Impact of social support on oral health among immigrants and ethnic minorities: A systematic review

Objective Adaptation to social life changes after migration may be beneficial or detrimental to migrants’ oral health outcomes and related behaviors. This systematic review aims to synthesize the scientific literature on the impact of social support on immigrants’ and ethnic minorities’ oral health status and/or behaviors. Methods A comprehensive electronic search, up to November 2018, was conducted using five electronic databases. We included cross-sectional and longitudinal quantitative studies that examine associations between social support and oral health outcomes among immigrants and ethnic minorities. Study selection, data extraction, and risk of bias assessment were completed in duplicate and the Newcastle-Ottawa checklist was used to appraise the methodological quality of the quantitative studies. Results A total of 26 studies met the eligibility criteria. Included studies examined multiple oral health outcomes such as dental care utilization, oral health behaviors, oral health problems, self-rated oral health, oral health knowledge, and oral health-related quality of life among immigrants and ethnic minorities. The social support level is assessed either by social support indicators or by adapting certain scales. Overall, social support was found to be positively associated with dental care utilization, number of carious teeth, periodontal disease, oral health behaviors, oral health knowledge, oral health-related quality of life, and self-rated oral health. Conclusion Although immigrants and ethnic minorities encounter several challenges after migration to a new country that could affect their oral health, social support from their surrounding environment in the form of structural or functional support plays an important role in improving their oral health outcomes.


Introduction
Post-migration challenges, including language and cultural barriers, housing, employment, poverty, and lack of medical and dental insurance, may affect immigrants' and ethnic minorities' general and oral health [1,2,3]. Additionally, social life changes such as a decreased number of close family members and friends may lead to isolation and loneliness among immigrants and ethnic minorities [1,2], which can consequently affect immigrants' health and social life negatively due to the adoption of detrimental habits as coping methods [2,3]. Therefore, the level of social support within the host country plays a crucial role in general and oral health outcomes among ethnic minorities.
Migration is a social determinant of health including oral health [4]. A higher level of dental diseases and underutilization of dental care have been reported among immigrants as compared to their native-born counterparts [5,6], specially among those who had lived in the host country for less than 10 years [7,8]. In addition, while many native-born children see dentists for preventive purposes, immigrants receive less preventative services and more treatments [9]. Therefore, disparities in oral health among immigrants is a serious public health matter that should not be neglected.
Social support has been defined variously as support "provided by other people [that] arises within the context of interpersonal relationships" [10,11] and support which is "accessible to an individual through social ties to other individuals, groups, and the larger community" [11,12]. Moreover, social support was defined as the social resources that people perceive to be available to them or that are actually offered either by formal support groups or informal relationships. [13] Therefore, social support can be perceived or received. The received social support is the actual support received by individuals. [14] While the perceived social support is "The individual's beliefs about the availability of varied types of support from network associates". [14] House and Cobb [15,16] divided the notion of social support into four distinct types-emotional, instrumental, informational and appraisal; this approach has been widely adopted by many researchers as a method for measuring social support levels [11,15,16]. Social support can also be defined by applying the two broad categories of structural and functional measures [17]. The structural measures of social support include elements such as strength of social connections, frequency of social contact, and size and characteristics of a social network. [17][18][19] The functional measures of social support are further divided into four components: 1) emotional/moral support, which involves expressions of empathy, love, trust and care from family members and friends; 2) instrumental support, which provides services such as transportation or financial assistance; 3) informational support, which provides information and suggestions that help with problem solving; and 4) appraisal support, which provides self-evaluation, affirmation, and feedback [17][18][19].
In attempting to find associations between social support and general health, a number of studies discovered that social support was positively associated with mental health, heart attack survival, cancer reoccurrence, psychological problems as depression, and subjective well-being in breast cancer patients [3,[20][21][22][23]. Similar correlations have been reported in oral health. Dental care utilization among Latino immigrants' children increased remarkably when social support was provided by family members or friends in different forms, such as booking an appointment (instrumental aid and influence), getting to the dentist (material aid), and accompanying them to the appointment (emotional aid) [18]. However, the provision of dental care information (instrumental aid) to Latino mothers by dentists or health care providers was not significantly associated with frequency of dental visits in children [18]. Social support provided by family members and friends was also a significant factor in receiving dental care among elderly Chinese immigrants living in the United States [24].
To the best of our knowledge, there is no systematic review that synthesize the existing evidence on associations between social support and oral health. Therefore, the purpose of the present report is to systematically review the available scientific literature on the impact of social support on immigrant and ethnic minorities' oral health outcomes.

