Human Brain Storage Capacity: Is It Really 2.5 Petabytes? You walk into the kitchen and stop. Whatever you came for is gone, and the refrigerator hums on no help at all. Three seconds ago the errand was fully formed. Yet catch the smell of one particular soap, the green one from a childhood bathroom, and thirty years fall away: the tile pattern, the drip of a tap, an argument murmuring through the wall. Same organ, two very different outcomes. The kitchen lapse is most likely working memory, a workspace that holds only a few chunks of information at once (about four, in many experiments) and loses them when attention moves on. The soap memory waited in long-term memory for three decades. That contrast sits awkwardly beside a figure repeated across countless web pages as the human brain storage capacity: 2.5 petabytes. A device with that much room should never misplace an errand. Either the brain is a spectacularly unreliable drive, or the number does not mean what it appear...
Tooth Regrowth Drug: Could Humans Really Grow a Third Set of Teeth?
Every so often, a routine dental X-ray turns up something unexpected: a fully formed extra tooth sitting quietly in the jaw of someone who already has a complete adult set. Dentists call it a supernumerary tooth. To a small group of researchers in Japan, that stray tooth became a clue that the instructions for building a tooth aren't entirely switched off once the permanent set comes in. That idea now sits behind one of regenerative medicine's more closely watched experimental therapies: a tooth regrowth drug currently in human clinical trials, built on the hope of a third set of teeth instead of only dentures or implants.
Humans follow a fixed script: twenty baby teeth in early childhood, replaced by thirty two permanent teeth meant to last a lifetime. Lose one as an adult and nothing grows back. The research behind this drug asks something narrower than whether humans can grow teeth from nothing: whether cellular machinery already sitting in the jaw, left over from tooth development, could be nudged back into action. Can a drug persuade the body to build another tooth using instructions it already has on file?
Two sets of teeth, and then nothing
Humans are diphyodont: built to produce exactly two generations of teeth. Milk teeth form before birth and finish erupting by about age three; tiny clusters of cells called the successional dental lamina then produce the permanent teeth that push the baby teeth out between roughly ages six and twelve. Once that second generation erupts, the tissue that built it mostly disappears, maturing into the tooth or dying off through apoptosis, which is why a lost adult molar simply leaves a gap.
Sharks and many reptiles work differently, continuously cycling replacement teeth into place, which can look like proof that humans harbor the same hidden capacity. Researchers resist that leap: sharks evolved a permanently active dental lamina, while human evolution favored two well-built sets, an entirely different strategy, not evidence of one lying unused in us.
What does third dentition actually mean?
Dentistry has a name for tooth development beyond the usual two generations: third dentition. It shows up mainly in case reports of extra teeth erupting later in life, and in supernumerary teeth, usually traced to dental-lamina remnants that failed to regress, sometimes alongside cleidocranial dysplasia, a genetic condition that can cause dozens of extra teeth.
This does not mean every adult carries a hidden, complete third set of thirty two teeth waiting for a switch. It suggests something narrower: scattered remnants of tooth-forming tissue can persist in the jaw, usually dormant and harmless, capable in principle of restarting development. That gap, between a possibility developmental biology raises and a proven treatment, is what current research is trying to close.
Meet USAG-1, the molecular brake on tooth growth
The protein at the center of this research has an unglamorous name: USAG-1, short for uterine sensitization associated gene-1, also known as SOSTDC1. It is secreted by cells in the jaw and binds two pathways essential for building a tooth: bone morphogenetic protein (BMP) signaling, and Wnt signaling, acting through a receptor called LRP5/6. Together they instruct clusters of cells to organize into an enamel organ, a dental papilla, and eventually a tooth.
USAG-1 behaves like a brake held down on that process. Once the permanent teeth are in place, the brake stays engaged, which is one reason dormant tooth-forming tissue stays quiet. The logic behind the drug is simple to state, even if the biology isn't: release that brake, specifically and safely, and does tooth development start up again?
What the mice and ferrets showed
The first strong evidence came from mice. A team led by Katsu Takahashi at Kyoto University reported in a 2021 Science Advances paper that removing USAG-1 genetically, or blocking it with an antibody, relieved congenital tooth agenesis across mouse models carrying different genetic defects, in some cases producing a whole new tooth, complete with enamel, dentin, and a root, where a mutation had prevented one from forming.
Mice are an imperfect stand-in for human teeth, since their molars don't replace the way ours do. Ferrets, diphyodont like humans, offered a closer test, and blocking USAG-1 in ferrets also produced new teeth without obvious serious side effects, justifying a move to human testing. But a treatment working cleanly in animals isn't the same as working in a person; immune systems, anatomy, and tissue aging differ between species.
