Abstract
This in vitro study evaluated the fatigue strength of different ceramic materials indicated for monolithic restorations. Disc-shaped specimens were made according to ISO 6872 from five different ceramic materials: feldspathic ceramic (FC), polymer-infiltrated ceramic network (PIC), lithium disilicate glass-ceramic (LD), zirconia-reinforced lithium silicate glass-ceramic (ZLS), and high translucent tetragonal zirconia polycrystals doped by yttrium (YZ-HT). After obtaining the mean of each material (n = 5) from monotonic load-to-failure tests, specimens (n = 20) were subjected to fatigue tests (staircase method) using a biaxial flexural setup (piston-on-three-balls), to determine the fatigue strength. The parameters used for fatigue tests were: 100,000 cycles at 10 Hz, initial load of ~ 60% of mean load-to-failure, and step size of 5% of the initial load (specific for each ceramic material). Kruskal-Wallis and Bonferroni's test (α = 0.05) were used to analyze the fatigue strength data. Fatigue strength (MPa) of the materials was statistically different among each other as follows: YZ-HT (370.2 ± 38.7) > LD (175.2 ± 7.5) > ZLS (152.1 ± 7.5) > PIC (81.8 ± 3.9) > FC (50.8 ± 1.9). Thus, it can be concluded that, in terms of fatigue, high translucent polycrystalline zirconia is the best choice for monolithic restorations as it bears the highest load before cracking/fracturing.
Highlights
The main intent of the industry is to refine the composition and microstructure of the ceramic materials to produce a tougher ceramic without compromising esthetics.[3]
Specimens Preparation Disc-shaped specimens (n = 25; 5 for biaxial monotonic load-to-failure test and 20 for biaxial fatigue strength test) of five different ceramic materials (Table 1) were produced according to ISO 6872.15 The ceramic blocks were water-ground into cylinders in a polishing machine (EcoMet/AutoMet 250, Buehler; Lake Bluff, EUA) with a #400 grit silicon carbide paper
The tested hypothesis was accepted, since the ceramic materials for monolithic restorations with different microstructures resulted in different flexural fatigue strengths (Figure 1)
Summary
A shift toward metal-free restorations has been observed in dentistry. To meet the increased demands of patients and dentists in terms of esthetics, biocompatibility, and long-term survival of the restorations, several types of all-ceramic systems have been developed, from glass ceramics to zirconia polycrystal materials.[1,2]. The main intent of the industry is to refine the composition and microstructure of the ceramic materials to produce a tougher ceramic without compromising esthetics.[3] The lithium disilicate IPS e.Max (Ivoclar Vivadent) falls into this category, having strong needle-like crystals embedded within a glassy matrix[4] that mimics the appearance of enamel and works well for crown applications.[5,6] Among the newer ceramics, the materials based on lithium silicate reinforced by zirconium oxide
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