First generation filler used in dental composite resin was:

Various transparent mineral fillers are employed to strengthen and reinforce composites as well as to reduce curing shrinkage and thermal expansion (generally between 30% to 70% by volume or 50% to 85% by weight of a composite). These include the so-called “soft glass” and borosilicate “hard glass”, fused quartz, aluminum silicate, lithium aluminum silicate (beta-eucryptite, which has a negative coefficient of thermal expansion), ytterbium fluoride, and barium (Ba), strontium (Sr), zirconium (Zr), and zinc glasses. The latter five types of fillers impart radiopacity because of their heavy metal atoms. Quartz had been used extensively as a filler in the early versions of dental composites. Inorganic quartz was one of the first materials to be used and is often considered as first-generation filler. Phillips Science of Dental Materials ed 12 pg 280