Test Your Knowledge: Impression Troubleshooting Challenge #2


One difficulty dentists face when dealing with the challenges of impressioning is inaccurate margins due to preparation design.

Often, dentists will find that there is no topography difference between tissue and preparation. The resulting stone model poured by your dental lab technician shows no noticeable differentiation between tooth and gum. Essentially, you are left with areas that indecipherable on the model, rather than the detailed impression. (An artist’s rendition of the view on the die trimmed model vs. the view intra-orally)

notopography copyThe best way to resolve this issue is by improving retraction. Though in the mouth the difference between enamel and pink tissue is clear, this is not so for the lab. When there is little to no retraction, accurate die trimming and intimate fit of restorations become nearly impossible.

If you allow impression material to flow between the margin of the prepared tooth and the surrounding gingival tissues, then the resulting stone model will be much more successful. Utilize a cord retraction or prep design that isn’t flush with tissue so that the visually gorgeous prep pours that way, too.

To quote Dr. Lee Ann Brady, the key ingredient to accurate impressions is obtaining adequate margin flash:

Crown Impressions“Flash is the amount of the impression material that captures the tooth beyond the preparation margin. This “extra” material that has gone past the margin is vital to the technician as they fabricate the final restoration. The first question is how much flash do we need to deem an impression accurate. My minimum is 1mm deep by 1mm wide, so the impression material has captured 1mm of tooth structure beyond the margin, and this band of material is 1mm in thickness.”

Dr. Brady continues, “The first thing I do when I pull an impression is to look at it and critically evaluate it through my loupes, ready to take another if I have any concerns.”

For more tips on impression troubleshooting and how Gold Dust Dental Lab can support you with great results, please call 800.513.6131 and connect with your account specialist!

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