Fractured Full-Arch Tooth-Supported Zirconia Bridge: Thin Design, Surface Damage, and Excessive Cement Layer Thickness

Zirconia is widely used in full-arch restorations due to its strength and aesthetics, but failures can still affect its performance in clinical practice. In this report, a full-arch tooth-supported zirconia bridge fractured prematurely (eleven months), encouraging an investigation into its design and failure mechanisms. STL files obtained from the dental laboratory revealed regions of reduced framework thickness, falling below the manufacturer's recommendations. Fractographic analysis of the fractured pieces indicated a multifactorial failure pattern. Notable features included a thick cement layer, surface damage likely caused by the CAM bur during milling, and occlusal wear affecting the glazed surface. Crack propagation was observed in an occlusal-to-cervical direction. While no single factor could be definitively identified as the primary cause, the failure is attributed to the combined effect of insufficient design, surface damage, and biomechanical overload. Importantly, most such factors are not visible before failure, raising questions about the proper evaluation of zirconia-based restorations prior to their cementation.