Objectives: The aim of this study was to comparethe oral health status of migrants to Japan with thatof Japanese using the questionnaire and the OralHealth Status Index (OHSI). Methods: The ques-tionnaire for collecting demographic and behav-ioral variables and the OHSI were applied in amixed migrant/Japanese sample of patients from adental clinic in Yokohama. A sample of 224 sub-jects, 52% of whom were migrants, was selectedfrom new patients. Results: The mean OHSIscores were 78.56 for migrants and 83.16 forJapanese (p＜0.01). Multiple regression analysis ofOHSI showed that the statistically significant con-tributors were: age, status (migrants / Japanese),reason for initial visit, perceived oral health, andflossing behavior. Conclusion: The oral healthstatus of migrants was worse than that ofJapanese even though they were younger thanJapanese. The present public support system forforeign patients and their self-care behavior wereconsidered to be the factors for the inequity in oralhealth status.

Key words: international health, migrant, oralhealth related factor, Oral HealthStatus Index, acculturation.

Introduction

According to the Ministry of Justice, the number offoreign residents in Japan (which are described as“migrants” in this study) has been increasing everyyear. As of the end of 2003, the number of migrantswas 1,915,030, and the proportion of migrants to thetotal Japanese population has also been increasingevery year. The proportion increased from 0.05% in1960 to 1.5% in 2003. Moreover the number of illegalforeign residents is estimated to be 250,000 andalmost half of them live in Tokyo metropolitan area1.While various kinds of health problems for migrantshave been investigated2-8, little work has been done inthe field of oral health in Japan9,10.

The aim of this study was to compare the oralhealth status of migrants with that of Japanesepatients using the questionnaire and the Oral HealthStatus Index (OHSI)11-17, so that we could determine theoral health status quantitatively and clarify the oralhealth related factors of migrants.

Methods

Study SampleParticipants were the patients of Minatomachi

Dental Clinic in Yokohama. Minatomachi Dental Clinic isa private facility that is owned by labors’ union, andabout half of the patients in this clinic are migrants toJapan, mainly from Asia and Latin America9.

Demographic, behavioral and dental status datawere collected from patients in 2003. A sample of 224

Original Article

A Comparative Study of Oral Health Status in a Migrant / Japanese Sample

Jiro Otsuru1,2, Masayuki Ueno1, Kayoko Shinada1, Vladimir W. Spolsky3, Carl A. Maida3 and Yoko Kawaguchi1

1) Department of Oral Health Promotion, Graduate School, Tokyo Medical and Dental University2) Minatomachi Dental Clinic, Kanagawa Workers' Medical Cooperative3) Division of Public Health and Community Dentistry and International Center for Dental Health Policy, Schoolof Dentistry, University of California, Los Angeles, USA

J Med Dent Sci 2006; 53: 27–33

Corresponding Author: Jiro OtsuruDepartment of Oral Health Promotion, Graduate School, TokyoMedical and Dental University,1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, JapanTel: +81-3-5803-5476 Fax: +81-3-5803-0194E-mail: jmin@hi-ho.ne.jpReceived October 6; Accepted December 2, 2005

subjects (over 18 years of age) was selected sequen-tially from new patients of the clinic. Each patient wasinformed about the nature of the study; an explanationof the research was provided in five different lan-guages (Japanese, Spanish, Tagalog, Korean andThai). Every participant read and signed a consent formbefore starting the study. All but three of the participantswho were asked to take part in the study agreed to par-ticipate. The three participants who declined to partic-ipate in the study received dental treatment in the sameclinic without disadvantage. The data were collected inthe process of routine examination and treatment,and they were also used beneficially in dental practicefor participants.

