Oral health inequalities in immigrant populations worldwide: a scoping review of dental caries and periodontal disease prevalence | BMC Public Health

Study selection

The initial search with the keywords resulted in 928 papers in Scopus, 116 results in Embase, and 298 results in PubMed (Fig. 1). The authors (SABR and AM) screened the studies by title after the removal of duplicates (n = 379). After the title and abstract screening, 76 studies were left for full-text screening. Data extraction was then performed on 30 articles that met the inclusion criteria. In addition, two papers [21, 22] were retrieved by hand search, so overall 32 studies were included. The studies excluded after the full-text review are listed in appendix (page 4). The list of the included studies sorted by country of study is reported in Table 1.

PRISMA flow diagram of study selection

Quality assessment

No papers were excluded solely based on methodological quality assessment. Despite aiming for high methodological quality studies, we recognized that excluding moderate quality studies could potentially miss valuable insights. Studies with a quality assessment score of 5,or 6 were included, even if they weren’t of the highest quality. Incorporating a broader range of evidence allowed us to gain a more comprehensive understanding of oral health disparities. Studies of moderate quality contribute valuable data and perspectives, and their inclusion helps mitigate publication bias.

Only two studies [34, 51] out of a total of 32 studies, had all the questions of the critical appraisal answered with a “yes”, gaining a score of 9 out of 9. The least favorable scores were given to questions regarding the frame and adequacy of the sample size. The lowest score was five [32, 44, 45] and four studies [25, 29, 38, 43] scored six because there was no description of the sampling frame, participant selection procedures, and sample size calculation. Only thirteen studies reported procedures for calculating sample size or if the sample size was acceptable for the target group. Nineteen studies provided a detailed description of the study’s setting and participants. Four studies [35, 38, 44, 45] failed to indicate the confidence interval (CI) for the mean value. The detailed quality assessment can be found in Appendix (page 3).

Characteristics of included studies

Seventeen studies had a control group [21, 22, 31,32,33,34,35,36,37, 39, 40, 42, 45, 47,48,49,50]. The control groups were the local population of the host country, except for three papers [21, 25, 32] which had a refugee population as a control group.

Among the included papers, three papers [25, 29, 47] assessed the treatment need of immigrants. Ten papers [2, 23, 26,27,28,29, 33, 38, 49, 50] reported the utilization of oral health services. Four papers [27, 30, 38, 48] investigated the dietary factors and two papers measured the household acculturation rate [28, 52]. Two papers studied the oral health status of pregnant immigrant women [40, 49] and two papers [33, 44] only included elderly population. None of the included studies had access to the oral health status of the sample group prior to their immigration.

The study participants were children in twenty-four studies, in two studies both children and adults [40, 41] and in six studies only adults [32, 33, 39, 44, 49, 51] were involved. Immigrants originated from a wide range of countries, with a majority coming from South Asia, Africa, Eastern Europe and Central and South America as listed in Table 1. The frequency and distribution of the geographical location of countries of study are shown in Fig. 2, where it is clearly observable the highest number of studies on immigrants have been conducted in Canada and Spain.

World map showing the host countries, where the studies on the oral health of immigrants have been conducted. The key on the left shows the number of studies per country, with the countries sorted by number of studies (from the highest to the lowest). Countries in which no studies could be found are marked in grey

Dental caries in immigrants

Regarding dentin caries in children, two papers [47, 48] reported higher d₃mft counts compared to other studies included in the review (mean d₃mft > 5), both studies were conducted in Taiwan. The overall d₃mft count (primary dentition) of studies identified was 3.63 (2.47) and for D₃MFT (permanent teeth), it was 1.7 (1.2). Four papers [28, 35, 36, 42] also showed an expanded version of the decayed missing filled teeth (D₃MFT) index with individual components, as seen in Table 2.

Upon comparing the overall caries means of the included studies, untreated dental Caries (D₃T and d₃t) constituted the dominant share of the caries experience (D₃MFT and d₃mft) in immigrant children. While, within their respective control groups, the highest proportion of caries experience was attributed to Filled Teeth (FT and ft).

Among the papers that had the local population as control group, the immigrant children had a higher mean D₃MFT/d₃mft (SD) compared to local children. This difference was significant except for two papers [31, 42], which only showed a significant difference for primary dentition and not the permanent dentition.

