Arch oral Biol. Vol. 36, No 9, pp. 665470, 1991 Printed in Great Britain. All rightsreserved
0003-9969/91 $3.00 + 0.00 Copyright 0 1991 Pergamon Press plc
CHANGES IN FACIAL SKIN TEMPERATURE ASSOCIATED WITH CHEWING EFFORTS IN MAN: A THERMOGRAPHIC EVALUATION T. MORIMOTO,’K. TAICADA,~ H. HIJIYA,’Y. YASUDA~and M. SAKUDA’ Departments of ‘Oral Physiology and ZOrthodontics, Faculty of Dentistry, Osaka University, 1-g Yamadaoka, Suita, Osaka 565, Japan (Accepted 12 March 1991) Summary-Eleven healthy male adults chewed hard and soft chewing-gums for 5 min. A thermographic record of the face on the chewing side was made at the beginning of, during and after the effort. Facial temperature distributions during open/close cyclic unloaded jaw movements were recorded at a later date. The dimensions of the zones whose temperatures were 1.4”C or more higher than the central temperature during the experiment were determined. There was a linear increase in the dimensions of these zones after the chewing. In contrast, the cyclic jaw movements did not result in significant increases. Chewing the hard gum produced significantly higher temperature rises than did the soft in the masseter area. After the chewing effort, the temperature fell gradually, but did not return to the initial state even after 30 min. The overall decreasing pattern of the temperature distribution for chewing the soft gum was similar to that for the hard gum. The facial temperature associated with chewing efforts rose in accordance with the resistance offered by the chewing-gums. Key words: chewing, facial skin temperature, masseter, thermography.
hlATRRULSANDMETHODS
IN1’RODUCT’ION Muscle activity during chewing has been mostly investigated by electromyography. It is also possible to estimate this activity indirectly by measuring the muscle temperature, which rises in accordance with muscular contraction. Skin surface temperature over muscles has been measured either with a thermocouple (Akerman and Kopp, 1988) or by thermography (Berry and Yemm, 1971). The former method measures the temperature of a localized area; the latter determines the overall temperature distribution of the skin surface overlying muscles. Infrared thermography has been used in clinical dentistry for diagnosis of mandibular dysfunctions (Crandell, 1966; Berry and Yemm, 1971; Irwin et al., 1971; Berry and Yemm, 1974a). The infrared energy emission from the skin or soft tissue surface is detected by a non-contact method to determine the temperature of the a.rea under observation (Beres, 1964). It is not harmful like radiography, allows prompt recording and facilitates evaluation of symptoms and treatment (effects without producing pain and/or discomfort. Berry and Yemm ((1974b) determined changes in facial skin temperature associated with chewing thermographically. As they did not report quantitative measurements of temperature, little is known of the actual changes. We have now investigated changes in surface temperature of the face associated with chewing efforts by comparing temperature distributions over the lateral half of the face before, during and after chewing.
