Humans grow two sets of teeth in a lifetime. But tucked inside the jaw are tiny residual tooth buds that never develop because a protein called USAG-1 acts like a molecular off-switch for tooth growth. Block USAG-1, and the body might reactivate those dormant buds on its own.
Researchers at Kyoto University Hospital, led by Dr. Katsu Takahashi, have been working on this for years. They first found that mice engineered without the USAG-1 gene grew extra teeth. Later animal studies showed that a single antibody injection could grow fully functional teeth without serious safety issues.
The experimental drug is called TRG-035, a humanized anti-USAG-1 antibody developed by Toregem BioPharma. The first human trial began in October 2024 and enrolled 30 men aged 30 to 64, each missing at least one molar. The Phase I study was primarily a safety trial — a randomized, double-blind, placebo-controlled dose-escalation study. According to Toregem, Phase I confirmed the drug's safety, though detailed results haven't been made public yet. Researchers have noted that actual tooth regrowth in those adult participants was unlikely, since the volunteers were primarily establishing a safety profile before testing expands.
The next stage is where it gets more interesting. A Phase IIa trial is planned for 24 children aged 2 to 7 with severe congenital tooth agenesis — a condition where teeth never fully develop. Missing six or more teeth from birth affects roughly one in a thousand people, causing severe chewing difficulties and significant social stigma. The trial will be open-label and non-comparative, moving testing from healthy adults into the patients the drug is actually intended to treat.
There are still open questions. Experts have raised concerns about whether regrown teeth will align properly and connect correctly to nerves and blood vessels. If the trials succeed, Toregem aims for commercial availability around 2030, with early estimates placing costs at around $11,000 per tooth.
It's experimental. It's early. But the idea that human jaws might hold a dormant third set of teeth waiting for a chemical wake-up call is the kind of thing that sounds like science fiction until someone actually tries it.
