Which characteristic of porcelain-to-metal restorations most commonly leads to failure?

The most common characteristic of porcelain-to-metal restorations that leads to failure is the poor fit of the metal framework. A well-fitting metal substructure is essential to the integrity and longevity of the restoration. When the fit is not optimal, it can result in several complications, including debonding of the porcelain, fracture due to improper stress distribution, and even recurrent caries or periodontal issues due to gaps that allow plaque accumulation.

A properly fitting metal framework enables adequate support for the porcelain, which is subject to various stresses during function. If the framework does not fit well, it can create points of stress concentration that may exceed the strength of the porcelain, leading to chipping or complete fracture of the restoration. Additionally, a poor fit may compromise the sealing and aesthetic outcomes of the restoration, further contributing to its failure.

Other characteristics, such as excessive thickness of porcelain, long curing times, and inconsistent porcelain firing temperatures, can also affect the success of the restoration but do not pose as immediate a source of failure as the foundation of a poor-fitting metal framework. Proper attention to the fit of the metal framework during the laboratory phase is crucial to ensure the overall success of porcelain-to-metal restorations.