Shear bond strength tests of zirconia veneering ceramics after chipping repair

All ceramic systems are replacing the classical metal–ceramic crowns in dental practice. Zirconium dioxide (zirconia) core associated with veneering ceramic provides both good mechanical and aesthetic properties of prosthetic restorations. However, such zirconia crowns may be affected by defects of adaptation, too tight contacts in the proximal area and fissures of the ceramic veneer. The latter produces chipping; this requires a reattachment, therefore a second burning of the zirconia–ceramic interface. Such an additional procedure may affect the mechanical resistance of the ceramic veneer and the bond between the zirconia core and the ceramic veneer. The aim of this study was to evaluate the alterations of this shear bond strength (SB) between the zirconia core and the ceramic veneer, as produced by the first set of complete burning procedures and by the second correction burning of the dental restorations. Thirty-three zirconia discs were veneered with ceramic material and the SB was evaluated for each sample. Each ceramic cylinder detached from the zirconia was bonded on the core through a new layer of dentin and another burning procedure; the SB was tested again. The results of the two SB tests were compared; the statistical analysis concluded that there is an approximately 10% decrease of the resistance after the second burning. Also, the spread of the values for each test showed the high impact of the human factor on such dental restorations. In all the tests, the weakest area proved to be the interface between the zirconia core and the layered ceramics.