My last molar,under bridge, treated with root canal hurts a lot during day. it quitens at night. xray revealed no abscess but i still worry what it is?

Tooth Pain: Radiographs often don't reveal all issues. The tooth may be fractured, or there may be an infection that is not visible on the radiograph. Seek a second opinion from an endodontist, a root canal specialist.

More sleuthing : More investigation required. You may have a tooth in hyperfunction, or a fractured root, or a parafunctional habit, or decay under the bridge, or swollen gums, or so many other reasons. Please seek evaluation by an Endodontist.