Impressions
Of all the various steps involved in the process of making dentures having impressions taken is one patients look forward to the least. Patients conjure up memories of gagging on materials, bitter taste and seemingly endless setting times. Fortunately times have changed, but let's start at the beginning back when my grandfather practiced in the thirties and forties. He was using plaster of Paris to accomplish this task. One can only imagine the discomfort particularly given the very rigid set of this material. If the shape of a patients ridge was such that reasonable undercuts were present the impression could become literally locked into place making removal somewhat painful as the tissue was heavily compressed. When dealing with natural dentition, he could spend upwards of one hour simply blocking out spaces between teeth and any undercut areas, to avoid causing damage.
By the time my father was on the scene in the fifties, impressions were largely being done with compound, a material of a waxy plastic nature that was warmed up in hot water and applied strip by strip with gentle compression's on to a patients ridge. Temperature was a key issue, too hot and patient's mouth burned, too cold it was not malleable enough to accurately form shape of the ridge. Although less traumatic for a patient than a plaster impression the process could still take upwards of one hour to simply accomplish one impression.
When I began working with my father alginate had now become the material of choice. This would come in a powder form that when mixed with water would become putty like substance, which had the fortunate property of setting in under a minute. Now impressions were getting to a point where patients found them little or no trouble. Today the most common impression taking process is to start with a stock tray. Usually of metal this tray would be chosen to basically cover the entire ridge. At this stage alginate would be used and a preliminary impression is formed. Into this impression, once removed from the patients' mouth, stone or plaster is poured creating a model of the patient's ridge. On this a second impression tray is constructed which might be made of vacuum-formed plastic, plastic putty or even wax. This tray approximates the shape of the patient's ridge much more closely. Around the border of this tray is laid, and a soft molding material that when inserted back into the patients mouth would create an accurate border shape. This is referred to as muscle molding. Now with this very precise tray we take our final impression. The final impression material may simply be alginate, a rubber base, or polysiloxane. The end result is an extremely accurate impression and a foundation to make a very accurate fitting denture.
Impressions of today are nothing like the gagging mouthfuls of material patients used to endure. However every week it seems I encounter a patient whose finally, reluctantly dragged themselves into my office to reveal they have been wearing the same dentures for thirty years because they were petrified of the impression taking process. I'll explain to them the differences in materials and kinder gentler techniques of today as I see their fingers tighten like vises on the vinyl arms of my dental chair in anticipation. In less than thirty seconds I pop the impression out and to the patients surprise the procedure was a breeze. With the patient proclaiming, "I would have done this twenty years ago if I had know it was this easy." Patient tolerance levels for intra oral procedures, and particularly impressions, vary widely. Some have fears so deeply rooted that they start gagging the moment they see me approaching, to the ultimate in stoic composure. When I was attending college part of our training was done on volunteers who would avail themselves for students to practice on. It was not uncommon for a patient to endure upwards of twenty impressions to achieve an acceptable result. I can recall one day watching a fellow student remove an impression that was over a foot long! It seems the student had so massively overloaded the tray that as it set the patient had slowly swallowed over half the material. When removed it was an impression that must have reached near the bottom of the patient's stomach, and yet the patient barely blinked. Now that's stoic.