I've had a crown for two years.. the pain eases up when i clench my teeth. any ideas why?

Fractured tooth: Please check with your dentist, you most likely have a cracked tooth. A cracked tooth is very unpredictible, and needed to be treated asap. Most cracked teeth can be treated with a root canal, core build up and a crown. Some teeth will fail due to a large crack, and may need to be extracted. here is a great link: http://www.aae.org/patients/symptoms/cracked-teeth.aspx Good luck.