Protocol and registration
The systematic review protocol was registered at PROSPERO (registration number CRD42018095199; http://www.crd.york.ac.uk/prospero/), and the review has been conducted and reported in accordance with the Cochrane Handbook [25] and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statements for reporting systematic reviews of health sciences [26].

Eligibility criteria
We included cross-sectional and longitudinal quantitative studies that met the following predefined inclusion criteria: 1) examined the associations between social support and at least one oral health problem (such as dental caries, periodontal disease, self-reported oral pain, denture problems, sore or bleeding gums, and dry mouth) or oral health behaviors (such as dental care utilization, brushing, flossing, or diet); 2) included a clearly-defined measure of social support and a well-described assessment tool for oral health status or behaviors; and 3) were conducted with at least one immigrant or ethnic group; a group of people of a particular race or nationality, who have different ethnicity or culture from that of the majority in a certain country. Excluded from this study were literature reviews, conference abstracts, and editorials. No restrictions were applied on age, sex, or socioeconomic status.  Table 1). The search strategy was developed with the assistance of a specialized health sciences librarian at the University of Alberta, Edmonton, Canada. The search terms included the following: "oral health", "dental health", "dentist"," periodontal disease", "tooth diseases", "dental caries", "immigrant", "ethnic groups", "immigration", "social support", "social network", "social relationships", "social integration", "social connectedness", and "social tie". Table 1 provides details on the specific search terms and combinations used in each individual database. Manual screening was completed by searching through bibliographies and reference lists of the included papers to determine   (MH "Dental Caries") OR (MH "Oral Health (Omaha)") OR (MH "Oral Health (Iowa NOC)") OR (MH "Oral Health") OR "dental health OR oral health OR dentist � OR periodontal disease � OR tooth disease � OR dental caries OR caries OR tooth decay" AND (MH "Emigration and Immigration") OR (MH "Immigrants+") OR (MH "Ethnic Groups+") OR "emigrant � OR immigrant � OR emigration OR immigration OR transient � OR migrant � OR ethnic group � " OR (MH "Minority Groups") AND (MH "Social Support (Iowa NOC)") OR (MH "Social Networks") OR (MH "Social Networking") OR (MH "Social Involvement (Iowa NOC)") OR (MH "Social Interaction Skills (Iowa NOC)") OR (MH "Social Interaction (Iowa NOC)+") OR "Social Support � OR Social Networking � OR social network � OR Social relationship � OR social tie � OR Interpersonal Relation � OR social engagement � OR social integration � OR social connectedness OR social support network � " Final 3355 potential papers that were not found in the electronic search. Finally, a grey literature search was conducted by using the Google Scholar and Google search engines. All references resulting from the searches were exported to EndNote X8.2, and within this program, duplicates were electronically removed.

Study selection
Two reviewers (RD and EG) independently screened the list of titles and abstracts to identify potentially relevant papers based on the inclusion criteria. If the abstracts were judged to contain insufficient information, the full articles were reviewed to decide whether or not they should be included based on the selection criteria. When a discrepancy in the selection decision occurred, the two reviewers discussed how to deal with the discrepancy until a consensus was reached.

Data extraction and data items
Two reviewers (RD and EG) independently extracted data from the selected papers on the following items: host country, participants' origins and ages, sampling, sample size, type of study, social support measure, association with oral health outcomes, and results. Inconsistencies were discussed and resolved between the two authors. Missing or unclear information was sought from the authors of the selected papers.

Risk of bias in individual studies
Two reviewers (RD and EG) independently assessed the methodological quality of the selected studies by using the Newcastle-Ottawa Scale [25] for cohort and cross-sectional studies, by scoring the three main categories of group selection (four items), comparability (one item), and outcome (two items) [27]. A study was awarded a maximum of five stars for selection, a maximum of two stars for group comparability, and a maximum of three stars for outcome categories. The highest methodological quality was indicated by the maximum score (10 points). Studies scoring less than 3 were considered low quality, while those scoring between 3 and 8 were considered medium quality and those above 8 were considered high quality. Although the NOS is an easy-to-apply and adaptable tool, it has some limitations in that there is no manual tool to use as a guide and it is not validated for cross-sectional studies [28,29].

Synthesis of results
Due to the heterogeneity of the included studies, the findings were evaluated in a descriptive manner. It was not possible to conduct a meta-analysis.

