An evaluation of self-reported oral health and health-related quality of life

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1 J Med Dent Sci 2005; 52: Original Article An evaluation of self-reported oral health and health-related quality of life Akiko Shimada 1, Yoshiyuki Sasaki 2 and Shiro Mataki 1 1) Behavioral Dentistry, Department of Comprehensive Oral Health Care, Division of Comprehensive Patient Care, Graduate School, Tokyo Medical and Dental University 2) Center for Education and Research in Oral Health Care, Faculty of Dentistry, Tokyo Medical and Dental University The purpose of this study was to investigate the general and oral health status of patients at a dental hospital in Tokyo and examine the correlations between general health and oral health items. One hundred and seventy-four (174) new patients at the Dental Hospital of Tokyo Medical and Dental University participated in this study. The Visual Analog Scale (VAS) was employed to investigate dental demands and symptoms, as well as satisfaction with oral and general health conditions, while SF-36 served an indicator for healthrelated quality of life (HRQOL). The results were statistically analyzed at a significance level of p = The results of VAS were further examined using factor analysis. Several VAS items showed significant correlations with SF-36 subscales (p 0.05). The factor analysis of VAS items suggested a structure involving three factors: self-cognition of oral status, related function and pain, and dental fear and discomfort. The dental fear and discomfort factor showed no significant correlations with SF-36 subscales (p 0.05). Emotional elements and esthetic demands on dental status, as well as physical symptoms, influence HRQOL. Dental discomfort proved to be independent of general health status and was Corresponding Author: Akiko Shimada Behavioral Dentistry, Department of Comprehensive Oral Health Care, Division of Comprehensive Patient Care, Graduate School, Tokyo Medical and Dental University, , Yushima, Bunkyo-ku, Tokyo , Japan shimada.behd@tmd.ac.jp Received October 25; Accepted December 3, 2004 considered a dental-specific item that needs to be measured separately from general health status. Key words: oral health, general health, quality of life, SF-36, VAS Introduction The measurement of oral health-related quality of life (OHRQOL) has been increasingly accepted as an essential component of oral health surveys. Dental practitioners used to rate subjects oral health status according to clinical markers of disease; e.g. number of missing teeth, caries teeth, or mobile teeth, and dryness of the oral mucosa. 1 However, some debate exists about whether clinicians should provide oral health ratings that more closely resemble those given by subjects. 2 While the OHRQOL represents the individual s perception of health, including pain, mental health, and satisfaction with oral health status, objective evaluation or ranking of problems recognized by subjects as important has been difficult for dental practitioners. 1,2 In order to reflect patients assessment of oral health status, a variety of self-reported indicators of oral health have been developed that evaluate patients problems with their health, functional limitations, social impacts, self-ratings of health, and their perceptions about the need for treatment. 1,2,3 Using various subjective measures, several researchers have demonstrated a connection between oral health and general health status. 1-7 While results are mixed, several studies have shown that oral health status is related not only to local oral

2 66 A. SHIMADA, Y. SASAKI and S. MATAKI J Med Dent Sci factors but also to several medical, socioeconomic, and lifestyle factors. 1-7 The purpose of this study was to investigate oral health status and health-related quality of life (HRQOL) of patients at a dental hospital in Japan on the basis of self-reported general and oral health information. HRQOL was assessed using the SF-36 (Short-Form 36 items) health survey. 8 This widely used generalized measure, developed in the US, has been translated into Japanese and validated among the Japanese population. 