A root canaled tooth becomes brittle after the procedure because there is no longer a blood supply to the tooth. This is why a crown is necessary, especially on a molar which takes a lot of stress. You had better hope that the fracture isn't severe enough to warrant an extraction. Some fractures, depending on severity, are fixable by a build up and sometimes require a post in conjunction with a build up (like rebar in cement.) The tooth will then be prepared and impressed for a custom fit crown and it will look as good as new.By the time you visit your dentist,avoid eating from that side.Take liquid or semi-solid diet.
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