A High Value CAD Verification Bridge (CVB) for Predictability

For decades laboratory technicians have fabricated diagnostic wax-ups as treatment planning aids when providing services for comprehensive dentistry. This diagnostic wax-up had multiple uses. First, it enables working out esthetic and function needs on an adjustable articulator.  By doing so, many of the treatment plan perameters become obvious. This reduces potential  problems with the final restoration.  Secondly, the wax up can be used as a tool to show the patient what their final case would look like. In addition, a silicon matrix can easily be fabricated over the wax-up and used to facilitate provision fabrication and an intraoral mock up. This mock can be effectively done on about 50% of cases. In case you’re not familiar with a mock up here is the protocol:

Diagnostic wax up is performed and a silicone matrix is fabricated over the wax up.

• Try the silicone (SilTech by Ivoclar) matrix in the patients mouth. It should have a positive seat. With a felt tip pen place a line in the matrix that is aligned to the labial frenulum. This will aid when reseating in the following steps.
• Remove the matrix and fill or syringe the teeth portion to about 1/3 full with a self cure composite such as Luxatemp.
• Seat the matrix back in the patients mouth and wait until the composite cures.
• Remove the matrix. Now you can evaluate all essential aspects of the diagnostic wax up intraorally. This is especially great when restoring maxillary anterior teeth.

Through the more recent advancements in CAD CAM a new, much more accurate, predictable workflow is now available for comprehensive cases. This does not necessarily replace a diagnostic wax up, but in many cases, it can. It involves milling of a CVB prior to fabrication of the definitive restoration. The protocol includes an intraoral try-in of a final case design prior to fabrication of the definitive restoration. By doing so, one can check intraorally all the essential design elements and parameters.  A CVB is a milled PMMA (polymethyl methacrylate) try-in bridge.  The CVB is essentially a milled acrylic bridge that is milled from a CAD design intended to be used for the final restoration. Once the try-in is performed and evaluated, the original CVB design can be brought back to the CAD stage and altered or tweaked as needed to insure predictability and accuracy of the final restoration. Here is how it works:

• Final digital or analog impressions are obtained. If the workflow includes analog impressions the subsequent models are scanned in a desktop laboratory scanner. Once scanned, a qualified CAD designer will design the final prosthesis, meeting all essential criteria that has been prescribed.
• Once designed, the STL file is put through CAM and rather than milling in ceramics the case first gets milled in PMMA. After some post processing the acrylic CVB is ready for try-in.
• At clinical try-in, the PMMA bridge is seated and all criteria are checked. these include but are not limited to: occlusion, function, esthetics, phonetics and hygiene. This is also an opportunity to obtain the patients opinion of shade and tooth form.
• If the CVB goes well and meets criteria, the CVB can be utilized as a new provisional. This will give the dentist and patient additional time to evaluate the CAD and determine other small changes needed.
• After a week, notes can be made as to any changes necessary and the case is returned to the lab for the definitive restoration.
• The case now goes directly to the design technician and the original STL file that was used for the CVB is uploaded. Changes as prescribed are performed to the CAD finalizing all case design criteria.
• Once again, the final STL design file goes through CAM and is now milled in the final desired material. After milling and sintering post processing is finalized and the case is ready for patient delivery.

The utilization of a CVB will provide a far more predictable result. In addition, the quality of the final prosthesis will be more favorable to both the dentist and patient. Lastly, through the fabrication of a CVB first, clinical appointment objectives are much more likely to be accomplished on a more routine basis.