Implant Specialist Alex Rugh, CDT, explains what UCLA abutments are and how they work. They can be used to make traditional screw-retained PFM or FCG crowns as well as custom abutments.
The UCLA technique was the only way to fabricate custom abutments before CAD/CAM abutments became available. These days we only use this technique when a CAD/CAM abutment is not available.
UCLA abutments are stock parts and are made of a gold/palladium alloy interface with a plastic chimney. They can be used to make traditional screw-retained PFM (porcelain fused to metal) or FCG (full cast gold) crowns as well as custom abutments.
Even though they are stock parts, they are often regarded as custom abutments since they aren’t prosthetically useful until they are customized by the lab.
To make a screw retained crown, wax is added directly to the plastic chimney of the UCLA abutment to create the desired crown or coping shape. That waxup, along with the metal base, is invested and cast in to a high noble metal alloy. For PFM crowns, the porcelain is then stacked and fired directly to the UCLA abutment.
Making custom abutments with UCLA abutments works the same way except that the waxup will be in an ideal abutment shape that will then be cast and used for a cement retained crown. This was the only technique for fabricating custom abutments before CAD/CAM abutments became available. These days we only use this technique when a CAD/CAM abutment is not available.
UCLA Abutments come in both engaging and non-engaging styles. The engaging style has anti-rotational features at the interface and is used for making screw retained crowns and custom abutments. The non-engaging style has no anti-rotational features at the interface and is only used for making screw retained bridges.