The dream is wild enough to sound like science fiction: lose a tooth, grow another real one without implants or dentures.

A Japanese team has been working toward that possibility by targeting USAG-1, a protein involved in tooth development. The idea is that blocking that protein could remove one of the brakes on tooth formation. In animals, the work has already produced new teeth. In humans, the most important question is still open.

The work follows a 2021 Scientific Reports study showing that local treatment aimed at USAG-1 could change tooth number in mice. Since then, the program has moved from animal work into human testing. Japan’s national clinical-trials portal now lists the first-in-human study of TRG035 as complete. That trial was a Phase I, single-dose, dose-escalation study in 30 healthy adult men, ages 30 to under 65, each missing at least one molar. It tested five dose levels, from 0.4 mg/kg to 24.0 mg/kg, with safety as the primary endpoint.

The company behind the drug, Toregem BioPharma, has also said it completed the domestic Phase I study. While that’s real progress, it isn’t yet proof that the drug regrows teeth in people.

“The idea of growing new teeth is every dentist’s dream. I’ve been working on this since I was a graduate student. I was confident I’d be able to make it happen,” Katsu Takahashi, lead researcher and head of the dentistry and oral surgery department at the Medical Research Institute Kitano Hospital in Osaka, told Mainichi. “We’re hoping to see a time when tooth regrowth medicine is a third choice alongside dentures and implants.”

Takahashi has spent years studying tooth-regrowth biology, especially the genetic controls that help determine how many teeth form. “The number of teeth varied through the mutation of just one gene,” he told Mainichi. “If we make that the target of our research, there should be a way to change the number of teeth (people have).”

Researchers found that the USAG-1 protein could limit the growth of teeth in mice, so ensuring that the protein didn’t form could potentially invite teeth to grow. The team developed a medication to block the protein, and successfully allowed mice to grow new teeth.

A 2023 paper in Regenerative Therapy noted the lack of established treatments for tooth regrowth and described anti-USAG-1 antibody work in mice as a possible breakthrough for treating human tooth anomalies. A newer 2026 review in Stem Cell Reviews and Reports kept the door open, but used more cautious language: USAG-1 may be a useful developmental gatekeeper, and anti-USAG-1 strategies may make continued tooth formation biologically plausible under restricted conditions.

The first likely patients aren’t adults who lost teeth to cavities, gum disease, trauma, or age. Toregem’s current materials point first to congenital tooth agenesis—especially severe congenital hypodontia or oligodontia, conditions in which people are born missing multiple permanent teeth. A May 2026 investor-linked note described the initial rare-disease target as congenital absence of six or more permanent teeth, with prevalence around 0.1 percent of the population.

So yes, humans may retain latent tooth-forming potential beyond the two sets we normally use. Takahashi has argued that earlier work points to the beginnings of a possible third dentition, and hyperdontia—when people grow extra teeth—helps explain why the idea has appeal.

Toregem’s own technology page says that if anti-USAG-1 is administered to the “third dental crest,” it may be possible to grow a third tooth in adults. But that “if” is doing a lot of work. Researchers still have to show that a drug can produce a properly placed, clinically useful human tooth, and that the tooth erupts, integrates, and functions without creating new problems.

There’s certainly the money to try to make it happen. In May 2026, Toregem announced roughly $5.3 million, or ¥850 million, in Pre-Series C financing and said its total funding, including grants and subsidies, had topped $29 million, or ¥4.6 billion. The company said the new money would support Phase II clinical trials of TRG035 in Japan and preparations for future U.S. development.

Toregem points to 2030 as a goal for practical use, but it’s a target, not a promise. While the drug has cleared an early safety stage, we still need proof that TRG035 can regrow a useful tooth in a human mouth.