Toothaches have many causes: decay, trauma, infections, and recession of the gums are just several of the potential causes.
A toothache caused by decay usually will result in a root canal. This procedure cleans the nerve and infected blood supply from the middle of the tooth. Patients usually feel immediately better, despite the bad reputation of the "root canal".
Diagnosis of a toothache usually requires an X-ray. This picture shows the entire tooth and the bone around it. The "check-up" x-rays are used mostly to detect decay, and therefore aren't always helpful with diagnosing the source of the pain.
Antibiotics are often used to reduce pain and swelling. However, if the nerve is infected, the pain will likely return at a later date. It is important to not consider yourself cured just because it feels better. Tylenol or Advil, if appropriate, are also usually prescribed for moderate pain and swelling.