Histological Comparison of New Biodegradable Magnesium-Based Implants for Maxillofacial Applications.

BACKGROUND: A variety of materials have been used for bone augmentation, distraction osteotomy, and in post-cancer patients following tumor removal. However, a temporary metal implant that would resorb after successful treatment is a new concept. Magnesium was suggested as a suitable material for these purposes because it is biocompatible, has better mechanical properties than titanium, and stimulates new bone formation. This study evaluates histological appearance of magnesium-based implants and the surrounding bone. MATERIALS AND METHODS: Three magnesium-based biomaterials were tested in a rabbit bone defect model: magnesium-hydroxyapatite (Mg-HA), W4 (96 % magnesium, 4 % yttrium), and pure magnesium (pure Mg). Animals were sacrificed after 6 and 12 weeks and the samples were analyzed histologically and histomorphometrically. RESULTS: Mg-HA had the highest mean amount of tartrate-resistant acid phosphatase (TRAP) positive cells at the implantation site of all groups. It had shown the fastest degradation rate already at 6 weeks but the least amount of new bone formation. New bone was seen forming in direct contact with pure Mg and W4. The mean gas volume was highest in W4 compared to pure Mg and Mg-HA but this difference was not statistically significant. W4 had the lowest mean number of TRAP-positive cells of all materials. CONCLUSION: Pure Mg and W4 were shown to be the most promising materials in this study in respect to the bone response to the implant material. They could be used for screws and plates in bone augmentation procedures.

The biocompatibility of degradable magnesium interference screws: an experimental study with sheep.

Screws for ligament reconstruction are nowadays mostly made of poly-L-lactide (PLLA). However, magnesium-based biomaterials are gathering increased interest in this research field because of their good mechanical property and osteoanabolic influence on bone metabolism. The aim of this pilot study was to evaluate the biocompatibility of an interference screw for ligament reconstruction made of magnesium alloy W4 by diecasting and milling and using different PEO-coatings with calcium phosphates. PLLA and titanium screws were used as control samples. The screws were implanted in the femur condyle of the hind leg of a merino sheep. The observation period was six and twelve weeks and one year. Histomorphometric, immunohistochemical, immunofluorescence, and molecular biological evaluation were conducted. Further TEM analysis was done. In all magnesium screws a clinically relevant gas formation in the vicinity of the biomaterial was observed. Except for the PLLA and titanium control samples, no screw was fully integrated in the surrounding bone tissue. Regarding the fabrication process, milling seems to produce less gas liberation and has a better influence on bone metabolism than diecasting. Coating by PEO with calcium phosphates could not reduce the initial gas liberation but rather reduced the bone metabolism in the vicinity of the biomaterial.

Evaluation of a novel nanocrystalline hydroxyapatite paste Ostim in comparison to Alpha-BSM - more bone ingrowth inside the implanted material with Ostim compared to Alpha BSM.

BACKGROUND: The purpose of this study was to evaluate the performance a newly developed nanocrystalline hydroxyapatite, OSTIM following functional implantation in femoral sites in thirty-eight sheep for 1, 2 or 3 months. Ostim 35 was compared to an established calcium phosphate, Alpha BSM. METHODS: Biomechanical testing, micro-CT analysis, histological and histomorphological analyses were conducted to compare the treatments including evaluation of bone regeneration level, material degradation, implant biomechanical characteristics. RESULTS: The micro-computed tomography (microCT) analysis and macroscopic observations showed that Ostim seemed to diffuse easily particularly when the defects were created in a cancellous bone area. Alpha BSM remained in the defect.The performance of Ostim was good in terms of mechanical properties that were similar to Alpha BSM and the histological analysis showed that the bone regeneration was better with Ostim than with Alpha BSM. The histomorphometric analysis confirmed the qualitative analysis and showed more bone ingrowth inside the implanted material with Ostim when compared to Alpha BSM at all time points. CONCLUSIONS: The successful bone healing with osseous consolidation verifies the importance of the nanocrystalline hydroxyapatite in the treatment of metaphyseal osseous volume defects in the metaphyseal spongiosa.