If you’re an adult, chances are you already know a thing or two about tooth regeneration. Around age sixmost of us begin to lose baby teeth in a process called eruption, in which our delicate, first set teeth are exchanged for sturdier, permanent teeth. The phenomenon is reminiscent of the creatures that continuously grow their chompers, for example sandbar sharks, which sprout tens of thousands of serrated teeth over time; and rabbits, whose incisors continuously growing because they are worn out by roughage. If fish, bunnies and children do this in their sleep, why don’t adults naturally evict their aging molars with shiny, new replacements? And for that matter, how close is science to achieving such a feat? Please, I feel a toothache coming on…
Why aren’t we doing this already? To better understand what we are dealing with in this difficult quest, Dr. Ophir Klein– a professor of orofacial sciences and pediatrics at the University of California, San Francisco – offered Popular science a brief history lesson.
Long ago, before there were celebrity veneers, bleach kits or even dental floss, “animals were divided into invertebrates and vertebrates,” Klein explains. Back then, hundreds of millions of years ago, “these were the earliest vertebrates [were] kind of reptilian creatures,” and “from that came mammals, as did dinosaurs, birds and amphibians.”
[ Related: Why do humans have toenails? Because we’re evolutionary ‘weirdos.’ ]
As fate would have it, Klein explained, “teeth became an integral part of the mouth of vertebrates,” but it is “not exactly clear where they came from,” he added — “whether they started in the mouth or like scales, as fish have done, which have migrated from outside to inside.” Okay, gross! We know that these early teeth were simple, and perhaps they looked a bit like the teeth we see in fish today. “When you open a salmon’s mouth, all the teeth are the same and are constantly being replaced,” Klein explains. “That is a stem cell-driven process.”
Teeth became more complicated with the rise of mammals, and eventually humans. “Instead of all teeth within a species being the same, which is called homodont dentition, we have heterodont dentition,” Klein said. With the development of roots, “we have molars and premolars, canines and incisors,” each with specific tasks to perform. While many mammals developed teeth and tusks that grow continuously, a defense strategy against wear and tear, humans did not. When our adult teeth arrive, the hard, outer part (enamel) “is permanent and we no longer have the cells to make it.” In other words, somewhere along the evolutionary process we have lost some of the special precursor cells needed to continually replace teeth.
So perhaps our perma-teeth represent some kind of ancestral trade-off, where we traded replicability for complexity. Either way, how close are experts to undermining (or strengthening) this evolutionary development?
An “intermediate step” on the path to regrowing permanent human teeth could involve a mix of synthetic materials and stem cells.
“We’re pretty good at making art glazes,” says Klein. “Perhaps we could use the stem cells present in the tooth to regrow the living part of the tooth and then create a crown – just like we do now for a root canal – to bio-create a new tooth. -engineering.” Klein later added, “If we can learn how other animals can grow their teeth from stem cells, we could actually grow a complete, new tooth in vitro.” This isn’t something Klein thinks we’ll see in the next five years, but he said he “wouldn’t be shocked if this happened in the next few decades, just because things are moving so quickly.”
It may sound like science fiction at first glance, but there’s a lot to chew on here.
“The tooth itself is a challenge; making it part of the bone and integrated into your jaw is another aspect of regeneration,” he explains. Dr. Salvador Naresa professor in the department of periodontics at the University of Illinois, Chicago’s College of Dentistry. Nares spoke Popular science in conversation with Dr. Afsar Naqviassociate professor in the same department.
“Ultimately the vision would be to seed, if you like, some kind of capsule or something like that into the gum tissue, and then let it grow into a tooth,” Nares said. “However, there are challenges, because you have to have a certain morphology [that’s] accurate and complete.” The tooth must be durable and of the correct shape, plus it must stay in place and work well with the rest of the body. Moreover, “it has to stop growing because if it continues to grow, it’s called cancer,” Nares said. As for the state of play today, the professor pointed to research into stem cells in erupted baby teeth, which “certain laboratories have been able to use to actually manufacture parts of teeth.”
[ Related: Why do we have earlobes? They make no evolutionary sense. ]
Fields such as scaffolds (structures into which we can seed cells) and bioprinting have also made progress, as have gene editing techniques a la CRISPR.
Naqvi explained: “Gene editing could be a promising way to prevent organoid rejection by using patients’ own cell types, directing them to the desired cell type and using them for repair and regeneration.”
There is also research into An antibody drug that could, in theory, one day stimulate the growth of human teeth. However, Naqvi – who was not involved in the study – expressed concerns about the potential treatment, which would target a gene (USAG-1) that is “not specific to the dental tissues.”
“This gene is expressed in several tissues, including the kidneys, where it is expressed at very high levels.” Naqvi added, “What if, beyond the tooth [growth]it affects our bone growth in a positive, negative or any other way? It needs to be checked.”
Popular science emailed lead author Dr. Katsu Takahashi and Kyoto University Hospital for comment on their USAG-1 study, but neither responded.
Anyway, given the scope of research into tooth regeneration, something will surely work one day, right? Cleaning twice a year be damned?
“If you asked this question five, 10 years ago, you would probably get a different answer in terms of how far along we are in the whole process,” Nares said. “But because AI can make calculations quickly and see patterns and things that we don’t see, we can imagine that this will accelerate discovery and make this idea of growing teeth or growing other tissues a reality.” Still, Nares cautioned that he doesn’t expect all of this to be accomplished in the next decade; “I think we’re still a long way off,” he said, citing safety concerns, trials, regulatory rules and generally “a lot of work to do.”
[ Related: What does oil pulling do to your teeth? We asked dentists. ]
Meanwhile, Nares spoke with reverence about the adult teeth we do have. “The natural teeth we are born with are one of a kind,” he explained.
To function through adulthoodPermanent teeth require ongoing care, including brushing, flossing and cleaning. Furthermore, dental health is not limited to teeth and gums; the condition of your mouth is an indicator of this overall health. Researchers have linked gum disease Alzheimer’s, diabetes and other conditions.
“I would like to caution readers not to give up on their oral hygiene,” Nares said. “All the microbes that cause cavities and especially gum disease, which causes teeth to loosen and [cause them to fall] outwards, spreads to other parts of the body and can really create effects outside the mouth.”
He added: “So definitely keep your mouth clean.”
This story is part of Popular Science Ask Us Anything serieswhere we answer your most bizarre, mind-burning questions, from the common to the unusual. Do you have something you’ve always wanted to know? Ask us.
