Subjective food intake ability in relation to the Mixing Ability Index in Korean adults

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1 J o u r n a l o f Oral Rehabilitation Journal of Oral Rehabilitation ; Subjective food intake ability in relation to the Mixing Ability Index in Korean adults S.H. JEONG, S.M. KANG, J.H. RYU, H.K. KWON & B.I. KIM Department of Preventive Dentistry and Public Oral Health, Research Center for Orofacial Hard Tissue Regeneration, Brain Korea 21 Project, Yonsei University College of Dentistry, Seoul, Korea SUMMARY This study examined the association between the subjective food intake ability (FIA) using a questionnaire with 30 types of foods and the objective Mixing Ability Index (MAI) using a twocoloured wax cube. A total of 147 subjects (32 males, 115 females, mean age: 54Æ9 20Æ7) were enrolled in this study. The FIA for 30 food types and the key food intake ability (KFIA) for five key food types were obtained using a self-assessed questionnaire to evaluate the subjective chewing ability. The objective chewing ability was evaluated by asking the subjects to chew a wax cube for 10 strokes. The MAI was calculated by image analysis of the chewed wax cube. The Pearson s correlation between the subjective FIA and objective MAI was analysed according to age and number of post-canine teeth lost. The FIA for the 30 foods and five key food types showed a moderate correlation with the MAI (r = 0Æ51, 0Æ55, respectively, P <0Æ01). The KFIA of the denture wearing group (r =0Æ44, P <0Æ01) and over 60-yearold group (r =0Æ49, P <0Æ01) showed a significantly higher correlation with the MAI than the other groups. In conclusion, there was a moderate correlation between the subjective FIA and objective MAI in Korean adults. KEYWORDS: food intake ability, Mixing Ability Index, masticatory function, Korean adults Accepted for publication 6 December 2009 Introduction The ultimate aim of dental treatment is the recovery of normal mastication, esthetics and pronunciation. In particular, mastication is the first stage of digestion and the main function of the oral cavity. A chewing function improved by dental treatment can maintain the healthy status of patients through the intake of various foods (1) and improve their quality of life (2). Therefore, an evaluation of the chewing function can be an important indicator of the success of dental treatment and improvement in the quality of life. Several methods for evaluating the chewing function have been developed and can be categorized into two major areas. The first examines the objective masticatory performance, such as the chewing force or masticatory efficiency. The other assesses the subjective masticatory ability using a questionnaire. The objective masticatory performance can be evaluated using a range of methods. The static chewing function can be measured by the maximal bite force (3, 4), electromyogram (EMG) activity of the masticatory muscle (5) and occlusal contact area (6). The dynamic chewing function, which is called the chewing efficiency, can be evaluated by observing the changes in foods during mastication. Natural foods (7 9), such as peanuts, raw carrots and almonds, and artificial foods (10 15), such as gummy jelly, as well as silicone rubber, gelatin, hydrocolloid impression material, chewing gum and paraffin wax have been used as test materials in many studies. The sieving method, which measures the pulverization of peanuts and almonds, is considered the gold standard for assessing the masticatory efficiency (7, 16). Although the sieving method is a reliable and valid method for evaluating the chewing efficiency, there are some difficulties in its use clinically because of doi: /j x

2 RELATION BETWEEN FOOD INTAKE ABILITY AND MIXING ABILITY INDEX 243 the complicated procedure and considerable analysis time. Therefore, there have been many efforts to develop simple and easy methods for assessing the chewing efficiency. New trials that evaluate a mixing bolus of tests food with soft and cohesive properties can assess the chewing efficiency more easily than the sieving method. Recently, chewing gum and a wax cube with various shapes and colours were developed as test foods to evaluate the mixing ability (14, 15, 17). The mixing ability test (MAT) assesses the masticatory performance by calculating the Mixing Ability Index (MAI) with a discriminant function, by which the degree of colour mixing and the shape of the chewed test food are integrated into a one-dimensional value (15). The MAI is not only a reliable and valid method, but also a simple and objective way of evaluating the masticatory performance clinically (18 21). The subjective method includes an evaluation of the intake ability of various foods and self-reported satisfaction for the chewing function using questionnaires. Leake (22) reported that the self-reported ability to chew five hard foods may be related to the masticatory ability. Since then, Yamamoto s chewing ability test using typical Japanese foods has been used widely to evaluate the chewing function in Japan (23 25). The chewing ability can also be evaluated subjectively using questionnaires related to the psychosocial consequences of a limitation in chewing ability and selfsatisfaction with the chewing ability (26, 27). Recently, Kim et al. (28) reported that the food intake ability (FIA) questionnaires consisting of 30 types of Korean food were related to the objective maximal bite force. In addition, the key foods intake ability (KFIA) selected among these 30 foods showed a similar correlation to the bite force. The FIA questionnaire, which asked questions regarding the intake ability of concrete foods, can show more