Hey there! I'm glad the Gabapentin is helping. That's good.
In my experience with going to the dentist, I find that the pain increasing is unavoidable if I'm having a particularly bad pain day. If you are having work done then yes you very much need numbing. If you're up for it, ask them to add extra to all the areas where your pain is affecting you if they are working on that side. If it's just a cleaning, I would recommend trying nitrous gas vs numbing as I find the numbing can create tenderness on the injection sites which can lead to the pain flaring up. Make sure you take some Tylenol or Advil for any inflammation. It's very much a matter of trial and error to find out what helps and works for you.

I would suggest seeing a neurologist. It's always a good idea and can't hurt. They can rule out other possible causes and know the treatment for TN. They know which medications to prescribe and how to dose them. They are more knowledgeable of TN than other physicians.

Hope this helps.