QuestionnaireA self-administrated questionnaire was conducted for

collecting demographic and behavioral variables. Thequestionnaire was translated from English to five lan-guages (Japanese, Spanish, Tagalog, Korean andThai). Back-translation was performed to test theaccord among the languages18, following which equiv-ocally translated items were excluded in the finalquestionnaire. The questionnaire was divided into twoparts. The first-part, applied only to migrant patients,was a modified form of the Psychological BehavioralAcculturation Scale (P-BAS)19,20. The second part of thequestionnaire, investigating behavioral variables, wasbased on both the NIDCR21 and WHO question-naires22 (Table 1). The acculturation of the P-BAS wasclassified into three levels (High, Medium and Low) bythe dimensionality. Participants’ education and occu-pation were used as the measure of socio-economicstatus. Educational status was classified into twogroups: under high school and post high school. Andoccupational status was classified into unskilled andskilled categories.

Intra-Oral ExaminationA senior examiner performed all intra-oral examina-

tions prior to the initial treatment. Oral examination cri-teria were based on those developed by the NationalInstitute of Dental and Craniofacial Research(NIDCR)21,23. The components of the intra-oral exami-nation used in this paper were: the number ofdecayed and filled teeth (DFT), bleeding on probing, theappearance of calculus, attachment loss and tooth loss.Patients were also asked about the use of removableprosthesis if there was a missing tooth and no pros-thesis present. No dental implant appeared in this sam-ple.

For estimating periodontal destruction, two sites(mid-buccal and mesial buccal interproximal) ofattachment loss were measured at each tooth.Pressure-sensitive periodontal probes (PDT SensorProbe Type 2M-12) were used in this examination.Appearance of bleeding on probing of four sites (mid-buccal, mesial buccal interproximal, lingual and distallingual interproximal) and sub- and supragingival cal-culus, were also recorded.

The intra-examiner reliability using kappa statisticswas determined on caries experience, calculusdeposit, attachment loss, and bleeding on probing in agroup of 20 persons, and the same process wasrepeated in a few hours to a few days later24. The kappavalues ranged from 0.82 to 1.00. The changes thatoccurred during the progression of treatment wereexcluded from the reliability scores.

Oral Health Status IndexThe Oral Health Status Index (OHSI) was developed

using not only objective disease indicators but subjec-tive aspects based on the expert opinions of generaldentists11-17. The index has been applied to evaluate theoral health of broader racial groups. The OHSI inte-grates the status of the teeth and periodontium into onenumerical score. The theoretical range of OHSI

J. OTSURU et al. J Med Dent Sci28

Q1 . What is your total education period?Q2 . What is your occupation?Q3 . Do you have a dental insurance?Q4 . How would you describe the health of your teeth and gums?Q5 . What is the main reason for dental visit?Q6 . During the past 12 months, did you visit dental facilities?Q7 . How often do you brush your teeth?Q8 . How often do you use dental floss?

Table 1. The questionnaire items

scores is from -54 (every tooth has severe bone lossand frank decay) 0 (edentulous without tooth replace-ment) to 100 (no decay, missing teeth, or bone loss).The index was developed to provide a comprehensivecomposite indicator of oral health by their respectiveweighting factors (regression coefficients).

The regression coefficients are: decayed tooth (-1.79); missing tooth (-3.13); free ends (-3.13), whichrefers to the number of quadrants in the mouth in whichall molars are clinically missing; replaced tooth(+0.61); and length of attachment loss (AL) at themesial buccal interproximal surface that is sub-grouped into 4 to 6 mm of AL (-0.73) and ＞6 mm of AL(-3.02). Filled (restored) teeth are not included withinthe index as they are judged to be “restored to normal-ity.” The criteria for estimating a replaced toothincludes the number of artificial teeth such as bridgesand dentures. The OHSI value is calculated by multi-plying the number of affected teeth per person by theappropriate coefficient and summing all the scores.Coefficients, determined statistically from weightingfactors within the original study, are then used to cal-culate the OHSI. Table 2 illustrates an example of theOHSI calculation.

Data AnalysisThe Kruskal-Wallis test was used for analysis of dif-

ferences, including the examination of oral health statusand OHSI scores. The multiple regression analysis wasperformed with the OHSI as a dependent variable anddemographic and behavioral variables as indepen-dent variables. The SPSS 10.0J was used for statisticalanalyses.

