The Effect of Chair-Side Polishing Systems on Lithium-Disilicate Surface Roughness

Objectives: The purpose of this study is to measure the surface roughness (Ra) of glazed, adjusted and polished monolithic lithium disilicate glass ceramic (IPS e.max Press, Ivoclar Vivadent) and to evaluate the effect of two chair-side polishing systems; OptraGloss (Ivoclar Vivadent) and DIATECH ShapeGuard (Coltene) on the surface roughness of the adjusted surfaces following polishing.
Methods: 20 lithium disilicate discs (8mm ø x 2mm) were pressed in LT A2 IPS e.max and glazed as per standard protocols. Specimens then underwent superficial abrasion with a fine grit high speed diamond bur (25µm) by a single operator, mimicking intra-oral occlusal adjustments. Specimens were then randomly divided into two groups for polishing with either OptraGloss (OG) or DIATECH ShapeGuard (SG) systems. Specimens’ surface roughness (Ra) was measured using a white light profilometer (Proscan 2000, UK). Baseline Ra measurements of the glazed specimens were initially taken and considered as the control. Ra measurements were then taken after adjustments of the surfaces, and following polishing with either of the polishing systems. Statistical analysis was conducted using one-way ANOVA and Tukey tests at a significance level of p≤0.05.
Results: Glazed specimens showed the lowest Ra (0.07µm) when compared to the adjusted (0.86µm) and polished specimens (OG 0.31µm, SG 0.21µm), (p<0.001). Ra significantly reduced after polishing with either polishing systems when compared to the adjusted specimens, (p<0.001). SG produced superior outcome when compared to OG (p<0.05).
Conclusions: Despite that neither polishing system used in the study produced a similar initial surface roughness that was obtained with glaze, both systems decreased the surface roughness considerably. Therefore both OG and SG systems could be considered as suitable chair-side polishing systems for lithium disilicate glass ceramics. Conversely, chair-side adjustments of glass ceramics without further polishing demonstrates significant increase in surface roughness that is clinically not acceptable.