These measurements are the depth of the sulcus or periodontal pocket at six specific points on each tooth. The bottom of the “pocket” is where the gingiva attaches at the root of your tooth. A small probe with millimeter increments marked onto it is slid just under the gums until it rests at the bottom of the pocket. Then the corresponding measurement at the edge of the gums is recorded, so that your dentist knows how deep each pocket is.
We call this process a periodontal exam or probing.