We have covered 3 fairly basic methods of getting an edentulous impression so far. There is one more method that I will cover here, and this one may be a bit foreign to some of you. Last year, I was privileged to see Dr. Richard Turbyfill speak on the topic of removable prosthodontics. Dr. Turbyfill is an old school prosthodontist who really is a gem of the industry. He is world renowned on the lecture circuit and puts on quite an entertaining lecture.
Dr. Turbyfill utilizes only one technique for edentulous impressions, and that is a functional impression. He postulates that the only prosthodontic procedures where the patient does not get a temporary restoration is dentures and RPDs. We put the patient in temporaries for single unit crowns, however dentures are a much more in depth procedure, yet the patient recieves no provisional restoration. He changes that.
Dr. Turbyfill makes border molded alginate impressions of the arches and uses these to fabricate trial dentures for the patient. These trial dentures are flasked and processed and look identical to traditional dentures. The trial dentures are delivered in the usual manner. The patient is instructed to critique the function and esthetics of the dentures during the trial period.
Now that the trial denture is made, we now have a perfect custom impression tray. In order to utilize this to it's fullest, a material called hydrocast is put into the denture. Hydrocast resembles a soft reline material. The only difference is that it does not set up in 5 minutes like most soft reline materials. Hydrocast stays flexible for many hours to days. The patient wears the trial denture with the Hydrocast in it and functions as normal. The patient's own muscle movements over the set time border mold the hydrocast to a perfect vestibular depth.
After the hydrocast is set, the trial denture is used to fabricate a final denture. Hydrocast in and of itself is relatively inexpensive, especially when compared to other impression materials. The cost of this technique is much higher though when you consider the lab fee is double. This must be passed on to the patient so this method is quite expensive after all is said and done.
I feel that functional impressions are probably the most accurate when it comes to determining the functional limitations and muscle borders. This is an ideal technique to use when finances are not a factor for the patient.