The Dunedin Multidisciplinary Health and Development Study is a somewhat unusual but highly successful – and internationally recognised – collaborative research enterprise, involving investigators from many different disciplines tracking the lives of more than a thousand babies born in Dunedin between April 1972 and March 1973.

When I joined the team as a dentist in 2004 the Dunedin Study (as it has become known) already had a proven track record and a wealth of existing data.

While many other studies ignore teeth, or include minimal dental data as an afterthought only, the Dunedin Study had benefited from the expertise of a team of dentists since the 1970s, first led by Dr Harvey Brown and later by Professor Murray Thomson. For me it has been exciting to work as part of a dental team to build on the existing dental data and work with scientists from other disciplines to make new discoveries.

However, I must confess that as a dentist the most exciting aspect of all is simply looking at teeth. As the study is a birth cohort, we see people from all walks of life: from those with teeth as perfect as the day they “erupted” into the mouth, through to people who lost all their teeth in their twenties.

It is not uncommon to see a study member who normally avoids the dentist at all costs, but is willing to let me have a look for the sake of contributing to the research.

Now that the study members are adults, it is possible to investigate how their childhood influences their adult dental health. The Dunedin Study provides a unique opportunity to investigate one of the big questions we have: how do inequalities in dental health come about? Having dental data is an important first step, but combining this with data from other disciplines is where the value is really added.

By age 38 the average number of teeth lost was six times greater among those who had been born into disadvantaged families than for those born into well-off families.

So what do I think about the findings?

Up to age 18, more dental decay occurred among children from socio-economically disadvantaged families, but there were no serious differences in the dental treatment they received, thanks to New Zealand’s universal dental health care for children and adolescents.

However, this all changed once access to state-funded dental care ended after the study members turned 18. By the time they were 26, the average number of teeth with untreated decay was five times greater than it had been at age 18. This was worst among those who had been born into more deprived families.

“For example, by age 18 there was no difference in tooth loss measured by the occupations of the study members’ parents, but, during the following 20 years, the inequality gap got wider and wider. By age 38 the average number of teeth lost was six times greater among those who had been born into disadvantaged families than for those born into well-off families.”

Socio-economic differences in tooth decay rates don’t explain socio-economic inequality in dental health alone, because well-off people who eat too much sugar and have poor oral hygiene have a high rate of tooth decay too.

In dental research, we count a person’s total disease experience as the number of teeth affected by decay, whether the teeth are missing due to decay, have fillings, or have untreated decay. It tends to be tooth loss and untreated tooth decay that really stand out in the inequality difference.

Proponents of the “personal responsibility for your health” argument may contend that having tooth decay problems is “your own fault”, but this is an over-simplistic and unsympathetic viewpoint.

“If you have a high rate of decay as a child and are born into a family with low-income parents, this will affect your risk of having poor dental health right through your life, not just during childhood.”

We investigated some of these questions in one recent paper, in which we identified a pathway that helps to explain how we get from “who our parents are” to having dental problems as an adult.

Socio-economically disadvantaged parents were less likely to understand the dental problems caused by sugary foods or how to effectively care for the teeth. Their beliefs rubbed off on their children (the study members), who were more likely to hold similar unfavourable beliefs through their teens and into their 20s.

As adults, this was reflected in the frequency at which they brushed their teeth and went for dental check-ups. Add to this the fact that the relative poverty or affluence of parents also tended to be reflected by their grown children, which was also associated with whether and how often they went for dental check-ups as adults. What it all came down to was more untreated dental cavities, more teeth lost due to decay and a worse quality of life due to dental problems for those whose parents were less well-off.

Is it just that dentistry is too expensive?

Dentists are regularly given a hard time by the media for being “too expensive”, but most dental interventions are surgical and involve costly imported dental products, expensive equipment, compliance-related costs, salary for support staff – and a lot of time. Dental surgery is always going to be expensive relative to many other things in life. Acknowledging this, it doesn’t get around the problem that the people most in need of dental care are frequently the same people who can’t afford it.

It is not uncommon for a dentist to be unable to provide the most optimal, modern care to a patient because finances come in the way. Existing publicly-funded dental services (such as WINZ grants) cover only emergency dental care, while routine and preventive care is not covered.

Innovative public health interventions targeted to reduce inequalities ─ like a sugary drink tax ─ and expanded publicly-funded dental care (including preventive care for adults) deserve to be given a chance.

Associate Professor Jonathan Broadbent is based at the University of Otago dentistry faculty’s Sir John Walsh Research Institute and is the head of preventative and restorative dentistry. This opinion piece was first published in the University of Otago Magazine.

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