Objective This study investigated the influence of different designs and porcelain/glaze firing on the marginal and internal fit of three kinds of computer aided design/computer aided manufacturing (CAD/CAM) zirconia ceramic implantsupported crowns.Methods Three groups of zirconia ceramic implant-supported crowns with different designs were produced from copings by using a Cercon CAD/CAM system (n=8). The first two groups comprised double-layer crowns (zirconia coping+veneer) with regular (Group A) and full circumferential zirconia-collar marginal designs (Group B). The third group was composed of anatomic single-layer zirconia crowns without cores (Group C). Initially, the marginal and internal gaps of the copings and crowns were individually replicated by light-body silicon and then measured by micro-computed tomography scanning before and after porcelain/glaze firing. Five measurements were employed: vertical marginal gap (MG); horizontal marginal discrepancy (HMD); chamfer area (CA); axial wall (AW); and axial-occlusal transition area (AOT). Statistical analyses were performed by SPSS 17.0.Results HMD measurements in Group A were statistically higher than those in Groups B and C (P0.05). Moreover, no differences were noted in MG, CA, AW, and AOT among the three groups (P>0.05). All the measurements in the three groups showed no significant change after porcelain/glaze firing (P>0.05), except for MG in Group A, which significantly decreased (PConclusion The marginal fits of the double-layer crowns with full circumferential zirconia-collar and the anatomic single-layer zirconia crowns were superior to that of the double-layer crowns with regular margins. The MG of the crowns with regular margins was obviously influenced by porcelain firing.
