Can you tell me exactly when is it too late to do something about tooth decay?

Tricky Question: If the roots of the tooth are still in good bone and the decay has not damaged them, we can still rebuild a tooth. But the sooner you treat decay the better off you are. Never leave decay untreated, it only ever becomes more complicated and expensive to repair. And remember, brush and floss every day, and have your teeth checked and cleaned professionally, regularly. These teeth are repairable.

Gross decay: Prevention is the best thing to, do about decay. Once there is decay in the tooth, the only thing to do remove the decay and restore the tooth with a filling or a crown. If the decay goes into, the pulp then a root canal ned's to be done. If the decay is too extensive sometimes it is not possible to treat the tooth and extraction is the only thing that can be done.

Never: It is never too late to try and prevent decay. Once you have it you want it removed asap so it doesn't spread. You can't reverse it but the treatments are more conservative, less expensive and less discomfort when done when they are small. The best is good hygiene and dental visits as well as diet to prevent it in the first place. See a dentist.

When the: Tooth is broken down beyond repair. A filing is significantly cheaper than having to go through a root canal, crown lengthening procedure, post and core and crown. Many thousands versus a couple if hundred. Not to mention numerous visits and discomfort. It's a no brainier - please don't wait. Hope this helps.