| dc.description.abstract | Titanium implants in rabbit tibias were assessed by removing the metal and looking straight at the tissue interface boundary. Cylindrical or screw Ti implants, 3.2 mm diameter, placed in proximal tibias in 3 month old rabbits were retrieved at intervals from 1 week to 1 year [1]. Bones were fixed in glutaraldehyde, embedded in PMMA and implants sectioned longitudinally for reflected LM, confocal LM and compositional contrast BSE SEM. Hemisectioned implants were removed from the PMMA and the half beds recoated for BSE SEM. Other cases were sectioned to produce quarter beds and imaged using BSE SEM of uncoated samples at 50Pa chamber pressure before and after staining with ammonium tri-iodide to visualise cells and non-mineralised matrix components. In addition, plasma ashing was used to remove PMMA, cells and matrix from implant beds to investigate the nearest mineralised tissue surface with 3D BSE SEM. Conversely, HCl and NaOCl etching was used to remove all bone components and produce a non-bone space cast for study of osteocytes and their canalicular processes. The relatively smooth finish of the unetched, as-machined Ti implants mostly permitted separation of PMMA with all included tissue elements, the resin exactly replicating original machining marks. Direct viewing of the bed showed the exact extent of true bone contact, varying from very small areas with reticular, immature, highly cellular woven bone in early healing to large tracts of mature bone at 6 and 12 months - with the greatest areal coverage on smooth cylinder forms. Extensive bone-free patches bordered by scalloped osteoclastic resorption lacuna outlines indicated recent removal: similarly sized bone-covered patches had a lower mineralisation density, indicating recent re-formation, i.e., remodelling-turnover. Mature bone contained oriented osteocyte lacunae with canaliculi near the implant demonstrating growth from the implant. Tri-iodide staining additionally disclosed both osteoid and cells contacting the implant, with large numbers of multinucleated osteoclasts where bone was missing. Some regions showed direct contact of adipocytes and small blood vessels. Extensive patches of highly mineralised acellular material were often found in contact with the implant metal in earliest healing stages. Some of this might be categorised as cement line matrix. However, we consider that we demonstrate the occurrence of an undescribed repair phase involving a type of dystrophic calcification resembling the high density mineral infill crack closure mechanism seen in articular calcified cartilage and bone [2] and the formation of high density mineralised protrusions from the tidemark into hyaline articular cartilage [3]. References 1. Boyde A, Wolfe LA, in Bone Engineering, (Davies JE ed.), em squared Inc, Toronto, 321-331, 2000. 2. Boyde A, J Anat., 203,173-189, 2003. 3. Boyde A et al., J Anat., 225, 436-446, 2014. | en_US |