Subjects
Eleven healthy volunteer adult males (mean age 27.5 y; SD 2.8 y) with no symptoms of jaw dysfunction were selected for study. Recording procedure
Facial temperature was measured by an infrared sensing device (Thermo-Tracer 6T67, NEC-Sanei, Tokyo). Infrared radiation from the object under examination is detected and displayed on an oscilloscope as a coloured picture or thermogram (Hijiya et al., 1990). The device can measure temperatures with a resolution accuracy of 0.025”C. The recordings were made at least 1 h after meals, some time between 9.30 a.m. and 7.00 p.m. in late September. In a pilot study, we found that there was no significant change in temperature distribution over 35 min if the subject was in a resting state. Each subject rested for about 20 min in an air-conditioned experimental room before recording. The room temperature was maintained at 26°C. The subject was seated in a chair with no head or back support and with the head in a natural posture. Before thermographic recording, the oral temperature of each subject was measured with an electric thermometer (C20, Terumo Co., Tokyo). Thermography of the lateral half of the face was done before the start of chewing efforts with the teeth in maximum intercuspation and the lips in repose. Recordings were made so that ,the optical axis of the lens of the detector could be approximately perpen665
Thermographic evaluation of chewing dicular to the mid-sagittal plane of the head through the external auditory meatus. A central temperature was determined so that the dimension of the area of this temperature could be adjusted to within a range of 5-10% of that of the whole lateral facial image. The central temperature was a value midway between the highest and the lowest temperatures of the area sensed. The interval between the highest and the lowest temperatures of the sensed area was 56°C and this was displayed by eight colour tones representing intervals of 0.7”C. The subject was then asked to chew a piece of hard chewing-gum (7 x 20 x 1 mm, Ezaki Glico, Osaka) Ion his preferred side for 5 min. A thermographic record of the face on the chewing side was made 1, 3 and 5 min after the start of, and 5, 10 and 30 min after the completion of the effort. Images on the monitor were stored in an SLR camera on colour reversal films for subsequent processing. A week later, an identical recording procedure was repeated for the same group of subjects but soft chewing-gums were used instead of hard. Also, at a later date, facial temperature distributions associated with unloaded open/close, cyclic jaw movements for 5 min were recorded for six subjects at 1, 3 and 5 min after the beginning of the performance. Data analysis
Each photographic record was printed and enlarged to actual size, and tracings of the lateral half of the face (facial area) were constructed and digitized to specify the locations and dimensions of the zones whose temperatures were 1.4”C or more higher than the central temperature during the experiment (Plate Fig. 1). Zoning was done by a visual check of each thermogram. An earlier study (Hijiya et al., 1990) had shown that the ratio of the dimension of the current temperature zone measured at any given recording time-point with respect to that determined for the initial record was almost consistent, irrespective of the difference in central temperatures, if they were selected within a range of +0.6”C. In addition, the dimensions of the identical temperature zone in an area (masseter area) encased by lines connecting the potion, the intersection of porion-subnasal with the nasion-gnathion, the gnathion and the gonion were calculated (Plate Fig. 1). This area was selected because of the ease of identifying its landmarks on the soft tissue profile and because it essentially represents the temperature fluctuation in the area overlying the masseter. The dimensions of these zones at each time-point were normalized to that of the entire lateral half
667
of the face. The ratios of these dimensions with respect to those determined before the start of the chewing effort were calculated. If these ratios increased with the chewing effort, the temperature of the area under examination was judged to have risen. Statistical analysis
The significance of differences between normalized dimensions determined for the recording time-points after the start of the effort and the initial time point was determined by a paired t-test, as were the differences of temperature distribution patterns be.tween the efforts with hard and soft gums. Statistical significance was arbitrarily determined at the 5, 1 and 0.1% levels. Above 5% was interpreted as not significant. RESULTS
There was no significant correlation (r = 0.012, p > 0.1) between the central temperature of the face and the oral temperature. For all the subjects tested, the external auditory meatus and its anterior part, the temporal part, and the anterior margin of the masseter at the inferior border of the mandible showed high temperatures in the resting condition [Plate Fig. 2(a)]. After the chewing efforts, a characteristic increase in facial temperature was found in the skin overlying the masseter muscle, the anterior part of the temporalis muscle, the orbicularis oris muscle, and the mentalis muscle, together with the areas where the carotid and facial arteries lie [Plate Fig. 2(B)]. The high-temperature zones spread in two ways: in some individuals, they extended diffusely from loci that showed relatively higher temperature in the resting state, while in the others, they appeared as discontinuous islets. Text Fig. 3 compares changes in temperature distribution in the facial area obtained by chewing the soft and the hard gums for 5 min with those determined for the open/close cycle of jaw movement during the corresponding time period. The skin temperatures after chewing gums rose linearly as a function of time, while the open/close jaw movement did not produce any significant increase in temperature distribution when compared with the initial state. Although there was a slight tendency for the temperature distribution for chewing the hard gum to show more of an increase than that for the soft gum, these were not significantly different (p < 0.05).
