One sure-fire way to get a shell provisional is to have it fabricated by a laboratory. The first piece of this puzzle is to make sure that the fees you quoted for the case include the extra lab expense for the provisional. The second challenge is depending on how the lab fabricates the provisional you may have adjusting to do in order to seat it over your preps. Often what the lab does is prep a duplicate model to make the shell. Depending on how much they prep and the orientation, the shell may bind on your preps and require internal relief. I utilize a shell technique that we do in the office. It is another process I have trained my assistant to complete. This transfers the lab fee for the shell to an hourly rate for a team member plus expenses.
What I love about the technique is that it allows the shell to fit universally over the preps without needing to be adjusted internally. The first step is to take a stone model of the final wax-up. Run a 1-2mm wide bead of wax along the gingival margin of every tooth buccal and lingual.
Using silicone lab putty fabricate a full arch matrix on the stone model. Once the matrix has set, lightly paint all of the internal surfaces with bisacryl provisional material. I do this using the tip of the material on the gun. Allow the bisacryl to reach a full set, which can be up to five minutes or more bench top depending on what material you use.
Using a Bard Parker blade, slice the silicone matrix material from the cervical edge to the occlusal table over the interproximal of every pair of teeth around the arch.
Bend these tabs of silicone down until they snap off near the occlusal table, exposing the shell. This step is necessary due to the delicate nature of the shell, do not try and tease it out of the matrix.
Once the buccal wall of the matrix has been removed, the shell will ease off. Carefully trim the excess bisacryl off back to the wax line you created at the gingival margin. The air inhibited layer of bisacryl can be removed first with rubbing alcohol to prevent clogging up your bur. Once trimmed it is ready to be relined over the preps. If the shell breaks when you are trimming, simply place back in the silicone matrix and repair with bonding agent and flowable.