Socio-demographic disparity in oral health among the poor: a cross sectional study of early adolescents in Kilwa district, Tanzania

Social disparities in health- and oral health outcomes as measured by education, occupation, income and household assets or by indices derived by combining indicators constitute one of the main challenges for public health [1, 2]. Contemporary evidence suggest that the lower the material standard of living, the worse the health status irrespective of the measure (being it clinically assessed or self reported) used to assess it [1‐4]. Compared to adult populations, social disparities in health- and oral health among children and adolescents have received relatively little attention [5]. Torsheim et al. [4] observed substantial inequalities in adolescents' self-reported health status related to the distribution of family material resources across European- and North American countries. A pattern of poorer health was demonstrated among populations for whom family material resources were distributed less evenly. Recognizing oral health to be an integral part of general health, recent studies suggest a social gradient in oral health, with the magnitude of inequality being larger in some countries than in others [3, 6, 7]. The WHO International Collaborative studies (ICS-I or II), have demonstrated a social gradient in adolescents' caries experience across high-and low income countries and various oral health care systems [8]. Social- and behavioral inequality in dental caries and periodontal diseases has also been identified in comparative studies from sub Saharan Africa, South East Asian countries and Chile [8, 9]. Moreover, social disparities in adolescents' oral health behavior have been demonstrated in developing countries and elsewhere, with oral health detrimental behaviors being most common in subjects of lower socio-demographic status [10‐12]. Yet, mixed evidence exists with some studies reporting social disparity in adolescents' caries experience whereas others do not [5].

It is assumed that inequality has multiple causes and that the effect on oral health of socio-economic and demographic factors is mediated through environmental exposure, psychosocial factors, lifestyle and availability of health care services [13]. Petersen [8] presented a risk factor model for dental caries, suggesting that socio-environmental factors influence behavioral- and attitudinal factors which in turn impact on clinical- and subjective oral health outcomes. Socio-demographic factors, such as place of residence, age, gender, family income and education and individual factors in terms of oral health behaviors might influence oral health outcomes. Moreover, socio-demographic factors might influence oral health outcomes directly or indirectly through oral health related behaviors. Evaluating the mediating role of oral health behavior among adults in Australia, Sanders et al, [14] found that the slope of the socio-economic gradient in the Oral Health Impact Profile (OHIP 14) scores was significantly attenuated by dental visiting. Analyzing data from the 1998 Adult Dental Health Survey in the UK, Donaldson et al[15] concluded that the socio-economic gradient in the number of sound teeth was partially explained by dental attendance patterns. Sabbah et al[3] analyzed data from the US Third National Health and Nutrition Examination Survey focusing adults above 17 yrs and found attenuation of socio-economic disparities in oral health status after adjusting for various oral health related behaviors. Recent studies among US adolescents revealed that socio-economic disparities in caries experience could not be accounted for by similar disparities in oral health behaviors [5].

Tanzania has one of the poorest overall health indicators in the world [16]. Few studies have examined socio-economic disparities in oral health among adolescents in Tanzania where exposure to topical fluorides is inappropriate and where access to oral health care services at the local community level is at best very limited [17, 18]. Improved understanding of this issue might have important policy- and oral health program implications in Tanzania where the oral health policy gives priority to children and adolescents as target groups for health care services. A previous study focusing the same study group as the present one revealed that substantial proportions of Tanzanian adolescents admitted untreated dental caries, reduced oral health related quality of life and treatment needs [19]. This study takes the analysis a step further by exploring the socio-demographic distribution of oral impairment, oral impacts and treatment needs among adolescents in Tanzania.

Focusing early adolescents attending primary school in Kilwa, south -eastern Tanzania, this study aimed to assess socio-demographic disparities in caries experience, treatment need, self-reported oral health status and a number of oral health related behaviors. The extent to which oral health related behaviors accounted for socio-demographic disparities in oral health status was also investigated.

It is important to explore whether social disparities in adults' oral health present also in adolescents and whether the effects of the material distribution are mediated differently in adolescence and adulthood. This study revealed that a social gradient was present with respect to dental caries, treatment need, and reported oral health status as well as sugar intake, tooth brushing, use of fluoridated toothpaste and dental attendance patterns among adolescents in Kilwa, a generally deprived district with limited access to oral health care services. Differences across educational level, household wealth and place of residence groups were statistically significant for most oral health outcomes and oral health behaviors investigated, both in unadjusted and adjusted analyses. The results confirm previous findings in adolescent-and adult populations, globally [1, 10, 12, 26]. Adolescents belonging to the less poor households presented with treatment need and dental attendance more frequently than their counterparts in the poorest households. According to Grytten and Holst [27], several US studies reported a positive association between income and demand for dental care, particularly when treatment need was high. Although dental attendance, oral hygiene behavior and sugar intake varied systematically with oral health outcomes (Table 3), social disparities in caries experience and self reported oral health were not attenuated whilst adjusting for those lifestyle patterns (Table 4). In spite of some attenuation of the relationship between household wealth and treatment need after controlling for dental attendance (OR reduced from 2.6 to 2.2), a direct relationship persisted that was unexplained by adolescent's dental attendance profile. Thus, the present results accord at best partly with findings from industrialized countries, suggesting that unequal access to dental care explains socio-economic disparities in adults' oral health [7, 15, 28]. In contrast to the experience from US, suggesting that children with untreated caries are less likely to obtain regular dental care, the present study indicate that Tanzanian adolescents who had attended a dentists were those with the most severe caries in terms of moderate to high treatment need [29]. This is a common finding in developing countries [30, 31] and might reflect that dental attendance follows from a high treatment need rather than being an unexpected outcome of dental care. It might also reflect delayed treatment demand and limited access to dental care (only one assistant dental officer in Kilwa).