9 It covers both functioning and well-being and has been shown to be useful both in large populations and in clinical samples. A visual analog scale (VAS) was also employed to evaluate the dental demands and symptoms, as well as satisfaction with general health status. Correlations of oral health status and HRQOL were examined on the basis of VAS and SF-36 results. Materials and Methods Target population The target population comprised new patients that came to the Dental Hospital of Tokyo Medical and Dental University on June and August 19-21, They were all able to give informed consent. One hundred and seventy-seven (177) new patients were sampled in this study. Of these 177 participants, three did not answer any of the questions. Consequently, 174 patients, 63 male and 111 female, participated in this study. Their ages ranged from 16 to 79 years with a median of 41 (male, 40; female, 41). All survey procedures were approved by the appropriate committee of the Dental Hospital of Tokyo Medical and Dental University. Measurement of self-reported general and oral health status The Visual Analog Scale (VAS) was employed to evaluate patients dental demands and symptoms, as well as satisfaction with general health status while SF- 36 served as an indicator for HRQOL. The VAS employed in this study consisted of 10 items: tooth pain (V1), chewing ability (V2), eating ability (V3), dental fear (V4), dental discomfort (V5), satisfaction with teeth alignment (V6) and tooth color (V7), halitosis (V8), and satisfaction with oral (V9) and general health conditions (V10). Subjects were asked, To what degree are you self-conscious...because of problems with your teeth? Responses were scored on a 10 cm straight-line graph with a single dot. Each dot was marked by the respondents themselves: the left end of the line, 0, indicated no pain or no problem (0 %), and the right end, 100, indicated the most severe pain or problem for the individual. Consequently, a dot 5 cm from the left end indicated roughly 50% pain or subjective difficulty for the patient. After the marking by the respondent, the length from the left end (mm) was subtracted from 100 for use as a VAS subscore. Accordingly, higher VAS scores in this study indicate less pain or difficulty. The 36-item MOS (Medical Outcome Study) Shortform General Health Survey (SF-36) was selected to represent an individual s general health. SF-36 assesses health from the patient s point of view and is composed of 8 subscales: physical functioning (PF), role-physical (RP), bodily pain (BP), general health (GH), vitality (VT), social functioning (SF), role-emotional (RE), and mental health (MH). The obtained SF- 36 values were calculated into the standard scores of each age group of genders for use in this study. Higher SF-36 scores indicate better health. Thus, a higher PF score indicates better functioning and higher BP score indicates less pain. Statistical analysis The results were statistically analyzed with significance level of p = 0.05 using SPSS version 11.0J (SPSS Inc., IL, USA) statistical package. To assess the general health status of the participants in this study, the results of SF-36 subscales were compared with the national normative data for Japan 9 using Student s t-test. Correlations within the interfactors of VAS items and correlations between VAS items and SF-36 subscales were explored employing Spearman s ı correlation with t-test. Differences in VAS and SF-36 scores between the genders were detected using Mann-Whitney U-test (p 0.05). The effects of age on VAS and SF-36 scores were also analyzed using Spearman s ı correlation with t-test. Additionally, to identify clusters of items of oral health status, factor analysis by maximum-likelihood methods with varimax rotation was conducted on patients responses to the VAS items. The results of factor analysis were further examined in terms of correlations with SF-36 items.

3 CORRELATION BETWEEN SELF-REPORTED ORAL HEALTH AND HRQOL 67 Results SF-36 analysis Figure 1 shows SF-36 results in standard score. All the scores except for PF (physical functioning) were significantly lower than the national normative data for Japan (Student s t-test, p 0.05). 9 Correlation coefficients among the SF-36 subscales are shown in Table 1. Every item of SF-36 correlated significantly with other items (Spearman s ı correlation with t-test, p 0.05). VAS analysis Figure 2 shows the result of VAS analysis. Correlation coefficients among the VAS items are shown in Table 2. Significant correlations were detected between tooth pain (V1) and chewing ability (V2), tooth pain (V1) and eating ability (V3), tooth pain (V1) and satisfaction with oral health condition (V9), chewing ability (V2) and eating ability (V3), chewing ability (V2) and satisfaction with oral health condition (V9), chewing ability (V2) and satisfaction with general health condition (V10), dental fear (V4) and dental discomfort (V5), dental fear (V4) and satisfaction with teeth alignment (V6), dental fear (V4) and satisfaction with tooth color (V7), dental fear (V4) and halitosis (V8), dental fear (V4) and satisfaction with oral health condition (V9), dental discomfort (V5) and satisfaction with teeth alignment (V6), dental discomfort (V5) and satisfaction with tooth color (V7), dental