There was an incident a few years back when some female suicide bombers from Chechnya successfully blew up two aircraft in Russia by hiding explosives in their bras. They were detained prior to this, but bribed and charmed their way onto the planes anyway.
For awhile afterward, TSA agents had free reign to basically feel up any female traveler they wanted. Sure enough, there was some sexual abuse going on, and lawsuits ensued. From my understanding they don't do that anymore.
I really don't think that breast implants are any more of a danger than someone hiding explosives in his or her body cavity. Hopefully, when they try to implement screening for that, there will be enough sane and "unconditioned" people to stop flying.