There were only three studies [33, 40, 49] reported caries using D₃MFT in adults, suggesting that there is a lack of caries data in immigrant adults. The mean D₃MFT count among immigrant adults was higher than that of the local population. This difference was significant except for two studies [33, 40]. It is important to emphasize that we only reported the statistics generated by the included studies. As regards caries experience, due to the limited number of studies and heterogeneity of study participants in the adult population, the overall mean for caries experience was not calculated.

Caries prevalence and further detail of included papers

The main focus of all included studies was oral health (OH) except for two [21, 25], which also involved general health (GH). Only three studies [21, 42] reported a caries prevalence of below 20% for immigrant children. Caries prevalence in the primary dentition ranged from 22% to 88.7%, and in the permanent dentition from 5.6% to 90.9%. Overall, the caries prevalence, regardless of dentition stage, ranged from 17% to 97.3% among the immigrant population (Table 3).

When comparing the caries prevalence to the local population, the immigrants always had a higher prevalence. Only one study [21] reported a lower caries prevalence than in the control group however, in this instance the control group was a refugee population. Visual comparison of caries prevalence between immigrant groups and their corresponding control groups via bar charts can be found in the appendix (page 5).

Other indices to report caries: DMFS and ICDAS

Five papers [24, 26, 29, 34, 37] reported caries prevalence in other forms using D₃MF at the surface level (D₃MFS) or International Caries Detection and Assessment System (ICDAS). Two papers [26, 29] reported caries using D₃MFS (Table 4). Two papers [24, 34] used the dmfs index derived from the full range of ICDAS scores [53], as a result, their count of caries experience included both enamel and dentine caries since both are recorded by the ICDAS index [54]. Analysis of tooth surfaces found that early caries lesions were especially frequent in age groups 12 and 15, with respective mean values of 1.9(2.1) and 2.4(3.0) [34].

Periodontal Health in immigrants

Nine papers [25, 32, 33, 41, 44, 45, 49,50,51] examined the periodontal health. Four of them [25, 32, 45, 50] focused on children and five [33, 41, 44, 49, 51] on adults. Two paper [33, 44] only included an elderly population and one paper included only pregnant migrant women [49].

Regarding periodontal health in children, the prevalence of gingivitis ranged from 5.1% to 100%, indicating a high variation. In particular, the prevalence of gingivitis was reported as very high in three studies [25, 32, 45], with one paper reporting that almost all children had chronic gingivitis [45] and two papers reporting a prevalence of two thirds [25, 32]. Although gingival inflammation was apparently high from the aforementioned studies, one paper [50] reported a prevalence of gingivitis of 5.1%. Another paper showed a higher prevalence of gingivitis in immigrant children compared to the local population with a margin of 25% [45].

Regarding periodontal health in adults, the prevalence of periodontitis was present in half of the population observed [51], similar was observed in another study [44] which reported two-thirds of participants had periodontitis and a quarter of them were diagnosed with severe periodontitis (gingival pockets of 6 mm or deeper). Based on the Papillary Bleeding Index, a study [33] conducted on elderly immigrants showed a greater prevalence of papillary bleeding compared to their peers (46.3% vs 30.5%).

The one paper that included only pregnant Immigrant women, reported almost all participants had gingivitis, the periodontitis was three times more prevalent in immigrant pregnant women compared to local pregnant women (74.5% vs 22.4%). Moreover, 11% were diagnosed with severe periodontitis compared to only 0.5% in the host population, which showed a huge difference in periodontal health between pregnant migrant women and local pregnant ones [49].

Oral health accessibility

Access to oral health care is an important determinant of oral health status [55]. Unfamiliarity with the dental care delivery system, lack of proper insurance (where relevant) and high costs of dental treatment might make obtaining proper oral care difficult [26].

Eight papers [23, 26,27,28,29, 33, 49, 50] explored the history of dental visits in immigrants, all papers addressed children except for two [33, 49]. Four papers [27, 28, 33, 49] reported, whether the participants have had a dental visit in the last year while others asked about history of dental visit in their lifetime.

When asking immigrants’ children about the history of their last dentist visit, the percentage of children who never visited a dentist in their life, ranged from 52 to 88% (appendix page 6). For adults, there was a significant difference in dental visits between migrants and local women, with 61.1% of migrants never having visited the dentist or visiting less frequently than once a year [49]. Regarding last year dental visit, 88.2% of non-migrant Germans had at least one dental examination, compared to 68.9% of immigrants.