I am scared to death, i have to have oral surgery at 18 weeks?

i have a severly decaid tooth that previously had a root c on it. i need oral surgery to get it removed. i am scheduled to get the surgery next monday at which time i will be 18 weeks pregnant... i am sooooo scared, i am afraid this procedure will cause miscarriage or something to go wrong with the baby. i got a letter of permission from my ob but i am still really scared because i know there is no way the could deny me the surgery because the risk of infection is so great and i cant just keep taking antibiotics.. has anyone else had oral surgery while pregnant and was everything ok with your baby