Abstract
Objectives: To assess the overall dentition status of American adults, to investigate disparities and changes in dentition using the National Health and Nutrition Examination Surveys 2005–2006 and 2007–2008 and to study the effects of family poverty status, education, citizenship and language on dentition after adjusting for other demographics. Methods: Descriptive statistics were used to explore and summarise dentition status. The prevalence of dentition markers over two surveys were compared using tests of proportions and a series of regressions were used to estimate the strength of association of family poverty status, education, citizenship and language with the four markers of dentition status. Results: Overall, dentition status has improved in adults. However, gaps exist in that non-Hispanic Black and Mexican-Americans have a higher prevalence of dental decay and lower restoration rates than other races. After adjusting for selected demographics, adults with less education (<12 years) and lower family income had significantly higher dental decay rates, lower restoration rates and more missing teeth than those with more education (≥12 years) and those with higher family incomes. Conclusion: This study indicates that disparities in dentition associated with race/ethnicity, education and income still exist among adults in the USA. The results also indicate that to improve overall oral health and close the existing gaps in oral health, increased access to dental care would be needed for people who have low incomes and low levels of education.
Key words: Social disparities, NHANES, dentition, demographics
INTRODUCTION
Oral health is a very important component of health throughout life. Poor oral health and untreated oral diseases have a negative impact on the quality of life and can be risk factors for general health. Conversely, some diseases of other body systems can increase the risk of oral disease. Oral diseases affect the most basic daily activities, including eating, drinking, smiling and communication. Oral diseases such as dental caries and tooth loss have been considered to be the most important global oral health burdens1. For example, the treatment of dental caries accounts for 5–10% of total health-care expenditures2. Dentition status is one important component of oral health and untreated bad dentition status can adversely affect the quality of life. For example, missing teeth is a common problem and a source of great embarrassment for many people. Some of the problems associated with lost teeth include difficulty eating or chewing, speech problems and shifting of adjacent teeth. When teeth shift they can create further cosmetic problems and become more susceptible to cavities, bite problems and gum diseases.
Major improvements in recent decades have taken place in the oral health of the US population viewed as a single entity. However, because of the diversity of the US population, oral health disparities still exist and are profound among groups defined by race, socioeconomic status, gender and age. In particular, African-Americans, Hispanics, American Indians and Alaskan Natives generally have the poorest oral health of any racial groups in the USA3. Moreover, people in low socioeconomic levels are more likely to have poor health, including dentition, than those with high socioeconomic levels, regardless of their race/ethnicity.
Some dental studies have examined the relationship between dentition and demographics in children, adolescents4 and adults5., 6., 7., many using a bivariate relationship with a single marker of dentition. The association of multiple social characters with multiple markers of dentition has seldom been investigated simultaneously in the US population based on consecutive surveys.
The same oral health examination protocols and the same sampling schemes used in the National Health and Nutrition Examination Survey (NHANES) 2005–2006 and 2007–2008 afforded a reliable opportunity to: (1) investigate the changes in dentition status over a short period of time; (2) explore the distribution of disparities in dentition among different demographics and compare the changes in these two consecutive surveys; (3) investigate the effect of family poverty status, education, citizenship and language on dentition after adjusting for other demographics.
METHODS AND PARTICIPANTS
Data used in the present study are a subset of the series of National Health and Nutrition Examination Surveys conducted by the National Center for Health Statistics (NCHS). The two 2-year (NHANES 2005–2006 and 2007–2008) survey datasets, which collected nationally representative information, were based on a stratified, multistage design to monitor five ‘Healthy People 2010’ oral health objectives8. Full details of the survey methods used can be found at http://www.cdc.gov/nchs/nhanes.htm. For the current study, only subjects who were ≥20 years old and had completed an oral examination were included.
Ethics statement
This study was conducted in accordance with the latest version of the principles of the Declaration of Helsinki. The NCHS Research Ethics Review Board (ERB) approved the study (NCHS IRB/ERB Protocol #2005–06); further ethical approval for the use of NHANES data that is freely available on the web is not required.
