increased horizontal overlap. Silverman3 and Pound’ have long expounded the role of phonetics in the construction of complete dentures, using the /s/ sound as major criterion in the assessment 97
HOWELL
ANTERIOR SPEAKING SPACE HORIZONTAL
OVERLAP
N-
HORIZONT?
Fig. 7. Anterior
speaking
space plotted
of the occlusal vertical dimension and in the positioning of the maxillary and mandibular labial segments. This vertical dimension, is selected so that the teeth do not contact during speech, and there is a separation of the occlusal rims of about 2 mm. The horizontal overlap of the teeth are assessedby the degree of protrusion of the mandible during speech to its anterior speaking position. The implication of these methods is that there is a universal relationship between the horizontal and vertical overlap of the incisor teeth and the position adopted by the mandible as its most forward and upper position during speech. In the group of young dentate subjects included in this study, the correlation between the vertical overlap of the teeth and the closest speaking space yielded a regression coefficient (r = 0.6) that shows a degree of dependence statistically significant but without a strong correlation. This is illustrated by the wide scatter of points in Fig. 6. The relationship between the anterior speaking space and the horizontal overlap of the teeth shows only a weak correlation (r = 0.3) that is barely significant. SUMMARY 1. The dimensions of movement of the mandible during the reading of a standard passage of text have been measured and enable a speech envelope to be described. 2. The relationship between closest speaking space and the vertical overlap of the incisor teeth shows that there is a trend in this direction, but it is not as definitive a correlation as has been previously assumed. 3. The relationship between the anterior speaking space and the horizontal overlap of the incisor teeth 98
OUERLAP
95
R = 0.28
against horizontal
overlap
of incisor teeth.
shows a similar trend but with a much reduced correlation. 4. There was often a small space of approximately 0.2 mm between the mandibular incisor teeth and the palatal aspects of the maxillary incisor teeth that, although a common finding in this study, was by no means a constant feature for all subjects. REFERENCES 1. Niswonger ME: Rest position of the mandible and centric relation. J Am Dent Assoc 21:1572, 1934. 2. Silverman MM: Determination of vertical dimension by phonetics. J PROSTHE.T DENT 6~465, 1956. 3. Silverman MM: The speaking method in measuring vertical dimension. J PROSTHET DENT 3:193, 1953. 4. Silverman MM: Occlusion in Prosthodontics and in the Natural Dentition. Washington DC, 1962, Mutual Publishing Co. EJ: The use of speech patterns as an aid in 5. Mehringer prosthodontic reconstruction. J PROSTHE.~ DENT 13S2.5, 1963. 6. Pound E: The mandibular movements of speech and their seven related values. J PR~STHET DENT l&835, 1966. 7. Pound E: Controlling vertical dimension and speech. J PROSTHET DENT 36~125, 1976. 8. 9. 10.
11. 12.
Hildebrand GY: Studies in the masticatory movements of the human lower jaw. Skand Arch Physiol Suppl 61, 1931, Bates JF, Stafford GD, Harrison A: Masticatory function-a review of the literature. J Oral Rehabil 2~281, 1975. Benediktsson Is: Variation in tongue and jaw position in 3” sound production in relation to front teem occlusion. Acta Odontol Stand 15:275, 1958. Gibbs CH, Messerman T, Reswick JB, Dreda HJ: Functional movements of the mandible. J PROSTHKT DENT 26~604, 1971. Geissler PR: Studies of mandibular movement in speech. J Dent 3:256,
1975.
13.
Jankelson 0. Swain CW, Crane PF, Radke ,JC: Kinesiographic instrumentation: A new technology. J Am Dent Assoc 9Oz8.14,
14.
Hannam AG, Scott JD, De Cou RE: A computer-based system
1975.
for the simultaneous measurement of muscle activity and jaw JULY 1986
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56
NUMBER
I
INCISAL
15.
16. 17.
18.
19. 20.