discomfort(v5) and halitosis (V8), dental discomfort (V5) and satisfaction with oral health condition (V9), satisfaction with teeth alignment (V6) and satisfaction with tooth color (V7), satisfaction with teeth alignment (V6) and halitosis (V8), satisfaction with teeth alignment (V6) and satisfaction with oral health condition (V9), satisfaction with tooth color (V7) and halitosis (V8), satisfaction with tooth color (V7) and satisfaction with oral health condition (V9), satisfaction with tooth color (V7) and satisfaction with general health condition (V10), and satisfaction with oral health condition (V9) and satisfaction with general health condition (V10) (Spearman s ı correlation with t-test, p 0.05). The results from the varimax rotated factor loadings from the factor analysis suggested three multi-item scales: Factor 1 consisting mainly of satisfaction with PF RP BP GH VT SF RE MH Figure 1. Average and standard deviation of SF-36 in standard score V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 Figure 2. Average and standard deviation of VAS Table 1. Spearman s ı correlation coefficient among SF-36 subscales PF RP BP GH VT SF RE MH AGE * 0.252** 0.224** 0.240** 0.267** 0.200** 0.286** PF ** 0.337** 0.421** 0.362** 0.428** 0.243** 0.207** RP ** 0.380** 0.362** 0.375** 0.404** BP ** 0.320** 0.273** 0.525** GH PF: physical functioning, RP: role-physical, BP: bodily pain, GH: general health, VT: vitality, SF: social functioning, RE: roleemotional, MH: mental health ** 0.403** 0.618** VT ** 0.520** SF ** RE MH **p < 0.01 *p < 0.05

4 68 A. SHIMADA, Y. SASAKI and S. MATAKI J Med Dent Sci Table 2. Spearman s ı correlation coefficient among VAS items V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 AGE ** 0.375** ** * V ** * V * 0.149* ** V ** 0.235** 0.311** 0.248* 0.165* V ** 0.182* 0.223** 0.227** V ** 0.220** 0.266** V ** 0.398** 0.278** V7 V1: tooth pain, V2: chewing ability, V3: eating ability, V4: dental ** V8 fear, V5: dental discomfort, V6: satisfaction with teeth alignment, ** * V9 V7: satisfaction with tooth color, V8: halitosis, V9: satisfaction V10 with oral health condition, V10: satisfaction with general health condition **p < 0.01 *p < 0.05 teeth alignment (V6), satisfaction with tooth color (V7), halitosis (V8), satisfaction with oral health condition (V9), and satisfaction with general health condition (V10), Factor 2 consisting mainly of tooth pain (V1), chewing ability (V2), eating ability (V3) and satisfaction with general health condition (V10), and Factor 3 consisting mainly of dental fear (V4) and dental discomfort (V5). Satisfaction with general health condition (V10) was involved both in Factors 1 and 2 (Table 3). Correlation between VAS and SF-36 Table 4 shows the correlation coefficients between the VAS items and the subscales of SF-36. Satisfaction with general health condition (V10) showed significant correlation with all the subscales of SF-36 (Spearman s ı correlation with t-test, p 0.05). Tooth pain (V1) significantly correlated with SF and RE, chewing ability (V2) with PF, eating ability (V3) with RE, dental fear (V4) with GH, VT, and MH, satisfaction with tooth color (V7) with GH and MH, halitosis (V8) with RP, and satisfaction with oral health condition (V9) with PF, GH, VT, and MH (Spearman s ı correlation with t-test, p 0.05). The three multi-factors from the VAS factor analysis also showed significant correlations with several subscales of SF-36. Factor 1 had significant correlation with GH and MH, and Factor 2 with PF, BP, GH, RE and MH (Spearman s ı correlation with t-test, p 0.05, Table 5). However, Factor 3 showed no significant correlations with any subscales of SF-36 (p 0.05). Analysis between genders and among age The results of statistical analysis between males and females are shown in Table 6. Significant differences were observed in dental fear (V4), satisfaction with teeth alignment (V6), satisfaction with tooth color Table 3. Factor analysis of VAS items rotated factor loading factor V V V V V V V V V V eigenvalue proportion (%) cumulative (%) V1: tooth pain, V2: chewing ability, V3: eating ability, V4: dental fear, V5: dental discomfort, V6: satisfaction with teeth alignment, V7: satisfaction with tooth color, V8: halitosis, V9: satisfaction with oral health condition, V10: satisfaction with general health condition (V7), satisfaction with oral health condition (V9), RP (role-physical), and RE (role-emotional) (Mann- Whitney U-test, p 0.05). In case of the VAS analysis, females showed lower values for dental fear (V4), satisfaction with teeth alignment (V6), satisfaction with tooth color (V7) and satisfaction with oral health condition (V9), while RP and RE of SF-36 items were lower in males.

