Michelle,
I have a to add a word of caution here. You shouldn't be putting anything substances in your mouth or on your skin prior to a radiation treatment. It can have a bolus effect and enhance the radiation in very negative ways.

Many of us have kept all of our teeth and have no problems. I used dental trays with presciption flouride almost nightly and had no pain or additional nausea from it - who could tell anyway -almost everything made me sick when I was deep into it. The possibility of ORN was 10% when I researched it 3 years ago. Brian has found that the ORN risk numbers has decreased substantially since data has started coming in about treatment with targeted treatment modalities such as IMRT, 3D conformal or Tomo CT.

I also discovered, in my travels, that some persons get ORN despite having all of their teeth pulled.

The teeth and gums have to be in good shape to start with and it is risky to have extractions after treatment. Constant flouride treatments and rigorous dental hygiene are a must for the rest of your life. I used a foam type, with a neutral pH and I tolerated it well - even with all of the mouth sores.

As far as the tooth question, it depends on where it is. If it is directly in the radiation field I would hazard a guess that they would prefer it to be healed up first. Even with a neck disection I believe that they allow about 2 weeks prior to starting radiation.

After she gets fitted for the mask she will go through three more phases, a C-arm xray (usually during mask fitting), a CT, then they have to program the software, so there will be a lag from the mask fitting to start of radiation of about a week and finally a simulation on the actual LINAC.