One you should worry about their dentist than the body scan.
"The TSA's scanners use an imaging system known as backscatter technology, which works by hitting a passenger with low-dose X-ray radiation as they stand between two box detectors. The image is produced on a nearby computer and can reveal weapons and explosives hiding under clothing or stowed away inside a person's body.
The key here is "low-dose." The average radiation exposure, as quoted by the TSA, for each scan is about .15 uSv (a unit of radiation), which is many times less than what you're exposed to at the dentist's office. In fact, according to the American College of Radiology and the American Roentgen Ray Society, an airline passenger flying cross-country is exposed to more naturally-occurring cosmic radiation from the flight than from screening by one of these devices."
Good thing I hate flying.