Fracture Strength and Precision of Fit of Implant-Retained Monolithic Zirconia Crowns
New monolithic zirconia materials can be used to fabricate full-contour fixed dental prostheses with the computer-aided design/computer-aided manufacturing (CAD/CAM) method. The aim of this study was to examine the fracture strength and precision of fit of screw-retained monolithic zirconia crowns made directly on implants or by cementing on prefabricated titanium (Ti) bases. Monolithic screw-retained implant crowns (n = 6) were produced by CAD/CAM method using partially (PSZ) and fully stabilized (FSZ) zirconia. Industrially produced zirconia crowns were used as a reference. A lateral incisor study model was made onto an implant replica. Crowns were produced either directly on the implant or through cementing on a prefabricated titanium base (PSZ+Ti, FSZ+Ti). The crowns were tightened to implant replicas with a torque of 35 Ncm. The gap between the replica and the abutment or crown was measured from ×400 scanning electron microscope images for precision of fit. Mechanical testing until failure was completed with a universal testing machine with loading angle of 45°. Statistical analysis was performed (analysis of variance). Mean (±SD) failure loads were 259 ± 23 (PSZ), 140 ± 13 (FSZ), 453 ± 25 (PSZ+Ti), 439 ± 41 (FSZ+Ti), and 290 ± 39 (Procera). Mean (±SD) gap values were 2.2 ± 0.2 (PSZ), 2.5 ± 1.0 (FSZ), 7.0 ± 1.0 (PSZ+Ti), 7.7 ± 1.6 (FSZ+Ti), and 6.7 ± 1.7 (Procera). Monolithic zirconia crowns with a Ti base clearly show higher fracture strengths than the crowns fixed directly on the implant surface. Better marginal fit can be achieved with direct zirconia crowns than with crowns on a titanium base or industrially produced zirconia crowns.

Lateral incisor study models on replicas: partially stabilized zirconia (PSZ) direct, PSZ + titanium (Ti) base, fully stabilized zirconia (FSZ) direct, FSZ + Ti base, Procera.

Scanning electron microscope images (×400) of the gap between implant replica and different zirconia crowns. (a) Industrially produced Procera crown. (b) Fully stabilized zirconia direct. (c) Partially stabilized zirconia direct. (d) Titanium base.

Illustration of marginal gaps (μm) of partially (PSZ) and fully stabilized zirconia (FSZ) crowns made directly on an implant replica or through cementing on a titanium base. Industrially produced zirconia crown (Procera, Nobel Biocare) is shown as a reference.
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