This is a continuation of Part I discussing the treatment planning involved with the case study of retired dentist, Tom. Regarding the actual tooth preparation, particularly margin placement, he has existing anterior full crowns with margins right at tissue level. I probed the facial sulcus to determine its depth, which was 1 – 1.5mm. This step is especially important because it helps determine where I want to place the new margins. It's easy to place veneer margins at tissue, or even sometimes above tissue if the tooth color is good, but with full crowns it is harder to place a supragingival or equigingival margin and not have it visible.
There are two concerns with placing the margins below tissue; if I go too deep I can violate the biologic width and end up with inflammation, but if I don't prep deep enough, I could end up with recession exposing the new margins. I would classify Tom as a "Rule 1 "patient and he wasn't at risk for recession, so I will extend his margins .5mm below tissue.
To control the subgingival margin placement, and since his preparation margins were even with the tissue, I placed a blue #1 Ultrapak cord dipped in aluminum chloride in the sulcus and pushed it .5mm past the existing margins. Once I placed the cord, the tissue moved away exposing .5mm – .7mm of tooth structure. I then prepped to the top of the cord. Upon finishing the prep I placed a second layer of cord that pushed the first cord apical to the prepped margin. Even though I have both hard and soft tissue lasers in the office, in my hands this double layer technique produces a cleaner and more precise impression than any other technique.
The next step is to wet the cords with water so that when the top cord is pulled it doesn't remove any sulcular epithelium, which induces bleeding, now pull the top cord and dry the area. This leaves a nice, open sulcus simplifying material injection or optical scanning used for the impressions. The goal is to extend the impression .5mm past the margin to provide the technician a clear view of all the margins.
In my next article on Tom's case, I'll go over his provisional restorations, how the shell was fabricated and then relined.