Does diet or genetics stop some of us from achieving the perfect smile? In a growing area of controversy, Glenda Lewis reports on the debate among orthodontists and evolutionary biologists about why our teeth are increasingly crooked and crowded and our jaws malformed.
We know why some children today have appalling rates of tooth decay and gum disease: too much sugar, poor oral hygiene and lack of dental care. But why are teeth now so crowded and crooked, and why do so many wisdom teeth fail to come through?
Are these trends genetic, are they the result of our modern diets or is it a matter of complicated nature-nurture interactions? Are there major differences in jaw development and malocclusion – a catch-all term for crooked, crowded or congenitally missing teeth, and jaws that don’t meet as they should – among and within populations around the world?
We are, with few exceptions, born with the potential to develop jaws spacious enough for all our teeth, say the authors of Jaws: The Story of a Hidden Epidemic, which explores the reasons behind the “hidden epidemic of oral-facial problems”. The unusual collaboration between experienced US orthodontist Sandra Kahn and Stanford University population biologist Paul Ehrlich came about over dinner in California.
Their book, illustrated with crooked smiles, long narrow faces and weak, disappearing chins, is endorsed by no less a scientist than Jared Diamond. Ehrlich became famous for his 1968 book, The Population Bomb, co-authored with his wife, Dr Anne Ehrlich. It predicted widespread famine and environmental disaster as a result of overpopulation and advocated measures to control the growing numbers, to be led by the US. Jaws is no less controversial, albeit in the smaller echo chamber of orthodontic circles.
The argument of Jaws is neatly summarised in a response written by Ehrlich after a review of the book by three professors of orthodontics, who called it “sensationalist” and said it lacks scientific evidence for some of its claims.
“Over the past 10,000 years, there has been a huge self-administered set of changes in the human environment,” Ehrlich wrote. “People began to reduce the amount of breastfeeding, move to a more liquid diet and move indoors where they are exposed to more allergens.
“Over that period, there has also been a decline in human jaw size and a resultant increase in malocclusion and failure of the last molars [wisdom teeth] to erupt. The evidence, documented in the hundreds of scientific references in Jaws, strongly suggests that reduced chewing pressures and mouth-breathing as a result of softer food and stuffy noses, respectively, disrupt normal jaw development.”
A hidden epidemic?
In Jaws, Kahn and Ehrlich argue that none of the changes to our mandibles (lower jawbone), tooth alignment and facial shape is genetic; they all result from modern living.
In the same online debate, Ehrlich wrote: “Even if there were strong selection favouring small jaws (which seems unlikely, to say the least), there haven’t been enough generations. The idea that migrations have led mobs of big-toothed men to inseminate small-jawed women hardly needs rebuttal.
“We were very clear in Jaws to state where our conclusions were based on research, clinical results or speculation.” He added, “Those who say we are wrong need to present a coherent argument for another explanation of the epidemic and, to the degree possible, cite the scientific literature to back it up.”
The second main argument in Jaws is that children now live in allergenic environments and are constantly exposed to viruses in the close confines of childcare centres and schools. As a result, noses are often blocked and mouth-breathing becomes established, leading to receding chins, long, narrow faces and thin upper lips. If the mouth is not kept closed (when not eating or talking), the jaws and palate are not subject to the gentle pressure of the tongue, over time, to keep the oral cavity in shape.
Cosmetic considerations aside, Kahn and Ehrlich warn that there are serious potential health problems from disturbed sleep as a result of the tongue blocking the airway. Sleep apnoea is associated with many non-trivial health problems, including heart disease, high blood pressure and dementia. Road deaths increase and job or school performance drops off because of fatigue. Mouth-breathing also dries up saliva, which reduces protection against tooth decay.
More of the food we eat, such as yogurts and smoothies, bypasses our teeth altogether. Stewed fruits are sold in convenient pouches and squeezed into the mouths of babies; blenders, wands and bullets are doing a lot of the chewing for children and adults. Parents and childcare staff are also worried about giving raw carrot and apple to toddlers following such cases as the tragic choking incident at a Rotorua childcare centre in May 2016 that left an infant with brain damage.
