03 June 2021

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What are mechanical and biological properties of Zirconia-Reinforced Lithium Silicate (ZLS)?

Allegra Comba

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The constant research of new restorative materials has lead to the production of zirconia-reinforced lithium silicate ceramics (ZLS), a material with high mechanical and esthetic performances, that can be employed with CAD/CAM technologies. These ceramics have a microstructures characterized by an homogeneous glassy matrix that contains a crystalline component made of round and submicrometric elongated grains of lithium metasilicates and lithium orthophosphates; in addition to these, tetragonal zirconia fillers are added, aimed at increasing strength values. After a crystallization process, lithium disilicate grains are generated.

At present, a more in-depth look from a scientific point of view, in order to formulate a clear definition of clinical indications and limitations of the employment of ZLS is needed, thus the group of research conducted by Prof. Zarone et al., from the University of Naples, conducted a review of the literature on the mechanical and biological properties of ZLS in CAD/CAM systems. 

Materials and methods
The researchers conducted an extensive search of the literature for papers related to ZLS on the databases of PubMed/Medline, Scopus, Embase, Google Scholar, Dynamed, and Open Grey. The literature search was performed using a combinations of the keywords "zirconia-reinforced lithium silicate" or "ZLS". 

Prof. Zarone et al. considered as appropriate for the present literature review only the studies that met the following inclusion criteria: 1) studies focused on the biocompatibility and/or mechanical properties of ZLS for CAD/CAM systems; 2) studies performed in vitro, in silico, or in vivo; 3) case reports; 4) systematic reviews.

Results
The literature search was completed in February 2021 and the included studies were published between 2015 and January 2021. The authors of the present literature review found a total of 937 records. After the removal of duplicates and the exclusion of papers that did not meet the inclusion criteria, 71 papers were included and no disagreement was pointed out among the search investigators about the included records.

Conclusions
After reviewing the included records, the Italian research team conducted by Prof Zarone, concluded that two types of ZLS (Vita Suprinity PC; Vita Zahnfabrik and Celtra Duo; Dentsply Sirona) are nowadays available on the market for CAD/CAM systems. The two material are similar in their chemical composition, microstructure, and biological-mechanical properties. Furthermore, the authors reported that ZLS is a biocompatible material, whose fracture resistance can withstand physiological chewing loads and that the firing process influences the improvements of strength and fatigue failure load, with a volumetric shrinkage. Finally, ZLS can be considered a viable alternative to other glass-ceramics for fixed single restorations.

For additional information: Zirconia-Reinforced Lithium Silicate (ZLS) mechanical and biological properties: a literature review.