Austin Powers bites back: do the English have worse teeth than US citizens?
A cross sectional comparison of US and English oral health surveys
“Austin Powers bites back: a cross sectional comparison of US and English national oral health surveys” by Carol C Guarnizo-Herreño and colleagues (BMJ 2015;351:h6543).
Objective—To compare oral health in the US and England and to assess levels of educational and income related oral health inequalities between both countries.
Design—Cross sectional analysis of US and English national surveys.
Setting—Non-institutionalised adults living in their own homes.
Participants—Oral health measures and socioeconomic indicators were assessed in nationally representative samples: the Adult Dental Health Survey 2009 for England, and the US National Health and Nutrition Examination Survey 2005-08. Adults aged ≥25 years were included in analyses with samples of 8719 (England) and 9786 (US) for analyses by education, and 7184 (England) and 9094 (US) for analyses by income.
Main outcome measures—Outcomes were number of missing teeth, self rated oral health, and oral impacts on daily life. Educational attainment and household income were used as socioeconomic indicators. Age standardised estimates of oral health were compared between countries and across educational and income groups. Regression models were fitted, and relative and absolute inequalities were measured using the relative index of inequality (RII) and the slope index of inequality (SII).
Results—The mean number of missing teeth was significantly higher in the US (7.31; standard error 0.15) than in England (6.97; 0.09), while oral impacts were higher in England. There was evidence of significant social gradients in oral health in both countries, although differences in oral health by socioeconomic position varied according to the oral health measure used. Consistently higher RII and SII values were found in the US than in England, particularly for self rated oral health. RII estimates for self rated oral health by education were 3.67 (95% confidence interval 3.23 to 4.17) in the US and 1.83 (1.59 to 2.11) in England. In turn, SII values were 42.55 (38.14 to 46.96) in the US and 18.43 (14.01 to 22.85) in England.
Conclusions—The oral health of US citizens is not better than the English, and educational and income oral health inequalities are consistently greater in the US than in England.
Why do the study
This study is from the 2015 Christmas edition of the The BMJ and focuses on an important transatlantic health problem: bad teeth. For years, the British have had a reputation for bad teeth—but is this stereotype true? The researchers decided to settle the debate once and for all: do the English have worse teeth than their US counterparts?
The authors, from England and the United States, set out to compare oral health in England and US. Previous research comparing the two nations’ teeth have been descriptive,  but this study was the first one to assess oral health statistically.
What did the authors do?
Data were collected from the English Adult Dental Health Survey (ADHS) and US National Health and Nutrition Examination Survey (NHANES) and compared with each other.
The ADHS has been administered every decade since 1968. It was most recently administered between October 2009 and April 2010 to 13 400 households across England, Wales, and Northern Ireland. The response rate for the most recent survey was 60%. Interview data were obtained on 9663 adults, of whom 5622 were followed up with a clinical oral examination.
The US NHANES data are collected differently. This survey is administered annually to a nationally representative sample of about 5000 people across the US. Information on 11 791 adults’ oral health was collected from the 2005-06 and 2007-08 surveys.
The authors looked at three primary outcomes: number of missing teeth, self rated oral health, and the impact of oral health on daily life.
Number of missing teeth was assessed by direct clinical oral examination. Self rated oral health was assessed by asking people if they thought their oral health was “better” or “worse” than other members of the population. Impact of oral health on daily life was assessed by two surveys that covered questions assessing pain, function, and social impacts of their teeth (see appendix 1 of published paper for survey questions).
Differences in oral health inequalities were measured by looking at educational attainment and household income obtained from self reports and country specific income data according to three quantiles—low, medium, or high. Age, sex, marital status, and ethnicity were accounted for in the analysis.
Several statistical calculations were used to analyse the data. Age standardised means and incidence rate ratios were used to assess number of missing teeth. Incidence rate ratios are a relative difference measure, and in this case, were determined by incidence of missing teeth in the US/incidence of missing teeth in the UK.
Regression modelling was used to determine if there was an association between oral health and socioeconomic position. Prevalence ratios compare the prevalence of a disease in one population (x) with the prevalence of disease in another population (y). In this study, the prevalence ratio is calculated by x/y and was used to compare US with UK participants’ self rated oral health. The authors wanted to quantify the differences between the two countries in relation to health inequality and access (see box)
Absolute v relative inequality
For example, number of people going to university may be 60% and 50% in two subgroups of one population, and 50% and 40% in two subgroups of another population. The absolute level of inequality, obtained by subtracting the differences between two groups, would be 10%, demonstrating the magnitude of difference in health between two subgroups.
In comparison, calculating relative inequality is different. In a population where 50% and 40% of two subgroups attend university, the relative inequality would equal 1.25 (50/40 = 1.25). This figure would be the same as the relative inequality in a population where 5% and 4% in two subgroups attend university 5/4 = 1.25), demonstrating proportional differences in health among subgroups.
