Greetings Paul!
I cannot add anything to David's informative post, but will offer my experience. While I didn't have concurrent Cisplatin/IMRT, Cisplatin was in my induction chemo phase. I was lucky not to have any major issues while in chemo, wasn't until I got to the IMRT that most of my problems started.
I was able to work through all but the last week of my IMRT. I went 20 treatments (4 weeks) had a 2 week break, to heal a bit, and then forged on for the final lap.
One other thing you need to know. Just because the IMRT treatments are over, you will still have effects for a period of time afterwards. It is not simply turning off the switch.
Good luck with your visit with the Dentist. My Oncologist still to this day shakes his head when I remind him I've still got all of my teeth

Kevin