Reconstruction of calvarial defects by bioresorbable ceramics: an experimental study in rats

This study evaluated bioresorbable ceramics in the reconstruction of calvarial defects. Full-thickness defects were made in the calvaria of 40 adult Sprague-Dawley rats (350-450 g) with a standard 8-mm trephine drill. Three different materials were used for defect repair: (a) pure alpha-tricalcium phosphate (TCP), (b) surface-treated glass ceramic, (c) surface-treated glass ceramic plus 70/30 L/DL polylactic acid (volume ratio 45/55). The implants were pellets of 7.9 mm diameter and 2 mm thickness and were inserted press fit into the calvarial defects. Each of these materials was inserted into ten animals. Five animals were evaluated each after 6 weeks and 26 weeks. For each interval there was a control group of five animals. After 6 weeks the control defects exhibited negligible bone regeneration at the defect margins but showed substantially more bone regeneration after 26 weeks extending up to 2.5 mm into the defect space. The TCP specimens showed a number of multinuclear cells on the material surface and direct bone/implant contact in a few locations but no signs of gross degradation or volume reduction after 6 weeks. The amount of bone ingrowth and cellular behavior had not changed after 26 weeks with resorption still going on. Glass ceramic implants by contrast appeared to be even better tolerated after 6 weeks with remarkable bone ingrowth and broad osseous fixation of the pellet to the defect margins and beyond, while highly vascular connective tissue filled the remaining pores of the implant. After 26 weeks the material had been extensively degraded, leaving behind only a few remnants, which were surrounded by seams of highly vascularized and cell-rich resorptive connective tissue with newly formed bone tissue nearly bridging the defect. The polylactic acid/ceramic composite implants showed hardly any tissue ingrowth or degradation either after 6 or after 26 weeks. Hence all tested materials appeared to be well tolerated at the site of implantation. However, gradual replacement by bone ingrowth tended to occur only in implants without polylactic acid.