Effect of Aging on Stained Monolithic Resin-Ceramic CAD/CAM Materials: Quantitative and Qualitative Analysis of Surface Roughness

Purpose The aim of this in vitro study was to measure the effect of staining and artificial aging on the surface roughness of commercially available resin-ceramic computer-aided design and computer-aided manufacturing (CAD/CAM) materials both quantitatively and qualitatively and to compare it to feldspathic material. Materials and methods Test specimens (n = 15 per material) were prepared of CAD/CAM ingots from a resin nanoceramic (Lava Ultimate, LVU), a polymer-infiltrated ceramic (Vita Enamic, ENA), and a resin nanoceramic (Cerasmart, CER). In the staining protocol, test specimens were (i) roughened in a standardized manner and (ii) stained with the manufacturer's recommended staining kit by means of photo-polymerization (Bluephase Polywave). The control specimens were prepared out of a feldspathic ceramic (Vita Mark II,VM2) and stained in a ceramic furnace. As negative control of each group, 15 specimens were prepared and polished in a standardized manner. Surface roughness (Ra) was measured after finishing procedures and after simulation of clinical service up to 5 years by means of toothbrushing. After each year of aging, one specimen per group was randomly selected for scanning electron microscopy (SEM) analysis. Kruskal-Wallis test and paired post-hoc test were applied to detect differences between treatment groups (alpha = 0.05). Results The mean roughness measurements of the stained CAD/CAM materials were 0.14 +/- 0.04 mu m (ENA), 0.15 +/- 0.03 mu m (LVU), 0.22 +/- 0.03 mu m (VM2), and 0.26 +/- 0.12 mu m (CER). In the polished CAD/CAM materials the measurements were 0.01 +/- 0.01 mu m (CER), 0.02 +/- 0.01 mu m (LVU), 0.02 +/- 0.00 mu m (VM2), and 0.03 +/- 0.01 mu m (ENA). Irrespective of the restoration material, the applied staining protocol resulted in a higher surface roughness compared to the polished specimens (p < 0.001). After 5 years of simulated aging the mean surface roughness in the stained CAD/CAM materials were 0.22 +/- 0.03 mu m (VM2), 0.24 +/- 0.09 mu m (ENA), 0.25 +/- 0.06 mu m (CER), and 0.37 +/- 0.09 mu m (LVU). Aging had a significant effect on surface roughness in groups ENA and LVU (p < 0.001). SEM analysis showed that the staining layer on resin-ceramic CAD/CAM materials was partially removed over time. Conclusions The applied staining protocol significantly increased surface roughness of CAD/CAM materials. Instability of the staining layer on resin-ceramic CAD/CAM materials could be anticipated over time as a consequence of toothbrushing, whereas feldspathic ceramic did not suffer from such aging effect.