RELATIONSHIPS
DURING
SPEECH
movement during mastication in man. Arch Oral Biol 22:17, 1977. ,Jankelson B: Measurement accuracy of the mandibular kinesiograph-A computerized study. J PROSTHET DENT 44~656, 1980. Neil1 DJ: Masticatory function. J Dent Assoc SA 37:631, 1982. George JP: IJsing the Kinesiograph to measure mandibular movement during speech: A pilot study. J PROSTHET DENT 49:263, 1983. Neil1 DJ, Howell PGT: Kinesiograph studies of jaw movement using the Commodore Pet microcomputer for data storage and analysis. J Dent 12:53, 1984. Lemmer J, Lewin A, van Rensburg LB: The measurement of jaw movement: Part 1. J PROSTHETDENT 36:211, 1976. Jemt T. Positions of the mandible during chewing and swallowing recorded by light-emitting diodes. J PROSTHETDENT 48~206, 1982.
21.
22. 23.
Hobo S. Mochizuki S: A kinematic inves:tgation (11mandibular border movements by means of an electronic nleasuring system. Part I: Development of the measuring svstem J PKOSTWETI DENT 50:368, 1983. Fairbanks G: Voice and articulation drillboos ed 2. Nrw York 1940, Harper & B.os. Publishers, Inc. p 127 Dombrady L: Knvestigation into the transient notability of the rest position. J PROSTHET DEN-F 16:479, 1966
Refmnt request, to: DR. P. G. T. HOWELL. GUY’S Hos~r.4~ DENTAL SCHOOL LONDON SE1 9RT ENGLAND
Shear strength of lingual rest seats prepared in bonded composite Richard W. Toth, D.D.S., M.S.,* Guy E. Fiebiger, D.M.D.,*+ J. Rodway Mackert, Jr., D.M.D., Ph.D.,*** and Barry M. Goldman, D.D.S., M.S.**** Medical College of Georgia, School of Dentistry, Augusta, Ga.
A
ccurate rest seats are essential to the design of removable partial dentures to prevent gingival displacement and for the transmission of forces along the long axes of abutment teeth.‘,* The commonly accepted designs of rest seats prepared in the enamel of anterior teeth are the lingual (cingulum) rest and the incisal rest. Lingual rest seats are preferred because of their more favorable proximity to the abutment tooth’s center of rotation and for their superior esthetics. Most anterior teeth, especially in the mandible, do not present suitable contours or depth of enamel for adequate preparation. As a result, the dentist resorts to incisal rest seats with their disadvantages of poor esthetics, potential occlusal interference, and unfavorable torquing because of their
The opinions or assertions contained in this article are those of the authors and are not to be construed as official or as reflecting the views of the Department of the Navy. *Former Resident in Prosthodontics; currently Lieutenant Commander (DC) USN, Dental Officer, USS Nimitz. **Associate Professor, Prosthodontic Department. ***Associate Professor, Dental Materials Division. ****Professor and Director, Postgraduate Program in Prosthodontics. THE JOURNAL
OF PROSTHETIC
DENTISTRY
location farther from the tooth’s center of rotation. Cast restorations have been advocated even though they necessitate increased reduction of tooth structure and greater cost to the patient.* The use of bonded composites in abutment tooth preparation for removable partial dentures is a provocative concept. There are several desirable aspects to the use of lingual rest seats prepared in a bonded composite: (1) torquing forces are minimized by placing the rest seat closer to the tooth’s center of rotation, (2) the preparation is esthetic, (3) the technique conserves intact tooth structure, (4) the procedure is economical in terms of monetary cost to the dentist and patient and in terms of chair time, (5) no laboratory procedures are involved, and (6) the preparation of the abutment teeth after material placement is no more complicated than routine mouth preparation for any removable partial denture. Using these materials to create retentive undercuts, Hebel et a1.3reported favorable wear patterns of both the composite and the retentive clasp tip in an in vitro simulation of 3 years in function. Wong et a1.4proposed the clinical feasibility of cast lingual rest seats with the use of an orthodontic resin bonding system. In the dental clinics at the Medical
College of Georgia,
lingual
rest 99