Relationship between tongue volume and lower dental arch sizes Kazuhiko Tamari, DDS," Kenji Shimizu, DDS, DDSe, b Motoshi Ichinose, DSC, = Shunsuke Nakata, DDS, DDSc, d and Yasuhide Takahama, DDS, DMSc"
Fukuoka, Japan The interrelation between the tongue volume and the lower dental arch sizes (arch width and area) was studied by the original methods that we developed. A plane perpendicular to the occlusal plane and 40 mm posterior to the lower incisal point was taken as the posterior border of the tongue and the arch. The tongue volume and the lower dental arch sizes were measured anterior to this border with plaster models. The correlations between the parameters obtained from 74 Japanese adults (37 men and 37 women) with normal occlusion were statistically analyzed. The results showed that (1) both the mean tongue volume and the mean lower dental arch sizes were significantly larger in men than in women; (2) the tongue volume and the lower dental arch sizeswere significantly correlated; and (3) these correlations tended to be higher at the more posterior part of the dental arch. (AM J ORTHOD DENTOFACORTHOP 1991 ;100:453-8.)
S i n c e the tongue is located inside the dental arch and is almost always in contact with the teeth, unusual tongue volume or abnormal tongue movement may deform dentitions, especially when they are growing. The relationship between the tongue and the surrounding structures is a mutual interactior, with either part being a principal Or a subordinate factor.t5 The very mobile tongue consists of muscle bundles with a free end. As a result, it is difficult to assess its shape and size, so there have been few attempts to determine the tongue volume and to analyze the relationship between the tongue volume and the surround: ing structures. 6-s In this study, we attempted to clarify the morphologic relationship between the tongue volume and the lower dental arch size.
MATERIALS AND METHODS The subjects were 74 Japanese adults with normal occlusion (37 men with a mean age of 26 years and 37 women with a mean age of 21 years). The tongue volume and the lower dental arch sizes were measured from plaster models of each subject. From the Department of Orthodontics. Faculty of Dentistry, Kyushu University. This investigation was supported in part by a grant in aid No. 56771011 from the Japanese Ministry of Education. =Assistant. bAssistam professor. 'Assistant. aAssistant. 'Chairman and Professor. 811125898
Range of measurements To relate the tongue volume to the dental arch size, standard measurement dimensions were set. One point Served as the terminus at the back of the mouth for measurements of both the ~ch and the tongue (Fig. I, A). The posterior border is defined as a plane perpendicular to the occlusal plane just 40 mm posterior to the lower incisal point. That plane usually transects the lower second molars. The posterior border of the tongue was indicated with an ink mark on the dorsal surface of the tongue at 41.1 mm from the lower incisal point (Fig. 1, B). In our previous study, 9 the mean ( ± standard deviation) linear distance from the incisal point to the ink mark was found to be 41.1 --- 0.9 mm.
Measurement of tongue volume The tongue volume was measured as follows: First, the subject was instructed to hold his Or her tongue in a relaxed position in the mouth; then a mark was made on the dorsum of the tongue just 41.1 mm behind the lower incisal point to mark the posterior terminus with an instrument made for this purpose (Fig. 1, B). Next; to make the tongue impress!on, the subjec t protruded the tongue as far as possib!e into an individual tray of columned sheet wax filled with alginate impression material .(Fig. 2)~ The alginate impression was then removed, and a notch was made in it to enhance the location of the ink mark point. Then a model of the tongue was formed by pouring orthodontic stone into the alginate impression. The lingual frenum was removed from the plaiter model, and the posterior part was cut off at the notch perpendicular to the long axis of the tongue. The volume of the model was measured to the nearest 0.1 cm 3 by the Archimedes principle. Our previous study9 showed that there was no statistically significant difference in tongue volume
453
454
Tamari et al.
Am. J. Orthod. Dentofac. Orthop. November 1991
:
-
'
'
41] m,,
~"~- 40mtn
A
B Fig. 1. A, Schematic diagram showing posterior border (solid line) of tongue and lower dental arch used for measurements. B, Marking the posterior border on the dorsal surface of the tongue. A, pen point; B, guard; C, groove; D, mark 41.1 mm from the incisal point.
[, 1 Fig. 2. A, Schematic drawing of impression of tongue at maximally protruded position. B, Photograph of an alginate impression of the tongue.
at the anterior part between the position at rest and when maximally protruded. Therefore the protruded-tongue volume was used as a standard for measuring the tongue effect on lower dental arch sizes.
