Objectives: Zirconium-dioxide(ZD) frameworks are established for posterior fixed-partial-dentures (FPD). Main problem in clinical practice is chipping. Monolithic materials as lithium-disilicate (LS2) do not need to be veneered and might solve the problem, but are not indicated for posterior FDPs by manufacturer. Aim of the present study is the comparison of fracture-strength (FS) of posterior zirconia based and LS2 FDPs before and after aging. Methods: 16 three-unit LS2 FDPs (e.max CAD, Ivoclar Vivadent) and 32 three-unit ZD frameworks (Organic Zirkon, R+K CAD/CAM Technology) were fabricated by using computer-aided design and manufacturing (CAD/CAM). 16 ZD frameworks were conventionally veneered (VZ) with low fusing veneering porcelain (IPS e.max Ceram, Ivoclar Vivadent) and 16 overpressed (OZ; IPS e.max ZirPress, Ivoclar Vivadent). All FDPs were cemented using glass ionomer cement (Ketac cem Aplicap, 3M Espe). 8 FDPs per group were artificially aged (mastication simulation: 1.2 mio cyclesx50N, thermal cycling 10000x5°/55°C). FS of all FDPs were tested in an universal testing machine until fracturing at a test speed of v=1mm/min (Zwick 010, Zwick) and statistically analyzed (ANOVA, T-Test, p0.05). Results: FS of OZ before aging was 1609N±427N and after aging 1685N±480N, followed by VZ (1541N±438N/1557N±643N) and LS2 (1293N±237N/1131N±374N). After aging one LS2 abutment and 2 cusps fractured. 5 zirconia based veneering porcelain only showed superficial cracks. There were no significant differences between FS before and after aging, as well as between the different materials. Conclusion: All FS were above 1000N before and 900N after aging. LS2 FDPs showed good results compared to zirconium-dioxide based FDPs. Chipping of veneered porcelain did not appear. Further clinical tests are required. Keywords: ceramics, CAD/CAM, fixed partial dentures, zirconia, lithium disilicate glass ceramics