engleski

A Three-Dimensional Topography of CoCr Surface dependent on Polishing Procedure

PURPOSE: To aquire the 3-D nanotopographic data of the CoCr alloy surfaces submitted to different polishing protocols using atomic force microscopy (AFM). METHODS & MATERIALS: 18 samples were divided into 3 groups of 6 samples. The first group was only electropolished (EP), and the second and the third were further mechanically polished using green rubber discs and afterwards a high shine polishing paste and a rotating black brush (BB), or a high shine polishing paste and a rotating deer-leather brush (DL). Optical micrographs and 5 AFM images of each sample were obtained. The roughness (RMS, Ra and maximum Z-range)and the section analysis were performed. Mean values of 5 scanned surfaces of each sample were accounted for statistical analysis (ANOVA, Scheffe post hoc, 95% probability level). RESULTS: In the EP samples 2 distinct forms of surface structure were identified: clusters of nanocrystallytes (alligned in parallel rows 160 or 320 mm apart, 90-150 nm high) forming islands (matching the dark zones in optical micrographs) and a smooth undulating surface (matching the light zones). Dramatic changes were induced by further mechanical polishing: The islands' height was reduced to 40 nm due to decrease in their roughness (the crystallite peaks were polished away) and scratches appeared in parallel fashion on the undulating surface. Optical micrographs at that stage showed islands as lighter and undulating surface as slightly darker zones with dark lines (scratches). Mechanical polishing caused change of reflectivity as saw-tooth cristallyte peaks were taken away. The maximum Z range of EP samples (918.0 nm) was significantly higher than that of BB (537.23 nm) and DL (616.17) (p<0.01), regardless of the appearence of scratches. The RMS (EP=89.3 nm ; BB=77.9 nm and DL=86.9 nm) and the Ra values (EP=70.5 nm, BB=61.7 nm and DL=65.6 nm) were also the highest in the EP samples (p>0.05). The BB revealed the smoothest surface. CONCLUSION: Mechanical reduction of islands' height and roughness resulted in decrease of maximum Z range values. Surface roughness was also reduced, but not significantly due to appearence of shallow scratches on the undulating surface. BB surface smoothness was superior to EP and DL.

CoCrMo dental alloy; surface topology; AFM; polishing

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