This paper documents the development of oral health-related behaviors and their sociodemographic distribution across time focusing on a non-occidental study population. Methodological strengths of the present study include the large sample size, the availability of comparable survey instruments, the sampling strategies and methods of data collection, and also, the diverse nature of the various oral health-related behaviors. A repeat cross-sectional survey, with the same target population and sampling frame, is the most appropriate and straightforward design for providing a series of survey estimates by which changes in a population can be monitored over periods of time [17]. Trend studies of oral health-related behaviors, using a repeat cross-sectional design, have previously been reported mainly from the developed countries [18]. This study design, although scientifically less rigorous than that of longitudinal studies, has been widely advocated by the United Nations, particularly in countries with limited resources [19]. In the present study, data were gathered at different points in time from the same population, but not from the same individuals. Whereas a census survey was conducted in 2001, as intended, the analyzed data represent 64% of the intended sample in 1999. Lack of information about non-respondents precludes any conclusion about a possible selection bias, although the response rates seem to be high enough to ensure that the target population is reflected with a reasonable degree of accuracy. However, these estimates call for careful interpretation as the observed change may be due to differences between the samples rather than representing a true change in the population of MUCHS students.
The findings of the two surveys confirm that self-reported snacking of sugared food and drinks and dental attendance behavior were highest among females, higher degree students, and students of urban origin, thus corroborating previous studies of community populations in sub-Saharan African countries [4, 9, 10]. The present findings related to consumption of commercialized sugar products are in contrast to those reported from industrialized countries where the highest prevalence of sugar consumption has been observed among males and individuals of lower socioeconomic status [18]. Previous research in both occidental and non-occidental populations has, however, demonstrated positive associations between reported self-care practices (e.g., going for dental checkups) and socioeconomic status, with the more affluent behaving more healthily than the less affluent [4, 18, 20]. In Tanzania, the cost-sharing policy implemented to ensure equity in access to modern health care services has not yet introduced user fees for services delivered by government-run oral health clinics [21]. Since the government's health facilities are known to have shortages of drugs and other essential equipment, many seek care from private facilities where charges for services are high and there is no exemption system [22]. Although university students have access to a free dental service at the MUCHS, we found that students of rural origin were less likely to visit dentists than were their urban counterparts. It is possible that students from a rural background and lower socioeconomic status were less likely to go for regular dental checkups because they could not afford to pay for the private care services. Consistent with other studies conducted in sub-Saharan Africa, more females than males reported abstinence from smoking across both survey years [4, 12]. One reason may be that the Tanzanian society still frowns upon tobacco use among women. This contrasts with the recent trends being reported from developed countries, where females are more frequent, and heavier, smokers than males [23, 24].
The two data sets from two surveys allowed us to examine changes that had taken place between 1999 and 2001. The results point to a general increase in the consumption of commercialized sugar products (e.g., Coca-Cola), whereas a commensurate decrease appears to have occurred with respect to the more traditional habit of taking sugar in coffee and tea. Interestingly, the regional differences in soft drink consumption, with urban students taking more soft drinks on a weekly basis than rural students, decreased markedly across the survey period. There was in fact a more pronounced increase in soft drink consumption among students raised in rural areas than among students from an urban background. Second-order effects from multiple logistic regression analyses revealed that the age differences in soft drink consumption changed from 1999 to 2001, with younger (19–25-year-old) students being the most frequent consumers in 1999 and older students (>25 years) being the most frequent consumers in 2001. Stratified analyses revealed this to be primarily a consequence of a pronounced increase in soft drink consumption among the older students. Contemporary consumption of commercialized sugar products is recognized to be closely associated with Western lifestyles, portrayed through the mass media and demonstrated in practice by acculturated segments of the Tanzanian population. Evidently, soft drink consumption is already established and is still on the increase among university students in Tanzania. The pronounced increase among students above 25 years old and students of rural origin may be interpreted as diffusion from higher to lower socioeconomic strata within this particular segment of the Tanzanian population [15]. Contrary to what could be expected from an economic transitional point of view, the present analysis points to a general increase in reported total abstinence from tobacco use between 1999 to 2001.
The observed trend of an increase in oral hygiene measures and abstinence from tobacco among both sexes would suggest that the oral health education program in Tanzania's media is effective. This program targets mainly the urban population, of which university students constitute an important part. The finding that women are less likely than men to be informed by the mass media due to the Tanzanian sociocultural context [25] was not supported by the present study. Our finding and the observed decline in the social disparity between students of higher and lower degree with regard to dental checkup patterns between 1999 and 2001, corroborates the WHO target to achieve reduction in health inequalities between groups within countries by the year 2000 [26].
Since the present results rely on self-reported data, the rates of oral health behaviors may be biased through over- and underreporting due to social desirability and poor recall effects. Nevertheless, test-retest reliability of the oral health-related behaviors was examined in 1999 and found to be satisfactory [27]. There is no reason to suspect changes in the accuracy of self-reported oral health behaviors across the survey period. Given this, the reported change, and lack of change, in students' oral health-related behaviors is likely to be reasonably accurate.
In summary, the present analysis suggests an increasing trend in the proportion of Tanzanian university students reporting abstinence from tobacco products, weekly consumption of commercialized sugar products, and implementation of oral hygiene measures from 1999 to 2001. Across the survey period, a decline was seen in the social disparity with regard to soft drink consumption (urban-rural) and dental checkup (educational level) patterns. In spite of some compatibility problems, this study represents the first opportunity to approach trends in a subnational population of Tanzanian adults. A third data collection will be necessary in 4–5 years' time to generate more conclusive trend data for use by health workers and policy makers in planning preventive oral health programs.
