NTI guard is temporay for jaw/neck pain.

I am not on any splint or night guard.  Haven't used anything before. I have constant pain in the lower jaw under ear and neck for 10 months now. Dentist suggested NTI guard to try for a week or two to see if it helps. If it helps with my pain, he told me to try with splint or guard.  Does NTI relive jaw pain and symptoms? Is NTI an alternative for splint or orthotic? Dentist also suggested nerve shots diagnostic test on my right side teeth to see if the pain is from any of the tooth. This diagnostic test has been proposed since I am having tapping and biting pressure on one of the lower molar since the beginning of this pain episode. Had root canal and crown on that tooth, but still the same symptoms of tapping and biting pressure pain. Dentist want to try numbing nerve shots diagnostic test on this tooth and other molars  to see if the pain stops. are these really helpful for my diagnosis? suspecting root fracture in 46 but nothing found in CBCT. lump spots in jaw & neck.