Transparent, colorless, particulate glass ceramic having a low coefficient of expansion, a high absorptivity for X-rays and which is useful in dental filling compositions, has the following ingredients, expressed as percent by weight of oxides: SiO2 40-55%, Al2O3 15-25%, Li2O 3-5%, P2O5 3-10%, MgO 0-3%, ZnO 0-5%, ZrO2 2-7%, Ta2O5 0-7% and La2O3 12-20%.
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