Effect of nonsurgical periodontal therapy. V. Patterns of probing attachment loss in non-responding sites.

Incisors, cuspids and premolars in 33 patients with advanced chronic periodontitis were treated by plaque control and 1 single episode of supra- and subgingival debridement. The results were monitored by probing attachment level measurements for 6 sites of each tooth every 3rd month during a period of 24 months. A total of 1368 sites were observed. From these were selected 280 "non-responding" sites showing 1.0 mm or more loss of probing attachment at 24 months compared to baseline. Scatter diagrams of the sequence of 9 probing attachment recordings obtained during the 24-month study were produced for each of these 280 sites. Study of these scatter diagrams resulted in identification of 7 different patterns of probing attachment change over time. A linear pattern of gradual loss of probing attachment throughout the 24-month observation period was found for 73% of the non-responding sites. Of the less frequently seen patterns, 3 approximated a linear course and 3 were non-linear. Linear analysis of regression as a statistical method to determine attachment loss for individual sites seems to be suitable for sites with linear patterns and for sites approximating a linear pattern. The insensitivity of regression analysis in non-linear patterns may be acceptable if a cautious analysis is warranted.