Study selection
The electronic search of five databases resulted in 3,535 studies. Of these, 329 were found eligible for a full-text review and 18 met our inclusion criteria. With an additional 8 studies found by manual screening, a total of 26 studies were included in our review. The selection process of the included papers is presented in Fig 1.

Study characteristics
All 26 of the included studies were quantitative (22 were cross-sectional, 3 were cohort, and 1 was case-control) and all were written in English. Of these studies, 19 studies were conducted Impact of social support on oral health among immigrants and ethnic minorities: A systematic review in the United States and 7 were conducted in other countries, including Canada, Israel, Netherlands, Germany, Sweden, and China. The characteristics of the studies are presented in Table 2.
Next, multivariate analysis was applied among the included studies to determine the association between social support, oral health status/behavior, and controlling factors. Twenty studies used multivariate logistic regression [2, 18, 24, 31, 35-44, 46, 48, 49, 51, 53, 54], while other studies used multiple linear regression [30,51]], binominal logistic regression [32], negative binominal regression [46], hierarchical linear models [50], and hierarchical block design in multivariate analyses [52]. A generalized estimating equation approach was used by one study to estimate the probability of reporting dental problems among immigrants, taking into consideration individual heterogeneity and controlling for the individual stock of independent variables [56]. In addition, one study applied structural equation modelling, which is a statistical technique that integrates factor analysis and multiple regression analysis and permits the simultaneous testing of inter-relationships among a number of potentially interdependent variables [34].

Social support and oral health
Dental care utilization. The association between social support and dental care utilization was the most addressed oral health related factor among the included studies. Fifteen studies (58%) determined the effect of social support on dental care utilization [2,18,24,31,32,39,43,46,48,49,[52][53][54][55]57]. Immigrants and ethnic minorities who were socially integrated into a large network and received social support from individuals around them had visited the dental office in the past 1-2 years for treatment and preventive purposes [2,24,31,32,39,43,45,48,49,54,55,57]. In addition, mothers who were part of a social network and had received social support reported taking their children to the dentist for treatment and preventive appointments more frequently (starting from a young age) compared with children whose mothers had not received any form of social support [18,43]. In particular, functional support that was provided to mothers by family members or friends in the form of instrumental, influential, emotional and material aid was strongly associated with dental care use [18]. In contrast, children's dental care utilization was not affected by social support (specifically, instrumental support) that was offered by dental clinics or hospitals [18]. While financial support was positively associated with dental visits, emotional support was not in one study [39]. Another study, immigrants who received financial support were less likely to have visited a dentist [32] and 2 studies reported no significant correlation between dental care utilization and level of social support in two of the studies [52,53].  OHRQoL.
(Continued ) Six network characteristics were examined: Network size; Network closeness; Influence of network norms on dental behavior; Strength of the alters may exert on egos in terms of oral health helpseeking; Participants report the amount they talk with alters about dental issues; 48 The extent to which networks "push" egos to respond to dental problems Oral health problems. Oral health problems, including dental caries and periodontal disease, were addressed by eleven studies [30, 34-37, 48, 50-53, 56]. One study assessed oral health problems from a broader perspective by investigating the effect of social support on participants' self-reports of oral pain, denture problems, sore or bleeding gums, and dry mouth [30]. The findings showed that social integration was positively associated with fewer of these problems, while social network size did not attain statistical significance [30]. However, in another study, social support was reported to be associated with a high rate of dental problems [56].
The association between periodontal health and social support was reported by two studies [48,51]. Although having a large social network was inversely associated with periodontal attachment loss [48], social support (including emotional support) was not significantly related to the extent of periodontal disease [48,51].
Nine studies examined the relationship between social support and dental caries [34-37, 50-53, 57]. The effect of a high level of social support was associated with a reduced number of teeth with dental caries; this included adults as well as children, the latter who received social support indirectly through their parents' social support [34,35,50,51,57]. Emotional and instrumental support were significantly associated with a lower number of carious teeth [50]. Surprisingly, domestic Indonesian helpers who were living in Hong Kong with their family members had increased prevalence of dental caries [37] and social support was not significantly related to the number of carious teeth in another two studies [52,53].

