My mother had a root cancal, and a crown over 20 yrs now. For the last 4mths she has been having horrible pain in that tooth. The teeth beside of this one has also had a root canal, and crown. She does wear a night guard because she is a grinder, but would that cause only one tooth to hurt? It is on of the big front ones. She went to a local dentist but he only told her it would get better or worse. Thank you for you time, and help.