But if we exercised our jaws more by following a paleo-style diet free of processed foods and rich in meat, fish, eggs, seeds, nuts, fruits and vegetables, would we all have strong jaws and perfect smiles?
Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live, by US evolutionary biologist Marlene Zuk, debunks the myths about Stone Age diets and lifestyles and pokes academic fun at the silliness of those who try to replicate them. She cites a study of the dental health of modern humans compared with that of either our fossilised ancestors or modern peoples eating more traditional diets, such as the Maya of Mexico.
“People in industrialised societies not only have far more cavities than either of the other two groups … but their jaws are shaped differently, with malocclusion and overcrowding of the teeth,” she wrote.
“Ancient people and those consuming more fibrous foods simply chew more, which changes the development of the jawbones and associated musculature. The scientists who studied early dental health are quick to caution against a quick fix of a paleo diet for those seeking to avoid the dentist and orthodontist.”
The telegenic “all-American” smile is the ideal for many when they think about their teeth and jawline. But Kahn and Ehrlich warn that comes at a price. More than half of Americans now have orthodontic treatment. Increasingly, adults in this image-conscious age want cosmetic dentistry, no doubt influenced by Instagram and Facebook. There is no upper limit to the age at which you can have braces, provided your teeth and gums are healthy enough.
In New Zealand, porcelain and composite veneers are increasingly popular to mask broken, damaged or misshapen teeth and cover permanent discolouration. Along with tooth whitening, veneers have been popularised by reality TV shows such as Extreme Makeover. There is a biological cost to veneers, however, in that placing a veneer requires removal of (often healthy) tooth tissue. They may also need to be replaced several times across a lifespan, as they can break or chip, and represent an ongoing cost and commitment.
The role of genetics
The three orthodontic professors who reviewed Jaws – William Proffit, James Ackerman and Tate Jackson – believe there is evidence that genetics play a part in malocclusion.
“Labelling malocclusion as a disease of civilisation goes back to two parallel discoveries in the early 20th century: burial mounds with multiple human skeletal remains from the previous millennium, and observation of the dento-facial characteristics of previously unknown aboriginal groups who were found at the same time,” they wrote in the review.
“It was observed that crowding of the teeth was much less prevalent in remains from European populations from more than 400 years ago, and rare in most aboriginal populations. More recently, it was also noted that malocclusion is more prevalent in at least some large and crowded cities in India than in adjacent less-developed rural areas. Given that, is malocclusion a disease of civilisation? Not a bad description, if you don’t take it too far too fast.”
But, they added, “A major point not acknowledged in the book is that the jaws of current Europeans are quite similar in size to those [in] the burial mounds. Direct evidence of genetic control can be seen in the remarkable similarity of the facial proportions and jaws of identical twins, in whom minor deviations in jaw width appear in a mirror image.
“It also is seen in the large but internally consistent differences between aboriginal groups. Examples are the large and protrusive mandibles of Melanesian islanders, which have not changed although their diet has … even if you conclude that dental crowding is largely due to environmental influences, there is good evidence of genetic influence on both jaw size and jaw relationships.”
An orthodontics professor at the University of Otago, Mauro Farella, agrees with them. “The role of environment as a cause of misaligned teeth and jaws, although not insignificant, has certainly been overemphasised by Kahn and Ehrlich,” he says. Farella is taking DNA samples from all his patients to make a closer study of genetic factors.
“Current anthropological evidence is conflicting, hard to interpret and confounded by other factors, including ancestry and genes,” he says. “There is evidence, for example, showing that the mandible [lower jaw] over the past centuries is becoming bigger and not smaller. And this parallels the increase in height of new generations, as a result of an overall improvement in diet quality and lifestyle.
