Definitions and Descriptions

Various substances with local anesthetic effect are employed in dentistry. It's a family of molecules having common derivation and that are packed into disposable (one use only) ampoules, with an eventual little percentage of adrenaline.
All these substances inhibit the dolorific nervous transmission from the peripherial nerves to the receptive areas in the brain, working by means of chemical isolation for the nervous signal in the injected area.
Adrenaline is employed to enhance the effect but it also can be absent.
Carbocaine, Xilocaine, Articaine are some of the used substances.

The most used kind of syringe is the one designed for ampoules, and it simply is a steel device that is sterilyzed after each patient, into which an ampoule and a needle (both disposable) can be inserted.
There also are some special kinds of syringe, like for example the one used to do the so called intra-ligamental anesthesia: in this kind of device, the ampoule is closed in a sealed tube that avoids scattering of glass pieces in case the ampoule should break, since the pressure used for this kind of injection is higher.

For all the teeth belonging to the maxilla (upper jaw), plexic anesthesia is performed. It simply consists in delivering the substance "under the skin", within the mucosa that is, more or less at the presumed height of the root's apex of the tooth to be treated.
The same anesthesia can be used in the incisives of the mandibula (lower jaw), but offers increasing problems when it is performed on more posterior teeth: the reason is that the mandibular bone covering the teeth, increases its thickness towards the rear part, at the point that a plexic anesthesia on a lower molar could have a weak result.
Many operators prefer to do a troncular anesthesia instead. It's an injection on the lower alveolar nerve, controlling sensitivity on all the mandibula (one for the left and one for the right side). A mucosal area situated posteriorly to the last molar, almost next to the pharynx' opening is pinched.
The effect is slightly retarded and causes the anesthesia of all the mandibular side up to the lower lip's half, and also of the same half of the tongue (because of the proximity of the lingual nerve).
Whatever the anesthesia being used, its effect may last from 1 hour to over 4, according to the situation. The substance is being disposed along with the urine, doesn't leave any trace in the body and does not produce any collateral effect nor any addiction.