Demographic variables
Seven sociodemographic variables were included in data analysis: (1) age at screening, (2) gender, (3) race/ethnicity, (4) family poverty income ratio (PIR), (5) education, (6) citizenship status and (7) language. Age in years at time of screening was a continuous variable grouped into three levels: 20–39, 40–59 and ≥60. Race/ethnicity, determined on the basis of participants’ self-reporting, includes five categories: Mexican-American, non-Hispanic white, non-Hispanic black, other Hispanic and other race. The variable family poverty status is the ratio of family income to the federal poverty threshold (FTP), adjusted for family size and composition and categorised into three ordinal levels: poor (PIR < 1), near poor (1 ≤ PIR < 3) and non-poor (PRI ≥ 3). Education level for adult reflects the highest grade or level of school completed by the participant and was used in the data analysis as being <12 years, 12 years and >12 years.
Oral examination variables
Basic screening examination (BSE), a new assessment that was used in the dental examinations of 2005–2006 and 2007–2008, differs from previous NHANES oral health protocols, wherein each tooth surface was not assessed and the assessments were conducted by a health technologist rather than a dentist8. Four markers of dentition status were used: the missing teeth, dental decay present (at least one tooth with dental decay), dental restoration present (at least one tooth with a dental restoration), dental sealant present (at least one tooth with a dental sealant).
Statistical analysis
Descriptive statistics were used to summarise and explore the dentition status of the sample participants based on an oral examination. Tests of proportions were used to test for changes from 2005–2006 to 2007–2008 in the prevalence of three markers of dentition: tooth decay, restoration and dental sealant. Based on properties of the response variables, Poisson regression and logistic regression models were used in this study. Poisson regression was used to investigate the relationship between social gradients and the number of missing teeth acting as a response variable in the model. Logistic regression was used to investigate the strength of the association between demographic variables and dentition status, including decay, restoration and sealant, treated as a dichotomous variable present/not present. Data management and analyses were performed with the Statistical Analysis System (SAS, version 9.3; SAS Institute Inc., Cary, NC, USA). All percentages, risk ratios, mean and standard errors were weighted to be representative of the target population. A P-value <0.05 was considered statistically significant.
RESULTS
There were 4,979 and 5,935 participants aged 20 years and older with mean ages of 46.6 years and 46.8 years in NHANES 2005–2006 and NHANES 2007–2008, respectively. The descriptive summary of the overall dentition status from these two national surveys (Figure 1) indicates that there were statistically significant decreases in the percentages of individuals with decay (−2.49%), restorations (−3.05%) and sealants (−1.29%). The percentage of missing teeth (at least one missing tooth) also decreased, but this change did not achieve statistical significance.
Figure 1.
The prevalence of dentition markers among American adults 2005–2008.
A statistically significant reduction in dental decay was found in groups formed by age, gender, family poverty status, US citizens and English speakers. Other races and other Hispanic groupings did not reach a statistically significant reduction in dental decay (Table 1). The percentage of decay decreased as age increased. Mexican-American and non-Hispanic blacks had a consistently higher prevalence of decayed teeth, with 35.9% and 37.7% in 2005–2006 and 32.2% and 34.3% in 2007–2008, respectively. Adult Americans with more education (>12 years) and higher family poverty income ratios (PIR > 3) had a lower likelihood of tooth decay than those with less education (<12 years) and lower family incomes (PRI < 1). The prevalence of tooth decay among US citizens is around 20%, which is less than about 12% for non-US citizens, as found in these two surveys. Similarly, a consistently lower prevalence of tooth decay was found in English speakers compared with Spanish speakers (Table 1).
Table 1.
