Methods: 182 patients participated in this double-blind, randomized, controlled clinical trial. Having signed an informed consent, each patient filled a modified dental anxiety index upon entry. Based on random blocks, 91 patients received one placebo capsule 30 minutes before SRP as a potent painkiller, and 91 control subjects received SRP alone. Base-line periodontal and confounding variables were measured in each sextant by a blind examiner. Pain was recorded using a 10 cm line VAS as well as a 5-point verbal Likert scale (VRS-5) during SRP for each sextant of dentition. Statistical analysis was accomplished by SPSS version19.
Results: There was no statistical difference between placebo and control groups regarding VAS and VRS-5 scores using Mann-Whitney test. Multiple linear regression model controlling for co-variables revealed a statistical significant lower pain perception mean in placebo compared to control group based on VAS (β= 0.6, 95%CI=-0.3, -0.88, P<0.0001). Moreover, multiple ordinal logistic regression model showed lower mean of pain reported through VRS-5 by placebo group than controls (β=0.24, 95%CI=0.007, 0.465, P<0.043). Spearman rank test disclosed correlation between the two pain measuring methods (rsp=0.917, P<0.0001).
Conclusions: Within the limitation of this study, placebo effect was capable of reducing pain during SRP compared to control. Significant confounders for pain perception during SRP are age, anxiety, mean probing pocket depth, sub-gingival calculus, symptomatic dentin defects, and faulty restorations.