The problem with a lawsuit is that it's very difficult to get doctors/dentists to testify against each other. There are experts who do nothing but testify in cases like these, but they are very expensive, and you will put your expert before the jury (who the jury will be told is being paid to testify), and then the defense will put two doctors/dentists on to rebut everything your expert just told the jury.
If I were in your shoes, at least for the time being, I would focus exclusively on my own health and peace of mind. Maybe investigate some forums where people suffering with headaches, TMJ, or facial or dental injuries are sharing their experiences, treatments, outcomes, or other ways they have helped themselves overcome the injuries. I always start with Reddit, which has an undeserved negative reputation. I've gotten helpful advice there, or at least enough information to push me in the right direction. You might discover something crucial that you didn't know about your condition that helps in your understanding of exactly what happened, right down to the muscles and nerves affected. Then you can begin to form a plan of what to do about it.
Lastly, some things just go away. I thought for a time I would never be able to raise my left arm upwards again due to a weight-lifting injury, and it took more than a year, but it did go away. Same for a wrist injury, two foot issues. Please don't give up. The human body is very strange, but it has great intelligence. It wants to get better as badly as we want it to get better.
Keep us posted.