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Many studies show that chewing ability affects not only digestion but also “physical abilities” [1,2]. Particularly at a young age, such as primary schoolchildren or the junior high school students, exercise capacity increases substantially. Some studies in adults indicate that biting force is associated with exercise capacity [3], and that concentration and performance in sports are improved by chewing gum [4].

Various methods have been developed to evaluate masticatory performance objectively, such as sieving the degree of food breakdown [5], measuring the degree of glucose released from gummy jelly [6], or measuring changes of a chewed wax cube [7,8]. However, a colorchangeable chewing gum is the most effective method to simply and precisely evaluate masticatory function in large groups of people [9-11]. Subjects just chew gum and evaluate its color after chewing. A color scale method of evaluating the color of the gum is simple and convenient, with high analytic validity [12]. Previous studies using color-changeable chewing gum evaluated the masticatory performance of complete denture users and the relation between tongue and lip function [11,13].

There was the study which investigated the severity of malocclusion of school children [14]. However, no previous study has investigated masticatory performance using color-changeable chewing gum and examined an association between exercise capacities in school children.

The purpose of this study was to analyze the association between masticatory performance and exercise capacity of young people by examining masticatory function with color-changeable chewing gum.

This study involved 141 first-year junior high school students (72 boys and 69 girls; ages 12-13 years) from two public junior high schools in Japan. Oral examinations and measurement of masticatory performance were performed after obtaining informed consent in 2010. Participants from whom incomplete data were collected excluded from the analyses. A total of 127 students (boys: 65, girls: 62) were used for the analysis. This study was approved by the Ethical Committee in Tokyo Medical and Dental University (Approval No. 250).

Methods

Growth status: Height and weight measurements from each school were used for analyses. The Rohrer index, which is most suitable for adiposity screening in pubertal boys and girls [15], was calculated to evaluate the students’ growth status. The Rohrer index calculates body weight in grams times 100 divided by the cube of height in centimeters. The Rohrer index classifications are: less than 115 as “thin”, 115-144 as “standard” and 145 or more as “obese” [16,17].

Oral health status: Assessment criteria for the oral examination were standard procedures for the Japanese School Dental Examinations [18]. Oral health examinations were conducted using a dental mirror and an explorer under artificial light by one school dentist and two university dentists who were trained and calibrated.

The number of decayed teeth and present teeth, combining deciduous and permanent teeth, were assessed. Occlusion status was visually evaluated from 0 to 2 (0: Normal occlusion, 1: Slight malocclusion, 2: Severe malocclusion).

Exercise capacity: Data from physical fitness tests collected in each school were used for analysis. To indicate exercise capacity we used the following seven items that were included in the physical fitness tests of both schools

Grip strength (kilogram): Forearm muscular strength measured by a hand dynamometer. The test was completed twice each in the left and right arms, and the best records of the left and right arms were averaged.

Trunk extension (centimeter): Distance from floor to chin when bending the upper body upward in a face down posture. The test was completed twice and the best record was adopted.

Sitting trunk flexion (centimeter): Sit on the floor with legs fully extended and feet placed flat against the sit-and-reach box (the inner edge of the feet should be about 6 inches apart). Place hands side-byside with arms extended and reach forward as far forward as possible holding the final position for 2 seconds. Repeat the trial twice and record the maximum distance.

Side step (times): Number of side steps over three lines of a fixed interval in 20 seconds. The test was completed twice and the best record was adopted.

50-meter run (seconds): Time record of a 50 m run using a straight running track. The test was completed once.

Standing broad jump (centimeter): Long jump distance using a sandbox from a standing position. The record was measured from the take-off point. The test was completed twice and the best record was adopted.

Handball throw (meter): Distance of a ball thrown by hand. The test was completed twice and the best record was adopted [19,20].

Height, weight and the physical fitness test are measured at Japanese junior high schools every year, and national mean scores are reported by the Ministry of Education, Culture, Sports, Science and Technology in Japan [20,21].

Masticatory performance: A color-changeable chewing gum (Masticatory Performance Evaluating Gum XYLITOL®; Lotte Co., Ltd. Saitama, Japan) was used for measurement of masticatory performance. This gum base contains red, yellow, and blue dyes, citric acid and xylitol. The red dye is sensitive to pH and becomes visible under neutral or alkaline conditions. The pH inside the chewing gum is kept low by the citric acid, and the color of the chewing gum remains yellowish-green before chewing because of the presence of yellow and blue pigments. As mastication proceeds, the color of the chewing gum turns to red because the yellow and blue dyes seep into saliva while the red dye becomes visible as the citric acid leaches out.

The measurement of masticatory performance in this study was conducted at the beginning of an oral health education class in each junior high school. Each subject was instructed to chew the gum, irrespective of chewing side, for 80 strokes at a rate of 1 stroke/second [22]. Subjects were instructed of the timing and number of chewing strokes by a monitor, and all chewing was performed at the same time.

The color of the gum after chewing was checked with the modified color scale of Kamiyama [12], which records a score from 1 (yellow green) to 5 (red) with an interval color of 0.5 for each scale value. As the score rises, the masticatory performance becomes higher. We divided the boys and girls into two groups of as equal size as possible using masticatory performance scores.

Analysis method: Growth status (height, weight, Rohrer index), oral health status (the number of present teeth, the number of decayed teeth, and occlusal status), the 7 items of exercise capacity, and masticatory performance were compared between boys and girls using independent t-tests and Chi-square tests.