“The reason wisdom teeth fail to come through is still unknown. Changes in diet may affect tooth attrition. With a lot of raw food, the teeth become abraded and smaller. They tend to migrate forward and this generates space for wisdom teeth to erupt.
“The current practice, on the increase, to remove wisdom teeth to prevent problems, is highly contentious. And removing them has no effect on crowding.” Farella also notes that crowding, seen in about two-thirds of adults, gets worse with ageing: “This is especially the case for lower incisors.”
Bill O’Connor, president of the New Zealand Dental Association (NZDA), says there is now a move away from prophylactic removal of wisdom teeth. His own experience of treating parents and children suggests to him that jaw shape and crowding are strongly heritable.
The hollywood smile
University of Otago associate professor Jonathan Broadbent acknowledges both sides of the debate, and says it is very important to make a distinction between “need” and “demand” for orthodontic treatment. “Just like tooth whitening, orthodontic treatment is more common now because people want a Hollywood smile,” he says. “But I don’t think orthodontic treatment ‘need’ has shifted that much.” He points out that early loss of baby teeth is a common cause of crowded teeth and orthodontic need. “It is unfortunate,” says Broadbent, “that receiving orthodontic care has more to do with how well off your parents are than how crooked your teeth are.”
In terms of the argument that chewing helps prevent orthodontic problems, he says that tooth-jaw size discrepancies existed before the modern diet did.
“I don’t think you’re going to chew your way out of malocclusion. Having worked in Papua New Guinea, I have seen plenty of crowded teeth among people consuming a ‘natural’ non-modern diet.”
Just when you thought you had the story straight – that is, it’s complicated nature and nurture interplay – along comes a BBC article pointing squarely at mastication.
In 2011, Noreen von Cramon-Taubadel from the State University of New York at Buffalo, published a study she had made of skulls from collections all over the world, to see if you could tell where they came from by their size and shape. She found that you could, but there was one part that was unpredictable – the jaw.
“It soon became clear that instead of being determined by genetics, the shape of the jaw was mostly affected by whether that person had grown up in a hunter-gatherer society, or a community that relied on farming,” she says. Cramon-Taubadel says it’s all down to how much chewing we do as we’re growing up. “If you think about orthodontics, obviously the reason we do that with teenagers is because their bones are still growing. Bones are still malleable at that age and they will respond to different pressures.”
The effect chewing can have on the lower face is actually fairly subtle to the naked eye, says Cramon-Taubadel. Instead, it’s likely to show in our teeth. “So, the main problem is that, especially in post-industrial populations, we’re much more likely to suffer from dental problems – dental crowding, crooked teeth, etc,” she says. “Right now, what the research is showing is that having a slightly more biomechanically tough diet, particularly in children, might be useful for counteracting some of the imbalance between the way that our teeth grow and develop and push through.”
Our dental inequality
The nature-nurture debate aside, what can all parties agree on? Is there anything we can do to stop the next generation getting decayed, crooked, crowded teeth, and having their wisdom teeth removed at considerable expense?
Breastfeeding is good for starters. It is associated with reduced malocclusion, according to Kahn and Ehrlich, and has many additional benefits.
Pacifiers and thumb sucking have their place – especially on long-haul flights – but should be discouraged after a baby is weaned, as they push teeth out of alignment.
Too much sugar is bad for all sorts of reasons, including oral health. The NZDA advocates that it be taxed, along with other measures, including that only water be available in schools. In 2016, 250 schools had adopted this policy.
If passed, the Health (Fluoridation of Drinking Water) Amendment Bill going through Parliament will give district health boards the power to make decisions and give directions about the fluoridation of local government drinking water supplies in their areas. Only 54% of New Zealanders are drinking from a fluoridated water supply. Christchurch and Whangārei are notable exceptions. Fluoridation reduces fillings by up to 30%. However, it is prohibitively expensive for small towns, with populations of less than 1000 people, to fluoridate their water supplies.
