My dentist has ordered a Cone Bean CT scan, is it worth the radiation risk?

My dentist referred me to a lab to get "tomos". In talking to the lab, they would use Cat scans. My  dentist requires this  before he will attempt to straighten my teeth. He says this is the wave of the future. Unfortunately, I've also read recently, and my doctor has acknolweged, that they are learning now that there are non-trivial long term risks for lymphomas from diagnostic x-rays. For this reason, babies are no longer given x-rays unless it is absolutely necessary.

What would my dose for the iCAT scan be? The first thing you will hear if you ask is that the radiation dose is "minimal" or "negligable" or "trivial". Don't accept these answers. You want is actual numbers.

What the lab told me after doing some research is that the effective dose of the 20 second iCat scan is 68 uSV. The exposure is in pulses, 3.5 seconds for the 20 second scan. For comparison, an iCat 10 second scan gives you a 34 uSV dose, daily background radiation gives you an 8 uSV dose, a digital pano x-ray gives you a dose of 4.7 to 14.9 uSV.

Since I am concerned about minimizeing radiation, the lab said they can build the pano and latteral shots from the one 20 second iCat scan. What is the actual cancer risk from getting an extra weeks worth of radiation in 3.5 seconds of pulses?  Currently researching...