5 CORRELATION BETWEEN SELF-REPORTED ORAL HEALTH AND HRQOL 69 Table 4. Spearman s ı correlation matrix between VAS and SF-36 V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 PF ** * 0.164* RP ** BP ** GH ** * ** 0.467** VT * * 0.388** SF 0.183* ** RE 0.189* * ** MH ** * ** 0.340** **p < 0.01 *p < 0.05 V1: tooth pain, V2: chewing ability, V3: eating ability, V4: dental fear, V5: dental discomfort, V6: satisfaction with teeth alignment, V7: satisfaction with tooth color, V8: halitosis, V9: satisfaction with oral health condition, V10: satisfaction with general health condition PF: physical functioning, RP: role-physical, BP: bodily pain, GH: general health, VT: vitality, SF: social functioning, RE: role-emotional, MH: mental health Table 5. Spearman s ı correlation matrix among 3 factors and SF-36 PF RP BP GH VT SF RE MH factor 1 factor 2 factor 3 factor ** * factor * * 0.158* ** 0.173* * factor * **p < 0.01 *p < 0.05 PF: physical functioning, RP: role-physical, BP: bodily pain, GH: general health, VT: vitality, SF: social functioning, RE: roleemotional, MH: mental health Table 6. Mann-Whitney U-test results between male and female average rank average rank M M V1 NS PF NS F F M M V2 NS RP p = F F M M V3 NS BP NS F F M M V4 p < GH NS F F M M V5 NS VT NS F F M M V6 p = SF NS F F M M V7 p = RE p = F F M M V8 NS MH NS F F M V9 p = F M: male, F: female M V10 NS F V1: tooth pain, V2: chewing ability, V3: eating ability, V4: dental fear, V5: dental discomfort, V6: satisfaction with teeth alignment, V7: satisfaction with tooth color, V8: halitosis, V9: satisfaction with oral health condition, V10: satisfaction with general health condition PF: physical functioning, RP: role-physical, BP: bodily pain, GH: general health, VT: vitality, SF: social functioning, RE: role-emotional, MH: mental health

6 70 A. SHIMADA, Y. SASAKI and S. MATAKI J Med Dent Sci Effects of age on SF-36 and VAS are listed in Tables 1 and 2, respectively. Differences in age showed statistically significant correlations between tooth pain (V1), chewing ability (V2), eating ability (V3), satisfaction with oral health condition (V9) and RP (rolephysical) (Spearman s ı correlation with t-test, p 0.05). Discussion In this study, we investigated self-reported general health and oral health status of new patients at the dental hospital of Tokyo Medical and Dental University. Additionally, correlations between general health and oral health status were statistically examined. The results of SF-36 indicated that the general health status of the participants in this study was lower than the national normative data for Japan (p 0.05); only physical functioning (PF) showed no significant difference. Even though the chief complaints of our participants were strictly oral problems, the score of role-physical (RP), bodily pain (BP), social functioning (SF), general health (GH), vitality (VT), role-emotional (RE), and mental health (MH) showed lower values. While the reasons for the lower general health status of our participants was unclear, it is quite possible that dental problems such as tooth pain, reduced eating ability and so on, affect the general health status or its perception. 10,11 VAS results exhibited statistically significant correlations within several items. The correlations among tooth pain (V1), chewing ability (V2), eating ability (V3), and satisfaction with oral health condition (V9), indicate that tooth pain affects oral physical functions, such as chewing and eating ability, as well as oral health condition, in the sense of disease-specific measures. 4,12 Pain itself is inextricably related to one s ability to complete the natural functions associated with chewing and eating. 12 Meanwhile, dental fear (V4), dental discomfort (V5), satisfaction with teeth alignment (V6), satisfaction with tooth color (V7), halitosis (V8), and satisfaction with oral health condition (V9) were also significantly correlated with each other. While the correlation of dental appearance with halitosis, dental fear, and dental discomfort seems surprising, these items are all psychological elements. These results seem to indicate that oral health is distinguished by individuals from physical health and mental health as measured by the 10 items of the VAS. Correlations between the general health subscales of SF-36 and the oral health items of VAS were also examined in this study. Satisfaction with general health condition (V10) showed significant correlation with all the subscales of SF-36 (p 0.05), a logical outcome since satisfaction with general health condition (V10) indicates satisfaction with general health, the criteria of which were ascertained by SF-36. This high correlation detected between satisfaction with general health condition (V10) and each of the SF-36 subscales probably indicates the validity of these self-reported measures. Locker et al. reported that tooth pain, as well as chewing or eating ability, significantly impacted general health status. 13 Our results, which found correlations of tooth pain (V1), chewing ability (V2), eating ability (V3) and satisfaction with oral health condition (V9) with several SF-36 subscales seemed to agree with the previous results. As mentioned, it is quite possible that tooth pain (V1), reduced eating or chewing ability (V2 or V3), or poorer oral health condition (V9) contributed to making the values of SF-36 lower than those of the national normative data for Japan. The results of factor analysis with the varimax rotation suggested that VAS items were divided into three multi-item factors: Factor 1 consisting mainly of satisfaction with teeth alignment (V6), satisfaction with tooth color (V7), halitosis (V8), satisfaction with oral health condition (V9), and satisfaction with general health condition (V10), Factor 2 consisting mainly of tooth pain (V1), chewing ability (V2), eating ability (V3) and satisfaction with general health condition (V10), and Factor 3 consisting mainly of dental fear (V4) and dental discomfort (V5). Satisfaction with general health condition (V10) was involved in both Factor 1 and Factor 2. Factors 1, 2 and 3 were described as selfcognition of oral status, related function and pain, and dental fear and discomfort, respectively. Factor 1 and Factor 2 significantly correlated with several subscales of SF-36. Clearly, correlations of Factors 1 and 2 with SF-36 subscales reflected the results of correlations of VAS and SF-36 items. Since Factor 3 showed no significant correlations with SF-36, dental discomfort seemed to be independent from the general health-related QOL. Dental discomfort is considered an emotional orientation influenced by previous dental treatments, or a kind of estimation of the effects of dental therapy. Consequently, dental discomfort was considered as a dental-specific item that could not be evaluated by general health measures. It is noteworthy fact that dental fear (V4), satisfaction

7 CORRELATION BETWEEN SELF-REPORTED ORAL HEALTH AND HRQOL 71 with tooth color (V7), and halitosis (V8) significantly correlated with several SF-36 subscales, GH, VT, MH, and RP. While dental fear (V4), satisfaction with tooth color (V7) and halitosis (V8) are considered psychological elements, this correlation indicates that not only physical elements but also psychological elements affect the general health status. This result might reflect a recent trend of OHRQOL in urban areas of Japan, where dissatisfaction with appearance has been shown to lead to a generalized concern about individuals health. 4,14 Recently, demands for esthetic dentistry have been increasing. This growing interest in esthetic treatment may change the direction of dental demands from physical concerns to more psychological concerns. In Japan, many aspects of dental treatment are covered by health insurance and most citizens can receive inexpensive dental care. A survey of dental disease in Japan in 1999 reported that the rate of prosthodontic treatment on missing teeth was 82.1 %. 15 This high rate of prosthodontic treatment may also in part contribute to relatively lower correlation of physical dental problems with general health status. Atchison et al. examined the distinction between oral and general health measures and reported that the oral health items were distinct from general health items. 14 They also showed no correlations of general physical/social items with oral factors or mental health items. The result of our study in some degree coincided with their results because several items of SF-36 and VAS showed no significant correlations. Nevertheless, several items of the VAS showed significant correlation with the general health items of SF-36. This discrepancy may be derived from differences in target populations; Atchison et al. investigated lowincome neighborhood populations consisting of Hispanic and African-Americans and pointed out the particularity of their group. 14 Several studies have also shown differences in health status among ethnic groups. 4,14 Since our study was carried out in an urban area of Japan, oral health status seems to be more valued by the community and may affect the mental health, role-physical and so on. 4 The potent concern for esthetics existing in Japan s urban areas might be the cause of this variance. In this study, females showed lower values in some of the oral health items while males showed lower values in general health. In particular, females perceived esthetic problems in their mouth: dental fear (V4), satisfaction with teeth alignment (V6), satisfaction with tooth color (V7), satisfaction with oral health condition (V9). Meanwhile, males felt social difficulty from both physical (RP) and mental (RE) concerns. This result was in accordance with the results of a national survey in the United Kingdom by McGarth et al, which showed that females report their oral health less positively than do males. 16 Significant negative correlations for age were shown in tooth pain (V1), chewing ability (V2), eating ability (V3), satisfaction with oral health condition (V9) and RP (role-physical) in this study. As these items were all considered physical elements, the lower values of these items in advanced-age groups were easily comprehended. 7,10,12,14,16 Hägglin et al. showed that dental fear decreases with increasing age. 7 Contrary to their study, no significant correlations between dental fear and age were found in this study. This discrepancy might also result from differences in the target populations, since their study included both regularly and irregularly visiting patients. It has been reported that dental fear or discomfort is highly associated with irregular dental utilization. 