Why do they give you laughing gas and / or anesthesia for wisdom tooth extractions?

Pain/anxiety control: Local anesthesia is used to deaden the nerves in the area and insure the patient is physically comfortable during the surgery. Nitrous oxide or laughing gas is used in what is called conscious sedation to help patients be more relaxed during these procedures. It is also common to administer intra venous drugs to help with patient management.

Reduce Anxiety: Laughing gas is nitrous oxide which is an inhalation general anesthetic which lessens anxiety at lower doses. Valium or versid are drugs that cause dissociation where you are aware of things but, being a bit high, you don't care about what is happening. In some patients, these two drugs cause amnesia for the event, even though you can talk and respond to the dentist and people around you.

Patient Comfort: Although local anesthesia can provide adequate pain control for the procedure, the procedure itself is somewhat disconcerting to patients. If you can imagine the dentist working right at the back of your mouth, you can imagine that this might not be the most comfortable thing.

Pain control: The nitrous oxide (laughing gas) is a mild anxiolytic. That means it calms you down and makes you somewhat carefree about the situation. Some people don't like it because it makes them feel "weird" and out of control. Some patients love it. The local anesthetic (the injection) is to numb the area so that you don't feel anything during the extraction and for a few hours afterward.