By using 45 Ca-labeled calcium hydroxide, the fate of the calcium hydroxide component in a root canal filling paste, Vitapex, was investigated. It was made of calcium hydroxide and iodoform with the addition of silicone oil. Whole-body, light, and electron microscopic autoradiographic surveys were used. These investigations made it clear that the calciumcomponent moved to the bone tissue through the blood and that some of it was excreted through the digestive tract. Furthermore, it was established that in both types of heterotopic calcifications, dystrophic and matrix vesicle, calcium came partly from the calcium component in the paste.