7 While all the participants in our study were new patients, it is quite possible that many of our participants had irregular dental attendance. Since regularity of dental utilization is shown to reduce dental fear, a relatively high rate of irregular dental utilization might have screened the effect of age on dental fear. Nonetheless, the regularity or irregularity of dental attendance in our participants was not investigated. Further study on the effect of age on dental fear seems to be necessary. In case of SF-36, health status was evaluated using multiple item questionnaires. Each questionnaire was coded into 2 to 6 choices. While multiple dimensions may capture more statistical variation than do single item questions, there is no physical scale exist that can be anchored to the response categories, because there is no particular basis exist to identify the difference between excellent and fair. 12 Additionally, multiple item questionnaires sometimes composed from huge number of questionnaires, that might weight the patients to answer all. In case of VAS analysis, 10 cm scale was used with anchors set at 0 and 100, where the respondents placed a mark on the line that represented their oral health status. While obtained results seemed to be varied, because each respondent would use identical subconscious measure when deciding on where to mark, the VAS was considered as a facile scale that enable us to measure the variation of oral health status. Previous research on cancer patients showed that individuals perceptions of HRQOL changed over

8 72 A. SHIMADA, Y. SASAKI and S. MATAKI J Med Dent Sci time. 17 It is generally acknowledged that QOL is a dynamic concept, because previous health experiences may have altered individuals expectations and standards of functional well-being. 18 However, the existence of shifting standards in OHRQOL assessment raises the issue of how to quantify changing perceptions; OHRQOL at one time may not predict the same individual s rating at another time. 18 Within the limitations of this study, some of the emotional elements and esthetic demands on dental status were shown to be significantly correlated with general health status. In order to accurately grasp the dental demands of patients and furnish the adequate dental service, subsequent studies on OHRQOL targeting various populations seem necessary. Additionally, VAS results in combination with factor analysis indicated that some oral health items such as dental discomfort were independent of the general health subscales. Consequently, even though self-reported oral health has a significant relationship with HRQOL, OHRQOL seems to have a wide spectrum that needs to be measured separately. References 1. Atchison KA, Matthias RE, Dolan TA, et al. Comparison of oral health ratings by dentists and dentate elders. J Public Health Dent 1993;53: Atchison KA. In: Oral health-related quality of life. Chapter 3. Understanding the Quality in quality care and quality of life. Edited by Ingehart MR, Baramian RA, Quintessence Publishing Co, Inc., USA 2002; Atchison KA, Dolan TA. Development of the Geriatric Oral Health Assessment Index. J Dent Educ 1990;54: Matthias RE, Atchison KA, Lubben JE, et al. Factors affecting self-ratings of oral health. J Public Health Dent 1995;55: Chen MS, Hunter P. Oral health and quality of life in New Zealand: A social perspective. Soc Sci Med 1996;43: Dao TT, Lavigne GJ, Charbonneau A, et al. The efficacy of oral splints in the treatment of myofacial pain of the jaw muscles: A controlled clinical trial. Pain 1994;56: Hagglin C, Hakeberg M, Ahlqwist M, et al. Factors associated with dental anxiety and attendance in middle-aged and elderly women. Community Dent Oral Epidemiol 2000;28: Ware JE Jr., Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 1992;30: Fukuhara S, Suzukamo Y, Bito S, et al. Manual of SF-36 Japanese version 1.2: Public Health Research Foundation, Tokyo, Osterberg T, Mellstrom D, Sundh V. Dental health and functional aging. A study of 70-year-old people. Community Dent Oral Epidemiol 1990;18: Norlen P, Ostberg H, Bjorn A. Relationship between general health, social factors and oral health in women at the age of retirement. Community Dent Oral Epidemiol 1991;19: Slade GD. In: Oral health-related quality of life. Chapter 4. Assessment of oral health-related quality of life. Edited by Ingehart MR, Baramian RA, Quintessence Publishing Co, Inc., USA 2002; Locker D, Miller Y. Evaluation of subjective oral health status indicators. J Public Health Dent 1994;54: Atchison KA, Der-Martison C, Gift HC. Components of selfreported oral health and general health in racial and ethnic groups. J Public Health Dent 1998;58: Report on the survey of dental diseases. Edited by Dental Health Division of Health Policy Bureau Ministry of Health, Labour and Welfare Japan McGrath C, Bedi R, Gilthorpe MS. Oral health related quality of life: Views of public in the United Kingdom. Community Dent Health 2000;17: de Haes CJM, Van Knippenberg F. The quality of life of cancer patients: A review of the literature. Soc Sci Med 1985;20: Cimprich B, Paterson AG. In: Oral health-related quality of life. Chapter 5. Health-related quality of life: Conceptual issues and research applications. Edited by Ingehart MR, Baramian RA, Quintessence Publishing Co, Inc., USA 2002;47-53.