In a recent article, “Tom Case Study: Treatment Planning Part I“, I walked you through my treatment plan for retired dentist, Tom. In this article, I'm going to highlight the fabrication of the shell provisionals that were made for him.
Temporization becomes more challenging when treating a patient for a full mouth reconstruction, especially if changes need to be made in the occlusal plane or vertical dimension. The challenge in this case is once the arch is prepped, soft tissue is the only thing left to orient the matrix if putty or a clear vacuum-formed or pressure-formed matrix is involved to fabricate the temporary. An error in properly orienting the matrix can lead to the teeth being too short or too long, the occlusal plane being canted, or the matrix could be seated too far forward or too far back. Any errors become a major time problem to correct.
If you are doing a full arch prep and some of the preps are veneers or partial coverage this problem is eliminated since the unprepared tooth structure can orient the matrix. But in Tom's case the preps are already full coverage on every tooth. Whenever I'm doing a full arch of full crowns, I work with a shell temporary. The ideal way to create a shell provisional is to scan a diagnostic wax-up, then send the desired instructions from the scan to a milling machine and tell it to produce the shell. There is no doubt that this is an effective way to make temporaries, but the reality is not every dentist has access to a milling machine.
The technique we teach in the Worn Dentition Workshop is to make an alginate impression of the diagnostic wax-up and pour the alginate into stone. The purpose of this stone model is to allow you to bulk out the cervical third by 0.5mm on the buccal and lingual; this allows the shell to be fabricated slightly oversize in the cervical third, which makes it easier to seat in the mouth. The reason the shell typically doesn't seat into place is due to material shrinkage, or a wax-up that is slightly small in the cervical third; making this area bit larger a bit larger counteracts both problems. It's much easier to make an oversized shell and trim it quickly in the lab than it is to fight a shell that just won't fit.
When you're used to this process, it's actually more efficient to not duplicate the wax up into stone. With Tom, once the diagnostic wax-up was completed, the cervical third was bulked out by 0.5mm with different colored wax in the cervical third of all the teeth. This saves the time of making the separate alginate and model, but when you are learning it is helpful to make the separate model so you know how much wax you have added. I then use Sil-Tech putty and make an impression of the bulked out wax-up. Once the impression is made, the excess putty is trimmed down to the gingival margin.
The material that is typically used to fabricate the shell is Protemp Garant by 3M because it's very durable, especially if it is heat cured. With Tom, the Protemp was injected into the putty and wiped up the sides, and shaped like a shell as it was injected around the arch.
Once the material is set, a blade is then used to cut away the buccal surface of the putty to ensure the shell doesn't break. Once the whole shell is released, it is placed in a light and heat-curing oven for three minutes. After that the shell is trimmed to the gingival margins and hollowed out.
In my next article, I'll go over how these shells are relined in the mouth to the correct position matching the diagnostic wax up on all the prepared teeth.