Introduction

Esthetic aspects of dental treatment are becoming increasingly important to patients, thus, increasing the demand for ceramic restorations. All-ceramic restorations must satisfy clinical requirements for strength, accuracy of fit, and color stability if they are to be successful restorations.¹ To achieve this the chemical composition and manufacturing technique of dental porcelain has been altered to modify the physical properties of the porcelain frit.²

Amongst the newly developed all-ceramic restorations are the pressable ceramics. These are supplied in the form of ingots that are heated and molded under pressure. A full-contour crown is waxed, invested, and placed in a special mould that has an alumina plunger. The ingot is placed under the plunger, the entire assembly is heated to 1150ºC, and the plunger presses the ceramic into the mould. The final shade of the crown is adjusted either by shading or veneering with a layer of conventional ceramic.

IPS-Empress 2 (Ivoclar-Vivadent, Schaan, Liechtenstein) was introduced in 1998. Sorensen et al.³ described this type of ceramic as having a lithium-disilicate crystal content of 60% by volume that forms an interlocking structure after pressing which increases the strength and fracture toughness of the ceramic. This serves as the underlying framework of the restoration. A veneering ceramic (sintered glass ceramic) forms fluorapatite crystals resembling natural enamel in shape and composition. This layer provides the natural wear compatibility and optical properties of the ceramic. The manufacturer reported the highest flexural strength for the lithium-disilicate glass ceramic at a value of 433 MPa when compared to other materials including a fluormica-reinforced, a leucite-reinforced, an aluminous porcelain, and a glass-infiltrated presintered alumina. They also reported a fracture toughness value of 3.2 MN/m^1.5, which was lower than the glass-infiltrated pre-sintered alumina but higher than the leucite-reinforced porcelain.

Compared to many studies evaluating the fracture resistance of all-ceramic crowns, there are relatively few studies reporting on their clinical performance.^4-8 Kelly⁹ stated traditional fracture tests of single unit all-ceramic prosthesis are inappropriate since they do not create failure mechanisms similar to those seen in collected clinical specimens. Thus, clinical studies are needed to evaluate the clinical performance of all-ceramic crowns. Sjogren et al.¹⁰ pointed out most clinical studies on all-ceramic systems have been carried out on patients treated by specialists in hospital or university settings. However, most dental restorations are placed by general dental practitioners, and it is the performance of these restorations that might be a more valuable indication of their clinical success.

Thus, the aim of this study was to evaluate the quality and clinical success of IPS Empress 2 all-ceramic crowns placed by general dental practitioners in five dental centers in Jordan.