Abstract No materials placed within a living tissue can be considered to be completely inert. However, stable ceramics do not suffer from corrosion or degeneration as do metals or plastics. Extensive progress in ceramic technology has developed new functional bioceramics with a high degree of biocompatibility or bioinertness, or with bioadhesiveness with bioactive and biodegradable characteristics which can accelerate new bone growth. However, ceramics with a characteristically high Young's modulus are aptto produce biomechanical unbalance at the implant-tissue interface and cause chronic mechanical irritation which introduces tissue inflammation and probably conceals neoplastigenicity. To prevent such mechanical irritation, ceramic implants should be fixed strongly into bone tissue. Porous ceramics are effective in giving reliable fixation and have produced many successful oral and orthopaedic implants to date.