Measurement of lower dental arch An alginate impression of each lower dental arch was taken and filled with orthodontic stone. A camera was set with its optical axis at right angles to the occlusal plane of the lower dental arch model, and standardized photographs were taken. The photograph was enlarged to the same size as the plaster model and used for making measurements. Fig. 3 shows the reference points for each tooth and the measurement sites. The reference points were the center of
the incisal edge for the incisors, the cusp tip for the canines, and the center of the crown in the occlusal view for the premolars and molars. The continuous line connecting each reference point was defined as the dental arch. The line connecting the reference points of the first and second molars on each side was extrapolated posteriorly and, if necessary, extrapolated lines were used to measure the region posterior to the second molars (Fig. 3, A). Each reference point was put into a computer with a coordinate reader. The middle point of the line connecting the reference points of the bilateral central incisors was defined as the origin. Then along the median line (the line connecting the origin and the middle point of the line connecting the bilateral second molars) from the origin to the 40 mm point the arch width and the area of
Volume I00 Number 5
Tongue vohane and lower dental arch sizes 455
1
A
B
Fig. 3. A, Reference points for determining lower dental arch sizes. Incisors, center of edge; canines, cusp tip; premolars and molars, center of the crown area from the occlusal view. The dental arch was formed by connecting all points. The line connecting the first and second molars was extended distally (broken line), if necessary. B, Measurements of lower dental arch: width (Wl, W2, W3, W4) and area
(A1, A2, A3, A4).
Table I. M e a s u r e m e n t s o f t o n g u e v o l u m e a n d l o w e r d e n t a l a r c h sizes
Measurements Tongue volume (cm3) Dental arch width (mm) WI W2 W3 W4 Dental arch area (mm2) At A2 A3 A4
I
Sex
I
Mean
I
SD
Range
M/F ratio
M F
25.3** 22.6
3.8 4.5
17.7--33.9 15.6---33.1
1.1194
M F M F M F M F
31.5" 30.3 40.1"* 38,5 46.9*** 44.9 52.6*** 50.1
2.3 2.1 2.3 2.3 2.7 2.2 2.9 2.4
24.8--36.3 23.5--33.7 33.9----45.6 34.4-----43.2 42.8--52.5 40.5--49,0 45.8---59.6 46.1--54.7
i.0396
22. l 20.9 43.9 38.3 67.1 55.5 89.0 73.7
178.1--273.1 178.2--278.0 469.6----683.2 475.8----645.1 875.5----1173.7 865.4---1092.6 1327.3--1712.0 1314.4---1596.8
1.0200
M F M F M F M F
234.3 229.7 594.0* 575.9 1030.8"* 995.0 1529.0"* 1470.5
1.0415 1.0445 1.0499
t .0314 1.0359 1.0397
M: Male (n 37); F: female (n = 37). ***, **, and * indicate significant differences between male and female at the 0.001, 0.01, and 0.5 levels, respectively. M/F ratio: Ratio between sexes, obtained by dividing mean male values by mean female values.
the dental arch (Fig. 3, B) were caiculated by computer at 10 m m intervals.
Analysis of data Mean and standard deviation of the tongue volume and the lower dental arch size for each sex and male-to-female ratio of the mean values were calculated. The correlation coefficients between the tongue volume and the lower dental arch sizes were computed.
RESULTS T a b l e I s u m m a r i z e s the m e a s u r e m e n t s o f t o n g u e v o l u m e s a n d l o w e r d e n t a l a r c h sizes. T h e m e a n t o n g u e v o l u m e w a s 2 5 . 3 c m 3 for m e n a n d 2 2 . 6 c m 3 for w o m e n , a statistically s i g n i f i c a n t sex difference (p < 0.01). The tongue volume was 11.8% l a r g e r for m e n t h a n f o r w o m e n . T h e m e a n o f the l o w e r d e n t a l a r c h area (A4) w a s
Tamari et al.
