What one should do if teeth cavities are at first stage?

FIRST STAGE????: What do you mean by 1st stage? Is your dentist just watching them? If they are just watching them make sure you brush and floss at least twice a day to keep those areas clean. If you were told you have a cavity and need a filling, get the filling. The longer you wait the deeper and larger the decay will become. If you wait to long you may end up needing a root canal or extraction. Ask your dentist.

Fix it.: I'm not sure what you mean by "first stage", but the answer is....Get it fixed! the sooner the problem is corrected, the less complex, the less costly, and the less time consuming it will be. It will also be more comfortable. Please go see your dentist today.

Cavities: Teeth with cavities need to be treated and only deepen and worsen if untreated.

Filling: A cavity no matter what stage needs to be treated by a dentist. Once a cavity is started, it will only get worse. Have the cavity filled by your dentist as soon as possible.

Restore immediately!: It is always best to fix a problem when it's simple. Small cavities mean simple and easy procedures to correct. Waiting only means bigger cavities, more complicated dental visits, more expense, and possible pain! do not delay, if you have a medical or dental problem, be proactive!