Fractographic analysis of anterior bilayered ceramic crowns that failed by veneer chipping

Objective: To fractographically analyze the reasons for the chipping of veneering porcelain in clinically failed anterior lithium disilicate glass-ceramic (LDG) and glass-infiltrated alumina (GIA) crowns. Method and Materials: Five anterior bilayered ceramic crowns with clinical veneer chipping failure were retrieved, of which three were LDG crowns and two were GIA crowns. The fractured surfaces of the failed restorations were examined using stereomicroscopy and scanning electron microscopy (SEM). The principles of fractography were used to identify the location and dimensions of the critical crack and to estimate the stress at failure. Results: All five anterior crowns failed by cohesive failure within the veneer on the labial surface. Fractography showed that the critical crack initiated at the incisal contact area and propagated gingivally. The estimated stresses at failure for veneer chipping were lower than the characteristic strength of the veneer materials. Conclusion: Within the limitations of this in-vivo study, the contact damage, fatigue, and processing flaws within the veneer are important reasons leading to chipping of veneering porcelain in anterior LDG and GIA crowns. Keywords: ceramic restoration, failure analysis, fractography