456
Am. J. Orthod. Oentofac. Orthop. November 1991
0.282*
tongue volume was measured on plaster models prepared from impressions of the tongue. The reproducibility of the measurement of the tongue volume in the protruded position was analyzed for three volunteers in terms of changes (variations) in the volume in repeated measurements. In each volunteer, six tongue plaster models were prepared on different days, and the volume of each model was measured. The coefficients of variation (s/x) for the three volunteers were 0.064, 0.041, and 0.029, with a mean Value of 0.045. This shows that the measurement of tongue volume is satisfactorily reproducible. Takada et al.,7 who also measured tongue volume with a tongue model at the maximum protrusion, concluded that the reproducibility of the protruded tongue volume is stable. Their method of measuring the tongue volume, however, differs little from our method. It was discussed in our previous report. 9
0.371"*
Method of assessment of dental arch dimensions
0.415"*
BandYand Hunter 6 and Takada et al. 7 showed the relationship between the tongue volume and the lower dental arch sizes with the cafiines, the premo!ars, and the molars as points in measuring dental arch size. However, there are individual, sexual, and racial differences in the size of human teeth. H-14 Consequently, even when the shape and size of the dental arch are equal, no consistent data can be obtained by using anatomic characteristics of tooth structure, such as measuring the arch length from the incisal point to the distobuccal cusps of the first molars or measuring the arch width between such points. Consequently, we developed a method for impartial assessment of the lower dental arch size. The points representing the premolars and the molars were selected as the center of each crown on the occlusal view. Then a continuous line connecting those centers, the center points of the incisal edge, and the cusp tips of the canines was used as the dental arch line (Fig. 3, A). The lower dental arch sizes were measured in terms of the lower dental arch width and the area from the anterior origin to the posterior border at fixed intervals of 10 mm (Fig. 3, B). The measurement errors for the lower dental arch sizes were analyzed in terms of the changes (variations) in the dental arch area in repeated measurements. The same lower dental arch plaster model was photographed five times, and six prints were produced for each negative film for a total of 30 prints. The measuring points were marked, and the area of A4 (Fig. 3, B) was measured. The intragroup coefficients of variations (s/x) were 0.012, 0.008, 0.008, 0.008, and 0.006, with a mean of 0.008. The measurement errors would not have great influence on the measurement values.
Table II. Correlation coefficients between
tongue volume and dimensions of lower dental arch Tongue vohtme Dbnetzsions Dental arch width (W1) (W2) (W3) (W4) Dental arch area (A1) (A2) (A3) (A4)
Sex J
r
M F M F M F M F
0.387* 0.272 0.404* 0.404* 0.396* 0.435** 0.478** 0.388*
M F M F M F M F
0.353* 0.211 0.424** 0.318 0.433** 0.398* 0.463** 0.429**
j Common vahte
0.331"* 0.404** 0.416"* 0.434**
0.446**
M: Male (n = 37); F: female (n = 37). Significance level: * p < 0.05 and ** p < 0.01.
1529.0 mm z for men and 1470.5 mm 2 for women, a statistically significant sex difference (p < 0.01). The lower denial arch area was 3.9% larger for men than for women. The mean dental arch widths and areas were significantly larger for men than for women at all measuring sites except the most anterior dental arch area
(A1). The correlations between the tongue volume and the dental arch width and between the tongue volume and the dental arch area were significant (Table II). The correlations tended to be higher toward the posterior regions of the dental arch. The relationships between the tongue volume and the dental arch size (W4) are shown in terms of the distribution of measured values, regression equations, and regression lines (Fig. 4). DISCUSSION Method of assessment of tongue volume
With the recent progress in visualizat!on techniques, computerized tomography scans 8 and magnetic resonance imaging 1° are available to assess the tongue volume. However, thos e techniques have artifact problems because of the metal prostheses. Also, computerized tomography radiation is invasive. In this study, the
Volume 100 Number 5
Tongue volume and lower dental arch sizes
457
(cm 3) 35 0
.
•
~)
E --I o
25
Q) -I tO
}o
-~o _ _ ~ o ~ O
t5 Is o :Female
' 0
"//
'
45
s'
1 5
(mrn)
Dental arch width ( W 4 ) Fig. 4. Tongue volume-to-lower dental arch dimension ON4)relationships shown with regression line and 90% tolerance ellipse of distribution.
Results of measurements The mean size of the lower dental arch, as represented by the width and the area, and the mean tongue volume were all larger for men than for women. There were statistically significant differences in these values between sexes except for the mean dental arch area of the most anterior region (A1) (Table I). The sexual difference in the lower dental arch size of the Japanese was also reported by Outsbo. t3 In this study, the difference in the mean width between the lower first premolars was 2.29 mm, being 6.7% larger for men than for women. Yamauchi j~ reported that the dental arch width between the lower second molars was about 5.6% larger for men than for women. They also found a sexual difference in the mesiodistal diameter of the teeth. This might be self-evident since the measurement site was at a more posterior region of the dental arch for men than for women, reflecting the fact that men have significantly larger teeth than women. The male-to-female ratio of the mean tongue volume was larger than the ratio of the mean dental arch size. Probably this was due to the difference in the measurement dimensions. Therefore these ~arameters were transformed into the same dimension and then compared. Since the tongue volume ecas consistently obtained as the volume from al~nost the tip to 40 mm posterior to the tip, the oneJimensional expression is the square root of the quotient )f the volume divided by 4. The male-to-female ra-
tio of this mean tongue volume can be calculated as ~/(25.3/4)/~/(22.6/4) = 1.058, which is 5.8% larger for men than for women. The dental arch area of A4 was the area from the incisal point to 40 mm posterior to the incisal point, as was the case for the tongue volume. Thus a one-dimensional expression was obtained by dividing the mean area by 4. Then the male-to-female ratio can be calculated as (1529/4)/(1470.5/4) = 1.039, and it is 3.9% larger for men than for women. Similarly, the mean dental arch width of W4 is 4.9% larger for men than for women. As described previously, the male-to-female ratio of the mean tongue volume becomes almost equal to the ratios of the mean dental arch area and width if the values are transformed into the same dimension and compared. In the mean dental arch dimensions, the male-to-female ratios of both the area and the width became larger posteriorly and tended to approach the male-to-female ratio of tongue volume. J. Scott 2 wrote: "The thesis that normal dental arch form is determined by the forces exerted upon the teeth by the musculature of the tongue, lips, and cheeks is at the present time orthodox teaching and is more or less universally accepted. It has, however, never been proved." In this study, we detected statistically significant correlations between the tongue volume and the dental arch sizes (Table II). And the male-to-female ratio of the mean tongue volume was found to be almost equal to the ratio of the mean dental arch dimensions
458
Am. J. Orthod. Dentofac. Orthop. November 1991
Tamari et al.
