Root canal tooth, crack in crown, never had pain or discomfort, replaced crown & now pain?

Had a root canal 5 years ago, never had any issue after. New x-rays showed a crack / cliff like break in the back of the crown. New dentist recommended changing / putting new crown on. New crown was put on & initially when chewing on that side / tooth, it was hit or miss in terms of sensibility. Dentist said give... show more Had a root canal 5 years ago, never had any issue after. New x-rays showed a crack / cliff like break in the back of the crown. New dentist recommended changing / putting new crown on. New crown was put on & initially when chewing on that side / tooth, it was hit or miss in terms of sensibility. Dentist said give it a few weeks to adjust. It's now been 8 weeks and every time I chew on the tooth, it is sensitive & some what painful... why?
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