http://www.radiationcontrol.utah.gov/XRAY/Dental_e.htm
The Utah "Division of Radiation Control" claims that a "bite-wing" dental XRay requires 150-350mrem.
Don't want to get into a tif with you... I suspect that the "2mrem" you're recalling is "whole body exposure" that the subject gets in that procedure, not the amount of radiation that the Dental XRay uses to take a picture of that very localized area of the mouth.
