Objectives: The demand of dental professionals for all-ceramic restorations, yttria-stabilized tetragonal zirconia (Y-TZP) has been offered as a material for ceramic crown fabrication. The zirconia is used as a core material and veneering porcelain is added to it, creating final form and color of the teeth. The purpose of this study was to compare the load to fracture of zirconia with and without veneering porcelain.

Methods: 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 to act as the control with five samples of non-veneering zirconia. Group B consisted of five samples veneered with porcelain to an overall thickness of 1.0 mm and loaded to the veneered side. Group C consisted of five samples veneered with porcelain to an overall thickness of 0.95 mm and loaded to the zirconia side. The veneering porcelain used was Vita D (Vita, Germany). All samples were loaded to fracture using 3 point bending test in an Instron with the crosshead speed of 0.5 mm/min.

Results: The mean load to fracture of Group A= 15.77 KgF (2.54 S.D.). The mean load to fracture of Group B= 29.46 KgF (7.70 S.D.). The mean load to fracture of Group C= 13.46 KgF (1.47 S.D.). The Fisher's PLSD test was applied to the data and indicated that there was no statistical difference between groups A and C (P=.4566) but there was a significant statistical difference between groups A and B (P=.0007) and groups B and C (P=.0002).

Conclusions: It was concluded that under the conditions of this study, the load to fracture strength of the zirconia was significantly increased when veneering porcelain was added and loaded from the porcelain side.

Supported by Nobel Biocare/University of Michigan Center for Excellence.

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