[Influence of the design of zirconia framework on the fracture strength of veneering porcelain].

Abstract

Recently, new metal free materials for crown and bridges such as yttria stabilized tetragonal zirconia polycrystals (Y-TZP) have been introduced in the dental profession. These systems enable the fabrication of long-span bridges of more than 3 units in the posterior region. But occasionally chipping of the veneering porcelain was observed. The aim of this study was to analyze the influence of the design of the zirconia framework on the fracture strength of the veneering porcelain. Two types of Y-TZP framework were fabricated for the lower second premolar crown (normal type and support type) (Cercon base colored, DeguDent, Hanau-Wolfgang, Germany). The support-type framework has a 1 mm-wide collar around the margin to support the veneering porcelain. Twelve all-ceramic crowns were fabricated, six crowns for each group. The framework was covered by veneering ceramics (Vintage ZR Press Over, SHOFU INC., Kyoto, Japan) using the heat press method. All specimens were fixed using adhesive resin cement on the master die and the vertically loaded was measured at the distal ridge of the crown at a cross-head speed of 1 mm/min until fracture. The maximum compressive load required to cause a fracture was recorded for each specimen. The t test was used for the statistical analysis of the fracture loads, with a significance level of alpha = 0.05. The following conclusion was obtained. The fracture strength of the all-ceramic crowns with a support-type Y-TZP framework was significantly higher than that of the normal type. This result suggests that the design of the Y-TZP framework is important for all-ceramic restorations.