FABRICATE (screw retained)

A single screw retained all ceramic restoration maybe fabricated with a through and through stock zirconia abutment (BioHorizons) if the spacing is favorable. Some manufacturers produce stock zirconia abutments with a removable titanium interface (Nobel Biocare™), these types of abutments are also suitable for direct bake on procedures since the interface can be removed prior to baking the porcelain onto the abutment and repositioned in to the abutment after the porcelain fusing process.
Stock abutments with a prebonded titanium interface (Biomet 3i™) are not suitable for direct bake on procedures because the bonding agent breaks down during the porcelain fusing process in the oven.
In cases where stock zirconia abutments are inadequately dimensioned a custom zirconia abutment may be acquired through the implant manufacturers CAD CAM program (Biomet 3i™ Encode®, Nobel Biocare™ Procera, Straumann Etkon)or through third party manufacturers (Atlantis™, Whip Mix Vericore®, GC Aadva).
Screw retained all ceramic bridges and splinted restorations require custom CAM milled substructures. Substructures may be designed entirely through computer programs (CAD) or a mockup sub frame is manufactured by hand and then copy milled in zirconia.
The accuracy of the master model needs to be verified prior to the manufacturing process because ill fitting zirconia substructures can not be sectioned and reluted. A rocking zirconia sub frame will require a costly remanufacturing. Therefore a verification index needs to be tried in the patients mouth to assure the analogs in the master model are related to each other in the exact same way as the implants are related to each other in the patient. The verification index may be utilized during the manufacturing process for the zirconia substructure.
To fabricate a mockup frame, denture teeth need to be set up in wax to gain a full understanding of the spatial relationship between the position of the implants in relation to the planned final restoration. Screw access holes should emerge through the center, or close to it of the occlusal table of the final restoration. Screw access holes emerging through buccal or lingual cusps may indicate a necessary change in restoration type to a cementable or full metal restoration.
A putty matrix is then made to capture the buccal and occlusal aspect of the teeth in wax set up. The matrix should extend slightly over the occlusal on to the lingual surface of the denture teeth.
Remove the matrix and teeth in wax from the model after the matrix material has set adequately.
Steam clean the model and reposition the verification index on to the model. Utilizing the matrix, reduce the verification index until the matrix can be repositioned on to the model without interference from the verification index.
Block out any undercuts of adjacent teeth and obturate the screw access holes after securing the verification index with screws on the master model. Use #8 gage wax sprues, this will ensure adequate screw access hole dimensions later and eases locating the screw access channel after conversion of the wax up in to acrylic. Apply a acrylic separator to the stone model and fasten the matrix to the model.
Backfill the matrix with cold cure acrylic and place in a pressure pot to ensure a porosity free acrylic polymerization.
After the acrylic is polymerized to the manufacturers recommendation remove the master model from the pressure pot. Drill through the acrylic in the area of the screw access holes to gain access to the screw head and steam out the number 8 gage wax sprue. Detach the matrix and inspect the acrylic for voids and porosity.
Remove the flanges with rotary tools, taking care not to damage the implant/abutment interface. Utilizing the matrix, reduce the height of the mockup to allow for 1.5mm to 2mm of space between to mockup and the opposing occlusal surface.
After removal of the flange and reduction of the mockup height, modify the matrix by cutting the occlusal portion off. Now reduce the buccal aspect of the mockup by 1.5mm to 2mm followed by reduction of the lingual aspect. Basal surfaces also need to be cut back to allow for adequate bake on porcelain thickness.
At this point the mockup and master model could be sent to a CAD CAM milling center to copy mill the zirconia frame work.
If the substructure and model will be scanned in house for in house or off site milling, scan pegs are attached to the mockup and model for data acquisition through mechanical or optical scanners.
After the sintered zirconia substructure is received, passive seating of the zirconia frame needs to be verified by utilizing only one screw in a terminal abutment. Tighten the screw by hand and observe if seating discrepancies are evident at the remaining abutments.
Apply appropriate zirconia frame compatible porcelain according to manufacturers recommendation. This may be achieved through press on techniques or traditional build up with powder porcelain. A shortened slow speed drill shank, coated with a separator and inserted in to the screw access hole may be utilized to keep the screw access hole free of porcelain during the traditional porcelain build up technique. Although the drill shank needs to be removed before the bake on process. The seating surface of the zirconia frame needs to be kept free of any bake on porcelain to prevent seating discrepancies.
Shape the baked porcelain in the usual manner, ensuring the abutment screw will fit in to the screw access hole without premature binding. Glaze and stain the bisque stage restoration to desired shade. Care should be taken not to stain or glaze the seating surfaces of the abutments.