Objective: To evaluate the surface roughness and gloss of two experimental composites (Ivoclar Vivadent)  with particle sizes of 1.0 mm and 1.5 mm after polishing with different grits of SiC paper. Methods: Six specimens of each composite for each grit were cured against a Mylar strip and ground on a polishing machine with 400-, 600-, 1000-, 1200-, 1500-, or 2000-grit SiC paper. Surface roughness (Ra, mm, n=6) was measured with 5 tracings per specimen. Gloss (GU, n=6) was measured with 4 readings per specimen using a small-area glossmeter. Results: Means with standard deviations in parentheses are listed below. Fisher's PLSD intervals for comparisons between composites

Abrasive    1.0-mm, GU    1.0-mm, Ra (mm)   1.5-mm, GU    1.5-mm, Ra (mm)

400-grit            5(1)                   0.36(0.03)                4(0)              0.31(0.02)

600-grit            9(2)                   0.23(0.01)               7(1)             0.22(0.01)

1000-grit          21(2)                 0.09(0.00)              22(1)              0.10(0.01)

1200-grit          32(6)                 0.07(0.00)              22(3)              0.09(0.00)

1500-grit          53(6)                 0.05(0.00)              38(3)              0.07(0.00)

2000-grit          67(11)               0.04(0.00)              74(8)               0.04(0.00)

and among grit sizes at the 0.05 level of significance were 0.01 and 0.01 mm for Ra and were 2 and 4 GU for gloss, respectively. Regression analysis showed a logrithmic relationship between GU and Ra. Gloss was significantly different with the 1.5-mm particle composite between the 600- to1000-grit step, the 1200- to 1500-grit step, and the 1500- to 2000-grit step. Gloss was significantly different between the two composites at 1200-, 1500-, and 2000-grit. The 1.0-mm composite was significantly smoother than the 1.5-mm composite with 1500- and 1200- grit, the same for 1000- and 600-grit, and rougher with the 400-grit. Conclusions: Particle size affected gloss and surface roughness of two experimental composites. (This study was funded by Ivoclar Vivadent)