Limited information is available on the optimal cement thickness of monolithic zirconia crowns. This study was designed to evaluate the stress distribution in the posterior monolithic zirconia crowns with different cement thicknesses under masticatory force and maximum bite force using three-dimensional finite element analysis. The prepared and unprepared mandibular right first molar models were scanned and exported to the computer-aided design system. Solid models of monolithic zirconia crowns, which were cemented on prepared teeth were generated. Four models were fabricated applying different cement thicknesses (100 mu m, 200 mu m, 400 mu m, and 600 mu m). The solid models were imported into the finite element analysis software and meshed into tetrahedral elements. Four three-dimensional finite element models were simulated under masticatory force and maximum bite force: vertical (axial), angular (45 degrees) and horizontal loads of 280 N at 5 points; vertical load of 700 N at 8 points were loaded, respectively. The stress distribution varied with the different cement thicknesses and directions of applied loads. The monolithic zirconia crowns with cement thicknesses exceeding 200 mu m had wider distributions of peak maximum principal stress under the same loading conditions. Monolithic zirconia crowns have more stress concentrations on the occlusal surfaces, while the cement layers have more stress concentrations on the cervical areas. Thicker cement layers were associated with more concentrated stresses on the buccal and lingual cervical areas. The test results show that the cement thickness plays an essential role in the success of monolithic zirconia restorations in terms of reducing cement wash-out. Cement thickness of 100 mu m is recommended for monolithic zirconia crowns. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.