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3. Push-out Biomechanical AnalysisMeasurement of interfacial shear strength revealed statistically significant differences betweenthe grit-blasted, SLA, and MAO groups compared to the machined group (P ＜ 0.01), andthere was also a statistically significant difference between the grit-blasted and MAO groups (P= 0.023). However, there was no statistically significant difference between the SLA and MAOgroups (P = 0.182) (see Fig. 5).DiscussionThe effect of four different implant surface preparations on peri-implant bone healing wasevaluated in vivo by comparing the biomechanical strength of the bone – implant interface andhistomorphometric analyses.For all implant surfaces tested, SLA and MAO treatments enhanced bone healing around the Tialloy implants in comparison to the machined Ti alloy. In particular, the MAO group wasstatistically superior to the grit-blasted group in interfacial shear strength. There was nostatistically significant difference between the MAO and SLA groups.We note several limitations to this study. First, the number of dogs was too small to comparethe mechanical testing as a function of the postoperative time period. Future studies are neededto determine whether there are differences in mechanical testing with the time interval betweenvarious treatments of surfaces of Ti alloy. Second, a comparison with porous coated implantswas not performed. In the grit-blasted, SLA, and MAO implants, the osseointegration wascharacterized by bone ongrowth. In contrast, with porous-coated implants, the osseointegrationwas characterized by bone ingrowth. Because of this difference, we chose not to compare withporous coated implants.Roughened Ti surfaces are effective in enhancing the interfacial biomechanical properties ofbone-anchored implants by providing a mechanical interlock. 19 Interfacial bone formation mayalso be promoted by roughened surfaces, as a significantly greater percentage of bone-toimplantcontact has been observed in micro-roughened Ti surfaces in comparison to machinedor polished Ti surfaces. 20,21 However, too much surface roughness may cause an increase inperi-implant inflammation and in ionic leakage. 22 Therefore, the optimal average roughness ofcementless stems is reportedly 5 – 7 mm. 23 The results of this study confirm the benefits of gritblasted,SLA, and MAO surfaces, and as such, these surface treatments may still be consideredthe “gold standard”.Different implant treatments have been evaluated previously, and have been shown to promotefirmer bone anchorage. 24,25 CaP is the logical choice for biomimetic coatings, as the CaPreinforcedchemistry of such coatings enhances the rate of early bone formation. 18,26,27 Thepresent study demonstrated that MAO treatment was superior to grit-blasted treatment in termsof interfacial strength. Recently, a MAO method was successfully applied to form a roughenedTiO 2 layer on Ti surfaces in the dental field. MAO forms a relatively thick TiO 2 layer byapplying a positive voltage to the Ti. 16 In this process, the repeated breakdown andregeneration of TiO 2 results in porous and roughened surfaces. 16,28 Components of the surfacecommonly consist of calcium phosphate and contain a porous structure with pores ofapproximately micron or submicron diameter, which facilitates osseointegration. 3,6,28–30 Theproperties of the oxide layer, including thickness, microstructure, roughness, and concentrationof Ca and P, are easily controllable by adjusting the voltage, current, processing time, and theformulation of the electrolyte during the MAO process. 6,31 Despite these structuralcharacteristics and chemical advantages, MAO has not yet been introduced, and is currentlybeing used for the surface treatment of cementless stems. 15In summary, a variety surface modifications for orthopaedic cementless Ti implants werefile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]