Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain after root canal treatment as the blood supply of the tooth is lost due to cutting down of nerves and blood vessels the tooth becomes fragile and when forces are applied on it during chewing and other activities there are chances that the tooth will fracture and in your case as it is already three years passed when root canal was done thats why the tooth is getting fractured and when there is lost of tooth wall the filling cannot be retained and gets dislodged.. You should consult your dentist and get clinically evaluated as well as get an x ray done so that the exact status of the tooth and the root canal is evaluated as it is not always necessary to get re-root canal done if the treatment and the root canal filling is intact and there is no infection.. In this case if root canal is intact and if much of tooth structure is lost POST AND CORE TREATMENT followed by CAPPING can be done but if tooth structure is sufficient re-filling of tooth and capping can be done.. In case if there is some infection and if needed root canal can be repeated.. Till you get the tooth treated avoid chewing from that side to prevent fracture of tooth further.. Hope this information helps.. If you find the answer helpful please give me a Five Star Review and click on found the answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora..