An improved Mineral Trioxide Aggregate (MTA) filling material for dentistry and a device for its use to seal natural, pathogenic, or iatrogenic, tooth cavities. The filling material comprises Portland cement, or variations in the composition of such cement, calcium sulfate and a radio pacifier material. The improved filling material exhibits favorable physical and chemical attributes sufficient to form a biocompatible and effective seal against re-entrance of infectious organisms. A device for delivery of MTA filling material to the site of operation is also provided.