The aim of this study was to investigate the radiopacity of composite core materials. Radiopacity of composite core materials, filling materials and base cements were measured by densitometer. The elemental analysis of fillers were made by using an electron probe microanalyzer, and the filler substances were identified by a powder X-ray diffractometer. Radiopacity of composite core materials, except for some resin materials, showed low radiopacity. Silicate glass or crystal silica was found in

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... ll fillers. Zr or Yb was identified in some fillers, and Ba ions were detected in the glass fillers. Composite resin core material including Zr showed the highest radiopacity. These results suggest that the filler including Zr ion would be preferable for increasing the radiopacity of composite resin.