valid results on an individual s chewing ability than a vague questionnaire on the difficulties in chewing. Therefore, the FIA questionnaire is considered to be a useful screening method for assessing the masticatory function clinically with considerable cost and time savings. The validity of MAT was demonstrated by a comparison with the single (18) and multiple (21) sieving methods and EMG (20), as well as by applications to various dental patients (29, 30). However, the relationship with the subjective masticatory function has not been reported. The recently reported subjective FIA was only compared with the objective bite force (28). The aim of this study was to clarify the association between the subjective FIA using a questionnaire and the objective MAI using a two-coloured wax cube. Materials and methods Subjects One hundred and forty-seven subjects (32 males, 115 females, mean age: 54Æ9 20Æ7) with no dental pain, temporomandibular disorders or malocclusion were enrolled in this study. All the subjects were recruited from four dental clinics in Seoul and signed an informed consent form. The subjects were divided into three groups according to age (20 39, and 60-year-old) and four groups according to the number of post-canine teeth lost (no loss, 1 2 lost, 3 5 lost, denture group). Denture group was composed of three subgroups; only removable partial denture (RPD) wearing group (26 persons), combination of RPD and complete denture (CD) wearing group (10 persons), and only CD wearing group (two persons). Teeth without an occlusion because of severe dental caries were considered to be missing (Table 1). MAT using the two-coloured wax cube The MAT using a two-coloured wax cube ( mm) was employed to evaluate the objective masticatory function of the subjects (15). A new wax cube with the same design as in Sato s study (15) was prepared. Each subject chewed the wax cube for 10 strokes. A total of 441 chewed wax samples were obtained from the 147 subjects. Both sides of the chewed wax cube were imaged by a digital camera under standardized distance and light conditions. The digital images were analysed using a digital image analyser (Image-Pro Ò Plus v6.0*) to obtain information on the colour and shape. All procedures for the measurements were performed by a single independent examiner. Discriminant analysis was performed to develop a new discriminant function based on the previous method. The new discriminant function was as follows: MAI ¼ MIX þ TR þ LB þ AH (MIX, the ratio of the colour mixed area; TR, the ratio of an area >50 lm in thickness to the total projection area; *Media Cybernetics Inc., Bethesda, MD, USA.

3 244 S.H. JEONG et al. Table 1. Distribution of subjects and ages (mean s.d.) according to gender and number of post-canine teeth lost Groups Males Females Total Average ages No loss Æ7 18Æ2 1 2 loss Æ0 18Æ9 3 5 loss Æ6 17Æ6 Denture Æ5 9Æ9 Total Æ9 20Æ7 LB, the ratio of the maximum length to the maximum breadth; and AH, the total projection area). The hit ratio, which was the percentage of each group classified correctly by the discriminant analysis, was 92Æ6%. The MAI of each chewed sample was calculated by inserting each image analysis value of the chewed wax cube into the discriminant function. The mean value of the MAI for the three chewed wax samples was determined to be the objective MAI. FIA test using the questionnaire A self-assessed questionnaire with the food lists was used to evaluate the subjective masticatory ability (28). The FIA questionnaire asked whether the subjects could chew the 30 types of foods and was composed of a five Likert scale ranging from cannot chew at all (1 point) to can chew well (5 points). The average score for each of the 30 foods was determined to be the subjective FIA. In addition, the average score for five key foods (dried cuttlefish, raw carrot, dried peanuts, cubed radish kimchi and caramel) selected from a previous study was determined to be the subjective KFIA. Results Mixing Ability Index The MAI value of each subject was distributed normally between a minimum and maximum of )4Æ15 and 3Æ47, respectively (Fig. 1). The MAI decreased significantly with increasing number of post-canine teeth lost. In addition, the MAI decreased with age but only the 60-year-old group showed a significantly lower MAI than the other age groups. The denture wearing group showed a higher MAI score than the 3 5 post-canine teeth lost group (Table 2). Food intake ability The distribution of the FIA skewed to the right side because most subjects answered that they could chew the listed foods well. However, the KFIA showed a less skewed distribution than the FIA. Hard foods, such as dried cuttlefish (3Æ37 1Æ75), dried filefish (3Æ63 1 Æ73), French baguette (3Æ97 1Æ61), raw carrot (4Æ06 1Æ43) and hard persimmon (4Æ14 1Æ37), showed the lowest FIA. On the other hand, soft foods, such as soybean curd (4Æ95 0Æ42), steamed potato (4Æ90 0 Æ58), boiled rice (4Æ88 0Æ57), ham (4Æ84 0Æ73) and watermelon (4Æ83 0Æ75), showed a high FIA. The average FIA of the 30 foods and five key foods was Statistical analysis Fisher s discriminant analysis was performed to derive the discriminant function. Pearson s correlation analysis was carried out to determine the relationship between the FIA, KFIA and MAI. In addition, differences in the MAI, FIA and KFIA according to age and number of post-canine teeth lost were compared using a one-way ANOVA test. A Duncan test was used for the post hoc comparisons. All statistical analyses were carried out using the SPSS 15.0 statistical package program. Frequency Mixing ability index SPSS Inc., Chicago, IL, USA. Fig. 1. Distribution of the Mixing Ability Index of the subjects.

