During my tragically misdirected youth (all I can seem to remember is that the President was named "Herb" Something) I met a fellow in a Maine boatyard who filled a tooth cavity (his own) with Marine-Tex. Seemed to work OK. Good color match, too.
BTW, Tex, it is not widely known, but most of the antiquities in the care of the Gippo Museum are already Bondo.