NET-SHAPED HYDROXYAPATITE IMPLANTS FOR RELEASE OF AGENTS MODULATING PERIODONTAL-LIKE TISSUES

Periodontal-like tissues and. in particular, alveolar bone- and root c ementum-like material call theoretically be modulated by release of bi ochemical agents such as bisphosphonate (PCP), growth hormone (GH) and alkaline phosphatase (ALP) from the implant surface. The present rese arch focused on porous ceramic hydroxyapatite (PCHA) implants. In the past the PCHA implants were machined on a lathe out of simple blocks o f PCHA ceramic. This was a tedious and cumbersome method, often result ing in implants with undesirable characteristics: different porosities , cracks and fractures. Therefore a moulding technique was developed t o sinter near-net-shaped PCHA implants at 2 different sintering temper atures: 1170 degrees C and 1280 degrees C, resulting in PCHA implants with porosities of 62.06% (PCHA type 1) and 40.74% (PCHA type 2), resp ectively. After 1 h incubation in a 10(-2) M solution of PCP, the tota l amounts adsorbed onto PCHA type I and type 2 were 114.9+/-2.1 pg and 46.1+/-1.5 mu g, respectively. This was approximately 5 times higher than after incubation for 1 wk in a 10(-4) M solution of PCP. The tota l amounts of PCP released after the observation period of 75 d from PC HA type 1 and type 2 after incubation in the 10(-2) M solution were 10 3.1+/-1.8 mu g and 42.8+/-1.5 mu g, respectively. The total amounts re leased from type 1 and 2 after incubation in the 10(-4) M solution wer e 7.4+/-0.4 mu g and 4.1+/-0.1 mu g, respectively. After 2 wk of incub ation in a liver/bone/kidney ALP solution the total amount of ALP adso rbed onto PCHA type 1 implants was 5039+/-412 mU/ml. The total amounts of ALP released were 4674+/-438 mU/ml and 53+/-20 mU/ml after 1 and 2 wk, respectively. The release of ALP was high at the beginning but sl owed down thereafter. It was evident that despite the well-known high bonding affinity of PCP to HA the release of PCP occurred steadily, ov er along period of time in vitro.