Self-rated oral health and oral health-related quality of life.
The association between social support and self-rated oral health was assessed by four studies [30,40,52,56]. Social integration and having a high number of close friends or family members had a significant impact on immigrants' and ethnic minorities' self-rated oral health [30,40,52,56]. Furthermore, two studies examined the relationship between oral health-related quality of life (OHR-QoL) and social support (specifically, emotional and financial support) [42,44]. Interestingly, neither study showed any significant association between emotional support and OHRQoL [42,44], whereas financial support was positively associated with OHRQoL scores [44].
Oral health knowledge and behaviors. Two studies reported that immigrants and ethnic minorities who had a large network and more frequent discussions were more knowledgeable about dental care services and oral health knowledge, which consequently led to increased dental care utilization [45,54]. In addition, three studies investigated the association between social support and oral health behaviors [34,35,41]. They found that children of families who had a strong social network that they could rely on (such as relatives or friends) had more favorable oral hygiene behaviors such as brushing at an early age [35]. In contrast, poor social support was indirectly related to poor oral health behaviors due to parents' low level of education or individuals with low self-esteem [34,41].

Risk of bias in the included studies
Overall, the studies included in this systematic review attained medium to high methodological quality according to the grading method used [25,54]. Table 3 presents the quality assessment of the included papers.

