Net‐shaped hydroxyapatite implants for release of agents modulating periodontal‐like tissues

Abstract

Periodontal-like tissues and, in particular, alveolar bone- and root cementum-like material can theoretically be modulated by release of biochemical agents such as bisphosphonate (PCP), growth hormone (GH) and alkaline phosphatase (ALP) from the implant surface. The present research focused on porous ceramic hydroxyapatite (PCHA) implants. In the past the PCHA implants were machined on a lathe out of simple blocks of PCHA ceramic. This was a tedious and cumbersome method, often resulting in implants with undesirable characteristics: different porosities, cracks and fractures. Therefore a moulding technique was developed to sinter near-net-shaped PCHA implants at 2 different sintering temperatures: 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), respectively. After 1 h incubation in a 10(-2) M solution of PCP, the total amounts adsorbed onto PCHA type 1 and type 2 were 114.9 +/- 2.1 micrograms and 46.1 +/- 1.5 micrograms, respectively. This was approximately 5 times higher than after incubation for 1 wk in a 10(-4) M solution of PCP. The total amounts of PCP released after the observation period of 75 d from PCHA type 1 and type 2 after incubation in the 10(-2) M solution were 103.1 +/- 1.8 micrograms and 42.8 +/- 1.5 micrograms, respectively. The total amounts released from type 1 and 2 after incubation in the 10(-4) M solution were 7.4 +/- 0.4 micrograms and 4.1 +/- 0.1 micrograms, respectively. After 2 wk of incubation in a liver/bone/kidney ALP solution the total amount of ALP adsorbed 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 slowed down thereafter. It was evident that despite the well-known high bonding affinity of PCP to HA the release of PCP occurred steadily, over a long period of time in vitro.