TRG-035: from the lab to a human vein
The therapy that grew out of this research is TRG-035, a monoclonal antibody designed to neutralize human USAG-1, developed by Toregem BioPharma, a Kyoto University spin-out founded in 2020, with WuXi Biologics as manufacturing partner. In autumn 2024, Takahashi's team at Kitano Hospital launched the first human trial of TRG-035 at Kyoto University Hospital: thirty adult men aged 30 to 64, each missing at least one tooth, received the antibody intravenously over an eleven-month Phase I study.
A Phase I trial exists to check safety and tolerability, not to prove a drug works. By 2026 it had concluded without serious adverse events, an encouraging signal, though Toregem has not published data showing new teeth grew in any participant.
With that safety data in hand, the company moved toward Phase II testing in the group most likely to benefit first: people with severe congenital hypodontia, born missing six or more permanent teeth. Japan's health ministry has granted TRG-035 orphan drug status for the condition, and in 2026 Toregem raised roughly $5.3 million toward the trial, on top of more than $29 million raised since founding. These children are a pressing group, since implants can't be placed until the jaw finishes growing, often leaving them in dentures for years.
Would this regrow any missing tooth?
Congenital tooth agenesis happens when a tooth never developed, often from an inherited mutation in genes like PAX9, MSX1, or WNT10A, leaving a leftover germ switched off. That's different from tooth loss caused by decay, gum disease, injury, extraction, or aging, where a tooth fully formed, functioned for years, and was later physically removed, root and all.
That difference is why congenital agenesis is the logical first target: there may be dormant material to reactivate. Whether the same antibody could help someone whose molar was pulled in their thirties is an open question, not a settled no; researchers describe restoring adult tooth loss as a longer-term goal, not the current focus.
How a tooth-regrowth drug would actually work
In simplified steps: a dormant cluster of tooth-forming cells sits in the jaw, held in check by USAG-1. The antibody blocks USAG-1 from suppressing BMP signaling, and the renewed signaling is thought to reactivate the cluster into a tooth germ, which would then need to differentiate into cells laying down enamel, dentin, and pulp, form a root, and erupt through the gum. That's a simplified model based on animal data, not a confirmed human account.
Why growing a whole tooth is harder than it sounds
A lump of mineralized tissue is not a tooth. A functional replacement needs the right shape and size, correct alignment with neighboring teeth, a root anchored in the jawbone, and a periodontal ligament, the tissue that attaches a tooth to bone and absorbs the shocks of chewing. It needs a blood supply, nerve tissue in the pulp, and has to erupt in the right place.
There's a safety dimension too. BMP and Wnt signaling aren't specific to teeth; they also direct bone, skin, and hair follicle formation elsewhere in the body. A drug interfering with USAG-1 has to be controlled enough to affect tooth-forming tissue without disturbing those systems, with effects tracked over years, not an eleven-month trial.
Could this replace dental implants?
An implant is a well engineered substitute: a titanium post anchored in the jawbone with a ceramic crown on top, a mature technology with decades of clinical data. A regenerated tooth, if the science delivers one, would differ in kind: living tissue grown from the body's own developmental program, with a periodontal ligament giving it the slight give and biting sensitivity a bolted-in implant can't replicate. It isn't a competition yet: implants are established and widely available; tooth regeneration drugs remain experimental, tested so far in a few dozen people, with human efficacy unproven.
So when might this actually be available?
Japanese media, citing the research team, have reported a hope of reaching market by around 2030, starting with children with severe congenital hypodontia. Treat that figure as an early aspiration, not a scheduled date. Between where things stood in 2026 and an approved medicine on a shelf, a long list remains: a larger controlled trial proving the drug regenerates teeth, long-term safety data, regulatory approval, and scaled manufacturing. This marks an early step, not a finished treatment.
Can humans really grow a third set of teeth?
The honest answer is layered rather than yes or no. Is it biologically plausible that dormant tooth-forming tissue exists in the human jaw? Yes, based on supernumerary teeth and third dentition case reports. Has blocking USAG-1 regenerated teeth in animals? Yes, in mice and ferrets, in peer reviewed research. Has a drug been proven to regenerate fully functional teeth in humans? No, and no published data claims that. Is human clinical research underway? Yes, with a completed Phase I safety study and a Phase II trial beginning in severe hypodontia patients. Can someone buy a tooth regrowth drug today? No. All of that is true at once, and together it describes where this research stands.
What happens next
For now, losing a permanent tooth still means choosing between an implant, a bridge, or a denture, the same short list dentistry has offered for years. What's changed is that a drug built on a specific molecular target has moved from a mouse cage into a human trial, now being tested in the patients most likely to benefit first. Nobody involved is promising that a tooth lost decades ago will grow back on schedule. What they're testing is narrower, and more interesting: whether cells left dormant in a jaw far longer than in a mouse or a ferret still retain the instructions to build a tooth once the right signal arrives, a question about aging and developmental memory the Phase II data may only begin to answer.
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