In clinical practice, when preparing the proximal surface of a tooth for a metal-ceramic crown, textbooks recommend using a pointed diamond bur to lift and move through the proximal surface.
In actual practice, we often use burs like TF12 to directly grind away the proximal surface. Without the corresponding lifting motion, a common issue arises: if the contact point between two teeth is close to the gingiva and the gingival step of the prepared tooth is not opened towards the proximal gingival area of the adjacent tooth.
You can see in the image below, indicated by the red arrow, an example of a proximal gingival contact point that has not been opened on the model. This situation often occurs between the contact points of posterior molars and can also appear between canines and adjacent teeth.
During the fabrication of the model by the technician, whether they saw the model from the crown direction or from the root side of the prepared tooth model, it is inevitable that part of the gingival step on the proximal surface of the preparation will be cut away. This can lead to poor fit of the gingival shoulder of the proximal surface when the crown is placed, resulting in potential periodontal risks and secondary caries.
After preparing to the state shown in the figure, you can use a pointed diamond bur to carefully open the contact point of the gingival step on the proximal surface. Typically, at least 0.5 mm width is needed to ensure accuracy during fabrication by the technician.
We would like to thank Dr. Z for providing the model.
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