However, chipping and fracturing of layering porcelains applied to zirconia frameworks continue to be a problem, with p38 MAPK inhibitors clinical trials a reported incidence between 0 and 30% [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17] and [18]. Porcelain chipping and fracture can be disappointing for clinicians and patients, and should be regarded as a serious problem. Although simple polishing of the rough margins or repair of the fracture with composite material may suffice in some cases, patients occasionally require total replacement of the restoration. Several causes of porcelain chipping and fracture have been proposed,

including mechanical insufficiency of the layering porcelain,

inappropriate framework support for the layering porcelain, coefficient of thermal expansion (CTE) mismatch, and unfavorable shear forces between the zirconia framework and layering materials [19]. Studies have indicated that the mechanical integrity and bonding of the layering porcelain to the framework buy PLX4032 material are key factors in the successful performance of veneer/framework bilayered restorations [3] and [20]. This article reviews the literature on the bonding potential between layering materials and the zirconia framework of zirconia-based restorations. A search of electronic databases such as PubMed was conducted, involving in vitro studies that were published between 1966 and the present date. The reference lists of retrieved articles were screened for additional candidate publications. In addition to the database searches, relevant articles, abstracts, and proceedings were handsearched through 1990. Feldspathic porcelain is generally used for veneering zirconia frameworks in all-ceramic restorations. Numerous in vitro studies of the bond strength between layering porcelain and zirconia ceramics have been published in the last decade ( Table 1). Metal–ceramic systems have proven to be a reliable option for fixed prosthodontics and remain the gold standard [21] and [22]. In metal–ceramic restorations, a bond strength greater than 25 MPa between

the layering porcelain Edoxaban and metal is believed to be adequate according to the International Standards Organization (ISO) [23]; however, no such estimate for adequate bond strength in all-ceramic materials has been determined. Several test methods namely, shear bond, three- and four-point flexure, tensile, and microtensile bond tests have been suggested for bond strength evaluation of veneering porcelain to frameworks. It is important that the bonding interface between veneering porcelain and frameworks should be the stressed region, regardless of the test method being employed. Shear bond tests have been reported as one of the most prevalent bond strength tests in the literature [24], [25], [26], [27], [28], [29], [30], [31], [32], [33] and [34].