Plate 1 Fig. 1. Infrared thermogram of the facial area (thick tracing). The zones whose temperatures were 14°C or more higher than the central temperature are displayed in red and white colonrs and traced. The masseter area defined as the dimension of an area encased by lines connecting points 1,2, 3 and 4 is also schematically illustrated (thin tracing). 1, porion; 2, intersection of lines potion-subnasal and nasion-gnathionl 3, gnathion; 4, gonion. The location of the gonion was identified visually and by palpation. A sensing tape (4 mm dia) was placed for thermographic recording. Fig. 2. Infrare(d thermograms of the facial skin surface recorded before (A) and 5 min after (B) the start of the chewing effort. The zones whose temperatures were 1.4”C or more higher than the central temperature are displayed in red and white colours. AOB 36/9-C
T. MORIMOTOet al.
668 Focial
-
-*.--. -.A----
Initial
area
DISCUSSION
l-lord gum(n=ll) Soft ~umb7=111 Empty chewing (n-6)
1
3
Time
5
(min)
Fig. 3. Changes in mean temperature distribution over the facial area (n = 11) during the 5 min after the start of the chewing efforts with hard (-) and soft (. . .) gums. Changes in temperature distribution over the
same area after the start of open/close, cyclic jaw movements determined for six subjects are also shown (-e-a-). Measurements for each recording time-points were normalized and compared to those at the initial recording. Dots and vertical bars indicate means and 1 SD, respectively. +, ** and + designate 5, 1 and 0.1% levels of significance, respectively.
Text Fig. 4 shows the overall change in temperature distribution patterns over the facial area (top) and the masseter area (bottom) for chewing hard (solid lines) and soft (dotted lines) gums, respectively. The distribution over the facial area increased 16.4% (p < O.OOl), on average, for the hard gum and 9.0% (p < 0.01) for the soft, 5 min after the start of the chewing effort; these were not significantly different. In the masseter area, average increases of 31.0% (p
0003-9969/91 $3.00 + 0.00 Copyright 0 1991 Pergamon Press plc
CHANGES IN FACIAL SKIN TEMPERATURE ASSOCIATED WITH CHEWING EFFORTS IN MAN: A THERMOGRAPHIC EVALUATION T. MORIMOTO,’K. TAICADA,~ H. HIJIYA,’Y. YASUDA~and M. SAKUDA’ Departments of ‘Oral Physiology and ZOrthodontics, Faculty of Dentistry, Osaka University, 1-g Yamadaoka, Suita, Osaka 565, Japan (Accepted 12 March 1991) Summary-Eleven healthy male adults chewed hard and soft chewing-gums for 5 min. A thermographic record of the face on the chewing side was made at the beginning of, during and after the effort. Facial temperature distributions during open/close cyclic unloaded jaw movements were recorded at a later date. The dimensions of the zones whose temperatures were 1.4”C or more higher than the central temperature during the experiment were determined. There was a linear increase in the dimensions of these zones after the chewing. In contrast, the cyclic jaw movements did not result in significant increases. Chewing the hard gum produced significantly higher temperature rises than did the soft in the masseter area. After the chewing effort, the temperature fell gradually, but did not return to the initial state even after 30 min. The overall decreasing pattern of the temperature distribution for chewing the soft gum was similar to that for the hard gum. The facial temperature associated with chewing efforts rose in accordance with the resistance offered by the chewing-gums. Key words: chewing, facial skin temperature, masseter, thermography.