Also, independent t-tests and Chi-square tests were performed within each gender comparing high and low masticatory performance groups as the independent variable, and growth status, oral health status and exercise capacity as dependent variables.

The level of significance was set at p=0.05 and we used the statistical analysis software (SPSS Base 18.0 for Windows, SPSS Japan Inc., Tokyo, Japan).

Growth status, oral health status and exercise capacity by gender

The growth status, oral health status and exercise capacity of the subjects by gender are shown in Table 1. There were no significant differences for height, weight and the Rohrer index between boys and girls. According to the classification of the Rohrer index, 22 boys were “thin” (33.8%), 34 were “standard” (52.3%), and 9 were “obese” (13.8%); 17 were girls “thin” (27.4%), 37 were “standard” (59.7%), and were 8 “obese” (12.9%). The differences in distribution of these groups were not significant between boys and girls.

Table 1: Growth status, oral health status, exercise capacity by gender

No significant difference was found in the number of present teeth, decayed teeth and occlusal status between boys and girls. However, boys showed significantly better exercise capacities compared with girls in all physical fitness tests.

Masticatory performance by gender

The masticatory performance of boys and girls is shown in Table 2. We divided the masticatory performance of boys and girls into two groups as nearly equal in size as possible. Among the boys 28 (43.1%) were in the low masticatory performance group (3.0 and less) and 37 (56.9%) were in the high masticatory performance group (3.5 and more). Among the girls 30 (48.4%) were in the low masticatory performance group (2.5 and less) and 32 (51.6%) were in the high masticatory performance group (3.0 and more).

Table 2: The distribution of masticatory performance

Growth status, oral health status and exercise capacity by masticatory performance

When comparing high and low masticatory performance groups between boys and girls no significant differences were found for height, weight, Rohrer index, the number of present teeth or the number of decayed teeth (Tables 3 and 4). However, some exercise capacity items had a significant relation with masticatory performance. In the boys, the score of standing broad jump was significantly better in the high masticatory performance group than the low masticatory performance group. In the girls, the scores of sitting trunk flexion and standing broad jump were significantly better in the high masticatory performance group than the low masticatory performance group.

Table 3: Relationship among masticatory performance, growth status and oral health status in boys

Table 4: Relationship among masticatory performance, growth status and oral health status in girls　

This study revealed that better chewing efficiency was associated with some measures of exercise capacity in junior high school students.

Those with higher masticatory performance scores had a higher ability in the “standing broad jump” in both boys and girls. In previous studies, junior high school students with higher biting forces had better results in the standing broad jump [23]. We suggest that “standing broad jump” performance is associated with masticatory performance because the masticatory performance was associated with biting force in children [24]. Because, the biting force and occlusion contact were associated with body sway which is related to balance, coordination and adaptability of nerves and important factor of “The standing broad jump” [25].

Furthermore, the high masticatory performance group had a better score of sitting trunk flexion in girls. Previous research reported that nutrition improved the flexibility of the body [26], and efficient mastication leads to better digestion and absorption, thereby affecting muscular strength [27]. Better masticatory performance might contribute to better exercise capacity.

About the relations of masticatory efficiency and the exercise capacity, we must think about a paradox and the confounding factors. For example, the body size may contribute to both exercise capacity and masticatory efficiency. The body size may not be a confounding factor in this study because there was no significant difference. However, the investigation of such a viewpoint will be required in a future study.

Furthermore, oral health status was not related to masticatory performance in this study. This result may be due to that oral health status was only visually diagnosed without a detailed classification. More detailed investigations that include the number of caries and the collapsed state of the tooth crown may be required.

For analyses, we used school-supplied data such as height, weight, and physical fitness tests. The national mean average height of Japanese first-year junior high school students is 152.4 centimeter in boys and 151.9 centimeter in girls, and national mean weight is 44.1 kilogram in boys and 43.8 kilogram in girls. These values are similar to those of our research subjects [21]. Our scores of exercise capacity were similar to national means for Japanese first-year junior high school students [20]. Therefore, the subjects in our study are similar to average Japanese junior high school students.

Because using a color-changeable chewing gum allows a participant to recognize their masticatory performance themselves, it may provide good motivation for improvement of the oral health condition could be used effectively in oral health education of school age children. Some studies revealed that oral health education in the new viewpoint such as oral malodor influence to improve the oral health status of high school student [28,29]. Recently, the importance of chewing has been increasingly recognized in the field of oral health for dietary education [30]. To improve school oral health, dental professionals, schoolteachers and guardians must all cooperate. Color-changeable chewing gum makes it very easy to evaluate masticatory performance; even children or schoolteachers can make an evaluation using a color chart.

We suggest that future studies investigate confounding variables that might affect the relationship between masticatory performance and exercise capacities, such as nutritional status, biting force, and subjects’ gum chewing habits. Also, more detailed investigations of oral health status, such as caries classification or occlusal contact areas should be included to examine the effect of oral health on masticatory performance.

Exercise capacity is very important in the growth of children. We need further investigations of masticatory performance for improvement of exercise capacity of adolescents.

In conclusion, this study revealed that some measures of exercise capacity are higher in junior high school students who had higher masticatory performance. For the improvement of exercise capacity of adolescence, it is important to adopt masticatory performance checking in oral health education.

This study was supported by Grant-in-Aid for Scientific Research (based research C; No. 25862075) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

There are no potential conflicts