Mechanical fatigue degradation of ceramics versus resin composites for dental restorations

Objectives. For posterior partial restorations an overlap of indication exists where either ceramic or resin-based composite materials can be successfully applied. The aim of this study was to compare the fatigue resistance of modern dental ceramic materials versus dental resin composites in order to address such conflicts. Methods. Bar specimens of five ceramic materials and resin composites were produced according to ISO 4049 and stored for 14 days in distilled water at 37 degrees C. The following ceramic materials were selected for testing: a high-strength zirconium dioxide (e.max Zir-CAD, Ivoclar), a machinable lithium disilicate (e.max CAD, Ivoclar), a pressable lithium disilicate ceramic (e-max Press, Ivoclar), a fluorapatite-based glass-ceramic (e.max Ceram, Ivoclar), and a machinable color-graded feldspathic porcelain (Trilux Forte, Vita). The composite materials selected were: an indirect machinable composite (Lava Ultimate, 3M ESPE) and four direct composites with varying filler nature (Clearfil Majesty Posterior, Kuraray; GrandioSO, Voco; Tetric EvoCeram, Ivoclar-Vivadent; and CeramX Duo, Dentsply). Fifteen specimens were tested in water for initial strength (sigma(in)) in 4-point bending. Using the same test set-up, the residual flexural fatigue strength (sigma(ff)) was determined using the staircase approach after 10(4) cycles at 0.5 Hz (n = 25). Weibull parameters sigma(0) and m were calculated for the sigma(in) specimens, whereas the sigma(ff) and strength loss in percentage were obtained from the fatigue experiment. Results. The zirconium oxide ceramic showed the highest sigma(in) and sigma(ff) (768 and 440 MPa, respectively). Although both lithium disilicate ceramics were similar in the static test, the pressable version showed a significantly higher fatigue resistance after cyclic loading. Both the fluorapatite-based and the feldspathic porcelain showed equivalent initial and cyclic fatigue properties. From the composites, the highest filled direct material Clearfil Majesty Posterior showed superior fatigue performance. From all materials, e.max Press and Clearfil Majesty Posterior showed the lowest strength loss (29.6% and 32%, respectively), whereas the other materials lost between 41% and 62% of their flexural strength after cyclic loading. Conclusions. Dental ceramics and resin composite materials show equivalent fatigue strength degradation at loads around 0.5 sigma(in) values. Apart from the zirconium oxide and the lithium disilicate ceramics, resin composites generally showed better sigma(ff) after 10,000 cycles than the fluorapatite glass-ceramic and the feldspathic porcelain. Resin composite restorations may be used as an equivalent alternative to glass-rich-ceramic inlays regarding mechanical performance. (C) 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.