Hello dear, no worries about it, you mention that you had underwent for root canal treatment in your lower molar teeth and after that metal cap had got installed, while you having any hard food substance it get dislodged.
Next Steps
visit dentist by taking with that metal cap which got dislodged, they will send that metal cap for sand blasting and later they check out the proper fit if it's ok then cemented that metal cap on RCT treated teeth