The effect of subgingival calculus on the validity of clinical probing measurements

Objectives: The aims of this study were to assess the validity of the WHO 621 probe for the detection of subgingival calculus and to assess the effect of subgingival calculus on the measurement of probing pocket depths and clinical attachment levels. Methods: Teeth used in the study were designated for extraction under local analgesia. Prior to extraction the clinical detection of subgingival calculus was made with a WHO 621 probe. Probing pocket depths and clinical attachment levels were measured. The location and direction of the gingival margin and probing measurements were marked on the teeth with a fine, sterile pencil and following extraction, permanent reference grooves were cut with a fine, tapered diamond bur. The extracted teeth were stained with Gomoriʹs stain and examined for the presence of calculus, and the pocket depths and attachment levels were measured using a stereomicroscope. Results: There was an 80% agreement between the clinical and laboratory detection of subgingival calculus. There was no systematic difference between clinical and histopathological measurements when calculus was present or absent (P > 0.05). Analysis of variance indicated a random error effect due to the presence of subgingival calculus. Conclusion: This study has demonstrated the validity of the WHO 621 probe in detecting subgingival calculus and has shown that subgingival calculus could be a source of error in the measurement of probing depths and clinical attachment levels.