Strength and reliability of four-unit all-ceramic posterior bridges

sObjectives: The purpose of this study was to determine the in vitro load bearing capacity of four-unit posterior frameworks made of glass ceramic with lithium-disiticate crystals (E2), of zirconia-reinforced glass-infiltrated alumina (ICZ) and of zirconia stabilized with 3 mol% yttria (CEZ). Methods: All frameworks mimicked a four-unit posterior situation with 7.3 mm(2) interdental cross-sections and possessed exactly the same dimensions. The load bearing capacity was measured on a special bridge test setup with 15 specimens for each of the materials. The data were analyzed with Weibult statistics giving the characteristic load bearing capacity F-0 at 63% failure probability and the Weibull modulus m as indicator for the reliability and reproducibility. Results: For the E2 frameworks the average load bearing capacity and the SD was 260 (+/- 53) N, the characteristic toad F-0 282 N and the reliability m=5.7. For the ICZ frameworks the average load bearing capacity was 470 (+/- 101) N, F-0 518 N and m= 4.5. CEZ frameworks revealed the highest average toad bearing capacity of 706 (+/- 123) N, the highest characteristic load bearing capacity F-0 = 755 N and the best reliability m=7.0. Significance: CEZ frameworks showed the best mechanical properties as demonstrated by the high values of average load bearing capacity, reliability and characteristic toad bearing capacity with respect to the other ceramics studied. However, for four-unit posterior CEZ frameworks the connector size of 7.3 mm(2) is insufficient to withstand occlusat forces reported in the literature. Four-unit posterior frameworks require a connector size larger than 7.3 mm(2). (c) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.