There has been a similar story from last year when FDA red tape prevented certain types of pasta from being imported into the US.

https://www.grubstreet.com/2020/12/2020-bucatini-shortage-in...

To be fair this is not just limited to the US. In a theoretically free trade world, food safety regulation remains one of the few ways that states could still practice mercantilism.

https://www.livescience.com/47032-time-for-us-to-ban-ractopa...

https://www.bigissue.com/latest/the-truth-behind-the-chlorin...

Yeah, but it seems to be mostly because the change has been silent and under the covers. But what I gathered are two basic things:

One, GSK bought up the brand name NovaMin, possibly related patents. GSK took competitors (or their own product?) off the market, and pushed their premium and strongest brand Sensodyne to the front.

Two, toothpaste is considered a drug in the US and falls under strict rules. They can still use NovaMin / the chemical compound, it's still there, they're just not allowed to advertise with it.