###### Abstract  
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 Preclinical 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/oclusal adjustment, glazing/external staining, toothpushing, 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/oclusal adjustment, glazing/external staining, toothpushing, 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. monolithic ceramics; zirconia; color stability; esthetics; aging +
Footnote †: journal: Applied Sciences  
-fracture rates [14]. Additionally, monolithic zirconia possesses remarkable translucency; furthermore, monolithic zirconia is esthetic owing to the lack of metal exposure at the margin of the restoration, even in the case of gingival recession of the abutment tooth [15; 16]. Therefore, monolithic zirconia offers numerous benefits as an esthetic restorative dental material, making it the material of choice in the posterior region of the oral cavity due to its sufficient mechanical strength and toughness as well as tooth color [17; 18; 19]. Monolithic restorations, nevertheless, may pose challenges regarding esthetic shade matching and color stability [20; 21; 22; 23]. It has been reported that the translucency of monolithic zirconia restoration can be affected by extrinsic (i.e., clinical and laboratory factors) and intrinsic (i.e., material processing and microstructural features) factors [24]. The clinician cannot manipulate the intrinsic factors; however, extrinsic factors can be manipulated by the clinician. Clinical factors, including low-temperature degradation [25], cement color [26], dental background [27], the utility of monolithic zirconia ceramics as dental implant abutments [28], surface finishing procedures [29], the color of monolithic zirconia ceramics [30], cementation type [31], and thickness [31], which lie in the category of extrinsic determinants should also be considered while assessing the translucency of monolithic zirconia ceramics.