It could be several different things: grinding, gum recession, internal crack caused by deep filling, or recurrent decay blocked by the filling on the x-ray. Did she check for cracks with either a Tooth Slooth or Frac Finder? I have found if you have a large, deep amalgam filling, that over time, if you are a grinder and internal crack will develop. Then, when you grind your teeth, the cusp will wedge apart, causing the nerve endings to "stretch". This would lead to a reversible pulpitis and if not treated, an irreversible pulpitis. If it progressed to an irreversible pulpitis, a root canal would be needed.
Another thing with molars is that there are multiple roots, therefore multiple nerves. Usually, a molar will have 3 nerves (2, 4 or even 5 nerves in a molar are possibilities). One nerve will be a large nerve and the other 2 are small nerves, easy to damage. So you can have nerve damage or death of the small nerves, but have the big nerve (usually the palatal root nerve) be healthy and give a false positive that the tooth is healthy. So, after Prevident use and a nightguard, the symptoms persist, go back to the dentist for a re-evaluation. Stick with this one as it seems that she knows what she is doing.!! Good luck!!!!!!!!!!!!!!
Louis B. Sachs, DDS
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