The introduction of the new generation of particle-filled and high strength ceramics, hybrid composites and technopolymers in the last decade has offered an extensive palette of dental materials broadening the clinical indications in fixed prosthodontics, in the light of minimally invasive dentistry dictates. Moreover, last years have seen a dramatic increase in the patients’ demand for non-metallic materials, sometimes induced by metal-phobia or alleged allergies. Therefore, the attention of scientific research has been progressively focusing on such materials, particularly on lithium disilicate and zirconia, in order to shed light on properties, indications and limitations of the new protagonists of the prosthetic scene. This article is aimed at providing a narrative review regarding the state-of-the-art in the field of these popular ceramic materials, as to their physical-chemical, mechanical and optical properties, as well as to the proper dental applications, by means of scientific literature analysis and with reference to the authors’ clinical experience. A huge amount of data, sometimes conflicting, is available today. Both in vitro and in vivo studies pointed out the outstanding peculiarities of lithium disilicate and zirconia: unparalleled optical and esthetic properties, together with high biocompatibility, high mechanical resistance, reduced thickness and favorable wear behavior have been increasingly orientating the clinicians’ choice toward such ceramics. The noticeable properties and versatility make lithium disilicate and zirconia materials of choice for modern prosthetic dentistry, requiring high esthetic and mechanical performances combined with a minimal invasive approach, so that the utilization of such metal-free ceramics has become more and more widespread over time.

This paper aimed to provide a literature review of the mechanical and biological properties of zirconia-reinforced lithium silicate glass-ceramics (ZLS) in Computer-aided design / Computer-aided manufacturing (CAD/CAM) systems. An extensive search of the literature for papers related to ZLS was made on the databases of PubMed/Medline, Scopus, Embase, Google Scholar, Dynamed, and Open Grey. The papers were selected by 3 independent calibrated reviewers. The search strategy produced 937 records. After the removal of duplicates and the exclusion of papers that did not meet the inclusion criteria, 71 papers were included. After reviewing the included records, it was found 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, similar in their chemical composition, microstructure, and biological-mechanical properties. ZLS is reported to be a biocompatible material, whose fracture resistance can withstand physiological chewing loads. The firing process influences the improvements of strength and fatigue failure load, with a volumetric shrinkage. To date, ZLS can be considered a viable alternative to other glass-ceramics for fixed single restorations. . As to biocompatibility and mechanical properties of ZLS, data are still scarce, often controversial and limited to short-term observational periods. These promising ceramics require further in vitro/in vivo studies to accurately define mechanical and biological properties, mainly in the long-term performance of restorations produced with such materials.

To compare the fracture resistance and mode of failure of CAD-CAM monolithic zirconia crowns with different occlusal thickness. Forty CAD-CAM monolithic zirconia crowns with different occlusal thickness were randomly distributed into 4 experimental groups: 2.0mm (group 1), 1.5mm (group 2), 1.0mm (group 3) and 0.5mm (group 4). The restorations were cemented onto human molars with a self-adhesive resin cement. The specimens were loaded until fracture; the fracture resistance and mode of failure were recorded. The data were statistically analyzed with the one-way ANOVA followed by the Fisher׳s Exact test with Bonferroni׳s correction (p=0.05). The fracture resistance values of all the specimens exceeded the maximum physiological occlusal loads in molar regions. All the crowns showed cohesive microcracks of the zirconia core; only 1 crown with a thickness of 0.5mm was interested by a complete fracture. The occlusal thickness of CAD-CAM monolithic zirconia crowns did not influence either the fracture resistance and the mode of failure of the restorations; the occlusal thickness of CAD-CAM monolithic zirconia crowns can be reduced up to a lower bound of 0.5mm keeping a sufficient strength to withstand occlusal loads; CAD-CAM monolithic zirconia crowns showed sufficient fracture resistance to be used in molar regions, even in a thin configuration (0.5mm).

In recent years, digital technologies have significantlychanged the clinical approach to medicine and dentistry. Innovative operative techniques and restorative materials have paved the way to a significant active boost towards full digital workflows. Particularly, novel dental materials offer undeniable advantages such as optimal mechanical resistance, excellent esthetic and optical properties, and reliable accuracy and precision, widening the clinical scenario and allowing for innovative and less invasive restorative solutions.