I imagine it was the stress that raised your levels - stress hormones cause the liver to release more glucose (going back to ancient times, when we would need a boost of energy for 'fight or flight').
I've had root canal work on two teeth. Basically, what has happened is that the nerve tissue in the tooth has become infected and probably died. This tissue needs removing completely and the cavity filled. Effectively, this makes the tooth dead and you'll get no further pain from it, although it can also make the tooth more brittle so be careful when eating crunchy things afterwards! One of the teeth I had done eventually satrted cracking with bits coming off (only after several years though).
Interestingly, the year before I was diagnosed I developed an abcess on the gum by the tooth and my dentist discovered that there was some remaining nerve tissue that had become infected again. He had no real choice but to remove the tooth - the first (and only!) adult tooth I have lost! Basically, it had had so many repairs that it was likely to just shatter if he tried to remove the fillings. Inretrospect, it would appear that I was already losing pancreatic function at that time and my higher (but unknown) blood sugar levels had encouraged the infection in a tooth that had lain dormant for over ten years. It's quite possible that this is at the root (!) of your current problems!
Hope it all goes smoothly! 🙂