if these parameters are transformed into the same dimensions. It seems to imply that the tongue volume is involved, at least as one morphologic factor in maintaining the dental arch sizes. The lingual movement can be more mobile at the free end (tongue tip), like a whip, as the muscle bundles of the tongue have no skeletal insertion. The mobility of the tongue seems to be more limited posteriorly and more stable than the anterior part. To test the hypothesis that the relationship between the tongue and the lower dental arch varies according to its anteroposterior location in the arch, we divided the lower dental arch into four parts from the anterior to the posterior regions and analyzed the relationship in each part. The correlation coefficients between the tongue volume and each dental arch size tended to become larger toward the posterior parts of the dental arch, although the correlations between the respective correlation coefficients were not significantly different (Table II). This phenomenon led to the suggestion that the size effects of the tongue on the lower dentition, as one of the factors of tongue form (size, shape, and position), tend to become larger toward the posterior part. We extend our gratitude to Dr. Kiyoshi Abe and Dr. Sunitaya Chatkupt for pertinent discussion and advice. REFERENCES 1. Brash JC, Mckeage HTA, Scott JH. The aetiology of irregularity and malocclusion of the teeth. 2nd ed. London: Dental Board of the United Kingdom, 1956:240. 2. Scott JH. The role of soft tissue in determining normal and abnormal dental occlusion. Dent Pract Dent Rec 1961;!1: 302-8. 3. Brodie AG. Thoughts on the aetiology of malocclusion. Tr Eur Orthod Soc 1957;33:200-15.
4. Hovell JH. The relationship of the oro-faciat musculature to occlusion: current British thought. In: Kraus BS, Riedel RA, eds. Vistas in orthodontics. Philadelphia: Lea & Febiger, 1962:328-45. 5. Graber TM. Orthodontics, principles and practice. 3rd ed. Philadelphia: WB Saunders, 1972:325. 6. Bandy HE, Hunter WS. Tongue volume and the mandibular dentition. AM J ORTHOD 1969;56:134-42. 7. Takada K, Sakuta M, Yoshida K, Kawamura Y. Relations between tongue volume and capacity of the oral cavity proper. J Dent Res 1980;59:2026-31. 8. Lowe AA, Gionhaku N, Takeuchi K, Fleetham JA. Threedimensional CT reconstructions of tongue and airway in adult subjects with obstructive sleep apnea. AM J ORTHODDENTOFAC ORTHOP 1986;90:364-74. 9. Tamafi K, Murakami T, Takahama Y. The dimensions of the tongue in relation to its motility. AMJ ORTtIODD~,Xrl'OFACORTHOP 1991 ;99:140-6. I0. Hoover LA, Wortham DG, Lutkin RB, ttanafee WN. Magnetic resonance imaging of the larynx and tongue base: clinical applications. Otolaryngol Head Neck Surg 1987;97:245-56. 11. Moyers RE. ttandbook of orthodontics. 3rd ed. Chicago: Year Book, 1972:193-4. 12. Moorrees CFA, Thomsen SO, Jensen E, Yen PK. Mesiodistal crown diameters of the deciduous and permanent teeth in individuals. J Dent Res 1957;36:39-47. 13. Otusbo J. A study on the tooth material in Japanese adults of normal occlusion: its relationship to coronal and basal arches. J Jpn Orthod Soc 1957;16:36-46. 14. Yamauchi K, Ito K, Suematsu H. Standard for the measurements of plaster-cast from Japanese young adults with normal occlusion. J Jpn Orthod Soc 1965;24:1-7. Reprint requests to: Dr. Kazuhiko Tamari Department of Orthodontics Faculty of Dentistry Kyushu University 3-1-1 Maidashi, Higashi-ku 812 Japan
Fukuoka, Japan The interrelation between the tongue volume and the lower dental arch sizes (arch width and area) was studied by the original methods that we developed. A plane perpendicular to the occlusal plane and 40 mm posterior to the lower incisal point was taken as the posterior border of the tongue and the arch. The tongue volume and the lower dental arch sizes were measured anterior to this border with plaster models. The correlations between the parameters obtained from 74 Japanese adults (37 men and 37 women) with normal occlusion were statistically analyzed. The results showed that (1) both the mean tongue volume and the mean lower dental arch sizes were significantly larger in men than in women; (2) the tongue volume and the lower dental arch sizeswere significantly correlated; and (3) these correlations tended to be higher at the more posterior part of the dental arch. (AM J ORTHOD DENTOFACORTHOP 1991 ;100:453-8.)
