Figure 1 - Adjustable cylinder manipulated before casting up to 17 degrees.

Figure 2 - The two invested casting (left) and machined (right) components, each precisely milled with Cresco.

Figure 3 - Cresco milling unit in action.

Figure 4 - The two components laser welded to form one bridge.

Figure 5-Finished substructure before porcelain application with access holes moved to mid-occlusal table

There are many options available today for both crown and bridge and over-denture applications, many of which we have discussed in previous articles. Although the most common crown and bridge application at this point is the separate abutment and cement retained crowns and bridges, there are times when a screw retained option is preferred (e.g., more retrievability chair side, when the patient has less than ideal oral hygiene or even when there is bone and tissue loss due to disease). Another common reason where this option might be preferred is when a lack of occlusal clearance requires the lab to reduce the abutment height to the screw top, not allowing for enough clearance for a separate crown or even for porcelain occlusion. Most of the contraindications that might make the screw retained option less preferable are aesthetically driven (e.g., the unsightly access holes that are necessary when the implant placement has buccal or mesial angulation, or when the porcelain cannot be supported properly and porcelain fracture or shear is a concern). When a bridge is required, a screw-retained restoration can have internal stresses caused by warpage in the casting process. If these stresses aren’t relieved through laser welding or soldering properly to allow for a passive fit, the forces will be transferred directly to the implant and cause premature bone loss and possible implant failure.

Now, there is a new option available for screw- retained, hybrid and over denture bars that allows these issues to be dealt while avoiding the problems. The Cresco (Astra) technique directs the access hole to be placed in the center of the occlusal surface even if the implant angulation is not ideal. By utilizing the unique adjustable burn out cylinder for casting (Figure 1), the access hole that would have been at a buccal incisal angle can be moved to a more ideal and aesthetically manageable position. The Cresco milling unit is then incorporated via precise horizontal milling procedures and then the two components are laser welded together. (Figures 2-5) This method can be used for both bridge and bar application. For bar applications, it is not problematic to have buccally angled access holes. However, the totally passive fit (to model) is necessary to avoid the stresses being passed to the implant directly.

This technique allows more options in a compromised situation where screw access is limited, and that allow passive fit after casting bar or bridge. The Cresco (Astra) technique is compatible with many implant systems and is just one more option that may fit a specific situation or restoration need for you and your patient.

Technique Overview

Bar Application:

1st appointment

• Take preliminary fixture level impression, impression of opposing dentition and bite if possible.
• Verification index/bar will be fabricated in lab in separate pieces as well as an occlusal rim (edentulous bar application where required).

2nd appointment

• Verification index pieces placed and luted together using GC Pattern Resin (has less warpage than other acrylics) and picked up with an open tray technique for best accuracy.
• Bite taken.
• Lab then pours final soft tissue model and sets up teeth with screw in base for stability.

3rd appointment

• Teeth tried in and checked for aesthetic and bite/occlusal acceptability.
• Lab then makes any changes to tooth set up, and fabricates bar to finish.
• Teeth transferred to bar in wax.

4th appointment

• Bar tried for passive fit, aesthetics and bite checked again for acceptability.
• Lab finishes processing removable or fixed denture for final appointment.

Screw Retained Porcelain Bridge:

1st appointment

• Take preliminary fixture level impression (polyvinyl siloxane), opposing impression and bite if possible.
• Verification index/bar will be fabricated in lab in separate pieces..

2nd appointment

• Verification index pieces placed and luted together using GC Pattern Resin (has less warpage than other acrylics) and picked up with an open tray polyvinyl siloxane impression for best accuracy.
• Bite taken.
• Lab fabricates bridge substructure. Preferably sent to office for try in, but can be fabricated to bisque bake or even finalized.