Subcritical crack growth in porcelains, glass-ceramics, and glass-infiltrated alumina composite for dental restorations

Abstract

The objective was to compare fracture toughness (K(Ic)), stress corrosion susceptibility coefficient (n), and stress intensity factor threshold for crack propagation (K(I0)) of two porcelains [VM7/Vita (V) and d.Sign/Ivoclar (D)], two glass-ceramics [Empress/Ivolcar (E1) and Empress2/Ivlocar (E2)] and a glass-infiltrated alumina composite [In-Ceram Alumina/Vita (IC)]. Disks were constructed according to each manufacturer's processing method, and polished before induction of cracks by a Vickers indenter. Crack lengths were measured under optical microscopy at times between 0.1 and 100 h. Specimens were stored in artificial saliva at 37 degrees C during the whole experiment. K(Ic) and n were determined using indentation fracture method. K(I0) was determined by plotting log crack velocity versus log K(I). Microstructure characterization was carried out under SEM, EDS, X-ray diffraction and X-ray fluorescence. IC and E2 presented higher K(Ic) and K(I0) compared to E1, V, and D. IC presented the highest n value, followed by E2, D, E1, and V in a decreasing order. V and D presented similar K(Ic), but porcelain V showed higher K(I0) and lower n compared to D. Microstructure features (volume fraction, size, aspect ratio of crystalline phases and chemical composition of glassy matrix) determined K(Ic). The increase of K(Ic) value favored the increases of n and K(I0).

Performance of Dental Ceramics: Challenges for Improvements

“…Of the non-zirconia core materials, glassinfiltrated alumina (InCeram Alumina) is the most susceptible, followed by lithium disilicate (IPS Empress 2) (Gonzaga et al, 2009). Of the veneering materials, leucite glass ceramic (Empress), leucite low-fusing porcelain (d.Sign, Ivoclar Vivadent), and an experimental high-fusing porcelain for alumina frameworks (VM7, Vita Zahnfabrik) are equally susceptible (Gonzaga et al, 2009). It is noteworthy that there are non-dental ceramics that increase their strength in aqueous environments; their reaction with water blunts sharp flaws (Taskonak et al, 2008a).…”

“…The influence of microstructure on the mechanical properties of porcelains compared with those of glass-ceramics and glassinfiltrated alumina has been detailed by Gonzaga et al (2009). Flexural strength of veneering materials generally ranges between 60 and 120 MPa (Fischer et al, 2008;Thompson and Rekow, 2008;Bottino et al, 2009) (compared with > 450 MPa of core materials).…”

Chipping of Veneering Ceramics in Zirconium Dioxide Fixed Dental Prosthesis

“…The low fracture toughness of veneering ceramics on the other hand is related to their microstructure that is composed of essentially a relatively weak glassy matrix and small amounts of leucite crystals, ranging from 5 to 30 %, depending on the commercial brand and the application type [14]. The glass composition of the ceramic matrix is highly susceptible to subcritical crack growth (SCG) [15,16], which occurs as a consequence of corrosive action of water in combination with tensile stresses concentrated around the crack tip [17,18].…”

Effect of temperature and heating rate on the sintering of leucite-based dental porcelains

“…This crystalline phase was initially added only to adjust the thermal expansion coefficient of the porcelain, making it compatible with that of the metal substructure. However, it has been demonstrated that these second-phase particles are also responsible for the improvement of the material's fracture toughness [1][2][3].…”