4 RELATION BETWEEN FOOD INTAKE ABILITY AND MIXING ABILITY INDEX 245 Table 2. Descriptive statistics of the MAI, FIA and KFIA Groups N MAI FIA KFIA Ages Æ44 0Æ85 a 4Æ93 0Æ14 a 4Æ80 0Æ36 a Æ23 0Æ55 a 4Æ84 0Æ24 a 4Æ53 0Æ64 a )0Æ51 1Æ28 b 4Æ10 1Æ04 b 3Æ49 1Æ41 b Number of post-canine teeth lost Æ57 0Æ82 a 4Æ87 0Æ37 a 4Æ71 0Æ63 a )0Æ08 0Æ56 b 4Æ89 0Æ14 a 4Æ67 0Æ34 a )1Æ32 1Æ36 d 3Æ87 1Æ42 b 3Æ42 1Æ71 b Denture 38 )0Æ69 1Æ11 c 3Æ81 0Æ88 b 2Æ88 1Æ13 c Total 147 )0Æ08 1Æ16 4Æ49 0Æ86 4Æ08 1Æ23 All values are (mean S.D.) The same superscript characters are not significant according to Duncan s multiple comparison at a = 0Æ05. N, number of subjects; MAI, Mixing Ability Index; FIA, food intake ability; KFIA, key food intake ability. 4Æ49 0Æ86 and 4Æ08 1Æ23, respectively. Both the FIA and KFIA score decreased with increasing number of post-canine teeth lost and age. In particular, both scores decreased significantly when more than three teeth were lost (P <0Æ05, Table 2). The KFIA showed more distinct differences in each group than the FIA. The difference in the KFIA between the age group and over 60-age group was higher than in the FIA (1Æ31, 0Æ83, respectively). A similar result was observed in the number of post-canine teeth lost. The difference in the FIA between the no tooth loss group and 3 5 post-canine teeth lost group was 1Æ00. On the other hand, the difference in KFIA between the two groups was 1Æ29. The difference in KFIA between the no tooth loss group and denture group was higher than that in the FIA (1Æ83, 1Æ06, respectively, Table 2). Table 3. Pearson s correlation coefficient between the FIA, KFIA and MAI Group FIA vs. MAI KFIA vs. MAI Ages Æ20 0Æ Æ32 0Æ Æ45** 0Æ49** Number of post-canine teeth lost 0 0Æ14 0Æ )0Æ20 )0Æ Æ41 0Æ49* Denture 0Æ36* 0Æ44** Total 0Æ51** 0Æ55** MAI, Mixing Ability Index; FIA, food intake ability; KFIA, key food intake ability. *Correlation is significant at the 0Æ05 level (two-tailed); **Correlation is significant at the 0Æ01 level (two-tailed). Correlation between FIA and MAI The Pearson s correlation coefficient between the FIA and MAI, and between the KFIA and MAI was 0Æ51 and 0Æ55, respectively (P <0Æ01). In particular, the over 60-year-old group and denture wearing group showed a significant higher correlation between the FIA and MAI than the other groups. In addition, the KFIA showed a higher correlation with the MAI than with the FIA (Table 3). Discussion To obtain the MAI, it is important to develop a new discriminant function according to a previous study (15). The previous discriminant function for the MAI was developed by Sato (2003) in Japan. Although the design of the test material used in this study was similar to that in the previous study, a new discriminant function would be needed because of the physical differences in the raw wax materials. Therefore, a new discriminant function optimized for Koreans was derived using the procedure suggested by Sato (2003). The hit ratio of the new discriminant function was 92Æ6%, which is similar to the previous one (97Æ0%). Therefore, the new discriminant function was considered to be a well-organized function. A total of 441 wax samples, which were chewed ten times by the 147

5 246 S.H. JEONG et al. subjects, were used to obtain a more valid discriminant function. However, the previous study only used 100 wax samples, which were chewed for a random number of strokes from 5 to 50 times by 37 subjects. Although components of the equation were different from previous one, this function was considered to have higher validity by increasing the number of wax samples, the application of a larger number of subjects, and a set chewing frequency of 10 strokes. The validity of the new equation was also confirmed by the normal distribution of the MAI score (Fig. 1). Both the FIA and MAI decreased with age. The over 60-year-old group showed a significant decrease when