Final answer:
A PFM crown has a metal substructure with a layer of porcelain fused to it, while an all-porcelain crown is made entirely of porcelain. The difference lies in aesthetics and the potential for a gray line with PFM crowns.
Step-by-step explanation:
A PFM crown stands for Porcelain-Fused-to-Metal crown. It is a type of dental crown that has a metal substructure with a layer of porcelain fused to it. The metal substructure provides strength and durability, while the porcelain layer gives it a natural appearance.
On the other hand, an all-porcelain crown, as the name suggests, is made entirely of porcelain with no metal substructure. These crowns are known for their excellent aesthetics, as they closely mimic the color and translucency of natural teeth.
The main difference between the two is the presence of metal in PFM crowns, which can sometimes cause a gray line to appear where the crown meets the gum. All-porcelain crowns, on the other hand, do not have this issue and are often preferred for front teeth.