A case-control study of determinants for high and low dental caries prevalence in Nevada youth

By the year 2000, the World Health Organization (WHO) announced the global average goal for dental caries was to be no more than 3 DMFT (decayed, missing, filled teeth) at 12 years of age [1]. Although there has been a significant decline in dental caries prevalence since the early 1970s, oral disease, including caries, remains a major public health challenge [2‐4]. In 2004, most American children reported good oral health, but subsets suffered a higher level of oral disease, primarily children living in poverty and some racial/ethnic minority populations [5]. American children born into poverty have suffered twice as much tooth decay as their more affluent peers and have likely had less access to oral health care [5]. Problems with access to health care result in uninsured children being 2.5 times less likely than insured children to receive dental care and 3 times more likely than insured children to have unmet dental needs [5].

The decayed, missing, and filled teeth (DMFT) index is commonly accepted by the dental community for measuring caries prevalence in the population and has been used repeatedly in the National Health and Nutrition Examination Survey (NHANES) [4]. Over time, a skewed distribution of caries prevalence has developed in many countries, with a significant proportion of 12-year-olds found with high or very high DMFT values even though a proportion is totally caries free [6]. Some suggest that mean DMFT does not accurately reflect this skewed distribution leading to incorrect conclusions that the caries situation for the whole population is under control, while in reality population subgroups still suffer from high caries rates. WHO reported that oral disease, including dental caries, remains a major public health challenge [2]. In the USA, dental caries is the single most common childhood disease, occurring 5 times more frequently than asthma and 7 times more than hay fever [3].

Studies have identified associations between numerous factors and dental caries, supporting agreement that dental caries is a multi-factorial disease modulated by genetics, behavior, and environment [2, 7]. Understanding the influence of demographic variables, such as sex, race, community water fluoridation, environmental smoke, and lifestyle and social conditions will contribute to the development of improved prevention and treatment approaches [2, 4‐6]. Thus, identifying the subpopulations at greatest risk (those presenting with the highest DMFT scores) and discovering the significant correlations of selected factors associated with dental caries prevalence provides the rationale for this study.

The purpose of this study was two-fold. Firstly, to identify the 30% of Nevada Youth assessed during a statewide, school-based oral health screening initiative who presented with the highest DMFT score and compare it with a cohort who were caries free and with comparable national NHANES data. Secondly, to explore the factors associated with caries prevalence among those who presented with the highest DMFT scores compared to the caries-free group.

This study included an equal proportion of males and females (49% male; 51% female), with an approximately equal proportion split between areas with community water fluoridation (46%) and those without community water fluoridation (54%). A majority of the sample was non-Hispanic (62%), non-smokers (80%), and with dental insurance (70%). Table 1 details the demographics between the case and control groups within all select variables. Table 1 also details the mean untreated decay scores (D-Score) and mean DMFT scores of the case group by select variables.

Table 2 compares sex, age group, and race groups of the case group to population data reported in NHANES 1999-2004 [4]. Only the 30% of Nevada adolescents with the highest mean DMFT were compared. A review of the D-Scores and DMFT Indices of this subpopulation reflected a much higher percentage within each comparison group. These data confirmed a skewed distribution of dental caries in this subpopulation.

Significant differences in mean D-scores (untreated decay) were found in seven of the eight variables in the case group (Table 1). The only variable with no significant difference in the mean D-Score was sex. There were significant differences between the case and control groups in mean DMFT Scores on all eight predictor variables.

Chi-Square analysis revealed significant differences between the case and controls in all selected variables (Table 3). The Wald statistic confirmed significance in seven of the eight variables in the bivariate logistic regression between the case and control groups (Table 3). There were no significant differences found in those who smoked and those who did not smoke between the case and control groups. Chi-Square validated the model's goodness-of-fit (χ² = 172.04, p = 0.0009). Odds ratios produced the relative odds of the groups within each factor between the case and controls (Table 3). The strongest contributors were race group (F = 152.78, p < 0.001), increasing age (F = 58.40, p < 0.001), community water fluoridation (F = 57.73, p < 0.001), and applied sealants (F = 52.88, p < 0.001). Odds ratios found that Hispanics with the highest reported mean DMFT scores were more than 2 times (OR = 2.135, CI = 0.29-0.59) more likely than White, Non-Hispanics to have the highest reported mean DMFT. Similarly, Nevada youth between 16 and 19 years of age were more than 2 times (OR = 2.04, CI = 0.41 - 0.59) more likely than those between age 12-15 to be among the adolescents with the highest DMFT score. Those living in areas where there is no community water fluoridation were almost 2 times (OR = 1.98, CI = 0.40-0.59) more likely than those living in communities with fluoridated municipal water supply to be among the highest DMFT scores. Those without sealants are 1 1/2 times (OR = 1.52, CI = 1.59 - 2.25) more likely than those with sealants to present with the highest mean DMFT.

The relative strength of the variables selected was further explored using multivariate logistic regression analysis (Table 4). All eight variables contributed significantly to the final model (F = 458.93, p < 0.001) R² = 0.443). The R² of 0.443 (Adjusted R² = 0.412) indicated approximately 40% of the variables combined contributed to increased DMFT indices. Beta coefficients placed race, age, fluoridation, and applied sealants as the strongest contributors, respectively. Gender, second hand smoke, insurance status, and tobacco were significant, but to a lesser extent.

This study reported caries prevalence between 30% of Nevada youth with the highest DMFT and Nevada youth who are caries free. Both the mean untreated decay score (D-Score) and the mean DMFT index were computed. Results reflect a skewed distribution of caries among those with the highest mean D-Score and mean DMFT on all selected variables. This study confirmed that dental caries remains a common chronic disease among Nevada youth and is especially prevalent among a select subpopulation.

