It depends into what area the Local is being administered and also the volume being given. Usually a block will last longer than an infiltration. It also depends on the technique being used and finally the particular aramatic moity of the local. All things being equal a block on the mandible (lower) one cartridge 1.8 ml will last about 30 minutes in the bone (deep anesthesia) and about same time for soft tissue to return to sensitivity. The thiophene molecule (articaine hcl) is dose related. In other words, if you have achieved profound anesthesia (pulp test) with 0.9 ml, by increasing the volume to one full cartridge will extend the duration. The benzene molecule does not have these properties. Haynes Darlington M.Sc. PharmD