Objective: To compare the stress corrosion susceptibility coefficient (n_s) of two dental porcelains (D and V) and two glass-ceramics (E1 and E2) using dynamic fatigue test. Methods: 60 discs (1mm-thick and diameter of 12mm) of each material were constructed according to manufacturers' processing methods. After that they were ground and polished to their final dimensions. The n_s values were obtained by dynamic fatigue test, using a biaxial flexural strength fixture (piston-on-three-balls) and five constant stress rates (0.01, 0.1, 1, 10, and 100 MPa/s, n=10). During the tests, specimens were immersed in artificial saliva at 37^oC. Inert strength (IS) was determined at 100 MPa/s in silicon oil (n=10). Linear regression analysis of log stress rate versus log strength was performed to calculate n_s, considering that the slope of the curve was 1/(n_s+1). Results: E2 showed the lowest n_s. E1 and V showed similar n_s values, which were higher than that of porcelain D. As to flexural strength, the highest values were obtained for E2, followed by E1, V and D regardless of the stress rate. The mean strength of the materials obtained at 100 MPa/s in artificial saliva was 64 to 80% lower than the IS. Conclusion: E2 is more susceptible to slow crack propagation than the other materials tested. E1 and V responded similarly with respect to slow crack growth; however they were less susceptible to this phenomenon than porcelain D. Acknowledgments: FAPESP, CNPq and CAPES.

Material	Mean fracture strength (MPa)					IS (MPa)	ns
	0.01MPa/s	0.1MPa/s	1MPa/s	10MPa/s	100MPa/s
D (d.Sign/Ivoclar)	40.8±3.3	42.1±2.8	46.8±4.9	58.4±4.2	60.1±6.8	94.2±9.4	20.4
V (VM7/Vita)	62.5±11.3	65.6±11.9	70.8±15.2	78.8±11.3	88.5±19.7	123.4±21.6	26.8
E1 (Empress/Ivoclar)	86.3±11.2	95.5±8.2	98.9±12.2	115.0±15.7	118.1±16.1	166.9±21.7	29.7
E2 (Empress-2/Ivoclar)	151.1±12.6	160.3±13.9	180.6±19.7	216.4±22.8	246.4±29.8	307.3±38.4	17.1

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