18 October 2021

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Bacterial adhesion to zirconia and lithium disilicate: data from a recent in vitro study

Lara Figini

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Restorative materials used in dentistry should have surface characteristics that inhibit bacterial adhesion and biofilm formation. Understanding bacterial adhesion (quantitatively) to different materials is crucial when designing for the long-term success of dental restorations.

Materials and Methods
In an in vitro study, published in the June 2021 Journal of Prosthodontic, the authors compared bacterial adhesion to zirconia versus lithium disilicate crowns after undergoing an artificial aging process. Seventy-five discs were tested in this study: 25 Cr-Co metal discs (control group), 25 zirconia discs and 25 lithium disilicate discs. Each specimen was properly polished and glazed. The discs were subjected to thermocycling (1000 cycles between 5 and 55 ° C), which provided for the permanence of the specimens in a hot or cold bath for 20 seconds alternately. The discs were then placed in contact with a 10 μL suspension of Streptococcus sanguinis. Samples were scanned to assess surface roughness before and after the aging process, and after incubation. Sp and Sa (Sa expresses the difference in height of each point with respect to the arithmetic mean of the surface, Sp is the height of the highest peak within the delimited area) were measured with a visible light confocal scan. The optical density of the discs was evaluated using a spectrophotometer. One-way ANOVA was performed to evaluate differences after aging and incubation.

Results
Statistical analysis showed significant differences in surface roughness between the control group and the zirconia and lithium disilicate group both before and after the aging process. Mean Sa was found to be 0.36 ± 0.12 μm, 0.638 ± 0.24 μm and 1.23 ± 0.42 μm, respectively. Lithium disilicate demonstrated higher surface roughness values. There was a significant difference even after incubation. The mean and standard deviation of the surface roughness of the Cr-Co metal, zirconia and lithium disilicate was found to be 0.99 ± 0.49 μm, 1.40 ± 0.46 μm and 2.44 ± 1.21 μm, respectively. Although no significant differences were found in the accumulation of S. sanguinis between zirconia and lithium disilicate, there was a significant difference in optical density between these 2 experimental groups and the control (metal) group. The optical density of the metal (0.94 ± 0.15) was found to be higher than that of 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.

Conclusions
From the data of this study, which must be confirmed in other similar studies, it can be concluded that in vitro after the aging process and bacterial contamination, zirconia maintains a smoother surface than lithium disilicate, with bacterial accumulation however similar to that of lithium disilicate.

For additional information: The Effect of Aging on the Roughness and Bacterial Adhesion of Lithium Disilicate and Zirconia Ceramics