S i n c e the tongue is located inside the dental arch and is almost always in contact with the teeth, unusual tongue volume or abnormal tongue movement may deform dentitions, especially when they are growing. The relationship between the tongue and the surrounding structures is a mutual interactior, with either part being a principal Or a subordinate factor.t5 The very mobile tongue consists of muscle bundles with a free end. As a result, it is difficult to assess its shape and size, so there have been few attempts to determine the tongue volume and to analyze the relationship between the tongue volume and the surround: ing structures. 6-s In this study, we attempted to clarify the morphologic relationship between the tongue volume and the lower dental arch size.
MATERIALS AND METHODS The subjects were 74 Japanese adults with normal occlusion (37 men with a mean age of 26 years and 37 women with a mean age of 21 years). The tongue volume and the lower dental arch sizes were measured from plaster models of each subject. From the Department of Orthodontics. Faculty of Dentistry, Kyushu University. This investigation was supported in part by a grant in aid No. 56771011 from the Japanese Ministry of Education. =Assistant. bAssistam professor. 'Assistant. aAssistant. 'Chairman and Professor. 811125898
Range of measurements To relate the tongue volume to the dental arch size, standard measurement dimensions were set. One point Served as the terminus at the back of the mouth for measurements of both the ~ch and the tongue (Fig. I, A). The posterior border is defined as a plane perpendicular to the occlusal plane just 40 mm posterior to the lower incisal point. That plane usually transects the lower second molars. The posterior border of the tongue was indicated with an ink mark on the dorsal surface of the tongue at 41.1 mm from the lower incisal point (Fig. 1, B). In our previous study, 9 the mean ( ± standard deviation) linear distance from the incisal point to the ink mark was found to be 41.1 --- 0.9 mm.
Measurement of tongue volume The tongue volume was measured as follows: First, the subject was instructed to hold his Or her tongue in a relaxed position in the mouth; then a mark was made on the dorsum of the tongue just 41.1 mm behind the lower incisal point to mark the posterior terminus with an instrument made for this purpose (Fig. 1, B). Next; to make the tongue impress!on, the subjec t protruded the tongue as far as possib!e into an individual tray of columned sheet wax filled with alginate impression material .(Fig. 2)~ The alginate impression was then removed, and a notch was made in it to enhance the location of the ink mark point. Then a model of the tongue was formed by pouring orthodontic stone into the alginate impression. The lingual frenum was removed from the plaiter model, and the posterior part was cut off at the notch perpendicular to the long axis of the tongue. The volume of the model was measured to the nearest 0.1 cm 3 by the Archimedes principle. Our previous study9 showed that there was no statistically significant difference in tongue volume
453
454
Tamari et al.
Am. J. Orthod. Dentofac. Orthop. November 1991
:
-
'
'
41] m,,
~"~- 40mtn
A
B Fig. 1. A, Schematic diagram showing posterior border (solid line) of tongue and lower dental arch used for measurements. B, Marking the posterior border on the dorsal surface of the tongue. A, pen point; B, guard; C, groove; D, mark 41.1 mm from the incisal point.
[, 1 Fig. 2. A, Schematic drawing of impression of tongue at maximally protruded position. B, Photograph of an alginate impression of the tongue.
at the anterior part between the position at rest and when maximally protruded. Therefore the protruded-tongue volume was used as a standard for measuring the tongue effect on lower dental arch sizes.
