Baseline adjustment and change revisited: effect of smoking on change in periodontal status following periodontal therapy.
Smokers have frequently been reported to have more severe periodontitis, to respond less favorably to periodontal therapy, and to show elevated rate of recurrence compared with non-smokers. The aims of this study was to compare the results of baseline-adjusted and -unadjusted analyses when assessing the effect of smoking on change in periodontal status following therapy and to discuss the methodological issues involved. This is a secondary analysis of data from 180 periodontitis patients enrolled in a randomized controlled clinical intervention trial. Information on smoking habits was elicited from the participants before, and 12 months after, therapy. The clinical parameters analyzed were probing pocket depth and clinical attachment level, using both simple analysis of change (SAC) and analysis of covariance (ancova), adjusting for age, gender, and treatment group. The current smokers presented with more severe periodontitis at baseline than did former and never smokers. Results of the SAC indicated that the current smokers benefitted more from treatment than did former or never smokers, whereas the results of the baseline-adjusted ancova indicated no such differences. Both sets of results are likely to be biased with respect to valid conclusions regarding the 'causal' effect of smoking. Possible sources of bias are discussed.
Department of Periodontology, Institute of Clinical Odontology, Faculty of Dentistry, University of Oslo, Oslo, Norway.
Hans R
HR
Preus
Leiv
L
Sandvik
Per
P
Gjermo
Vibeke
V
Baelum
D000328:Adult; D000367:Age Factors; D000368:Aged; D000704:Analysis of Variance; D000890:Anti-Infective Agents / Q000627:therapeutic use; D015982:Bias; D003131:Combined Modality Therapy; D012534:Dental Scaling / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008795:Metronidazole / Q000627:therapeutic use; D008875:Middle Aged; D017622:Periodontal Attachment Loss / Q000145:classification / Q000628:therapy; D010512:Periodontal Index; D010514:Periodontal Pocket / Q000145:classification / Q000628:therapy; D010518:Periodontitis / Q000145:classification / Q000628:therapy*; D012044:Regression Analysis; D016745:Root Planing / Q000379:methods; D012737:Sex Factors; D012907:Smoking / Q000009:adverse effects
D000890:Anti-Infective Agents; D008795:Metronidazole
clinical periodontal attachment level; observational study; periodontal pocket depth