Results

Overall, 224 subjects were examined and included inthe analyses. The number of migrants was 118(52.7%). The greatest proportion of migrants (33.1%)was born in the Philippines, 22.9% were born inColombia, 18.6% in Peru, 14.4% in Korea, and 5.9% inThailand. Almost all of the participants, therefore,came from either Asia (53.4%) or Latin America(45.8%). The mean length of staying in Japan was6.85+0.47 years. Ninety-two percent of migrants wereof low acculturation, based upon the results of the P-BAS measure.

Clinical characteristics on oral health of migrant andJapanese groups are shown in Table 3. There were sig-nificant differences in caries experiences between thetwo groups. The migrants had more decayed teeth (p＜0.001) and fewer filled teeth (p＜0.001) compared tothe Japanese. Bleeding (p＜0.01) and calculus status(p＜0.001) of migrants were worse than those ofJapanese. There were no significant differences on theloss of attachment and tooth loss between themigrants and Japanese.

Table 4 shows the number of migrants andJapanese by demographic and behavioral variablesand the mean OHSI according to each categories.The migrants had a larger proportion of women and

29COMPARISON OF ORAL HEALTH STATUS IN MIGRANTS/JAPANESE

Table 2. Example of OHSI calculation.

Table 3. Clinical characteristics for migrants and Japanese (Mean±SE).

J. OTSURU et al. J Med Dent Sci30

Table 4. The number of migrants and Japanese by demographic and behavioral variables and the mean OHSI accord-ing to each categories.

tended to be younger than the Japanese. Less thanhalf (N=45) of migrants had post high school education,compared to 76% (N=68) of Japanese. By occupation,only 14.4% (N=15) were skilled workers in themigrants, on the contrary, the Japanese were predom-inantly skilled workers (86.6%, N=71). Only 12%(N=14) of migrant subjects were insured, while 99%(N=105) of the Japanese subjects were insured. As forthe self-perceived oral health status, 51% (N=60) ofmigrants answered “good”, on the other hand 74% ofJapanese subjects answered that their oral healthwas “poor”. There was no apparent difference on thereason for initial visit (preventive or symptomatic)between the two groups. During the previous oneyear, the migrants visited dental facilities less fre-quently than Japanese. More than 90% (N=107) of themigrants brushed more than 2 times in a day, while theJapanese were more floss users.

Regarding the mean OHSI score, it was 78.56 for themigrant group and 83.16 for the Japanese group. TheOHSI of migrants was significantly lower than that ofJapanese (p＜0.01).

In the comparison of the mean OHSI scores by age,the migrants had significantly lower OHSI scores thanJapanese in all except 55 years and over age group.The OHSI scores tended to become lower withincreasing age in both the migrant (p＜0.01) andJapanese (p＜0.001) groups. By occupation, skilledworkers had the better OHSI scores than unskilledworkers in both groups. Perceived oral health was pos-itively associated with OHSI scores, and the migrantshad significantly lower OHSI scores than theJapanese. The OHSI scores of the subjects who per-ceived their health as “good” were significantly higherthan those perceived their health as “poor” in both themigrants (p＜0.01) and Japanese (p＜0.001). As to thereason for initial visit (preventive or symptomatic),patients for preventive visit had the significantly betterOHSI score than symptomatic patients in bothgroups.

Table 5 presents the standardized regression coeffi-cients and adjusted R-square for demographic andbehavioral variables on the OHSI in the multipleregression analysis. First, all demographic and behav-ioral variables were added as independent variables inthe regression model. Since the variance inflation fac-tors (VIFs) of acculturation, insurance and occupationstatus were larger than 10, these variables wereassumed to be collinear with respect to other indepen-dent variables and add no new information to theregression. Thereby these variables were excluded

from the regression model. The OHSI was positivelycorrelated with subjects’ status (migrant orJapanese), perceived oral health, reason for initialvisit (preventive or symptomatic) and flossing behavior,and negatively correlated with age. This combination ofthese demographic and behavioral variablesexplained 33.4% of the variance in the regression ofOHSI.

