Structural reliability of alumina-, feldspar-, leucite-, mica- and zirconia-based ceramics

Objectives: The objective of this study was to test the hypothesis that ind ustrially manufactured ceramic materials, such as Gene Mark II and Zirconia -TZP, have a smaller range of fracture strength variation and therefore gre ater structural reliability than laboratory-processed dental ceramic materi als. Methods: Thirty bar specimens per material were prepared and tested. The fo ur-point bend test was used to determine the flexure strength of all cerami c materials. The fracture stress values were analyzed by Weibull analysis t o determine the Weibull modulus values (m) and the 1 and 5% probabilities o f failure. Results: The mean strength and standard deviation values for these ceramics are as follows: (MPa +/- SD) were: Cerec Mark II, 86.3 +/- 4.3; Dicor, 70. 3 +/- 12.2; In-Ceram Alumina, 429.3 +/- 87.2; IPS Empress, 83.9 +/- 11.3; V itadur Alpha Core, 131.0 +/- 9.5; Vitadur Alpha Dentin, 60.7 +/- 6.8; Vita VMK 68, 82.7 +/- 10.0; and Zirconia-TZP, 913.0 +/- 50.2. There was no stati stically significant difference among the flexure strength of Cerec Mark II , Dicor, IFS Empress, Vitadur Alpha Dentin, and Vita VMK 68 ceramics (p > 0 .05). The highest Weibull moduli were associated with Cerec Mark II and Zir conia-TZP ceramics (23.6 and 18.4). Dicor glass-ceramic and In-Ceram Alumin a had the lowest m values (5.5 and 5.7), whereas intermediate values were o bserved for IPS-Empress, Vita VMK 68, Vitadur Alpha Dentin and Vitadur Alph a Core ceramics (8.6, 8.9, 10.0 and 13.0, respectively). Conclusions: Except for In-Ceram Alumina, Vitadur Alpha and Zirconia-TZP co re ceramics; most of the investigated ceramic materials fabricated under th e condition of a dental laboratory were not stronger or more structurally r eliable than Vita VMK 68 veneering porcelain. Only Cerec Mark II and Zircon ia-TZP specimens, which were prepared from an industrially optimized cerami c material, exhibited in values greater than 18. Hence, we conclude that in dustrially prepared ceramics art: more structurally reliable materials for dental applications although CAD-CAM procedures may induce surface and subs urface flaws that may adversely affect this property. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.