Measurement of lower dental arch An alginate impression of each lower dental arch was taken and filled with orthodontic stone. A camera was set with its optical axis at right angles to the occlusal plane of the lower dental arch model, and standardized photographs were taken. The photograph was enlarged to the same size as the plaster model and used for making measurements. Fig. 3 shows the reference points for each tooth and the measurement sites. The reference points were the center of
the incisal edge for the incisors, the cusp tip for the canines, and the center of the crown in the occlusal view for the premolars and molars. The continuous line connecting each reference point was defined as the dental arch. The line connecting the reference points of the first and second molars on each side was extrapolated posteriorly and, if necessary, extrapolated lines were used to measure the region posterior to the second molars (Fig. 3, A). Each reference point was put into a computer with a coordinate reader. The middle point of the line connecting the reference points of the bilateral central incisors was defined as the origin. Then along the median line (the line connecting the origin and the middle point of the line connecting the bilateral second molars) from the origin to the 40 mm point the arch width and the area of
Volume I00 Number 5
Tongue vohane and lower dental arch sizes 455
1
A
B
Fig. 3. A, Reference points for determining lower dental arch sizes. Incisors, center of edge; canines, cusp tip; premolars and molars, center of the crown area from the occlusal view. The dental arch was formed by connecting all points. The line connecting the first and second molars was extended distally (broken line), if necessary. B, Measurements of lower dental arch: width (Wl, W2, W3, W4) and area
(A1, A2, A3, A4).
Table I. M e a s u r e m e n t s o f t o n g u e v o l u m e a n d l o w e r d e n t a l a r c h sizes
Measurements Tongue volume (cm3) Dental arch width (mm) WI W2 W3 W4 Dental arch area (mm2) At A2 A3 A4
I
Sex
I
Mean
I
SD
Range
M/F ratio
M F
25.3** 22.6
3.8 4.5
17.7--33.9 15.6---33.1
1.1194
M F M F M F M F
31.5" 30.3 40.1"* 38,5 46.9*** 44.9 52.6*** 50.1
2.3 2.1 2.3 2.3 2.7 2.2 2.9 2.4
24.8--36.3 23.5--33.7 33.9----45.6 34.4-----43.2 42.8--52.5 40.5--49,0 45.8---59.6 46.1--54.7
i.0396
22. l 20.9 43.9 38.3 67.1 55.5 89.0 73.7
178.1--273.1 178.2--278.0 469.6----683.2 475.8----645.1 875.5----1173.7 865.4---1092.6 1327.3--1712.0 1314.4---1596.8
1.0200
M F M F M F M F
234.3 229.7 594.0* 575.9 1030.8"* 995.0 1529.0"* 1470.5
1.0415 1.0445 1.0499
t .0314 1.0359 1.0397
M: Male (n 37); F: female (n = 37). ***, **, and * indicate significant differences between male and female at the 0.001, 0.01, and 0.5 levels, respectively. M/F ratio: Ratio between sexes, obtained by dividing mean male values by mean female values.
the dental arch (Fig. 3, B) were caiculated by computer at 10 m m intervals.
Analysis of data Mean and standard deviation of the tongue volume and the lower dental arch size for each sex and male-to-female ratio of the mean values were calculated. The correlation coefficients between the tongue volume and the lower dental arch sizes were computed.
RESULTS T a b l e I s u m m a r i z e s the m e a s u r e m e n t s o f t o n g u e v o l u m e s a n d l o w e r d e n t a l a r c h sizes. T h e m e a n t o n g u e v o l u m e w a s 2 5 . 3 c m 3 for m e n a n d 2 2 . 6 c m 3 for w o m e n , a statistically s i g n i f i c a n t sex difference (p < 0.01). The tongue volume was 11.8% l a r g e r for m e n t h a n f o r w o m e n . T h e m e a n o f the l o w e r d e n t a l a r c h area (A4) w a s
Tamari et al.
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Am. J. Orthod. Oentofac. Orthop. November 1991
0.282*
tongue volume was measured on plaster models prepared from impressions of the tongue. The reproducibility of the measurement of the tongue volume in the protruded position was analyzed for three volunteers in terms of changes (variations) in the volume in repeated measurements. In each volunteer, six tongue plaster models were prepared on different days, and the volume of each model was measured. The coefficients of variation (s/x) for the three volunteers were 0.064, 0.041, and 0.029, with a mean Value of 0.045. This shows that the measurement of tongue volume is satisfactorily reproducible. Takada et al.,7 who also measured tongue volume with a tongue model at the maximum protrusion, concluded that the reproducibility of the protruded tongue volume is stable. Their method of measuring the tongue volume, however, differs little from our method. It was discussed in our previous report. 9
0.371"*
Method of assessment of dental arch dimensions
0.415"*
BandYand Hunter 6 and Takada et al. 7 showed the relationship between the tongue volume and the lower dental arch sizes with the cafiines, the premo!ars, and the molars as points in measuring dental arch size. However, there are individual, sexual, and racial differences in the size of human teeth. H-14 Consequently, even when the shape and size of the dental arch are equal, no consistent data can be obtained by using anatomic characteristics of tooth structure, such as measuring the arch length from the incisal point to the distobuccal cusps of the first molars or measuring the arch width between such points. Consequently, we developed a method for impartial assessment of the lower dental arch size. The points representing the premolars and the molars were selected as the center of each crown on the occlusal view. Then a continuous line connecting those centers, the center points of the incisal edge, and the cusp tips of the canines was used as the dental arch line (Fig. 3, A). The lower dental arch sizes were measured in terms of the lower dental arch width and the area from the anterior origin to the posterior border at fixed intervals of 10 mm (Fig. 3, B). The measurement errors for the lower dental arch sizes were analyzed in terms of the changes (variations) in the dental arch area in repeated measurements. The same lower dental arch plaster model was photographed five times, and six prints were produced for each negative film for a total of 30 prints. The measuring points were marked, and the area of A4 (Fig. 3, B) was measured. The intragroup coefficients of variations (s/x) were 0.012, 0.008, 0.008, 0.008, and 0.006, with a mean of 0.008. The measurement errors would not have great influence on the measurement values.