Discussion
Social life changes after migration play a crucial role in immigrants' and ethnic minorities' health, including their oral health. Therefore, this paper has systematically reviewed the literature on the associations between social support and oral health outcomes among this population, finding positive associations. Immigrants and ethnic minorities who experience social support either from their close surroundings (e.g., family members and friends) or from greater society had increased dental care utilization and improved oral health status, including caries level and periodontal disease. In addition, social support had a positive influence on self-rated oral health and oral health-related quality of life. Immigrants and ethnic minorities with strong social ties were also more knowledgeable about oral health and oral health care.
Increased dental care utilization among different ethnic groups was the most noticeable dental-related change as a result of social support [30]. In addition, social support promoted medical care utilization, physician contact, mental health services, and formal home care services among the elderly from different ethnicities [58][59][60][61]. Having a large network was also associated with ethnic minorities' pediatric medical care utilization [62]. A possible explanation is that the process of care-seeking may be influenced by different types of functional support [32]. For instance, through informational and instrumental supports, individuals will receive health information and help with booking doctors' appointments and transportation [18].
Surprisingly, less frequent dental care utilization was seen among some immigrants who received financial support [32]. Perhaps individuals who are eligible for financial assistance are   more financially distressed and therefore feel they need to spend the received money on housing and education rather than on dental or health problems [32]. Another explanation for reduced health care utilization might be that individuals who receive tangible support may lead to lower self-esteem and low responsibility with a high sense of dependency, which can result in less favorable health behaviors like visiting a dentist [32]. Interestingly, not only was increased social support positively associated with health care utilization, but lack of social support and feelings of loneliness also resulted in seeking health care for more interaction and socialization rather than the need for treatment among individuals from different ethnic groups [62][63][64][65][66].
The positive effect of social support was not only improvement in adults' oral health but also improvement in children's oral health indirectly through their parents, especially the mothers. Aspects such as increased dental care utilization, better adaptation to positive oral health behaviors, and decreased dental caries levels among children could be a reflection of increased opportunities and resources for mothers to receive help from their surrounding individuals and to access more information about oral health and oral health care services [67]. Furthermore, mothers who are socially integrated are more capable of making relationships with not only friends and relatives, but also professionals and community resources, which in turn can contribute to a more positive impact on their children's oral health [67].
Although social support was positively related to oral health outcomes in the included studies, one study reported a higher caries rate among Indonesian helpers in Hong Kong who had Impact of social support on oral health among immigrants and ethnic minorities: A systematic review been surrounded by family members [37]. As well, living for a longer time in a host country was associated with a high rate of dental problems [51,56]. These problems may occur due to a variety of factors, including financial problems [68]. Additionally, it is possible that immigrants' stressful changes that result from resettlement after migration may promote negative oral health behaviors, which consequently lead to increased dental problems through consumption of a sugary diet [69]. Facing psychological stresses (e.g., discrimination) in the host country could also be associated with poor oral health [51,56]. Another explanation is that immigrants who come from a country where poverty is common may simply be more susceptible to poor oral health [37]. Four studies explicitly compared between immigrant and non-immigrant populations on the impact of social support on oral health [31,34,35,42]. Immigrants had lower level of social support compared to their counterparts and were 36% lower than non-immigrants in utilizing dental care utilization [31]. Moreover, being an immigrant child was associated with increased possibility of being part of a family receiving less social support [35]. In contrast, oral health related quality of life was reported better among non-US born when compared to US born participants [42]. However, in another study, no clear comparison was reported between immigrants and non immigrants [34]. These contradictory findings may be explained partially by the differences in predisposing factors, including sex, age, socioeconomic status, and marital status, and in enabling factors, such as type oh dental coverage, social support, place of resident, and type of residents [31,[70][71][72][73]. Furthermore, the level of social support act as a mediator to oral health outcomes [35,42].
These associations between social support and oral health-related changes may be due to variations among ethnic groups in their adaptation toward social life changes after migration. For example, African Americans tended to have better social integration than Indian Americans or Whites [30], while older Chinese immigrants had more social interaction and were more frequently visited by their friends than did older Russian immigrants [24]. These variances may be due to some cultural background differences, the size of certain communities, or limited opportunity to participate in larger social events. Social support also varies among individuals based on their interpersonal characteristics, such as age, sex, socioeconomic status, cultural differences and type or stage of a disease, all of which may have an impact on health comes [74].
In measuring social support among the included studies, it was clear that there was a lack of attention paid to the multi-dimensional concept of social support [75]. Of the reviewed studies, 58% used unidimensional measures, such as number of close family members and friends, network closeness, marital status, social integration, frequency of visiting friends and relatives, perceived help and trust, and financial and emotional support. Other included studies (42%) adopted certain scales to measure social support [18, 31, 34, 35, 40-43, 45, 51, 55], some of which were validated tools, such as the Social Support scale for immigrants from Israel [51], the Medical Outcomes Study Social Support Survey (MOS-SSS) [42], and five NHANES variables [39].
Some of these scales were modified from original ones. [38,40,51] As an example, only three items from the original Lubben's Social Network Scale was used, which has 6-or 12item scales, and demonstrated an internal consistency (α = .75) among the included sample, which was satisfactory. [40] Furthermore, the Gezinsvragenlijst (GVL, translation; Family Questionnaire) that was used by several psychometric studies among large representative sample of the Dutch population to measure perceived social support was reported to be internally consistent (α = 0.83 to 0.95) and reliable over a period of 3-4 week. [35,76] Six of the adopted scales assessed the perceived social support and four measured actual or received social support. Structural support was assessed by two of these scales and functional support by one. In addition to using unidimensional measures, some researchers tended to use general instruments to measure the construct without any specifications regarding a certain population or measuring a certain dimension of social support [75,77,78]. However, overreliance on unidimensional measures that make no distinction between different components of social support, structural and functional will lead to an incomplete assessment of social support [17,75,[77][78][79].
The quality of the reviewed studies ranged from medium to high according to their total score based on the number of stars each study gained for sample and measurement tool selection, group compatibility, and outcome assessment. Study scores less than 3 were considered low quality, between 3 and 8 were medium quality and those above 8 were high quality. For example, a study conducted among the children of Latino immigrants to assess the association between dental care utilization and social support was considered medium quality due to issues such as non-random sampling, unjustified sample size, or lack of description of the response rate or responders'/non-responders' characteristics [18]. In contrast, another study investigated the influence of psychological distress and social support on Ethiopian immigrants' oral health. This study attained a high quality level, since the sample size was justified and satisfactory, a validated measurement social support tool was utilized, the study controlled for different factors, the oral health outcomes were assessed independently through dental examination, the statistical test was clearly described and appropriate, and the measurement of the association was presented, including confidence intervals and the probability level (p-value) [51]. The majority of the included studies were of medium quality due to the application of a non-validated social support measurement tool and self-reported oral health status/behaviors. This review had some limitations that should be noted. We included studies that were conducted among immigrants and ethnic groups based on their reported definitions and main categories because it was difficult to differentiate between these two categories with hindsight [80]. In addition, the impact of social support on oral health may vary among these 2 groups due to the diversity at the individual and social level. Reasons for migration, origin and host countries, timing of migration within political, social environment, and individual life stage are examples of the. Therefore, it would be difficult, if not impossible, to include all these variables for analysis in one systematic review. Although there are some limitations in the quality appraisal tool used in this review, no validated methodological assessment tool has been designed specifically for observational studies.

Conclusion
In this systematic review, the most addressed oral health outcomes among immigrants and ethnic minorities were dental care utilization (15 studies) and dental caries (9 studies). Social support was positively associated with dental care utilization in 13 studies and with dental caries in all 9 studies. Although, a lower number of studies investigated the associations between social support and periodontal disease, self-rated oral health, oral health-related quality of life, oral health knowledge, and oral health behaviors, the majority of them reported a relatively positive correlation. Further studies are needed, especially longitudinal and qualitative studies, to explore the detailed effect of social support on oral health by using validated multidimensional scales that are designed to address this association among certain population with the distinction between the functional and structural components to generate more comprehensive and comparable findings.
Supporting information S1