The Surface Characters Of Dental Ceramic After Finishing And Polishing

Ceramic is one of the most frequently used materials for restoring tooth defect or denture defect, which has a lot of advantages, such as excellent mechanical properties, stable chemical stabilities and beautiful appearance.Before cementing, ceramic restorations may be modified by diamond bur grinding. However, after grinding, the specular gloss of restorations may be destroyed, which make it rough on the surface. For reducing the bacteria attachment as well as improving the appearance, further surface treatment for ceramic after grinding is of great importance. Glazing is the traditional method for decreasing the surface roughness, nevertheless, polishing technique is more frequently employed in clinic with the development of polishing instruments, which may provide more conveniences in clinic while avoid the obvious changes of color or occlusion caused by glazing. Some existing researches reported that, ceramic surface may achieve enough smoothness when polishing was used properly. However, most of these researches focused on single polishing way, while the methods were restricted in roughness measurement or SEM observation. There were too many researches focused on different combinations of polishing instruments and employed multiple methods.The present study polishing with a three-step programme, grinding, polishing and fine polishing, treated the VITA VMK ceramic specimens made in different combinations. The surface roughness specular gloss and color were measured and compared for different polishing ways with glazing. Micro indentation cracking method was also employed for evaluating the surface residual stresses in corresponding conditions. This study systematically evaluated the effect of different polishing processes, which may provide some references for clinicthe results of this research can be summarized to as follow:1. After being polished step by step, the surface roughness of low-fused dental ceramic would decrease steadily, and achieve the comparable effect as that of glazed when proper polishing process used. During transition phrase between grinding and polishing, using proper instruments to remove the nicks on ceramic surface is necessary. In each phrase, instruments should be chosen with proper particle size and used in sequence for removing the cracks caused by precious operations.2. The effect of fine polishing on surface gloss was better than that of grinding or polishing, while the differences were not significantly different in statistics. After polishing, the surface glosses on ceramic restorations were higher than that on enamel and lower than that on glazed ceramic. Therefore, polishing ceramic surface may be more suitable in vision.3. The color of polished surface of ceramic was significantly different with single-glazed ceramic (ΔE>1.5 NBS). The contribution of lightness for chromatic aberration is higher than that of chroma a/b values. The Chromatic Aberration between one-time glazed ceramic and two-time glazed ceramic was 1.45 NBS.4. Different polishing processes produced different residual stress on ceramic surface. Polishing by green stone or white stone produced more tensile stress on ceramic than those of diamond bur or fissure bur. Glazed or polished ceramic were in lower press stress condition. Therefore, both glazing and polishing could improve the mechanical properties of ceramic restorastions.