Sharks, fish, reptiles, and a handful of unusual mammals can all regrow their teeth. Most of these animals are polyphyodonts, meaning they continuously regenerate teeth throughout their entire lives. This ability was actually the ancestral default for vertebrates. Humans and most other mammals lost it somewhere along the evolutionary line.
How Tooth Regeneration Works
The key structure behind tooth regrowth is a thin sheet of tissue called the dental lamina. This tissue sits at the base of developing teeth and houses stem cells that can produce new teeth on demand. In animals that regrow teeth endlessly, the dental lamina stays active for life, constantly producing replacement teeth from its stem cell reserves.
In mammals like us, the dental lamina breaks down after producing just two sets of teeth (baby teeth and adult teeth). That breakdown is what locks most mammals into a fixed number of teeth with no ability to grow more. The difference between a shark and a human, at the cellular level, comes down to whether this one tissue stays intact or deteriorates.
Sharks: The Champions of Tooth Replacement
Sharks are the most famous tooth regenerators, and for good reason. Their replacement rates vary from every few days to every several weeks, depending on the species. A single shark can produce thousands of teeth over its lifetime. New teeth form in rows behind the functional ones and rotate forward like a conveyor belt, replacing worn or broken teeth in a continuous cycle.
This works because the entire length of a shark’s dental lamina remains proliferatively active. There’s no dormant period, no shutdown signal. Stem cells in the tissue keep dividing and producing new tooth buds without interruption. Rays, which are closely related to sharks, share this same perpetual regeneration system.
Fish Replace Teeth Constantly Too
Bony fish, the group that includes everything from salmon to cichlids to zebrafish, are also lifelong tooth replacers. Zebrafish have become one of the most studied models for understanding how tooth regeneration is genetically controlled. Research has shown that a signaling pathway called Wnt plays a central role, switching on during a specific window between late development of one tooth and early formation of its successor.
The details get complicated. When researchers artificially activated Wnt signaling in zebrafish, it sometimes accelerated tooth development. But in cichlids, the same treatment delayed replacement. This variability suggests the timing and regulation of tooth cycling differs even among closely related fish species, though the core machinery is the same.
Reptiles: Alligators, Geckos, and More
Reptiles as a group retain the ancestral ability to replace teeth. Crocodilians are especially well studied. Each alligator tooth is really a three-part unit: the functional tooth you can see, a successor tooth developing behind it, and the dental lamina that will produce the next one after that.
Researchers at the University of Southern California mapped the stem cells in alligator jaws and found them clustered in an enlarged bulge at the tip of the dental lamina. These cells sit quietly until a tooth is lost or shed, at which point a growth signal activates them to begin forming a replacement. An alligator can cycle through each tooth position dozens of times over its life.
Geckos and other lizards also replace teeth continuously, but their dental lamina is structured differently. In geckos, the stem cells are spread more diffusely across a broad, plate-like lamina rather than concentrated in a distinct bulge. The result is the same (new teeth keep coming) but the cellular architecture varies across reptile groups.
The Mammalian Exceptions
Almost all mammals get just two sets of teeth. But a few species broke that rule.
Manatees have one of the most unusual dental systems in the animal kingdom. Their teeth continuously migrate forward through the jaw at a rate of about 1 millimeter per month, like items on a conveyor belt. New molars erupt at the back of the jaw while worn-out teeth fall out at the front. This horizontal replacement continues throughout the manatee’s adult life, giving them an effectively unlimited supply of fresh grinding surfaces for the abrasive aquatic plants they eat.
Elephants use a similar but more limited version of this system. Their molars also push forward horizontally, with new teeth replacing old ones from back to front. The difference is that elephants get only six sets of molars in a lifetime. Once the final set wears down, typically in the animal’s 60s or 70s, no more replacements come. For elephants, tooth wear is ultimately what limits their lifespan in the wild.
Rodents Grow Teeth, but Don’t Replace Them
Rodents sometimes get mentioned in conversations about tooth regrowth, but what they do is fundamentally different. Rats, mice, beavers, and other rodents have incisors that grow continuously from the base, compensating for the constant wear from gnawing. Some rodent species also have ever-growing molars. These teeth have stem cell niches at their roots called cervical loops that keep producing new mineralized tissue, pushing the tooth outward as the tip wears down.
This is continuous growth, not replacement. A rodent never sheds an incisor and sprouts a brand-new one. If a rodent loses a tooth entirely, it’s gone. The distinction matters: growing more of the same tooth and generating a whole new tooth from scratch are two different biological feats.
Why Most Mammals Lost This Ability
Continuous tooth replacement is the evolutionary default. Sharks, fish, and reptiles kept it. Mammals, for the most part, traded it away. The likely reason is that mammals evolved highly specialized teeth (incisors, canines, premolars, molars) that fit together precisely for chewing. A complex bite like this requires stable tooth positions and a predictable jaw relationship. Constantly cycling through new teeth would make it harder to maintain the tight fit between upper and lower teeth that mammals depend on to process food efficiently.
The trade-off is clear: mammals get better chewing performance from their specialized, precisely interlocking dentition, but they’re stuck with a finite supply. The dental lamina that could produce unlimited replacements breaks down after generating just two sets.
Could Humans Ever Regrow Teeth?
The same genetic pathways that drive tooth regeneration in sharks and reptiles still exist in the human genome. They’re just switched off. This has made tooth regrowth a serious target for medical research, not just a curiosity.
The most advanced effort targets a protein called USAG-1 that acts as a brake on tooth development. By blocking USAG-1 with engineered antibodies, researchers have triggered the growth of new teeth in animal models. A Phase I clinical trial launched at Kyoto University Hospital in 2024 is currently enrolling adults with tooth loss to test the safety of this approach in humans. Phase II trials targeting people born with missing teeth are planned for 2026, with broader Phase III studies expected by 2028 and potential commercialization projected for 2030 if results hold up.
The idea is that humans may retain dormant tooth buds left over from development, and blocking the USAG-1 protein could reactivate them. If it works, it would be the first therapy to regrow a complete, natural human tooth, something no dental implant or prosthetic can replicate.