Table II. Correlation coefficients between
tongue volume and dimensions of lower dental arch Tongue vohtme Dbnetzsions Dental arch width (W1) (W2) (W3) (W4) Dental arch area (A1) (A2) (A3) (A4)
Sex J
r
M F M F M F M F
0.387* 0.272 0.404* 0.404* 0.396* 0.435** 0.478** 0.388*
M F M F M F M F
0.353* 0.211 0.424** 0.318 0.433** 0.398* 0.463** 0.429**
j Common vahte
0.331"* 0.404** 0.416"* 0.434**
0.446**
M: Male (n = 37); F: female (n = 37). Significance level: * p < 0.05 and ** p < 0.01.
1529.0 mm z for men and 1470.5 mm 2 for women, a statistically significant sex difference (p < 0.01). The lower denial arch area was 3.9% larger for men than for women. The mean dental arch widths and areas were significantly larger for men than for women at all measuring sites except the most anterior dental arch area
(A1). The correlations between the tongue volume and the dental arch width and between the tongue volume and the dental arch area were significant (Table II). The correlations tended to be higher toward the posterior regions of the dental arch. The relationships between the tongue volume and the dental arch size (W4) are shown in terms of the distribution of measured values, regression equations, and regression lines (Fig. 4). DISCUSSION Method of assessment of tongue volume
With the recent progress in visualizat!on techniques, computerized tomography scans 8 and magnetic resonance imaging 1° are available to assess the tongue volume. However, thos e techniques have artifact problems because of the metal prostheses. Also, computerized tomography radiation is invasive. In this study, the
Volume 100 Number 5
Tongue volume and lower dental arch sizes
457
(cm 3) 35 0
.
•
~)
E --I o
25
Q) -I tO
}o
-~o _ _ ~ o ~ O
t5 Is o :Female
' 0
"//
'
45
s'
1 5
(mrn)
Dental arch width ( W 4 ) Fig. 4. Tongue volume-to-lower dental arch dimension ON4)relationships shown with regression line and 90% tolerance ellipse of distribution.
Results of measurements The mean size of the lower dental arch, as represented by the width and the area, and the mean tongue volume were all larger for men than for women. There were statistically significant differences in these values between sexes except for the mean dental arch area of the most anterior region (A1) (Table I). The sexual difference in the lower dental arch size of the Japanese was also reported by Outsbo. t3 In this study, the difference in the mean width between the lower first premolars was 2.29 mm, being 6.7% larger for men than for women. Yamauchi j~ reported that the dental arch width between the lower second molars was about 5.6% larger for men than for women. They also found a sexual difference in the mesiodistal diameter of the teeth. This might be self-evident since the measurement site was at a more posterior region of the dental arch for men than for women, reflecting the fact that men have significantly larger teeth than women. The male-to-female ratio of the mean tongue volume was larger than the ratio of the mean dental arch size. Probably this was due to the difference in the measurement dimensions. Therefore these ~arameters were transformed into the same dimension and then compared. Since the tongue volume ecas consistently obtained as the volume from al~nost the tip to 40 mm posterior to the tip, the oneJimensional expression is the square root of the quotient )f the volume divided by 4. The male-to-female ra-
tio of this mean tongue volume can be calculated as ~/(25.3/4)/~/(22.6/4) = 1.058, which is 5.8% larger for men than for women. The dental arch area of A4 was the area from the incisal point to 40 mm posterior to the incisal point, as was the case for the tongue volume. Thus a one-dimensional expression was obtained by dividing the mean area by 4. Then the male-to-female ratio can be calculated as (1529/4)/(1470.5/4) = 1.039, and it is 3.9% larger for men than for women. Similarly, the mean dental arch width of W4 is 4.9% larger for men than for women. As described previously, the male-to-female ratio of the mean tongue volume becomes almost equal to the ratios of the mean dental arch area and width if the values are transformed into the same dimension and compared. In the mean dental arch dimensions, the male-to-female ratios of both the area and the width became larger posteriorly and tended to approach the male-to-female ratio of tongue volume. J. Scott 2 wrote: "The thesis that normal dental arch form is determined by the forces exerted upon the teeth by the musculature of the tongue, lips, and cheeks is at the present time orthodox teaching and is more or less universally accepted. It has, however, never been proved." In this study, we detected statistically significant correlations between the tongue volume and the dental arch sizes (Table II). And the male-to-female ratio of the mean tongue volume was found to be almost equal to the ratio of the mean dental arch dimensions
458
Am. J. Orthod. Dentofac. Orthop. November 1991
Tamari et al.
