What is the maximum permitted amount of unsupported porcelain in a PFM fixed partial denture?

• A. 1.0mm
• B. 1.5mm
• C. 2.0mm
• D. 2.5mm

Answer: (C)

The maximum permitted amount of unsupported porcelain in a porcelain-fused-to-metal (PFM) fixed partial denture is 2.0 mm. This guideline is essential because it ensures adequate strength and durability of the porcelain.

When creating a PFM restoration, the porcelain layer is bonded to a metal substructure, which provides strength and resistance to fracture. If the porcelain is excessively unsupported, it may be prone to chipping or cracking, resulting in failure of the restoration. The 2.0 mm standard is established based on both clinical experience and material properties that contribute to the longevity of the denture. By adhering to this guideline, dental practitioners can ensure that the dental prosthesis can withstand functional forces during use, thus enhancing its success and longevity.