Abstract: Objective To compare the effects of different instruments of interproximal enamel reduction(IER) on enamel surface roughness before and after polishing. Methods Sixty healthy premolars were used after removal for orthodontic reasons and divided into six groups. Each group underwent IER with different IER instruments:Ⅰ:diamond burs(medium);Ⅱ:diamond burs(fine);Ⅲ: handheld diamond strips(medium);Ⅳ: handheld diamond strips(fine);Ⅴ:diamond discs; Ⅵ:control group(no IER). One proximal surface of sample after IER was polished with SofLex polishing discs.Striped and polished surface roughness was assessed and morphology was observed respectively using laser scaning confocal microscopy(LSCM). Results ①After IER but before polishing, groupⅠand groupⅢ had the roughest surfaces (no statistically significant,P= 0.632),followed by groupⅡ, Ⅳ, Ⅴ,and these surfaces were significantly rougher than the control surfaces; ②The enamel surface roughness of the groupⅠ,Ⅱ, Ⅲ, Ⅳ,Ⅴdecreased significantly after polishing(no significant difference between groups), and these surfaces are smoother than the control surfaces. ③LSCM image: After IER,groupⅠ,Ⅱ, Ⅲ, Ⅳ,Ⅴ all produced enamel furrows and scratches, groupⅠ,Ⅱcreated deeper furrows and scratches than group Ⅲ, Ⅳ,Ⅴ, and group Ⅴproduced the shallowest scratches. Polishing with SofLex polishing discs after IER basically eliminated the scratches that were created by IER(no significant difference between groups Ⅰ, Ⅱ, Ⅲ, Ⅳ and Ⅴ). Conclusions ①Different IER instruments will increase enamel surfaces roughness to different extents. Enamel surfaces treated with diamond burs (medium)and diamond strips(medium) were the roughest, followed by diamond burs (fine), diamond strips(fine) strips,and treated with diamond discs are the smoothest. ②Polishing with SofLex polishing discs after IER with different instruments reduced the enamel surface roughness(no significant difference between groups), and these surfaces are smoother than untreated enamel. 

Key words: interproximal enamel reduction(IER), roughness, laser scaning confocal microscopy(LSCM), enamel