I will be in a dental surgery of two hours, how long does the effect of a local anesthetic?

1/12 to 3 hrs: The lifespan of the strongest anesthetic.3 hours.But usually less than 2 hrs.

Local anesthetics: Local anesthesia normally lasts from 30 minutes to 4 hours. This depends upon which local anesthetics are used, whether it is an infiltration or block injection and your own metabolism. There are some long acting local anesthetics that last up to 12 hours.