Abstract
Purpose of the study: The osteoconductive properties of hydroxyapatite surfacing improves the biointegration of orthopedic implants. Current high- and low-temperature resurfacing techniques have several drawbacks, particularly concerning the control of phases. The «low-temperature nanocrystalline apatite resurfacing technique using amorphous phosphate» was developed to avoid this type of inconvenience. The purpose of this study was to examine the biocompatibility of resurfacings produced with this patented technique and to compare biological efficacy with that of the reference technique of plasma torch resurfacing.
Material and methods: The cytocompatibility tests included cell proliferation and attachment tests using human osteoprogenesis cells, and phenotypic characterization of phosphatase alkaline (PAL) and pro-collagen (type I) activity. Biocompatibility studies were performed. Cylinders of natural titanium or titanium resurfaced with the plasma method and the low-temperature method (single layer, bilayer) were implanted in 16 rabbits in condylar and tibial sites. Histological examinations without decalcification were performed one and three months after implantation (n=8 for each time and condition). The implant-quantity of bone in contact ratio was determined by histomorphometry. Scan electron microscopy was used to ascertain the persistence of the resurfacing.
Results: The cell attachment rate of 30–40% confirmed earlier results. The cells grew, and preserved and maintained their differentiation properties (PAL activity at 7, 14 and 21 days). The histological results revealed that all types of resurfacing were well tolerated. HIstomorphometry confirmed the influence of the implantation site on the tissue reaction. One month after implantation, the low-temperature amorphous resurfacing appeared to produce a better result with an optimal ratio for the bilayer in the tibial site and an optimal ratio for the monolayer in the condylar site. The trend was the same three months after implantation, but was less pronounced compared with the plasma torch resurfacing. Paradoxically, the absence of treatment produced a very satisfactory ratio at the condylar level. Scan electron microscopy demonstrated rapid resorption of amorphous resurfacing unlike plasma torch resurfacing with was detectable three months after implantation.
Discussion and conclusion: The different performance levels of bilayer and single-layer resurfacings depending on the implantation site might be explained by the cortical or cancellous nature of the neighboring bone. Low-temperature resurfacing would be more appropriate for implants inserted into cortical bone. In vivo, this resurfacing is resorbed but appears to enable, like the plasma process, the formation of peri-implant bone formation. It offers the advantage of enabling incorporation of compounds of interest (antibiotics, growth factors).
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