Procera® Zirconia
Crown

New
Material Strength of Zirconia
Load to Fracture of Veneered Zirconia
Wear of Enamel Opposing YPSZ Zirconia Core Material With Two Surface Finishes

Abstract: Due to the reported outstanding mechanical properties and excellent biocompatibility of yttria-stabilized tetragonal zirconia (Y-TZP), it is being offered as a core material to fabricate all ceramic restorations. While engineering literature contains material strength data, there are several methods that exist for producing Zirconia for use in dental applications. This study compared material strength of dental use Zirconia produced by 2 separate methods. Five specimens each were fabricated in discs with a thickness of 1.5 mm and 2.0 mm and a radius of 12.0 mm from DC-Zirkon® used by DCS “Smart-Fit’ Cad-Cam system. Ten specimens of Procera® AllZirkon (Nobel Biocare) core material were fabricated in discs of 1.2 mm thickness and a radius of 13 mm. All samples were loaded to fracture using a biaxial flexural strength test fixture in an Instron machine with a cross-head speed of 0.5 mm/min. The radius of the supporting circle and loading area was kept constant. Using the formula S=0.2387P (X-Y)/dŸ2, (ISO 6872:1995 8.3.2.4) the flexural strength was calculated from the values of the total load causing fracture, the dimensions of the discs and the dimensions of the biaxial flexural strength test fixture. The 1.5 mm DC-Zirkon® samples gave a mean load causing fracture of 1232 N. The 2.0 mm DC-Zirkon® samples gave a mean load causing fracture of 2450 N. The 1.2 Procera® AllZirkon samples gave a mean load causing fracture of 1068 N. After analyzing the data for material thickness, the flexural strength of Procera® AllZirkon was 1158 MPa, while the DC-Zirkon® was 927 MPa. The Fisher’s PLSD test demonstrated a statistically significant difference between the two groups.
Conclusions: Procera® AllZirkon demonstrated a higher flexural strength when compared to DC-Zirkon®.

Abstract: The demand for all-ceramic restorations has resulted in yttria-stabilized tetragonal zirconia (Y-TZP) being offered as a material for ceramic crown fabrication. The zirconia is used as a core material and veneering porcelain is added to this core ceating the final form and color for the restoration. The purpose of this study was to compare the load to fracture of zirconia with and without veneering porcelain. Fifteen samples of zirconia (Y-TZP) were fabricated in disks of 10 mm in diameter and 0.4 mm thick. The samples were divided into three groups. Group A was the control with five samples of non-veneered zirconia. Group B consisted of five samples veneered with porcelain to an overall thickness of 1.0 mm and loaded on the veneered side. Group C consisted of five samples veneered with porcelain to an overall thickness of 0.95 mm and loaded on the zirconia side. The veneering porcelain used was Vita D (Vita, Germany). All samples were loaded to fracture using a 3 point bending test in an Instron machine with the cross-head speed of 0.5 mm/min. The mean load to fracture of Group A was 15.77 KgF (2.54 s.d.). The mean load to fracture of Group B was 29.46 KgF (7.70 s.d.). The mean load to fracture of Group C was 13.46 KgF (1.47 s.d.). The Fisher’s PLSD test was applied to the data and indicated that there was no statistically significant difference between Groups A and C (P=.4566) but there was a significant difference between Groups A and B (P=.0007) and Groups B and C (P=.0002).
Conclusions: Under the conditions of the study, the load to fracture strength of the zirconia was significantly increased with the addition of veneering porcelain and when loaded from the veneering porcelain side.

Abstract: Yttrium-Oxide-Partially-Stabilized-Zirconia (YPSZ) has been suggested as a core material for all-ceramic crowns. However, it is possible in the clinical environment that the veneering porcelain in an all-ceramic crown may experience wear and the core material becomes exposed. The effect of the exposed core surface on enamel and other restorative materials opposing them has not been reported. The purpose of this in-vitro study was to examined the wear of enamel when abraded against the zirconia core material in an as-produced state and as-polished state. Discs of YPSZ core material 13.0 mm in diameter and 2.0 mm in thickness were fabricated by the manufacturer (Nobel Biocare, Sweden). Samples were divided into two groups: For Group 1) The as-produced group with the surface finish as delivered from the manufacturer, and Group 2) The polished group with the surface polished using both abrasive wheels and diamond polishing paste. The samples were placed in a wear machine where they were opposed by enamel samples and abraded under a constant applied load of 500 gram at a frequency of 60 rpm in an artificial saliva environment for a total of 10,000 cycles. Length measurements of the enamel samples were made befoe and after abrading using a digital micrometer. Discs of type IV gold were also abraded against enamel as the control samples. The mean wear of enamel opposing the zirconia samples for Group 1 as-produced samples was 0.044 mm, and for Group 2 as-polished was 0.040 mm. The enamel wear against the gold control was 0.024 mm.
Conclusions: The polished zirconia caused less wear to the enamel abrader than the as-produced zirconia. The zirconia caused greater enamel wear than did the gold control.