hlATRRULSANDMETHODS
IN1’RODUCT’ION Muscle activity during chewing has been mostly investigated by electromyography. It is also possible to estimate this activity indirectly by measuring the muscle temperature, which rises in accordance with muscular contraction. Skin surface temperature over muscles has been measured either with a thermocouple (Akerman and Kopp, 1988) or by thermography (Berry and Yemm, 1971). The former method measures the temperature of a localized area; the latter determines the overall temperature distribution of the skin surface overlying muscles. Infrared thermography has been used in clinical dentistry for diagnosis of mandibular dysfunctions (Crandell, 1966; Berry and Yemm, 1971; Irwin et al., 1971; Berry and Yemm, 1974a). The infrared energy emission from the skin or soft tissue surface is detected by a non-contact method to determine the temperature of the a.rea under observation (Beres, 1964). It is not harmful like radiography, allows prompt recording and facilitates evaluation of symptoms and treatment (effects without producing pain and/or discomfort. Berry and Yemm ((1974b) determined changes in facial skin temperature associated with chewing thermographically. As they did not report quantitative measurements of temperature, little is known of the actual changes. We have now investigated changes in surface temperature of the face associated with chewing efforts by comparing temperature distributions over the lateral half of the face before, during and after chewing.
Subjects
Eleven healthy volunteer adult males (mean age 27.5 y; SD 2.8 y) with no symptoms of jaw dysfunction were selected for study. Recording procedure
Facial temperature was measured by an infrared sensing device (Thermo-Tracer 6T67, NEC-Sanei, Tokyo). Infrared radiation from the object under examination is detected and displayed on an oscilloscope as a coloured picture or thermogram (Hijiya et al., 1990). The device can measure temperatures with a resolution accuracy of 0.025”C. The recordings were made at least 1 h after meals, some time between 9.30 a.m. and 7.00 p.m. in late September. In a pilot study, we found that there was no significant change in temperature distribution over 35 min if the subject was in a resting state. Each subject rested for about 20 min in an air-conditioned experimental room before recording. The room temperature was maintained at 26°C. The subject was seated in a chair with no head or back support and with the head in a natural posture. Before thermographic recording, the oral temperature of each subject was measured with an electric thermometer (C20, Terumo Co., Tokyo). Thermography of the lateral half of the face was done before the start of chewing efforts with the teeth in maximum intercuspation and the lips in repose. Recordings were made so that ,the optical axis of the lens of the detector could be approximately perpen665
Thermographic evaluation of chewing dicular to the mid-sagittal plane of the head through the external auditory meatus. A central temperature was determined so that the dimension of the area of this temperature could be adjusted to within a range of 5-10% of that of the whole lateral facial image. The central temperature was a value midway between the highest and the lowest temperatures of the area sensed. The interval between the highest and the lowest temperatures of the sensed area was 56°C and this was displayed by eight colour tones representing intervals of 0.7”C. The subject was then asked to chew a piece of hard chewing-gum (7 x 20 x 1 mm, Ezaki Glico, Osaka) Ion his preferred side for 5 min. A thermographic record of the face on the chewing side was made 1, 3 and 5 min after the start of, and 5, 10 and 30 min after the completion of the effort. Images on the monitor were stored in an SLR camera on colour reversal films for subsequent processing. A week later, an identical recording procedure was repeated for the same group of subjects but soft chewing-gums were used instead of hard. Also, at a later date, facial temperature distributions associated with unloaded open/close, cyclic jaw movements for 5 min were recorded for six subjects at 1, 3 and 5 min after the beginning of the performance. Data analysis
Each photographic record was printed and enlarged to actual size, and tracings of the lateral half of the face (facial area) were constructed and digitized to specify the locations and dimensions of the zones whose temperatures were 1.4”C or more higher than the central temperature during the experiment (Plate Fig. 1). Zoning was done by a visual check of each thermogram. An earlier study (Hijiya et al., 1990) had shown that the ratio of the dimension of the current temperature zone measured at any given recording time-point with respect to that determined for the initial record was almost consistent, irrespective of the difference in central temperatures, if they were selected within a range of +0.6”C. In addition, the dimensions of the identical temperature zone in an area (masseter area) encased by lines connecting the potion, the intersection of porion-subnasal with the nasion-gnathion, the gnathion and the gonion were calculated (Plate Fig. 1). This area was selected because of the ease of identifying its landmarks on the soft tissue profile and because it essentially represents the temperature fluctuation in the area overlying the masseter. The dimensions of these zones at each time-point were normalized to that of the entire lateral half
