Evaluation of zirconia–porcelain interface using X-ray diffraction

The aim of this study was to determine if accelerated aging of porcelain veneering had an effect on the surface properties specific to a tetragonal-to-monoclinic transformation (TMT) of zirconia restorations. Thirty-six zirconia samples were milled and sintered to simulate core fabrication followed by exposure to various combinations of surface treatments including as-received (control), hydrofluoric acid (HF), application of liner plus firings, application of porcelain by manual layering and pressing with firing, plus accelerated aging. The quantity of transformed tetragonal to monoclinic phases was analyzed utilized an X-ray diffractometer and one-way analysis of variance was used to analyze data. The control samples as provided from the dental laboratory after milling and sintering process had no TMT (Xm = 0). There was an effect on zirconia samples of HF application with TMT (Xm = 0.8%) and liner plus HF application with TMT (Xm = 8.7%). There was an effect of aging on zirconia samples (no veneering) with significant TMT (Xm = 70.25%). Both manual and pressing techniques of porcelain applications reduced the TMT (manual, Xm = 4.41%, pressing, Xm = 11.57%), although there was no statistical difference between them. It can be concluded that simulated applications of porcelain demonstrated the ability to protect zirconia from TMT after aging with no effect of a liner between different porcelain applications. The HF treatment also caused TMT. Porcelain veneers protect zirconia dental restorations on aging but how the porcelain is applied has little effect on zirconia stability. Porcelain is added to zirconia restorations principally for cosmetic reasons, however, it is prone to chipping. The phase transformation of zirconia from a tetragonal to a monoclinic crystal structure is believed to be a contributing factor to chipping. This transformation may be influenced by the preparation conditions of the restorations and aging within the oral environment. Using X-ray diffraction, Tariq Alghazzawi and Gregg Janowski at the University of Alabama at Birmingham, US, showed that porcelain protected zirconia samples from the structural transformation under accelerated aging conditions. There was no significant difference in the protection offered between manual layering and pressing methods of porcelain application.