One of the first bioactive glasses to show an extended working range suitable for sintering or fibre drawing without crystallization occurring was 13–93 [4]. However, this glass has a high silica content (54.6 mol.%, compared to 46.1 mol.% in 45S5), a high network connectivity (2.6 vs. 2.1 in 45S5) and a relatively high MgO content (7.7 mol.%), all of which have been shown to decrease bioactivity [2] and [5]. In addition, clinical studies show that bioactive glasses with a high silica content and high network connectivity are tolerated well by the human body but degrade very slowly, with remnants of glass still being present in the patient after 14 years [6].