The decade-old global average goal for dental caries to be no more than 3 DMFT (decayed, missing, filled teeth) at 12 years of age [1] was an aspirational goal set by the WHO at a time where it looked like caries would explode in developing as well as developed countries [15]. In many countries the goal was achieved, but oftentimes was replaced by a polarized situation where some had no and some had a significant number of dental caries; thus, the case group presented with a significantly higher prevalence rate in mean DMFT in all select variables, and a greater mean DMFT and mean D-score than the national average (Table 2). Dental professionals should be aware of these factors when developing educational programs, and when designing and implementing prevention strategies

The logistic regression produced significance among all but one of the select variables, smoking status. The strongest contributor was race group. The Nevada Oral Health Screening Initiative recorded race and ethnicity separately. Race and ethnicity were combined into the same groups used in NHANES studies for subsequent comparison (Table 2). When comparing DMFT indices by ethnicity category (non-Hispanic White, non-Hispanic Black, and Hispanic) of the 30% of Nevada youth with the highest DMFT scores with national averages reported in NHANES, the prevalence of the 30% of Nevada youth with the highest DMFT were significantly higher. In both Nevada and national data, Non-Hispanic Blacks and Hispanics presented with higher rates respectively. African Americans and Hispanics were between 1.75 and 2.35 times more likely than non-Hispanic Whites to present with higher mean DMFT scores. Identified reasons for racial disparities in oral health include both microbiological and behavioral factors including income, education, and residence [16]. The percent increase in diversity within the Nevada population overall from April 1, 2000 to July 1, 2006 was 24.9% as compared to the percent increase in the US of 6.4% [17]. The larger than national average increase may explain the oral health disparity seen in these data between the various races in Nevada, but also presents a bigger challenge to the dental community to choose the correct preventive approach in such a diverse population.

Comparisons of age categories revealed higher mean DMFT indices in those between 15-19 years of age from those who were younger (12-15 years of age), indicating a significant increase with age [3]. Odds Ratios confirm the finding that those who were ages 16-19 were more than 2 times more likely than the younger age group to present with higher DMFT indices. Although age is not a modifiable factor, dental professionals should educate parents and adolescents of the importance of good oral hygiene practices.

Community water fluoridation has been documented as the most cost-effective, equitable, and safe community-based approach to improving oral health [18]. Participants living in areas without community water fluoridation in Nevada were almost 2 times more likely to present with higher DMFT indices. The benefits of water fluoridation are proportionally higher for people who do not have regular access to other sources of fluoride [18]. Therefore, dental professionals should counsel patients living in non-fluoridated geographic areas on the importance of using other sources of fluoride. It is of special significance that several futile attempts have been made in Nevada to introduce community water fluoridation to other counties, such as Washoe County, which comprises around 15% of the population.

Dental sealants help to reduce incidence of dental caries. Without dental sealants, caries prevalence and severity will likely continue to increase in children [19]. Nevada's successful sealant program has demonstrated decreases in prevalence rates that are greater than the national average. This study confirmed that Nevada youth who have not received dental sealants are 1 1/2 times more likely to present with higher mean DMFT scores than those with sealants [19].

Some suggest that inadequate dental care for children of low-income families is due, in part, to lack of dental insurance [20]. Participants without dental insurance were 1 1/2 times more likely to present with higher mean DMFT indices than those with dental insurance. Despite improvements in children's oral health through prevention, disparities still exist among subpopulations [20]. Lack of dental insurance could explain the negative oral health outcomes experienced by children and minorities [3, 20].

Secondhand smoke exposure reportedly causes immediate harm [21]. Nonsmokers, living in a smoking environment, are at greatest risk for negative health effects from secondhand smoke exposure. Investigators reported an association between environmental tobacco and risk of dental caries among children; suggesting children exposed to secondhand smoke have significantly higher rates of dental caries [22]. Participants exposed to environmental smoke were 33% more likely to present with higher mean DMFT indices than those not exposed.

In a meta-analysis of more than 50 epidemiological studies, females had a higher prevalence and severity of dental caries than males [23]. For both genders, their untreated decay was around 40% of the DMFT index and no significant gender difference was found in the decayed component. The significantly higher DMFT index for females is taken as an indicator that females may have received more dental treatment expressed as higher M or F in the index, girls presented with 1.25 times greater likelihood than boys of presenting with a higher mean DMFT Score. Although, like race and age, sex is not a modifiable risk factor, dental professionals should target female patients for education and aggressive preventive measures [23].

Tobacco has been linked to poor oral health, including smoker's palate and melanosis, oral candidosis, dental caries, periodontal disease, and oral cancers [24]. In this study, the likelihood of presenting with higher mean DMFT scores was no greater between those adolescents who smoke and those who do not smoke. There was a very low number of adolescent participants who reported smoking (N = 215) compared to those who reported not smoking (N = 1177) in the case group. This factor combined with the expectedly brief period of smoking likely contributed to the non-significant results found with this factor.

We found that a young person of Hispanic background, older age, living in a community without water fluoridation, and not having had sealants placed was at a significant higher probability of being in the high DMFT group compared to being cariesfree. Findings from this study will aid in creating educational programs and other primary and secondary interventions to help promote oral health for Nevada youth, especially in the subgroup that presents with the highest mean DMFT scores. Because dental professionals have frequent contact with adolescents and their parents/guardians, findings from this study can provide a guide for early detection, prevention, and treatment practices.