Prevalence of decay, restoration and sealant and number of missing teeth within groups of explanatory variables among American adults
| Explanatory variables | Decay (%) |
Restoration (%) |
Sealant (%) |
Missing teeth (#) |
||||
|---|---|---|---|---|---|---|---|---|
| 2005–2006 | 2007–2008 | 2005–2006 | 2007–2008 | 2005–2006 | 2007–2008 | 2005–2006 | 2007–2008 | |
| Age (years) | ||||||||
| 20–39 | 25.9(1.3) | 24.3(1.2)* | 78.1(1.2) | 73.2(1.3)* | 11.4(1.0) | 7.8(0.8)* | 2.3(0.1) | 2.5(0.1)# |
| 40–59 | 22.5(1.3) | 19.7(1.1)* | 89.0(0.8) | 86.8(0.9)* | 1.3(0.4) | 1.4(0.4)* | 5.4(0.2) | 5.6(0.2)NS |
| 60+ | 16.4(1.2) | 13.5(0.9)* | 73.3(1.4) | 72.3(1.2)NS | 0.2(0.1) | 0.5(0.3)# | 12.1(0.3) | 11.9(0.2)NS |
| Gender | ||||||||
| Male | 25.9(1.1) | 23.6(1.0)* | 78.7(1.0 | 75.2(1.0)* | 4.6(0.6) | 3.3(0.5)* | 5.5(0.2) | 5.5(0.1)NS |
| Female | 19.1(1.1) | 16.4(0.5)* | 83.7(0.8) | 81.0(0.9)* | 5.5(0.6) | 3.8(0.5)* | 5.9(0.1) | 6.2(0.1)# |
| Race | ||||||||
| Mexican-American | 35.9(1.8) | 32.2(1.7)* | 65.2(1.8) | 67.3(1.8)NS | 2.3(0.5) | 1.9(0.5)NS | 3.6(0.2) | 3.3(0.2)NS |
| Other Hispanic | 19.5(3.5) | 24.1(2.0)NS | 81.4(3.5) | 79.9(1.9)NS | 4.6(2.1) | 3.6(1.0)NS | 5.4(0.5) | 5.8(0.3)NS |
| Non-Hispanic White | 18.5(0.9) | 15.8(0.8)* | 85.3(0.8) | 81.4(0.8)* | 5.5(0.5) | 3.8(0.5)* | 6.0(0.2) | 6.2(0.2)NS |
| Non-Hispanic Black | 37.7(1.7) | 34.3(1.6)* | 65.9(1.6) | 68.0(1.5)NS | 1.9(0.5) | 3.2(0.6)# | 6.2(0.2) | 6.3(0.2)NS |
| Other race | 26.1(3.8) | 21.5(3.4)NS | 82.3(3.1) | 73(3.5)* | 5.9(2.0) | 3.6(1.6)NS | 4.6(0.4) | 5.5(0.5)NS |
| Family poverty income ratio (PIR) | ||||||||
| Poor | 36.3(2.0) | 32.0(1.5)* | 71.7(1.7) | 66.5(1.5)* | 4.3(1.0) | 3.9(0.6)NS | 7.2(0.2) | 7.3(0.2)NS |
| Near-poor | 29.5(1.4) | 24.1(1.1)* | 72.8(1.3) | 73.1(1.2)* | 5.3(0.7) | 3.3(0.5)NS | 4.6(0.1) | 4.5(0.1)NS |
| Non-poor | 14.2(1.0) | 11.7(0.9)* | 89.3(0.8) | 87.0(0.9)NS | 4.7(0.6) | 3.7(0.7)* | 6.3(0.3) | 6.7(0.2)NS |
| Education (years) | ||||||||
| <12 | 34.5(1.8) | 32.6(1.5)NS | 61.4(1.8) | 62.4(1.5)NS | 1.7(0.5) | 1.8(0.5)NS | 9.2(0.3) | 8.9(0.2)NS |
| 12 | 29.0(1.7) | 23.2(1.4)* | 79.3(1.4) | 74.7(1.4)NS | 3.8(0.7) | 3.0(0.5)NS | 6.6(0.2) | 7.0(0.2)NS |
| >12 | 16.1(0.9) | 13.7(0.8)* | 88.0(0.8) | 88.7(0.8)NS | 6.3(0.6) | 4.4(06)* | 4.3(0.12) | 4.3(0.1)NS |
| US citizenship | ||||||||
| Yes | 21.4(0.8) | 18.7(0.7)* | 82.7(0.7) | 79.4(0.7)* | 5.0(0.4) | 3.7(0.4)* | 5.9(0.1) | 6.3(0.1)# |
| No | 33.6(2.4) | 32.5(2.3)NS | 65.9(2.3) | 66.2(2.3)NS | 2.9(1.1) | 2.0(0.8)NS | 3.8(0.2) | 3.5(0.2)NS |
| Language | ||||||||
| English | 21.4(0.8) | 18.9(0.7)* | 82.7(0.7) | 79.1(0.7)* | 5.1(0.4) | 3.7(0.4)* | 5.9(0.1) | 6.0(0.1)NS |
| Spanish | 40.1(2.6) | 35.4(2.0)NS | 57.6(2.6) | 65.9(2.2)# | 1.4(0.6) | 1.4(0.5)NS | 4.2(0.3) | 4.7(0.2)NS |
Significant decrease from 2005–2006 to 2007–2008 and P < 0.05.