A low caries prevalence of about 20% presented among a minority of the participants is consistent with the caries trends of younger age groups in Tanzania [18, 32, 33]. In accordance with a suggested positive relationship between dental caries and the level of social development, previous studies have provided evidence of a higher caries prevalence in urban than in rural societies [10, 12, 34]. In contrast, the present findings accord to some extent with those observed among Brazilian schoolchildren, where living in a rural area almost doubled the odds of having dental caries [35]. Rural participants showed the highest prevalence of dental caries, but they were less dissatisfied with their oral health and visited a dentist less frequently than their urban counterparts. This is consistent with previous studies of schoolchildren in sub Saharan Africa [12, 36]. Affordability, accessibility and structural barriers reflected by place of residence as a more area based measure of deprivation, have previously been reported to be important reasons for rural dwellers' non-use of dental services in Tanzania [36]. Nevertheless, independent of socio-economic position, students with caries experience and moderate to high need for dental treatment were the most frequent dental attendees suggesting a demand for dental care among young people in Kilwa.

The Lorenz curves presented in this study were based on the participating rural and urban population groups. Each group showed almost similar skewness dominance. Previously polarization mostly has been reported from western industrial populations. Macek et al. [37] described highly skewed caries data from young children, while the caries data from adolescents were more dispersed. However, more recent data of 15-yr-old Danish children collected from the Danish National Board of Health in 2006 [38], were more comparable to the present findings. Seventy-five percent of the total number of DMF-surfaces was found in 13% of Danish 15-yr-old children with the highest DMFS. It is interesting that the caries distribution among adolescents in a poor Tanzanian district is comparable to western industrial populations.

Socio-economic status of parents as assessed in terms of income, education and occupation, might be difficult to assess because of unawareness and unwillingness to reveal such information on the part of the adolescents, resulting in high rates of non responses particularly among lower socio-economic status groups [39]. The present study assessed socioeconomic status using a wealth index based on a weighted sum of self-reported household assets and the more conventional measure of parental education [1, 21]. The wealth index showed good discriminate power against moderate to high need for treatment and oral health related behaviors even in the small, social homogeneous and generally deprived district of Kilwa. It bears similarity to the family affluence scale, FAS, developed as a supplementary measure of socioeconomic status for adolescents by the WHO Collaborative cross national study of Health Behavior in School aged Children [26]. Both the weighted wealth index and the FAS contain items reflecting family expenditure and consumption that are relevant to the family circumstances. In addition, this study used a surrogate area based social indicator of place of residence, as suggested by Locker [1].

The present study contributes to the knowledge of adolescents' oral health situation in deprived areas of Tanzania. However, the present results should be interpreted in the light of limitations that include a cross- sectional design and use of self-reported measures. Some schools in the selected wards were not accessible due to natural calamities in the area at the time of data collection and the number of enrolled standard six adolescents and attendance rates in rural schools were particularly low. Nevertheless, use of an unequal sampling fraction in urban and rural parts of Kilwa was compensated by providing weighted estimates for all oral health outcomes and oral health behaviors investigated. Since the present data rely on self reporting, they might have been biased by under-and over reporting due to socially desirable responses and poor recall effect. However, the core questions utilized in this study have shown a good validity and reliability in previous studies focusing children, adolescents and adults in sub Saharan Africa. The self-reported use of fluoridated toothpaste is questionable as we did not validate whether the toothpaste used contained the recommended free fluoride ions concentration. As it has been reported that toothpaste manufactured and sold in Tanzania has free fluoride concentrations below the recommended levels for prevention of caries [40]. Given that the data collection was conducted in a relatively short period of time, the presence of any temporal changes could hardly have confused the data.

Substantial proportions of adolescents reported oral health detrimental behaviors indicating that there is room for improving oral self care, diet and access to and utilization of dental services among Tanzanian adolescents. In spite of demonstrating strong social disparities across oral health and oral health behaviors, sugar intake, oral hygiene and dental attendance patterns did not explain the socio-economic gradient in oral health status. Developing policies and programs targeting both social structural and individual behavioral determinants of oral health should be an urgent public oral health strategy in Tanzania.