BONDING CAPACITY IN BONE OF HIP-PROCESSED HA-COATED TITANIUM - MECHANICAL AND HISTOLOGICAL INVESTIGATIONS

The main problems using plasma-sprayed hydroxyapatite (HA) as a coatin g material on metallic implants are its porosity, low fatigue strength , and weak adherence to the metallic substrate. To overcome these prob lems a new technique using hot isostatic pressing (HIP) has been devel oped for producing HA-coated titanium (Ti) implants. Specimens produce d at a maximum temperature of 850 degrees C and a maximum pressure of 720 bar displayed a dense, glassy, 25-mu m thick coating with small am ounts of porosity and a mean surface roughness of 0.7 mu m, as compare d with 1.6 mu m for sandblasted Ti. Twenty conical HA-coated (720 and 100 bar pressure) and 10 noncoated Ti implants were inserted through t he cortex of the lower margin of the mandibles of sheep and allowed to heal for 60 days. Push-out tests for implants processed at 720 bar pr essure showed substantially higher bone/implant bonding values than fo r sandblasted Ti implants. Histological studies indicated a direct con tact and probably chemical bonding between bone tissue and the HA coat ings. The area of contact was almost 3 times as large as for the Ti im plants. The adherence of the 100-bar coating to the Ti surface was inf erior to the 720-bar coating, as shown by the loosening of the coating s in several areas. (C) 1995 John Wiley & Sons, Inc.