667
of the face. The ratios of these dimensions with respect to those determined before the start of the chewing effort were calculated. If these ratios increased with the chewing effort, the temperature of the area under examination was judged to have risen. Statistical analysis
The significance of differences between normalized dimensions determined for the recording time-points after the start of the effort and the initial time point was determined by a paired t-test, as were the differences of temperature distribution patterns be.tween the efforts with hard and soft gums. Statistical significance was arbitrarily determined at the 5, 1 and 0.1% levels. Above 5% was interpreted as not significant. RESULTS
There was no significant correlation (r = 0.012, p > 0.1) between the central temperature of the face and the oral temperature. For all the subjects tested, the external auditory meatus and its anterior part, the temporal part, and the anterior margin of the masseter at the inferior border of the mandible showed high temperatures in the resting condition [Plate Fig. 2(a)]. After the chewing efforts, a characteristic increase in facial temperature was found in the skin overlying the masseter muscle, the anterior part of the temporalis muscle, the orbicularis oris muscle, and the mentalis muscle, together with the areas where the carotid and facial arteries lie [Plate Fig. 2(B)]. The high-temperature zones spread in two ways: in some individuals, they extended diffusely from loci that showed relatively higher temperature in the resting state, while in the others, they appeared as discontinuous islets. Text Fig. 3 compares changes in temperature distribution in the facial area obtained by chewing the soft and the hard gums for 5 min with those determined for the open/close cycle of jaw movement during the corresponding time period. The skin temperatures after chewing gums rose linearly as a function of time, while the open/close jaw movement did not produce any significant increase in temperature distribution when compared with the initial state. Although there was a slight tendency for the temperature distribution for chewing the hard gum to show more of an increase than that for the soft gum, these were not significantly different (p < 0.05).
Plate 1 Fig. 1. Infrared thermogram of the facial area (thick tracing). The zones whose temperatures were 14°C or more higher than the central temperature are displayed in red and white colonrs and traced. The masseter area defined as the dimension of an area encased by lines connecting points 1,2, 3 and 4 is also schematically illustrated (thin tracing). 1, porion; 2, intersection of lines potion-subnasal and nasion-gnathionl 3, gnathion; 4, gonion. The location of the gonion was identified visually and by palpation. A sensing tape (4 mm dia) was placed for thermographic recording. Fig. 2. Infrare(d thermograms of the facial skin surface recorded before (A) and 5 min after (B) the start of the chewing effort. The zones whose temperatures were 1.4”C or more higher than the central temperature are displayed in red and white colours. AOB 36/9-C
T. MORIMOTOet al.
668 Focial
-
-*.--. -.A----
Initial
area
DISCUSSION
l-lord gum(n=ll) Soft ~umb7=111 Empty chewing (n-6)
1
3
Time
5
(min)
Fig. 3. Changes in mean temperature distribution over the facial area (n = 11) during the 5 min after the start of the chewing efforts with hard (-) and soft (. . .) gums. Changes in temperature distribution over the
same area after the start of open/close, cyclic jaw movements determined for six subjects are also shown (-e-a-). Measurements for each recording time-points were normalized and compared to those at the initial recording. Dots and vertical bars indicate means and 1 SD, respectively. +, ** and + designate 5, 1 and 0.1% levels of significance, respectively.
Text Fig. 4 shows the overall change in temperature distribution patterns over the facial area (top) and the masseter area (bottom) for chewing hard (solid lines) and soft (dotted lines) gums, respectively. The distribution over the facial area increased 16.4% (p < O.OOl), on average, for the hard gum and 9.0% (p < 0.01) for the soft, 5 min after the start of the chewing effort; these were not significantly different. In the masseter area, average increases of 31.0% (p
