Huh. I've had several root canals, some in my upper jaw, and even one broken tooth in the upper jaw (it had a large filling, I bit on a hard bread, it broke apart and crumbled -- quite awful pain, it now has a crown), and there never has anything fallen down my throat. I think (of course I can only guess what exactly they are doing in my mouth), in these situations the assistant had the suction tube near the work area, so anything was sucked into it, rather than falling simply down.