They derived two indices to do this: a relative index of inequality (RII), likened to prevalence ratio, and the slope index of inequality (SII) to do this, respectively. The indices quantify the prevalence of the outcome between people at the bottom and at the top of the socioeconomic hierarchy.
RII (relative) values >1 and SII (absolute) values >0 indicate inequality and show that the outcome is higher among those with a lower level of education or income.
What did the authors find?
Age standardised estimates showed that among adults with teeth, US adults had more missing teeth with 7.31 teeth (standard error 0.15) than English adults who had, on average, 6.97 missing teeth (0.09) (P=0001). However, more English adults (15.07 people,95% confidence interval 14.05 to 16.08), than US adults (13.46, 12.39 to 14.52) reported ≥1oral impact affected their daily life (P=0.017).
Across both countries, men were more likely than women to report their self rated oral health as less than good, whereas women were more likely to report a greater number of missing teeth and higher prevalence of their oral health having an impact on their daily life.
Older adults were more likely to have missing teeth in both the US and England. US adults aged ≥65 years, however, rated their oral health as less than good than their English counterparts (31.37 adults (29.19 to 33.54) v 28.29 (26.00 to 30.58) (P=0.039).
Education and income
Across both countries, those with a high education attainment level did significantly better in all primary outcomes compared with people with a medium or low level of education, demonstrating a link between oral health inequality and educational attainment. Those with a higher income level also had better oral health.
Absolute and relative inequalities
Absolute inequalities in oral health measures were worse in the US than in England across all three primary outcomes. The slope index of inequality (SII) was >0 for all primary outcomes across both countries, when analysed separately for educational and income related inequalities.
RII was >1 for all outcomes in both countries; negative outcomes were higher among those with less education and income. Relative inequalities tended to be higher in the US than in England (see fig 1 ), in particular for oral health and impact.
Strengths and limitations
One of the strengths of the paper is that it looked at relative and absolute inequalities of oral health between England and the US, with the US being worse off. One of the major markers for assessing these inequalities was missing teeth, and although the difference was statistically significant it was very small.
The study is a cross sectional survey, which by design, means it is limited in what it can tell us. Because the data are collected as a snapshot, only point estimates have been obtained. This means only prevalence of disease, not incidence, can be calculated. No information over time, which would lend itself to a longitudinal study design, was collected on the same population.
Another strength lies in the quality of data obtained from the national surveys. It is unfortunate that oral health data are not routinely collected at every NHANES survey in the US. Instead, these surveys ask health questions “of priority” at any given time. Oral health data from 2008 were the most recent information available.
Ideally, a response rate of 70% or higher needs to be achieved when collecting data from a nationally representative sample. The ADHS survey had a response rate of 60%. Sampling bias may have been introduced if those who responded to the survey were different in exposure or outcome than those who did not respond to the survey.
The inherent differences in questionnaire design also limited the findings of the study. It is difficult to compare the responses of US and English citizens because most of the questions asked are not directly comparable, although six questions on the impact of oral health on daily health were.
Only one clinical measure, number of missing teeth, was used and, owing to differences of information collected, aesthetic and orthodontic outcomes were not studied.
The study reasonably quantified oral health outcomes between two populations, but did not ask why significant differences exist and what the reasons for differential levels of access and provision of treatment services might be. Insurance coverage and practices differ between the two countries andmay provide one explanation. Another is the difference in dietary and smoking habits, which are known to have a direct effect on teeth. The impact of health behaviours as an explanation for these inequalities is limited, but would be useful for future research. There was no information on wisdom teeth extraction, which is more common in the US (according to the paper’s authors), and could partly explain the increased number of missing teeth among the US cohort.
What does the study mean?
Can the claim that the English have worse teeth than US citizens be put to bed? Not quite, but this study shows that the US is not in a position to criticise the oral health of its transatlantic cousins.
On the basis of this study, oral health in the US is not better than that in England. US adults have more missing teeth, but the English think that their oral health affects them more.
This study also highlights that poor education and low income are associated with worse dental health. Those who have a lower socioeconomic standing had better oral health in England than in the US, whereas the reverse was seen for those in higher socioeconomic standing between the two countries. Poor, uneducated US adults fare worse on oral health than their English counterparts.
What this study has identified is the need to deal with health inequalities among those who are poorer and less educated than those with a better socioeconomic standing. This is particularly evident in the US.
Before comparisons between countries are made, ways to reduce intra-country differences should be explored by policy makers. Geographical health inequalities exist within England (north versus south) and their effect on oral health outcomes should be investigated, as well as access to and engagement with local dental services.
In terms of looking at reasons why there are differences between countries, more macro-level topics should be looked at in more depth. Some of these wider themes could include the existence of sugar taxes, smoking cessation campaigns, and the type of dental provision (state funded versus private) available to citizens.Neil Chanchlani, specialist trainee year one in paediatrics
Royal Free London NHS Foundation Trust
Competing interests: NC prides himself on his relatively white, somewhat misaligned Canadian smile. His teeth remain professionally unaltered, for now.
Provenance and peer review: Commissioned; not externally peer reviewed.
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