Root end filling material of choice is:

Mineral trioxide aggregate (MTA) is composed of tricalcium silicate, tricalcium aluminate, tricalcium oxide and silicate oxide. Bismuth oxide is added to the mixture for radiopacity. pH - 12.5 (when set). Setting time is 2 hours 45 minutes. Compressive strength—40 MPa (immediately after setting) which increases to 70 MPa after 21 days. Excellent biocompatibility. In contact with periradicular tissues, it forms connective tissue and cementum, causing only very low levels of inflammation. So, best material for root end filling.