significant increase from 2005–06 to 2007–08 and P < 0.05.
NS, not significant.
The prevalence of restorations in adults aged 40–59 years was higher than in other age groups from 2005–2008 (Table 1). Females had a higher restoration rate and lower tooth decay rate than their male peers. Both Mexican-Americans and non-Hispanic black people had lower restoration rates – around 65% in 2005–2006 and 67% in 2007–2008 and higher tooth decay rates compared with other races. The highest restoration rates were consistently found in the population having more than a 12-year education and family PIR > 3. The restoration rates of Spanish speakers had a statistically significant increase from 57.6% in 2005–2006 to 65.9% in 2007–2008 (P < 0.0001).
The use of dental sealants remained low among American adults. About 11% and 8% of adults aged 20–39 years had dental sealants on their permanent teeth in 2005–2006 and 2007–2008, respectively, which was higher than in other age groups (Table 1). The rates of use of dental sealants were higher in those who had more than 12 years of education compared with less than 12 years of education (4.9% and 4.6% in 2005–2006 and 2007–2008, respectively). However, there were similar rates of use of dental sealants among race, gender and family income ratio groups. The rate of sealant use decreased from 2005–2006 to 2007–2008 in most subgroups, except among non-Hispanic Blacks and those aged 60 and over.
The number of missing teeth among all groups stayed the same in these two surveys. However, females and people aged 20–39 years and US citizens experienced increases in the number of missing teeth (Table 1). Clearly, the number of missing teeth was significantly different among different age-groups and increases as people get older. The mean numbers of missing teeth among Mexican-Americans, (3.6 in 2005–2006 and 3.3 in 2007–2008) were less than the means of other races. A lower mean number of missing teeth was consistent in the population with more education (>12 years, 4.3 in both surveys). Non-US citizens and Spanish speakers had more missing teeth than US citizens and English speakers in these two surveys.
The associations between four social demographic variables (education, family poverty, citizenship and language) and four markers of dentition were also investigated (Table 2). Individuals without a high-school diploma (education <12 years) and with a high-school diploma (education = 12 years) had a higher prevalence of dental decay than those with education of more than 12 years, with risk ratios of 2.45 (95% CI 2.20, 2.74) and 1.84 (95% CI: 1.63, 2.07), respectively. After adjustment for other selected demographics (age, gender, race, etc.), participants with education ≤12 years still had statistically significant higher tooth decay prevalence rates compared with participants having more education (Table 2). Individuals with less education (≤12 years) also had a statistically significant higher rate of missing teeth than those with more than 12 years of education (rate ratio 1.30; 95% CI 1.28, 1.33). In contrast, individuals with less education (≤12 years) had a statistically significant lower dental restoration rate than others with more education (>12 years), even after being adjusted by other demographic variables.
Table 2.
Association between four social indicators and dentition status among American adults
| Decay (risk ratio) | Restoration (risk ratio) | Sealant (risk ratio) | Missing teeth (rate ratio) | |
|---|---|---|---|---|
| Education (reference group:>12 years) | ||||
| Model1: <12 years | 2.45(2.20,2.74)*** | 0.25(0.22,0.28)*** | 0.30(0.21,0.43)*** | 1.86(1.83,1.89)*** |
| Model1: 12 years | 1.84(1.63,2.07)*** | 0.48(0.43,0.55)*** | 0.72(0.55,0.95)* | 1.50(1.47,1.53)*** |
| Model2: <12 years | 1.78(1.57,2.03)*** | 0.35(0.31,0.39)*** | 0.54(0.36,0.80)* | 1.55(1.52,1.58)*** |
| Model2: 12 years | 1.60(1.41,1.81)*** | 0.57(0.51,0.65)*** | 0.84(0.63,1.13)NS | 1.30(1.28,1.33)*** |
| Family poverty (reference group: non poor) | ||||
| Model1: Poor | 2.27(2.02,2.55)*** | 0.36(0.32,0.40)*** | 0.79(0.61,1.02)NS | 1.57(1.54,1.60)*** |
| Model1: near poor | 3.20(2.82,3.64)*** | 0.28(0.25,0.32)*** | 0.69(0.50,0.93)* | 1.46(1.43,1.50)*** |
| Model2: Poor | 1.90(1.67,2.15)*** | 0.48(0.43,0.55)*** | 0.96(0.72,1.27)NS | 1.24(1.22,1.27)*** |
| Model2: near poor | 2.36(2.05,2.72)*** | 0.42(0.36,0.48)*** | 0.8(0.57,1.13)NS | 1.30(1.27,1.32)*** |
| Citizen (reference group: U.S. citizen) | ||||
| Model1: non-citizen | 1.99(1.76,2.26)*** | 0.53(0.47,0.61)*** | 0.47(0.3,0.74)** | 0.58(0.56,0.60)*** |
| Model2: non-citizen | 1.09(0.88,1.35)NS | 0.66(0.55,0.79)NS | 0.51(0.28, 0.92)* | 0.84(0.81,0.87)*** |
| Language (Reference group: English) | ||||
| Model1: Spanish | 0.53(0.46,0.60)*** | 0.57(0.50,0.65)*** | 0.34(0.20,0.57)*** | 0.77(0.75,0.79)*** |
| Model2: Spanish | 1.18(0.98,1.42)NS | 1.13(0.91,1.41)NS | 0.99(0.47,2.07)NS | 0.93(0.89,0.96)*** |
***P < 0.001, **P < 0.01, *P < 0.05.
Model 1 risk ratio and rate ratio calculated in separate models from education, family poverty ratio, citizenship and language.
Model 2 additionally adjusted by other demographic variables like age, gender, etc.
NS, not significant.
There was a clear family poverty gradient in three markers of dentition: dental decay, restoration and missing teeth. Poor or near-poor individuals generally had statistically significantly higher risks of dental decay and missing teeth than non-poor individuals. They also had less likelihood of having dental restoration compared with non-poor individuals. United States citizens were more likely to have dental decay (risk ratio 1.99; 95% CI 1.76, 2.26) and less likely to have restoration than non-citizens (risk ratio 0.53; 95% CI 0.47, 0.61). However, both relationships lost their statistical significance after adjusting for the other demographic variables. The US citizens had a statistically significant smaller rate of wearing sealants and number of missing teeth, with risk ratios of 0.47 (95% CI 0.3, 0.74) and 0.58 (95% CI 0.56, 0.60), respectively. This relationship remained after adjusting for other demographics. Participants who spoke Spanish generally had a significantly smaller likelihood of dental decay, restoration and sealants than those who spoke English. These relationships were eliminated by adjusting for other demographics. However, Spanish speakers had fewer missing teeth than English speakers (rate ratio 0.77; 95% CI 0.75, 0.79), even after adjusting for other demographics (Table 2).
DISCUSSION
The data used in this study were from two well-designed nationwide surveys conducted in the USA. By using repeated cross-sectional studies, it was possible to evaluate the change in dentition over a short period of time. The results indicated an improvement in dentition among American adults. Specifically, based on an oral examination, the prevalence of dental decay, and number of missing teeth decreased during this short period.
Tooth decay is the most common chronic disease among Americans. Although the results of this study indicate that dental decay of permanent teeth in adults has decreased, a relatively high prevalence of dental decay still exists among adults in the USA. Dental decay is a major oral health problem in most industrialised countries, which affects 60–90% of schoolchildren and a majority of adults9. Despite being highly preventable at early stages through good home care and regular professional preventive services, the high prevalence of dental decay among adults in the USA and its adverse overall health effects, especially among individuals having a low socioeconomic status, should not be underestimated.
Sealants, an effective method for protecting teeth against decay-causing bacteria, can save time, money and the discomfort of filling cavities. In addition to children and teenagers, adults can also benefit from dental sealants10. Unfortunately, dental sealants have been underused by adults in the USA. Less than 2% of all adults used dental sealants compared with around 20% of those with dental caries in the 40–59 years age group. Similar rates of the use of dental sealants among poor, near-poor and non-poor groups indicate that adults received approximately equal dental preventive service. People with more education (>12 years) had a higher percentage of dental sealant usage than those with less education (<12 years), possibly reflecting differences in attitude about the value of sealants or access to dental preventive services.
Dental insurance is typically associated with higher-paying positions. Consequently, people with low incomes are less likely to have dental insurance11. As previously reported, increased dental care and restoration are associated with dental insurance coverage rates12, which may explain the relatively high prevalence of dental decay and relatively low rates of dental restoration among poor people in this study. The study found that private dental insurance coverage has decreased in the USA.13. Thus, individuals without dental insurance would potentially have worse oral health and/or overall health status, which can lead to increased cost for overall health care. However, dental insurance, as an important protector of dentition status, was excluded in these two national surveys.
Oral health was associated with an array of factors, including age, race/ethnicity, economic status and education. An important perspective from this study is that poverty and education are important factors associated with overall dentition status. We found that the prevalence of dental decay in poor adults (family PIR < 1) was more than twice as high as in non-poor adults (family PIR > 3). Similarly, poor adults were more likely to have more missing teeth than non-poor adults.
Immigrants who are not US citizens are a rapidly growing section of the population. As of 2010, 37.6 million foreign-born people were living in the USA, a number that excludes millions of illegal immigrants whose numbers have more than doubled in the last decade14. Their health status, including dentition, is often neglected. Immigrants face barriers related to culture, economic condition and low rates of English proficiency. It is reasonable to speculate that the aforementioned barriers effect, add more challenges and limit the ability of non-US citizens to access and receive appropriate health care compared with US citizens. Other studies have showed that citizenship independently affects access to health insurance15., 16.. The consistently growing population of immigrants in the USA and changes in the composition of the US population will continue to have an impact on the overall dentition status of American adults. Further studies should focus on the change and relationship between citizenship and dentition status via longitudinal analysis.
As with any investigation, the results provided by this study have some limitations. Specifically, the current study was based on two cross-sectional surveys and the analysis only evaluated potential associations related to oral health rather than cause–effect relationships. The findings of this study support the results of several other studies on disparities of dentition, suggesting that oral health status has improved in recent decades17., 18.. However, owing to inconsistent sampling or examination measurement, direct comparisons were difficult. NHANES is limited to inferences on English and Spanish speakers, which ignores the diversity of native languages (i.e. Chinese and other languages) of immigrants in the USA.
Despite improvement in the nation’s oral health in recent decades, not everyone in the USA has benefited equally because of the diversity of the US population. Generally, oral health problems exist in low-income, disabled and institutionalised individuals. Our results indicate that dentition status is significantly associated with sociodemographics and that there is a need for better access to dental care for people with low household incomes and low levels of education. A significant improvement in markers of dentition in a very short period (2005–2006 and 2007–2008) was found in this study. Additional studies of potential indicators explaining these changes would be of interest and are in progress using the current data set.
Acknowledgement
The authors thank the Research Office at UMKC School of Dentistry for its support .
Conflict of interest
None declared.
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