Measurement issues in probing depth evaluation of periodontal pockets: An in vitro study concerning main sources of uncertainty

Measurement of periodontal pocket depth, a key step in detection and analysis of periodontal diseases, is frequently affected by substantial uncertainty. Estimation of distance between gingival margin and connective ligament, an apparently straightforward measurement task routinely performed with simple probes, entails a fairly complex pattern of single and combined effects. Layout of marks on probe affects readings, since, when interpolation is involved, operator’s experience comes into the picture. Compliance of tissues at pocket bottom implies dependence of probe penetration from insertion force, whose control again is affected by operator’s experience. Hazy definition of gingival margin further contributes to scatter in results, liable to lead to diagnostic mistakes and wrong therapeutic decisions. An investigation on measurement issues, aimed at identification of main factors affecting uncertainty in evaluation of pocket depth, was performed in vitro with an ad hoc device, developed in order to get traceability and evaluate reproducibility of measurements of pockets with different depths. Measurements were performed by operators with different experience and skill, using three types of periodontal probes currently in use. Results showed a different performance of the probes in terms both of bias and scatter. Occurrence of false positives and negatives were found to be strongly dependent upon operator experience.