I'm not sure about you, but taking a full arch crown and bridge impression on the lower arch is one of the most difficult and stressful procedures I do in my practice. You have to control saliva, heme, the tongue and tissue.
The tongue seems to be the hardest to control as you move from one side of the mouth to the other and insert the impression tray. Facing all of these factors, you are still hoping to get a perfect final impression so that your lab can fabricate the best fitting restorations. It's not the easiest thing to accomplish but I have found a simple and predictable technique for getting great full arch impressions.
I learned this technique in a Spear seminar a few years ago and have used it on most of my big cases since, especially where the patient's tongue was a factor, or if we missed our first impression.
I begin by placing retraction chord in the anterior region for tissue retraction and I usually use a laser to trough around the posterior crown margins. I then clean all the teeth with hydrogen peroxide and a micro brush. Next, my assistant uses a tongue depressor and retracts the patients tongue on one side and I retract the cheek. We then inject Aquasil Ultra XLV light body impression material in one posterior quadrant and keep the patient retracted for the full setting time, letting the impression material flow around the posterior teeth.
After setting, we move to the other side and complete the same steps. Once both posterior quadrants are done, we will then pull the anterior chords and take a traditional full arch C & B impression capturing the anterior preparations, which will also pick up the posterior quadrants in one impression. It really makes getting a good full arch impression on the lower more predictable.
My initial reservation with using this technique a few years ago was concern for movement of the set impression material prior to, or while I was inserting the full arch tray causing distortion and an inaccurate impression. However, after impressing and delivering a number of cases using this technique, I have not found it to be an issue.
The next time you have a difficult case to impress on the lower arch, give this technique a try - it works really well.
John Sweeney, DDS www.bluewavedentistry.com