Effect of Different Surface Treatments on Various Physical and Mechanical Properties of Veneered Nano-crystalline Zirconia

Abstract

During the last few decades, the demand for metal-free restorations, being conditioned by both social pressures and interests of dental profession has increased dramatically and a climate of non-acceptance of metal alloys in the oral cavity prevailed. Trying to meet those highly increasing esthetic demands while at the same time providing a long-term successful and biocompatible restoration, several types of all-ceramic systems have been developed. With the advances in computer aided design (CAD) and computer aided manufacturing (CAM) technologies, the high-strength ceramic systems have become increasingly popular and Yttria-stabilized tetragonal zirconia (Y-TZP), with its unsurpassed mechanical properties and biocompatibility has had its clinical applications expanded in the field of fixed prosthodontics. However, its whitish opaque color has imposed an esthetic problem and the need for veneering with a more esthetic glass ceramic became imperable. Advances in industrial facilities and the improvements in nano-technology, led to the evolution of nano-structured polycrystalline zirconia in an attempt to add esthetic value to the mechanical supremacy. Though nano-crystalline full-contour zirconia is reported to have high transcluceny, yet for better esthetic results, it’s advised to use individually veneered structures. Minor Chipping or delamination of the veneering porcelain from the zirconia framework has been reported to be one of the major causes of failure of zirconia-based restorations. Different surface treatment methods of zirconia surface have been tried in an attempt to overcome this probplem, but still the exact mechanism of bonding between the zirconia core and the veneering porcelain is unknown. This study was conducted to evaluate the effect of different surface treatment methods on shear bond strength between nano-crystalline Yttria-stabilized zirconia and veneering porcelain, as well as bi-axial flexural strength, color reproduction and translucency parameter of the core-veneered restoration. Nano-crystalline yttria-stabilized zirconia samples were constructed with different configurations according to the factor under research and classified according to whether they would be tested for shear bond strength or biaxial flexural strength, color reproduction and translucency parameter measurements. For shear bond strength test, samples were cut using a hard stainless steel disc mounted on a milling machine in the form of zirconia plates of final dimensions 12mm x 15 mm x 2 mm and veneered with porcelain discs of dimensions 3 mm x 3mm. For biaxial flexural strength test, color reproduction and translucency parameter measurement, samples were cut in the form of zirconia discs 12 mm in diameter and 0.8mm thick-after sintering- veneered with a layer of porcelain of 0.7 mm thickness and of the same diameter as the zirconia discs.