Strength and reliability of four-unit all-ceramic posterior bridges.
OBJECTIVE
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-disilicate 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 mm2 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 Weibull statistics giving the characteristic load bearing capacity F0 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 load F0 282 N and the reliability m = 5.7. For the ICZ frameworks the average load bearing capacity was 470 (+/-101) N, F0 518 N and m = 4.5. CEZ frameworks revealed the highest average load bearing capacity of 706 (+/-123) N, the highest characteristic load bearing capacity F0 = 755 N and the best reliability m = 7.0.


CONCLUSIONS
CEZ frameworks showed the best mechanical properties as demonstrated by the high values of average load bearing capacity, reliability and characteristic load bearing capacity with respect to the other ceramics studied. However, for four-unit posterior CEZ frameworks the connector size of 7.3 mm2 is insufficient to withstand occlusal forces reported in the literature. Four-unit posterior frameworks require a connector size larger than 7.3 mm2.
Lüthy
Heinz
H
Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, Center for Dental and Oral Medicine, University of Zurich, Plattenstrasse 11, CH-8028 Zurich, Switzerland. luethy@zzmk.unizh.ch
Filser
Frank
F
Loeffel
Olivier
O
Schumacher
Madeleine
M
Gauckler
Ludwig J
LJ
Hammerle
Christoph H F
CH
D000537:Aluminum Oxide / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D019232:Dental Restoration Failure; D003779:Denture Design; D003830:Denture, Partial, Fixed; D005898:Glass / Q000737:chemistry; D006801:Humans; D018020:Lithium Compounds / Q000737:chemistry; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
C118557:Empress 2; D018020:Lithium Compounds; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; C070870:In-Ceram; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide