Abstract: Objective To evaluate the effects of different sand particle sizes of polishing disc on composite resin surface roughness and bacterial adherence. Methods Specimens of resins were randomly divided into five groups and polished with polishing burs (group A)， and polishing discs of different particle sizes:70 μm particle size (group B)， 50 μm particle size (group C)， 30 μm particle size (group D) and 5 μm particle size (group E) respectively (n=10 for each group). Scanning electron microscopy (SEM) was used to observe the roughness and surface structure of the specimens. Bacterial adhesion on the surface of the specimens was calculated by CFU counting. Results Scanning electron microscopy (SEM) showed that with the decrease of particle size of polishing disc to 30 μm(group D)， the grooves on the surface became shallower， and the number of pits were reduced in group D and E. There was a significant difference in bacterial adhesion between group D， E and that of group A (P<0.005). No significant difference was detected between group A，B and C (P>0.005). Conclusions With the decrease of the particle size of the polishing disc， lower surface roughness and fewer bacterial adhesion will be observed. Polishing disc with at least 30μm particle size can reduce bacterial adhesion of composite resin.

Key words: composite resin, polishing, surface roughness, bacterial adherence