PART PREPARATION (screw retained)METAL SUBSTRUCTURE

Height reduction

Screw the UCLA with a lab screw (do not use final screw) on to the analog of the working model and lift up the soft tissue mulange to check for proper seating of the abutment. Reduce the height of the plastic tube to allow for appropriate restorative material thickness (1.5mm to 2mm).

Ready to wax

Sometimes the plastic tube needs to be reduced all the way down to the metal portion of the UCLA. The metal alloy used for the UCLA is not compatible with porcelain veneering material, therefore the abutment needs to be further reduced to allow a thick enough (0.5mm) overlay of wax and subsequently cast on metal. If there is not enough cast on metal thickness the veneering porcelain will fracture during cooling of the baked on porcelain.

Metal collar

The metal collar of the UCLA abutment at the analog-abutment interface may also need reduction for the same reason. Unless a all plastic UCLA is utilized, all screw retained porcelain fused to metal restorations are waxed and cast with a metal collar design.