Discussion

In this study, the oral health status of migrant subjectswas worse than that of Japanese even though themigrants were younger than Japanese. Furthermore,the migrant sample had a higher DT and a worse peri-odontal health condition, compared with Japanese.These results suggest migrant subjects don’t receivenecessary dental treatment and take care of theirdental health less than Japanese. From the quality oflife viewpoint, therefore the oral health status inJapanese is highly appraised in comparison with that ofmigrants. The OHSI considers a filled tooth to bequantitatively identical to a healthy tooth, thereby theindex would reflect the difference of oral health-relatedquality of life between migrants and Japanese more.Perceived oral health status was positively correlatedwith the OHSI, which result suggested that the subjectswho thought their dental health as “good,” in fact, hadfavorable oral health conditions. Oral health is difficult todefine in operational terms such as DMFT, but the

31COMPARISON OF ORAL HEALTH STATUS IN MIGRANTS/JAPANESE

Table 5. Standardized regression coefficients fordemographic and behavioral variables on OHSI

approach of OHSI is unique and interesting24. In dailylife, people think of filled teeth as sound, healthy teeththat are both cosmetically and functionally accept-able, and the OHSI was developed based on this con-cept. Judging from the dental professional viewpoint,the filled teeth could be regarded as sound teeth clini-cally and functionally. Hence the OHSI is considered asa comprehensive indicator.

In this study, more than half of migrants reported theirperceived oral health as “good.” Besides the migrantsubjects were relatively younger, the cultural differenceamong countries may influence on their self-perceptionof oral health status. In addition, reason for initial visitand flossing behavior were significant contributors ofthe oral health status in this study.

Given these results, the poor oral health status ofmigrants deserves consideration. Floss users areconsidered to have a better oral health status14, but35% of migrants were floss users. Dissemination ofdental floss in migrant society may be one of the effec-tive strategies to promote a better oral health. Oralhealth care-seeking behavior might influence the oralhealth status such as the number of decayed teeth andperiodontal status. Most of the migrants were of lowacculturation. To provide migrants equal opportunity inaccess to oral health care in Japan, the present publicsupport system for foreign patients should be modified.Most migrants are unskilled works such as factorylabors and construction workers, whose oral health sta-tus is worse than that of skilled workers. This fact alsoimplicates that many of them are engaged in illegalemployment and probably make an effort to survive insevere condition, like low wage and over-night duty,possibly without vacation.

Japan is a racially homogeneous nation and themigrants without valid status are difficult to reside. As tohealth insurance, 99% of Japanese subjects joined thenational health insurance that includes dental cares, onthe contrary, only 11.9% of migrants joined the insur-ance. Migrants who have valid visas less than one yearare denied to join the public insurance schemes,except for particularly humanity cases, and this mayexplain the lower percentage of insured migrants10.Under the current systems, foreigners can not receivethe public welfare services even if they want to.

The skewness of the sample may be a pitfall of thisstudy, since the subjects of this study were the newpatients of one clinic. This study, however, gives us aninsight to reveal that migrants in Japan are underservedcompared with Japanese.

In conclusion, the oral health status of migrants was

worse than that of Japanese even though they wereyounger than Japanese. The present public supportsystem for foreign patients and their self-care factorswere considered to be contributors for the unequal oralhealth status.

Acknowledgements

We acknowledge the contributions of the members inthe Dept. of Oral Health Promotion at the TokyoMedical and Dental University. We are also grateful toProf. F.A.C. Wright, who provided fruitful academicadvice. We acknowledge the contribution ofMinatomachi Medical Center, Kanagawa Workers’Medical Cooperative. We acknowledge the contribu-tions of Dr. Marvin Marcus and Dr. John Yamamoto ofthe Division of Public Health and CommunityDentistry and the International Center for DentalHealth Policy at the UCLA School of Dentistry for theirguidance in the interpretation of the OHSI.

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