Periodontal Disease

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 A primary aim of periodontal probing is to locate the most coronal level of the connective-tissue attachment. However, this generally is not attainable, as penetration of the probe tip in the pocket or the lining soft tissues correlates with periodontal health.^7,8 It has been established that the extent of probe penetration is influenced by the inflammatory status of the tissues.^7,9-12 In most instances when healthy tissues are examined, the probe tip stops coronal to the apical termination of the junctional epithelium (Figure 1), whereas at inflamed sites the probe tip frequently passes apical to this point (Figure 2). The depth of probe penetration partially depends on the extent to which the gingival connective tissue has been lysed or infiltrated by inflammatory cells. In other words, intact connective tissue underlying the crevicular epithelium is an important factor resisting probe penetration. Spray et al¹³ suggested that the state of health of the underlying connective-tissue fibers influences probing measurements. There is a “hammock effect” in health, where healthy fibers act as a barrier and prevent apical movement of the instrument, while inflamed connective tissue offers less resistance to penetration. With reduction in inflammation, an accurate estimate of the sulcus depth is more likely to be obtained. The probe penetration is significantly greater in the presence of visible inflammation, but not where there was bleeding after probing.⁸ These results suggest that the location of the inflamed connective tissue may be a critical factor. Anderson et al¹⁴ determined the correlation between clinical and histologic inflammation and probe-tip penetration of the pocket tissues in dogs. A strong correlation was found between probe penetration and degree of inflammation, and the difference in mean inflammation scores between sites where probes were located coronal or apical to the epithelium was statistically significant.

Anatomically, the gingival sulcus is defined as the distance from the gingival margin to the coronal extension of the junctional epithelium.¹⁵ However, the ability of the periodontal probe to measure this distance accurately is questionable. Results of human studies performed by Sivertson and Burgett¹⁶ indicate that the periodontal probe routinely penetrates to the coronal level of the connective tissue attachment of untreated periodontal pockets. Armitage et al⁷ found that, in healthy specimens, the probe failed to reach the apical termination of the junctional epithelium. In cases with experimental gingivitis, however, most probes came closer to the apical termination of the junctional epithelium, but on the average still fell short. In periodontitis specimens, the probes consistently went past the most apical cells of the junctional epithelium. A significant relationship between the degree of inflammation and level of probe penetration was found. Saglie et al¹⁷ noted that probing depths measured in the laboratory were always shallower than those recorded clinically. The authors attributed this discrepancy to the presence of a zone of completely and partially destroyed periodontal fibers, which allowed the probe to extend apically to the coronal level of connective-tissue attachment. The results of these studies illustrate that periodontal probes do not precisely measure, and often overestimate, the true histologic sulcus depth, and that inflammation has a significant influence on probe penetration. This has important implications regarding how measurements taken with periodontal probes are interpreted. Because probes rarely stop at the exact location of the most apical cells of the junctional epithelium, probing measurements are clearly not precise assessments of the actual level of connective-tissue attachment. PPD measurements overestimate connective-tissue attachment loss at inflamed sites and underestimate it at noninflamed sites. An increased probing depth is a sign of reduced tissue resistance to probing, which in turn can be interpreted as an indication of the presence of an inflammatory cell infiltrate in the gingival tissue.¹¹Most research has shown that the tendency for penetration of the probe into the tissues at the base of pocket resulting in an overestimate of probing depth is greater at inflamed sites^7,10,11 and in nonsmokers