Zirconium-containing BaO- and PbO-free X-ray opaque glasses having a refractive index nd of about 1.57 to about 1.61 and a high X-ray opacity with an aluminum equivalent thickness of at least about 400% are provided. Such glasses are based on a SiO2&mdashAl2O3&mdashLa2O3&mdashZrO2&mdashCs2O system with additions of Li2O, Na2O, ZnO and/or Ta2O5. Such glasses may be used, in particular, as dental glasses or as optical glasses.