The discomfort of a dental shot is mostly due to the feeling of pressure created by the flow of anesthetic. By controlling the pressure at which the anesthetic is delivered, a computerized injection system (called The Wand) can greatly relieve this discomfort.
Here's how it works: a very thin needle attached to a pen-sized wand is positioned near the gum, but before the needle actually touches the gum, a drop of anesthetic numbs the surface tissue.

As the dentist gently glides the needle into the gum, the tissue just ahead of the needle tip is numbed by the anesthesia. Once the needle is fully inserted, the computer slowly releases a stream of anesthetic. There is no sudden prick or burning sensation.
Many patients (82 percent in one study) who have experienced anesthesia with The Wand say it is a completely painless process. Some even say they experience less lingering numbness.