Creep functions of dental ceramics measured in a beam-bending viscometer

Objective. To characterize the high temperature viscoelastic properties of several dental ceramics by the determination of creep functions based on mid-span deflections measured in a beam-bending viscometer (BBV). Methods. Six groups of beam specimens (58×5.5×2.5 mm) were made from the following materials: (1) IPS Empress2® body—a glass veneer ceramic (E2V); (2) an experimental glass veneer (EXV); (3) Vita VMK 68 feldspathic body porcelain—a low-expansion body porcelain (VB); (4) Will-Ceram feldspathic body porcelain—a high-expansion body porcelain (WCB); (5) Vita feldspathic opaque porcelain-a medium-expansion opaque porcelain (VO); and (6) Will-Ceram feldspathic opaque porcelain—a high-expansion opaque porcelain (WCO). Midpoint deflections for each specimen were measured in a BBV under isothermal conditions at furnace temperatures ranging from 450 to 675 °C. Non-linear regression and linear regression analyses were used to determine creep functions and shear viscosities, respectively, for each material at each temperature. Results. The shear viscosities of each group of dental ceramics exhibited bilinear Arrhenius behavior with the slope ratios (x) ranging from 0.19 for WCB to 0.71 for EXV. At the higher temperature ranges, activation energies ranged from 363 kJ/mol for VO to 386 kJ/mol for E2V. Significance. The viscoelastic properties of dental ceramics at high temperatures are important factors in understanding how residual stresses develop in all-ceramic and metal–ceramic dental restorations.