Novocaine, that's the stuff that makes it possible to complete complex dentistry without discomfort. It's the stuff that "numbs" the tooth. Now really we don't use basic novocaine. I would guess the main drugs used these days are Lidocaine, Mepivicain, and Articaine. All these drugs are various derivatives in the same chemical family. They all do basically the same thing: make the area where we are working "numb".
It comes in little 1.8cc carpules that we put into the syringes. Yup, we still have to "squirt" the medication into the tissues, usually after placing some topical anesthetic. The numb feeling usually lasts a few hours. With kids you really worry about them biting their lip once they have left the office. I think the advent of local anesthesia is one of the the most significant advances in modern dentistry.