In this simple first molar case, we scan the pre-op condition as there is no room to add any contours to the pre-existing crown. In the video below, you can see how it occludes with the opposing and how it contacts the adjacent teeth. A pre-op scan is taken and the crown is removed. Images of the recurrent decay are taken and the preparation was modified. Final impressions were taken after tissue retraction and hemostasis.
The pre-existing condition must be trimmed away and you want to keep only the areas you want to make contact with in the proposal. This simple method gives you instant proposals where you only modify the contact areas and proceed to production