Giving children more challenging, chewier foods won’t hurt, even if it doesn’t help expand the jaw and prevent crowded or crooked teeth. At the same time, a good understanding of how to prevent choking in babies, toddlers and adults is important.
Research by Bryony James of the University of Auckland shows that more textural foods make people feel fuller sooner and may prevent unwanted weight gain. Farella and James are discussing a collaborative research project based on findings that overweight and obese children chew less.
Tooth-brushing programmes are another way to remove some of our oral-health inequalities.
In 2015, DHB dentist Ellen Clark started a controlled tooth-brushing trial in Northland schools for her master’s thesis in public health. A teacher aide was paid to supervise tooth-brushing sessions at Kaitāia Intermediate School, with four other schools selected as controls.
“Caries incidence [decay and crumbling of teeth] for those in the tooth-brushing group was 7.3% compared with 71.5% for the control group,” says Clark.
“This reinforces the need for policy to consider other approaches to improve children’s oral health in communities that experience high caries and poor oral health.”
Parts of Northland and Auckland experience twice the national average of tooth decay, and hundreds of children each year in Northland need surgery under general anaesthetic to treat or remove teeth.
The NZDA’s O’Connor agrees that tooth-brushing programmes may be part of the solution to socio-economic inequality in dental care. “This simple intervention, along with water only in schools, could be applied cheaply and easily,” he says.
The growing gap in dental care is also the focus of Broadbent’s research. “I believe dentistry is a case study of what happens when we commercialise healthcare,” he says. “Dental problems are serious health conditions and cause pain, embarrassment and worry, but most dental treatment is provided as a user-pays service. This doesn’t make sense, since those who are least able to afford care are also those who need it the most.”
Dental-health checklist for children
1. Ensure they are chewing their food properly. Model behaviour by sitting at the table and not bolting your meal.
2. Check they are not breathing through their mouths all the time. We are designed to breathe through our nose, which moderates air temperature and moisture and regulates breathing.
3. Question whether wisdom teeth really need to come out if they haven’t caused any problems.
4. If crooked teeth are a problem, and you’ve got the money, get orthodontic treatment for children and teenagers.
5. Brushing teeth regularly (with fluoride toothpaste) could save many thousands of teeth in New Zealand and prevent crowding of adult teeth.
6. Limit sugary food and drinks and eat plenty of fibre-rich fruit, vegetables, seeds and nuts.
Baby boomers, most of whom did not have the benefit of fluoridated water as children, are trying to maintain some rather nasty-looking, gappy teeth, held together with black amalgam and discoloured by cigarettes, coffee and antibiotics. They didn’t consume as many soft drinks as subsequent generations, but still had more than their fair share of sugar.
Orthodontic treatment was far less common, and less affordable, for relatively large baby-boomer families. Parents were often just happy that their children could keep their own teeth, however unattractive, thanks to the school dental service introduced in 1923. “Murder house” memories became a common bond among the post-war generation.
The parents of baby boomers routinely had all their teeth yanked out in their twenties, often before they had even developed gum disease. For some, dentures were a coming-of-age present. Three-quarters had dentures by the time they were in their sixties. Things were no better for their parents, the “bread and jam” generation born in the late-19th century, who were unlucky enough to mature in time for World War I. In the documentary film They Shall Not Grow Old, by Sir Peter Jackson, a Wellington cinema audience gasped aloud when soldiers of the British Empire smiled.
At Gallipoli in 1915, New Zealand set up a dental clinic, which treated 40 men on its first day. In an article on New Zealand’s wartime dental history, University of Otago professor Jonathan Broadbent wrote that “New Zealand’s dental profession was still fledgling at the time the country joined the war in 1914, and our first dental school had opened just seven years before.
“By the end of the war, just over a third of all those New Zealanders who volunteered for military service and were otherwise fit to serve were deferred or rejected because of dental problems. Of those who were accepted, about 60% needed dental treatment of some kind.”
This article was first published in the July 13, 2019 issue of the New Zealand Listener.