if these parameters are transformed into the same dimensions. It seems to imply that the tongue volume is involved, at least as one morphologic factor in maintaining the dental arch sizes. The lingual movement can be more mobile at the free end (tongue tip), like a whip, as the muscle bundles of the tongue have no skeletal insertion. The mobility of the tongue seems to be more limited posteriorly and more stable than the anterior part. To test the hypothesis that the relationship between the tongue and the lower dental arch varies according to its anteroposterior location in the arch, we divided the lower dental arch into four parts from the anterior to the posterior regions and analyzed the relationship in each part. The correlation coefficients between the tongue volume and each dental arch size tended to become larger toward the posterior parts of the dental arch, although the correlations between the respective correlation coefficients were not significantly different (Table II). This phenomenon led to the suggestion that the size effects of the tongue on the lower dentition, as one of the factors of tongue form (size, shape, and position), tend to become larger toward the posterior part. We extend our gratitude to Dr. Kiyoshi Abe and Dr. Sunitaya Chatkupt for pertinent discussion and advice. REFERENCES 1. Brash JC, Mckeage HTA, Scott JH. The aetiology of irregularity and malocclusion of the teeth. 2nd ed. London: Dental Board of the United Kingdom, 1956:240. 2. Scott JH. The role of soft tissue in determining normal and abnormal dental occlusion. Dent Pract Dent Rec 1961;!1: 302-8. 3. Brodie AG. Thoughts on the aetiology of malocclusion. Tr Eur Orthod Soc 1957;33:200-15.
4. Hovell JH. The relationship of the oro-faciat musculature to occlusion: current British thought. In: Kraus BS, Riedel RA, eds. Vistas in orthodontics. Philadelphia: Lea & Febiger, 1962:328-45. 5. Graber TM. Orthodontics, principles and practice. 3rd ed. Philadelphia: WB Saunders, 1972:325. 6. Bandy HE, Hunter WS. Tongue volume and the mandibular dentition. AM J ORTHOD 1969;56:134-42. 7. Takada K, Sakuta M, Yoshida K, Kawamura Y. Relations between tongue volume and capacity of the oral cavity proper. J Dent Res 1980;59:2026-31. 8. Lowe AA, Gionhaku N, Takeuchi K, Fleetham JA. Threedimensional CT reconstructions of tongue and airway in adult subjects with obstructive sleep apnea. AM J ORTHODDENTOFAC ORTHOP 1986;90:364-74. 9. Tamafi K, Murakami T, Takahama Y. The dimensions of the tongue in relation to its motility. AMJ ORTtIODD~,Xrl'OFACORTHOP 1991 ;99:140-6. I0. Hoover LA, Wortham DG, Lutkin RB, ttanafee WN. Magnetic resonance imaging of the larynx and tongue base: clinical applications. Otolaryngol Head Neck Surg 1987;97:245-56. 11. Moyers RE. ttandbook of orthodontics. 3rd ed. Chicago: Year Book, 1972:193-4. 12. Moorrees CFA, Thomsen SO, Jensen E, Yen PK. Mesiodistal crown diameters of the deciduous and permanent teeth in individuals. J Dent Res 1957;36:39-47. 13. Otusbo J. A study on the tooth material in Japanese adults of normal occlusion: its relationship to coronal and basal arches. J Jpn Orthod Soc 1957;16:36-46. 14. Yamauchi K, Ito K, Suematsu H. Standard for the measurements of plaster-cast from Japanese young adults with normal occlusion. J Jpn Orthod Soc 1965;24:1-7. Reprint requests to: Dr. Kazuhiko Tamari Department of Orthodontics Faculty of Dentistry Kyushu University 3-1-1 Maidashi, Higashi-ku 812 Japan
