The longest acting anesthetic available in dental cartridges is bupivacaine (0.5%). It can "freeze" teeth up to 240(!) minutes and soft tissues (gums) up to 440(!!) minutes.
Source: Becker D and Reed K, Essentials of Local Anesthetic Pharmacology, Oral Health, Feb 2007, Vol 97 No 2, pg 17-34.
Hans Skariah, B.Sc., DMD
Promenade Court Dental Health Group in Mississauga
2233 Hurontario St., Mississauga, ON, Canada
(1/2 km north of the QEW in the Dome Building)