Dental OSCE (Objective Structured Clinical Examination) Practice Exam

What is the maximum amount of unsupported porcelain allowed when making a porcelain-fused-to-metal (PFM) crown?

1. 1 mm

2. 2 mm

3. 3 mm

4. 4 mm

The correct answer is: 2 mm

When fabricating a porcelain-fused-to-metal (PFM) crown, the design must ensure adequate strength and aesthetics. The maximum amount of unsupported porcelain allowed is typically 2 mm. This limitation is crucial because excess unsupported porcelain can increase the risk of fracture or chipping during function, as unsupported porcelain lacks the necessary support from the underlying metal framework. The structure of the PFM crown relies on the metal core to provide strength, while the porcelain layer offers the desired appearance. When the porcelain exceeds 2 mm without support, it can become structurally compromised, leading to clinical failures. Therefore, adhering to the 2 mm limit helps in achieving a balance between durability and aesthetic appeal in dental restorations.