Root canals are not simple, straightforward procedures. They are difficult and complex. An upper right molar typically has 4 canals, however, there can be more. There can be lateral canals. There can be a strange apex or apicies . An x-ray may help determine the problem. Is there a radiolucent or black area (where it should be white bone) at the tip of a root, or up high, in between the roots of the tooth? Even when done well, a radiolucency at the root tip might mean the root may need an apicoectomy (the tip of the tooth is cut off after the Endodontist makes a window in the bone and gets to the root tip from the side). And assuming the Endodontist will want to do an apicoectomy on a #3, as there is a lot of bone around there due to the Zygomatic Process of the skull. A radiolucency in between the roots will indicate that the tooth is fractured and this is not a good thing. In all likelihood the tooth would need to be extracted if a fracture is suspected.
By the way, the problem is not if the filling is fractured. The question is did the tooth fracture?