compared to the other age groups. The average age of the subjects with more than three post-canine teeth lost was 67Æ6, and the over 60-year-old group had lost more than three post-canine teeth. Hence, these results can be explained by the loss of post-canine teeth not by ageing. The subjective FIA decreased with increasing the number of post-canine teeth lost. There was no significant difference in FIA between the no teeth loss group and the 1 2 loss of post-canine teeth group. However, the 3 5 loss of post-canine teeth group and denture wearing group showed a remarkable decrease in FIA (P < 0Æ05). Similar results were observed in the KFIA, which were also similar to a previous study (28). From these results, it is possible that the loss of more than three post-canine teeth results in a rapid decrease in the subjective masticatory function, and dentures could not recover the subjective chewing ability for hard and tough foods. Similar results reported elsewhere showed no difference in the objective chewing performance between the group who had lost 2Æ7 post-canine teeth group and the group who had lost no teeth (31). The objective MAI also decreased with increasing number of post-canine teeth lost. A remarkable decrease was observed in the group with more than three post-canine teeth lost, which is similar to the FIA results. However, the MAI of the denture wearing group was higher than that of the 3 5 post-canine teeth loss group. These results coincide with previous results in that denture wearing can increase the masticatory performance (29, 32). An increase in occluding teeth by a denture treatment can increase the chewing and blending ability of artificial wax food. Therefore, MAT would be useful for detecting an improvement in the masticatory performance with removable dentures. The MAI showed a moderate correlation with the FIA (r =0Æ51, P <0Æ01) and KFIA (r =0Æ55, P <0Æ01). Several studies reported correlations between the MAI and Comminuting Ability Index (r =0Æ56 0Æ77, P <0Æ001) (18), EMG parameters (r =0Æ450Æ49, P <0Æ05) (20) and multiple sieving method (r = )0Æ56 to )0Æ70, P < 0Æ001) (21). However, few studies have confirmed the correlation between the MAI and subjective chewing ability. Although the correlation between the MAI and FIA was moderate, it would be acceptable considering the subjective characteristics of the self-assessed questionnaire itself and other results showing that the self-assessed chewing ability was only weakly correlated with the dental state and bite force (33, 34). A previous study also reported that the FIA showed a moderate correlation (r =0Æ45 0Æ51, P < 0Æ01) with the objective bite force, which reflects the static chewing function (28). Although this study confirmed a significant correlation between FIA and MAI, this study had one limitation. An even distribution of each subgroup could not be obtained according to age and teeth lost because of the difficulty of recruiting subjects. It will be also important to collect the denture group according to the same criteria in a further study. There are several methods that can be used to evaluate the masticatory function. However, there are barriers to clinical applications, such as the need for expensive equipment and the considerable analysis time. Overall, the subjective FIA is a useful tool for evaluating the masticatory function as a simple screening test in the clinical and epidemiological field. In conclusion, there was a moderate correlation between the subjective FIA and objective MAI in Korean adults. Acknowledgment This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (R ). References 1. Horwath CC. Chewing difficulty and dietary intake in the elderly. J Nutr Elder. 1989;9: Appollonio I, Carabellese C, Frattola A, Trabucchi M. Dental status, quality of life, and mortality in an older community

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