I've been to another dentist and they said
  things completely different. I don't 
  understand how two professionals can draw 
  polar opposite conclusions.

Isn't there some kind of solution for these sort of diagnostic aberrations or difference in medical opinions?

I know they have tumor boards for cancers and such where they try to arrive at a consensus plan of treatment for an individual patient.[1]

Surely there are such solutions for dental / other medical issues, right?

Somewhat tangential from all this, I'm amazed that in this day and age we still have such a hit or miss approach to treating patients. Its mind blowing how little our medicine has advanced in some aspects despite cutting edge innovations.

[1]

What Is a Tumor Board? An Expert Q&A

https://www.cancer.net/blog/2017-07/what-tumor-board-expert-...