Purpose: to evaluate theeffectof two occlusalpreparation designsand threedifferent typesofceramicmaterials onthemarginalfitofbondedposteriorocclusalveneers.Statementof theproblem: Thinbondedposteriorocclusalveneersconstituteaconservativealternativeto traditionalmoreretentivecompletecoveragecrowns intreatmentofseverely worndentition. Materials and Methods: Sixty extracted human maxillary first molars were randomly distributed into twoequalgroups,30 teeth foreachaccording to thepreparationdesignas following: Non-ferruleand Ferrule (F). Eachofgroup (NFandF) weresubdivided into three subgroupsaccording to the typeofceramicmaterials:IPSe.max CAD (E),Lava™Ultimate CAD/CAM(L)andVITASUPRINITY® PC(S).Theocclusalveneerswerecementedover their respectiveteethwithresin cement TotalCem automix. Themarginalfitwasdeterminedby usingstereomicroscopewithdigitalcamerausingcomputersoftwarefortakingfourpointson eachaxialsurfaceofthe restoration so; therearesixteen readingspereachsample.Results: the meanvalueofverticalmarginalgapofLavaUltimaterecordedlowervalueinnoferuleand ferulegroup (28.4±3.9/34.95±4.02) respectively whichconsideredstatically significant differencefrom thantheothertwomaterials,followedbyIPSEmaxCadinferulegroup(49.7±5.6) then VITASUPRINITY in feruleandno ferule(50.8±7.43/51.9 ±3.70)respectively, then finallyIPSEmaxCad inno ferulegroup (52.4±5.5). Conclusion:Within the limitationof this study,itconcluded that, LavaUltimate occlusalveneers represent themoreadequate material to achievebettermarginaladaptabilityhowever,themarginalgapofthethreematerialswere within the clinicalacceptance range