The Effect of Aging on the Roughness and Bacterial Adhesion of Lithium Disilicate and Zirconia Ceramics.

PURPOSE

This in vitro study was designed to compare bacterial adhesion to zirconia versus lithium disilicate crowns after artificial aging.

MATERIALS AND METHODS

Seventy-five discs were tested in this study: 25 Cr-Co base metal discs (control), 25 zirconia discs, and 25 lithium disilicate discs. Each sample was polished and glazed appropriately. The discs were subjected to 1000 thermal cycles between 5 and 55°C, whereby samples stayed in the bath for 20 seconds, at each temperature. Then, 10 µL of Streptococcus sanguinis suspension was placed on the discs. The samples were scanned for surface roughness before and after aging, and after incubation. Sp and Sa were measured with a confocal, visible light disk-scanning system (Sa expresses the difference in height of each point compared to the arithmetical mean of the surface. Sp is the height of the highest peak within the defined area). Optical density of the discs was evaluated by a spectrophotometer. One-way ANOVA was performed to assess differences after aging and incubation.

RESULTS

Statistical analysis showed significant differences (p = 0.02) in surface roughness between the Cr-Co base metal, zirconia and lithium disilicate before and after aging. The mean Sa was 0.36 ± 0.12 µm, 0.638 ± 0.24 µm, and 1.23 ± 0.42 µm, respectively. Lithium disilicate had the highest surface roughness values. There was a significant difference (p = 0.001) after incubation. The mean and standard deviation surface roughness of Cr-Co base metal, zirconia and lithium disilicate were 0.99 ± 0.49 µm, 1.40 ± 0.46 µm, and 2.44 ± 1.21 µm, respectively. While no significant differences were found in the accumulation of S. sanguinis between zirconia and lithium disilicate, there was a significant difference (p = 0.02) in the optical density between these 2 test groups and the control group (metal). The optical density of metal (0.94 ± 0.15) was higher than for lithium disilicate (0.74 ± 0.10) and zirconia (0.75 ± 0.08). There was no statistical difference in bacterial adherence between lithium disilicate and zirconia.

CONCLUSION

Dental crown materials differed significantly in terms of surface roughness and bacterial adhesion between Cr-Co base metal and zirconia and lithium disilicate. After aging and bacterial adherence, the zirconia discs had the smoothest surface, with similar bacterial accumulation as lithium disilicate; suggesting that lithium disilicate may be less sensitive to bacterial adhesion than zirconia.