The right treatment is dependent on the location and type of cancer that you have. Gennerally IMRT can be used and would be preferred to avoid damage to healthy tissues as Gary indicated. However some treatments the IMRT may not help based on the location.
Again depending on where they need to treat the IMRT may help reduce some teeth exposure which may save some teeth. However if the teeth and jaw need to be treated, healthy teeth and gum a necessery to avoid problems latter if the teeth need to be extracted and then there could be healing of the gum problems which is why they are determining if you need to take some teeth out. I was lucky. My teeth (gums) were all 3+ probe reading and none needed to be extracted as well as the IMRT allowed minimim exposure of a large part of my jaw.