When a single tooth requires a crown, the prosthetic crown will in most instances rest upon whatever tooth structure was originally supporting the crown of the natural tooth. However, when restoring an edentulous area with a bridge, the bridge is almost always restoring more teeth than there are root structures to support. For instance, in the photo at right, the 5-unit bridge will only be supported on three abutment teeth. In order to determine whether or not the abutment teeth will be able to support a bridge without a virtually guaranteed failure due to lack of proper support from the remaining root structures, the dentist should employ Ante’s rule, which states that the roots of the remaining abutment teeth must possess a combined total surface area in three dimensions more than that of the missing root structures that are to be restored with the bridge. When the situation yields a poor prognosis for proper support, double abutments may be required to properly conform to Ante’s rule.
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