Mechanical performance of cement- and screw-retained all-ceramic single crowns on dental implants.

OBJECTIVES: This in-vitro study was performed to compare the contact wear, fracture strength and failure mode of implant-supported all-ceramic single crowns manufactured with various fabrication and fixation concepts. MATERIALS AND METHODS: Fifty dental implants (Conelog O 4,3mm/L11mm, Camlog Biotechnologies AG) were embedded and treated with all-ceramic molar single-crowns. Three groups received hand-layered zirconia crowns (IPS e.max Ceram/ IPS e.max ZirCAD, Ivoclar Vivadent AG): CZL (cement-retained zirconia-based layered) group crowns were cemented conventionally, SZL (screw-retained zirconia-based layered) group crowns were screw-retained, MZL (modified zirconia-based layered) group crowns showed a different coping design with screw retention. The specimens of SST (screw-retained sintering-technique) and SFL (screw-retained full-contour lithium-disilicate) group were CAD/CAM (Computer-aided design/computer-aided manufacturing) fabricated in the sintering technique (IPS e.max ZirCAD/IPS e.max CAD, Ivoclar Vivadent AG) and full-contour of lithium disilicate (IPS e.max CAD, Ivoclar Vivadent AG) respectively and screw-retained. All specimens underwent artificial aging, load until failure and a scanning electron microscopy (SEM) analysis. The received data were statistically compared (one-way ANOVA; Student-Newman-Keuls test; Mann-Whitney U-test) at a significance level of 5%. RESULTS: Mouth-motion fatigue testing caused two abutment fractures (SST group and SZL group) and two chipping events (CZL group). Specimens of MZL group showed statistically significant less contact wear compared to the other groups (p<0.001). There was no statistical difference between the groups in terms of the maximum fracture load. SEM-analysis showed a more homogenous structure and surface of CAD/CAM fabricated specimens towards manually veneered components. CONCLUSIONS: The mode of retention did not influence the fracture resistance but the failure patterns of the specimens. CAD/CAM milled lithium-disilicate crowns seemed to be a preserving factor for dental implants. CLINICAL RELEVANCE: The mode of retention and veneering influences the mechanical performance of implant-supported single crowns.