Fractography of Dental Restorations

The dental community is using a variety of ceramic restorative materials such as porcelains (leucite or alumina based), glass-ceramics (leucite, mica, lithium disilicates), alumina-glass infiltrated, and CAD-CAM ceramics including pure alumina and zirconia (3Y-TZP) core materials. Polycrystalline ceramics such as alumina and zirconia serve as substructure materials (i.e., framework or core) upon which glassy ceramics are veneered for an improved appearance. Under masticatory loads, sudden fracture of the full-thickness restoration or of the veneering ceramic (chips) may occur. Stereomicroscope and scanning electron microscope analyses were used to perform qualitative (descriptive) fractography on clinically failed dental ceramic restorations. The most common features visible on the fracture surfaces of the glassy veneering ceramic of recovered broken parts were hackle, wake hackle, twist hackle, arrest lines, and compression curls. The observed features are indicators of the local direction of crack propagation and were used to trace the crack’s progression back to its initial starting zone (the origin). This paper presents the applicability of fractographic failure analyses for understanding fracture processes in brittle dental restorative materials and it draws conclusions as to possible design or processing inadequacies in failed restorations.