Background: The objective of this clinical trial was to assess the relative contribution of patient-, tooth-, and site-associated variables on changes in probing depths (PD) following delivery of a standard non-surgical phase of periodontal therapy.
Methods: Ninety-four (94) systemically healthy subjects with severe generalized periodontitis were included in this 6-month prospective longitudinal study. Medical, periodontal, and microbiological parameters were collected at baseline and 2 and 6 months after completion of oral hygiene instructions, motivation, and subgingival debridement using a piezoelectric instrument. The relative contribution of patient-, tooth-, and site-associated variables was evaluated with a hierarchical multilevel analysis.
Results: Eighty percent (80%) of variability in PD reductions was attributed to site level parameters, while 12% was at the tooth level and 8% at the patient level. The multilevel analysis associated PD reductions with patient factors (cigarette smoking status and carriage of the rare allele of a specific polymorphism for the interleukin-6 [IL-6] gene), tooth factors (tooth mobility and tooth type), and site factors (mesial and distal location). Cigarette smoking and carriage of the rare allele of the IL- 6-174 G/C polymorphism were associated with less PD reduction. Incisors and canines responded better than premolars and molars. A dose-dependent effect of mobility was observed: teeth with higher baseline mobility resulted in significantly greater decreases in PD. At the site level, greater reductions were observed at interdental sites (compared to facial or oral), and at deeper sites (1.2 mm for 4 to 5 mm pockets and 2.4 mm for pockets > or =6 mm).
Conclusion: These data provided an estimation of the relative contribution of site-, tooth-, and patient-associated variables in terms of PD reductions following a standard course of machine-driven subgingival debridement.