Written by Stephen Killian, CDT Sunday, 31 December 2006 19:00
I’ve wanted to write a constructive article relating impression taking to die trimming for a long time. I’ve put it off because I knew no one would be interested in listening to an angry and bitter person.
You see, for 30 years and up until 3 years ago I had trimmed thousands and thousands of dies while all the time being the one who received every complaint for every short or open margin not recorded in the impression. In the last 3 years I’ve been able to get out of the lab at die-trimming time and observe the impression-taking process firsthand. I’ve grown to appreciate how easy we have it as dental technicians and how important it is to use to its fullest all the information given to us in the case pan. I’ve also seen how difficult it is to deal with blood, saliva, cheeks, lips, vomit, whining, and all that goes along with a live person. I’ve grown to realize how expensive a dentist’s chair time really is, and that to ask for a new impression is to ask the dentist, staff, and patient to shell out an additional several hundred dollars in time and material. So, here I am wanting to help those who fail to capture margins accurately while impressioning. At the same time I appreciate others who make it look easy to succeed.
There is plenty of cutting-edge information on impression taking from manufacturers, publishers, and of course from our dental gurus. All of these sources make it look easy to take a perfect impression. When I watch the gurus’ impression versus that of the average dentist, it seems that the dentist isn’t doing anything different, but the result might be much different. So what is the secret? In my 33 years of asking around I have found one and only one thing the gurus have done differently. It is consistently the same reason with them all. They have all trimmed and ditched the margins on their own dies at one time or another. A very few continue to trim and ditch their own dies. This one thing has taught them what no other experience can do, and that is to verify the quality of their own impressions. It teaches the practitioner to sharpen up on the minute details of the impressioning process.
I realize that I would be spitting into the wind if I tried to get everyone to buy this idea of trimming their own dies. But what if I could show you with photography what it’s like to trim your own dies? That is the goal of this article. Let’s get into it.
CLINICAL EXAMPLES: A PHOTO GALLERY
There is something very significant about the photos included in this article. They are a magnified size. Details are clearly visible. They are at or about the same magnification as what someone wearing 2.5x to 4.0x loupes or surgical telescopes might see. They are viewed with a single-source light to create high contrast. Some of the photos have fine detail that will require careful study. You may want to put on reading glasses or loupes while viewing these photos. I mention this to compel you to begin to view with magnification your own clean and dry impressions in the same way: carefully, meticulously, and with a single light source to create high contrast.
Example 1. Figures a through g.
In Example 1 we have 7 photographs. What do you notice as you take a quick glance at each of these 7? There is a sharp, traceable line that denotes the margin both in the impression photos and in the die photos. The margin is an unmistakable place that separates light and dark contrasting shadow. Next, we notice that the impression has recorded unprepared tooth structure subgingival to the margin. Last, we notice that the margin is so easy to see and locate that the trimming bur simply traces along below the margin without even touching it.
Think about how easy it is to attain perfect quality during die trimming in this case. Even the subgingival proximal margin is fully exposed above tooth structure subgingival to it. There is no risk of touching a margin or of over-trimming it short. These 7 photographs have recorded a perfect impression and the stone die that results. Anything less than this is a compromise to the integrity of the restoration. This is the order of excellence. A perfect restoration from your lab is only attainable with a perfect impression that has been verified by you through close study under magnification.
Example 2. Figures a through c.
Look at Example 2 with 3 photographs. This is more typical of what we see from many practices. We do see a traceable line around most of the margin, but something is missing…something is missing at the mesial. Do you see it? The impression doesn’t look so bad. The stone model and die make it obvious that only “ooze” was recorded at the mesial, but the impression seems to have a clean sulcus there. Look closer at the impression, then at the stone. There is no tooth structure recorded subgingival to the mesial margin, and therefore no traceable line along the mesial. I can trim the die in the last photo (2c), but any margin I would trim along the mesial would only be a guess. This crown came back to be remade with an accompanying x-ray showing a grossly open mesial margin as “proof” that I had overtrimmed the die from a “perfect” impression. Hmmm…I think a tremendous amount of lost chair time can be avoided by creating a sharp, traceable (unbroken) fine line that can be verified through careful study under magnification before it is sent out to the lab.
Example 3. Figures a through d
Example 3 with 4 photographs shows 2 common problems: bubbles and unretracted papilla. What at first glance (in the impression) appears to be an “almost” traceable line turns out to be a 3.5-mm area to “guess our way to success” with. Shall we check the impression now while the patient is in the chair, or should we just check our x-ray on recall to see if the lab created a short margin?! Please save your chair time and everyone else’s time. Verify that you have taken a perfect impression before you send it to the lab.
Example 4. Figures a and b.
Example 4 has 2 photos showing that someone has expertly learned to walk a tightrope over a pit of alligators. This is a cordless impression technique. You need higher magnification than in my photo to see the traceable line in the impression. The die trim will be challenging so as not to chip the margin. Although I can trace the line with my eye, I will have to touch the margin with my bur as I trace along the 25-µm line. It is risky even with super strong, resin-reinforced die stone, but I’m not complaining. It does have a perfect, 360°, traceable line.
Example 5. Figures a and b.
Example 5 shows another typical cordless technique impression and cast. There is no traceable line. There is a soft, rounded line. I could trim 10 dies from this impression, and the margin would look slightly different on each one. This dentist assures me that the margin is clearly visible in the sulcus, and I’m sure that it is…in the mouth, where soft pink tissue stops and bone-colored dentin begins. You can’t figure that into a yellow stone cast. The doctor suggests we return any questionable dies for trimming 2,800 miles away, and still has a 10% remake factor due to poor margins. Hmmm…everyone loses.
Example 6. Figures a and b.
Example 6…Aaaahhhh! Nirvana! This was done by the same doctor as in Example 1. It is an honor to work with this doctor. I give this doctor my best work because I have been given the doctor’s best. We are incredibly successful together. These photos represent the basis for our success. Let me summarize. In order to deliver accurately fitting restorations successfully and predictably you must first verify the existence of a sharp and traceable margin in your clean and dry impression through careful examination under magnification by a high-contrasting, single light source. This margin is made most identifiable by recording unprepared tooth structure just subgingival to the prepared tooth structure, thus creating a sharp line of contrast or demarcation that is traceable 360° around the impression of the prepared tooth. Anything less is a compromise…but that is a whole other subject.
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