Why two layers?
The dense base mass sets the overall shape and creates pressure, and the liquid corrective silicone flows into the gingival sulcus and imprints a ledge with micron precision. This is what determines how tightly the edge of the crown will fit. Silicone is stable and does not deform during storage, so a model can be cast using it the next day.
Why are the stages counted separately?
Orthopedic treatment consists of clinical and laboratory stages. Some of them - taking impressions, making an individual tray, gum retraction, fixing or removing a crown - are performed independently and are not always included in the main work.
The result directly depends on the quality of these stages: an inaccurate impression or an under-opened edge of the ledge will lead to the fact that the crown will not fit, no matter how well it is made in the laboratory.
What affects accuracy
- selection of impression material for a specific task
- dry field and lack of blood in the ledge area
- correctly opened gingival sulcus
- no deformation of the impression during removal