When I teach provisional fabrication I discuss three methods for veneers, direct, indirect and shrink wrap. For many years I have preferred using an indirect technique for the fabrication of veneer provisionals, and last week reminded me why it is my favorite approach. So I can’t even tell you why, but last week I attempted to make a set of veneer provisionals for six maxillary anterior teeth directly in the mouth, after the third failed attempt my brain kicked in and I remembered why I do them indirectly. The learning was in regards to the setting of bisacryl provisional material. Ideally we remove the material from the mouth when it is in a gel phase, it comes out inside the matrix and then we can allow it to reach a full set. Veneers present two challenges, one is that in the gel phase for conservatively prepared teeth the bisacryl pulls and tears and is not easy to remove without damaging it.
The second is that bisacryl does undergo polymerization shrinkage, and when not on the preps for veneers the material warps enough that reseating on the teeth is not possible. Hence the development of a shrink wrap technique which allows the bisacryl to reach a full set in the mouth, and all the trimming and shaping is done in the mouth. Also the development of an indirect technique, which again allows us to over come both challenges, early removal and shrinkage. Of course working indirectly always has the advantage of allowing the patient to rest, no taste of bisacyl in their mouth, no uncured bisacryl against the preps and quiet time in the lab for me to make the provisionals.
After taking my final impression I capture a quick alginate impression of the final preps. From this impression I fabricate a silicone model made from Mach II die silicone and bite registration silicone. The flexibility of the silicone model and it’s smooth surface are an advantage over stone, not to mention the rapid set. I use a silicone matrix, but copyplast or other types of matrix will work. I load the matrix with bisacryl, the model which has a flat base is resting on the counter, I seat the matrix and apply light pressure while the bisacryl sets. Do not do this with the model and the matrix in your hands as you can flex it and introduce distortion. After the provisional has been trimmed and shaped another advantage is being able to polish it on the model and prevent breaking it at the very last stage.