What is best to do when a tooth decay occurs? scrape it?

Then Have Filled: If you scrape or drill out decay, you have to fill the empty area. If the decay is small enough, instead it can be chemically treated and re-calcified without removing tooth structure. Decay left alone will only do more damage.

See a dentist: Treating tooth decay is not a "do-it-yourself" project. Depending on the extent and location of the decay, you may need a small filling, a root canal, a large filling, or a major restoration like a crown. If the damage is severe enough, an extraction may be required. Only a licensed dentist can properly diagnose the problem and suggest a treatment plan, as well as options.

Tooth decay: You have to correct the problem. The decayed part of the tooth needs to be removed, it can be scraped, but generally this requires drilling. After this the missing part of the tooth should be restored, a filling or crown.