How many times do I need to undergo teeth whitening?

As you age, your teeth tend to become yellowed and discolored.

Since the condition is also not good

I also worry about it when I smile.

If you undergo whitening treatment

Is it enough to do it only once?

Do I have to do it again at each interval after completing it?

I'm curious about that.

I'll be waiting for those who have tried it to respond.