If you don’t like going to the dentist, you’re not alone. Most people have some anxiety about visiting the dentist, with one study in the Netherlands indicating that 24% of adults feared the dentist. Moreover, significant amounts of people who fear the dentist avoid visiting until they really need to. That could help explain why 92% of American adults have tooth decay in their permanent teeth.
But there is good news on the horizon as well—recent research also suggests that we might soon be able to refill the holes in our teeth with healthy, living tissue, giving our permanent teeth a second chance.
Compared to other species, you may think we humans are extraordinarily unlucky to have to depend on the same set of adult teeth for the majority of our life. Shark enthusiasts are familiar with the fact that sharks have unlimited sets of teeth during their lifetimes. Galeophobes in particular might be terrified to learn that sharks have rows of baby teeth underneath the skin waiting to replace the functional ones, and shed and replace teeth as often as every three weeks, causing experts to believe that the sea floor is littered with the teeth of sharks.
So if sharks, and most reptiles and amphibians can replace their teeth over a lifetime, why do humans and most mammals only get two sets of teeth?
Abigail Tucker, a professor of development and evolution at King’s College London says that there is a trade-off between the complexity of the teeth and the amount of sets the species gets. Since mammals have the ability to chew, meaning they can grind their teeth sideways (think of the movement a cow or horse makes) we have developed complex sets of teeth with multiple cusps, the bumps and mounds that define the shape of our teeth. While our pointy canine teeth (cuspids) each have only one cusp, our premolars (bicuspids) each have two cusps and our molars each have four or five cusps.
“The complexity is linked to diet, with bamboo eaters having the most complex teeth,” she says. “Something like a giant panda or a bamboo eating lemur have complex back teeth with lots of cusps so they can really chew and grind the hard tissue. So their teeth look similar even though they’re completely unrelated to [other] mammals.”
There are other fascinating examples of animals with unique dental abilities. Piranhas have teeth that are fused together to make large teeth that resemble a type of sharp knife. When they shed teeth, they lose an entire quadrant all at once, and rely on the other three quadrants to survive while the new teeth come in.
While mammals are typically restricted to two sets of teeth – a set of deciduous teeth and a set of permanent teeth – some mammals have retained the ability to create more teeth or have evolved to have the ability again. Manatees for example keep forming new teeth in the back their mouths over the course of their entire lives.
Other animals only get one set of teeth, but they continuously grow, including the aye aye lemur and rodents like rats and mice. “Rodents and rabbits typically have a stem cell population at the base of the tooth that keeps growing dentin and enamel. It’s an adaptation to the hard foods that they’re eating,” says Tucker.
It’s unlikely that humans will ever evolve to have more than two sets of teeth, since evolution requires that differences influence whether or not offspring survive. But it is true that we are still evolving in a way – experts believe that fewer and fewer people are now getting wisdom teeth, the third molars that arrive in early adulthood, when our jaw is fully grown. “We’re cooking our food and it’s more tender so there’s no need to have the third molar. In addition, our jaws are getting smaller so there’s less space,” Tucker says. “Because of that we’re seeing a higher percentage of people who are missing their third molars. About 20% of the population doesn’t have wisdom teeth.”
We may never evolve to grow a third set of teeth, but that hasn’t stopped scientists from attempting to find a way to replace extracted teeth with new, live replacements. One lab at King’s College London has successfully implanted bio-teeth into mice. Using gum tissue from humans and tooth forming cells in mice, they were able to grow teeth with dentin and enamel in mice. “What’s incredible is that the researchers can implant this developing tooth germ and it’s able to re-orientate itself to form and recruit blood vessels from surrounding tissue to make a live tooth,” Tucker says.
One of the challenges of using the therapy in humans, she says, comes from culturing stem cells in-vitro, which tends to make them lose their potency.
Other recent approaches have focused on finding ways to get our teeth to heal themselves. Ruchi Sahota, a dentist in California and a spokesperson for the American Dental Association, suggests visualising the anatomy of a tooth like an apple. “They have a thin enamel shell, like the skin of an apple, that protects the inner core, which is the dentin of the tooth. And just like the seeds of an apple, we have the nerve of our tooth,” she said. “A cavity tends to form in the enamel. When it gets into the dentin, you need to fill it at the dentist. When it gets to the nerve, that’s when you need a root canal.”
A company called Reminova is already working to bring a new approach to market. Also based on research at King’s College London, the technique uses painless electric currents to encourage re-mineralisation of the enamel at the earliest signs of decay.
Other approaches use the cells that are in our teeth to heal cavities that have already penetrated the enamel, by stimulating the creation of dentin, the calcified tissue that makes up the inner portion of our teeth. Recent research published in the journal Science Translational Medicine for example, found that treating exposed tooth pulp in rats with low-power laser light before filling the cavity could induce stem cells to create dentin in the tooth.
In another approach, researchers from the University of Nottingham and Harvard University are developing a therapeutic biomaterial that can work to heal a cavity, and intervene before a root canal is necessary. The material can stimulate a particular type of stem cells in the pulp tissue to interact with other material that forms a new kind of dentin-producing cell.
“This material can be injected in contact with pulp tissue and hardened with UV light to form a plastic,” says Adam Celiz, a postdoctoral fellow that is working on its development. “The native cells interact with the plastic and differentiate into a different kind of cell that produces dentin. So we’re hoping to restore that dentin layer to return vitality to the tooth, which means the pulp tissue wouldn’t have to be removed by a root canal.”
Prevention is key
Of course, dentists will tell you that preventing cavities from forming in the first place is the key to your dental longevity, starting with good oral hygiene—brushing twice a day with fluoridated toothpaste, flossing once a day and making regular trips to the dentist – and eating the right kind of foods.
“The most important food and thing for us to keep in mind in terms of prevention is water – especially fluoridated water,” says Sahota. “Not only does the fluoride help mineralise and regenerate tooth structures that may have become infected by a cavity, the physical motion of drinking water helps to flush away food, bacteria and any debris that may be stuck in your teeth as well.” She adds that dairy is also great because it’s high in calcium and that lean protein helps strengthen and rebuild enamel.
Even if we can rebuild this material in our mouths, we still have to fend off a modern menace in our industrialised diets – refined sugar. That’s because bacteria secrete acid when it breaks sugar down, and that acid can cause decay in our teeth.
So what type of candy is best avoided? Sahota says hard candies like lollipops are especially bad since they give you a constant exposure to sugar, while sticky candies get stuck in your teeth for long periods of time.
At least she has good news for the chocoholics among us. “Chocolate after lunch or dinner is a better choice than a lot of other candy because it can get flushed out more easily. So go ahead and enjoy a bite after your meal.”
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