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coating, have been developed with the aim of promoting bone ongrowth of cementless femoralstems. These two methods are widely used, and the long-term clinical survival rates are 66% to100% at a 10-year follow-up. 7–9 In the dental field, acid etching and anodized surfacemodification methods have recently been developed to enhance osseointegration. Etching withstrong acids, such as HCl, H 2 SO 4 , HNO 3 , and HF, is used to modify the surface of Ti dentalimplants, and results in micro pits on the Ti surface with diameters in the range 0.5 – 2 μm. 10,11Such etching has been shown to greatly enhance osseointegration. 12 Micro-arc oxidation(MAO) leads to nanoporous pits, thick oxide layers, and the incorporation of calcium andphosphorus into the coating layer, which results in improved osteoblast cell responses. 6,13–15The TiO 2 layer generated by the MAO treatment has been found to significantly improve thecellular activities of Ti in vitro, as well as the bone-implant bonding properties in vivo. 16–18Clearly, there are many potential candidates for the “optimal” surface of a cementless implant;however, there is a lack of comparative data. The purpose of this study is to provide abiomechanical comparison of the implant osteointegration of four surface modifications to theTi alloy Ti6Al4V: machined, grit-blasted, acid etched (SLA), and MAO.Materials and Methods1. Specimen PreparationWe used 32 Ti6Al4V discs, measuring 4 mm in diameter and 10 mm in length, to create eightspecimens of each of the four different surface modifications. Grit blasting was achieved usingAl 2 O 3 particles with a diameter of 200 – 500 μm in a high-velocity air stream (KSSA-5FD;Kumkang Tech, Seoul, Korea). The roughness of the grit-blasted specimens was in the range 5– 7 μm. The SLA specimens were prepared by grit blasting with 200 – 500-μm-diameterparticles and subsequent acid etching with HCl/H 2 SO 4 , as used in clinical practice. To createthe MAO specimens, the Ti6Al4V discs were placed in an electrolytic bath, forming the anodes,and stainless steel plates were used as cathodes. The Ti6Al4V plates were ground with abrasivepapers, ultrasonically washed with acetone and distilled water, and dried at 40°C. A freshelectrolyte was prepared by dissolving reagent-grade Ca (CH 3 COO) 2 · H 2 O (6.3 g L −1 ),Ca(H 2 PO 4 ) 2 · H 2 O (13.2 g L −1 ), EDTA-2Na (15 g L −1 ), and NaOH (15 g L −1 ) in deionizedwater. The applied voltage, frequency, duty cycle, and oxidizing time were 230 V, 600 Hz, 8%,and 5 minutes, respectively. All implants were packed and sterilized using gamma radiation.The highest surface roughness (Ra values) was that of the MAO group (mean ± standarddeviation, 6.5 ± 0.13 μm), followed by grit blasted (5.0 ± 0.24 μm), SLA (3.1 ± 0.11 μm), andmachined (1.8 ± 0.13 μm). Scanning electron microscopy (SEM) images (JEOL JSM-6700F;JEOL Ltd, Tokyo, Japan) were used to examine the surface morphologies. The grit-blastedsurface was finely textured (Fig. 1A). The SLA surfaces showed 1 – 2-μm micropits but no pore(Fig. 1B). The MAO surface showed a multilayered porosity of 0.6 – 7.1 μm (average, 3.0 μm)(Fig. 1C).2. Surgical ProceduresEight full-grown beagles over 15 kg in body mass (16.5 ± 0.75 kg) were assigned as theexperimental subjects. The animals were purchased from the Orient Bio Company (Sungnam,Korea). All experimental procedures were approved by the “Animal Experimental Committeeof the Catholic University of Korea”. There was a one-week-long adaptation period before theexperiment began. The operations were performed after intravenously administered generalanesthesia. Painting and draping was carried out using aseptic techniques after the skinpreparation of the thigh. The femur shaft metaphysic was obtained by the anterolateral approachresecting the femoral iliotibial band and the musculus vastus lateralis, and meticuloushemostasis was performed. A 4‑mm-diameter drill was used to create a recess in the lateralcortical bone of the femur; and the hole was drilled with caution in order to avoid medialfile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]