Tooth enamel — the hardest substance in the human body — cannot regenerate once lost. This has been a foundational axiom of dental science for over a century. All treatment is prevention or prosthetic replacement.
A gel made from elastin-like recombinamers, proteins engineered to mimic those active during infant tooth development, can regrow structurally integrated enamel on adult teeth. The gel contains no fluoride. Applied like a standard dental treatment, it captures calcium and phosphate ions from saliva and organizes them into new enamel crystals through epitaxial mineralization — crystal-on-crystal growth where the existing enamel surface templates the orientation of new crystals.
The mechanism is indirect. The protein gel does not build enamel. It creates the geometric conditions for saliva's own minerals to crystallize in the correct orientation. The body does the construction; the gel provides the blueprint. Once the mineral structure locks in, the protein scaffold dissolves. The thing that enables the repair disappears from the final product.
This is structurally distinct from filling a cavity with composite resin. Resin sits on top of enamel — a foreign material bonded to a biological surface. Regrown enamel is continuous with the original crystal structure. There is no interface, no boundary, no joint. The repair becomes indistinguishable from the original.
The hardest substance in the body is rebuilt not by adding hardness but by providing softness — a temporary protein scaffold that organizes the environment and then vanishes. Strength is scaffolded by what disappears.