I've lived in at least two places where that treatment is available for adults. Insurance may cover it depending on what kind of insurance you got, it is expensive but not ridiculously so in comparison to other dental procedures.

Uh, no, i don't. Sounds weird, where do they do this?

They do that?

My wife works in dental insurance so I asked her. She said for the general public, the effectiveness of the sealant decreases as the client ages, because an adult's tooth is more smooth than a child's. So there's a critical age where the cons outweighs the pros.

It's useful in immature teeth because the grooves have not yet taken up enough fluoride to be acid resistant enough against the modern diet. Not all immature teeth need them either, as not everyone has those deep grooves. Furthermore, this only protects against decay on that surface if it's done well - and a lot of the time a wriggly kid means saliva has contaminated the surface and now you have an extra interface of failure.

In adults the benefit is a lot less (if the groove was decay prone, they would have formed a cavity there by the time they see a dentist), and doing this procedure may actually increase the risk of decay than reduce (due to the extra interface of failure).

Lastly, this only protects that surface - not in between teeth. A lot of cavities happen between because there's a lot of plaque being left behind there... Because almost nobody flosses properly.

Use your interdental brushes folks! And stop drinking soda... And use extra high fluoride toothpaste.

One of the reasons we don't seal adult teeth is because insurance doesn't cover it and people don't want to pay for it (there are other reasons like prior fillings, loss of tooth structure, groove being less prominent, etc). If someone asks for it to be done and agrees to pay out of pocket we'll definitely do it.

I've had it done as a young adult. Fluoride treatments too. Maybe my dentist is weird, but some places definitely do it.