Zirconium: Characteristics, Technology and Performance

Different ceramics have been proposed as materials for medical devices. Alumina, zirconium oxide and zirconia toughened alumina are the most studied ceramic materials for biomedical applications. These materials were proposed firstly for orthopaedic prostheses and successively for other purpose such as dental restorations. Alumina showed atoxicity and is well tolerated by bone and soft tissue. Solid specimens showed to be well tolerated by fibroblasts and osteocites. Also inflammatory reaction of alumina, compared with titanium appears lower. Alumina biocompatibility resulted to be comparable to other dental ceramic. Zirconia biocompatibility was studied in vivo and in vitro. In vivo studies were the first to be performed since 1970. Bone and muscle reaction after insertion of a zirconia sample was evaluated. No adverse response was evidenced in these studies. In vitro studies focused on different topics: tissue reaction, mutagenic and carcinogenic power, cell behaviour. Tissue reaction was influenced by the specimen, but in general bulk samples didn't result to be citotoxic. Zirconia didn't show ability to generate mutation or degeneration on cell cultures. Moreover fibroblast showed great ability to grow on zirconia surface. Moreover both zirconia and alumina showed less proinflammatory properties if compared with other biocompatible specimens such as titanium and high density polyethylene. Recently the development of a new class of ceramics Zirconia Toughened Alumina (ZTA), and more recently Zirconia Plateled Toughened Alumina (ZPTA) combining the mechanical properties of Alumina and Zirconia has improved the use of these ceramics in biomedical applications (especially in orthopaedic surgery). In vitro tests demonstrated the absence of citotoxicity and mutagenic and carcinogenic power of these materials when cocultured with cells. In vivo tests of bulk materials showed the absence of local and systemic toxicity after implantation into bone. there were no statistically significant differences in direct bone contact when ZPTA was compared to Alumina and Zirconia ceramics. After Pierre Boutin introduced alumina into orthopaedic surgery, research efforts were concentrated on improving the mechanical behaviour of the materials. This process led to today's high performance alumina. The development of zirconia overcame many of alumina limits, but its future in orthopaedic surgery is unclear today. The advent of ZPTA ceramics with the hardness, inertia and stability of alumina and the durability and strength of zirconia ceramics will drive the development of innovative ceramic devices.