Clinical Application of Glass Ceramics

Abstract

Synthetic hydroxyapatite (HA) is now widely used as a bone substitute and as a coating material of joint prostheses, for the reason that HA has a character of osteoconduction and a capability of forming direct bond to the living bone tissue. In the clinical practice, however, often there is a need for a material which has both stronger bioactivity and higher mechanical strength than HA in order to obtain earlier bone bonding with bone substitute and to let patients put their body weight earlier on the affected site promoting their ambulatory life. Apatite- and wollastonite-containing glass-ceramic (AW-GC) synthesized at Kyoto University in 1982 has stronger bioactivity as well as higher mechanical strength than HA, and therefore, AW-GC has been used to fabricate various types of prostheses and spacers to be used in the spinal surgery and tumor surgery. Particularly, lumbar intervertebral spacers and cervical laminoplastic spacers have been used in thousands of clinical cases with excellent clinical, radiological and biomechanical results. AW-GC has also been used as a coating material of hip prosthesis by the technique of bottom coating over the porous surface. A mid-term follow-up study of several thousands of clinical cases of hip replacement demonstrated the significantly early osseointegration at the AW-GC bottom coated area comparing to the HA coated area. It is also anticipated based on animal experiments that the AW-GC bottom coating will ensure much longer stability of joint prosthesis than the AW-GC full coating or HA full coating. Thus, it was shown clinically that the AW-GC is useful as a bone substitute as well as a coating material even in locations where HA can not adequately be used.