Influence of Different Treatments and Conditions on Optical Properties of Monolithic Zirconia: A Systematic Review

The present systematic review aimed to evaluate the influence of different treatments and conditions on the optical properties of monolithic zirconia. An electronic search was performed using the following databases: PubMed (National Library of Medicine, Bethesda, MD, USA), Web of Science (Clarivate, London, UK), Scopus (Elsevier, Amsterdam, Netherlands), Google Scholar (Google, Mountain View, CA, USA), and Embase (Elsevier, Amsterdam, Netherlands), with no restrictions on publication year and language. Based on the PICO format, the primary research question of this review was: "What is the impact of different treatments and conditions on the optical properties of monolithic zirconia?" From 145 relevant articles, 12 studies were chosen for systematic review (qualitative synthesis). A modified version of the "Guidelines for Reporting Pre-Clinical In-Vitro Studies on Dental Materials" was used to assess the overall quality of the included studies and any bias within them. The included studies assessed the optical properties (such as color stability, translucency, and surface gloss) of monolithic zirconia and other relevant ceramic materials using different treatments and conditions including aging (i.e., artificial, simulated, chemical, and hydrothermal), grinding/occlusal adjustment, glazing/external staining, toothbrushing, bleaching, and artificial gastric acid exposure. All the included studies (100%) reported a significant decrease (p < 0.05) in the optical properties of monolithic zirconia samples as compared to those of other relevant ceramic materials. Overall, different treatments and conditions had a negative impact on the optical properties of monolithic zirconia. In conclusion, the optical features assessed for monolithic zirconia, such as color stability, translucency, and surface gloss, appeared to be significantly compromised by different treatments and conditions including aging, grinding/occlusal adjustment, glazing/external staining, toothbrushing, bleaching, and artificial gastric acid exposure. However, the change was clinically not perceivable in 25% (n = 3/12) of the included studies. Due to the heterogenic parameters in the included studies, it is recommended to perform future studies using standardized conditions with different stains of zirconia over an extended duration to obtain conclusive evidence.