Final answer:
The measurement of 6-mm pockets on certain teeth is a clinical assessment of the depth of the gum tissue around the teeth, which indicates the severity of gum disease.
Step-by-step explanation:
The 6-mm pockets on teeth #5, #9, #16, and #17 described in the question are measurements that determine the depth of the space between the tooth and the surrounding gum tissue. This 'pocket' is an important indicator used by dental professionals to assess the presence and severity of gum disease. A tool called a periodontal probe is gently inserted between the gum and tooth to measure the depth of the pocket in millimeters, hence the 6-mm measurement. The presence of deeper pockets often correlates with more advanced gum disease, and can be used to guide treatment decisions.