Which type of restoration is not effective as a retainer for a fixed dental prosthesis (FDP)?

The choice indicating that all-ceramic restorations are not effective as retainers for fixed dental prostheses (FDP) is grounded in the characteristics and mechanical properties of all-ceramic materials. While all-ceramic restorations can achieve excellent aesthetics and mimic the natural appearance of teeth, they often lack the required strength and durability needed to function effectively as retainers in FDPs.

A retainer needs to withstand significant occlusal forces, which can be more effectively managed with materials that have higher tensile and compressive strength, like cast metals or metal-ceramic combinations. These materials provide the necessary rigidity and resistance to deformation, ensuring that the fixed prosthesis remains stable over time.

All-ceramic prefabricated or custom restorations, while beneficial for their aesthetic properties, may be more prone to fracturing when subjected to the same stress levels encountered in a functional occlusion. As a result, although they can be used in certain scenarios, particularly for anterior teeth where aesthetics are prioritized, they do not possess the robust qualities typically needed for retainer applications in fixed prosthodontics to the same extent as their metal counterparts.