Have you ever had the bases come off your models? Chances are, your answer is yes – I know I have. And as we know, it is never convenient and the reasons for this happening are simple. Unless you want to bead and box your impressions, you need to complete the models in two separate pours. Pouring the teeth and soft tissue first, and after it sets, you need turn it over and place it into your base pour.
The issue, of course, is that the adhesion of these two pours can be problematic; once the first layer is set it, won’t stick super well to the second pour that you use for your base and you have to let the first pour set completely prior to turning it over, otherwise the stone may slump while setting and potentially compromise the accuracy of your model.
As alluded to above, beading and boxing our impressions is one solution to this issue and it definitely results in a nice model, however, it adds a bunch of steps and takes a bunch of time. In this article, I will go over what I have found to be a quick and easy solution to this issue.
The DQ Curl for Models
The key here, is we have to increase mechanical retention of our first pour to the second pour – naturally the more retention the better. In my practice, I have tried a lot of things; from scratching grooves into the first pour to grinding grooves and undercuts in with a lab bur. While the latter works well, the former typically fails. Both are way more time-consuming and less effective than my favorite solution – not to mention that grinding nice undercut grooves into the first pour creates lots of dust and, unless you have a vacuum system in your lab, a big mess.
A much easier solution is to create your mechanical retention in your first pour as it’s poured. To do this rather than pouring the impression, you simply want to create some tails in your pour. My assistants like to call them DQ curls, like you see in the image.
As you can imagine, these DQ curls act as tremendous retention allowing any issues with your bases coming off the models to be virtually eliminated. In fact, I cannot remember a time when a base separated when the first pour had the proper DQ curls.
John R. Carson, DDS, PC, Spear Visiting Faculty and Contributing Author www.johncarsondds.com