Use of Hawthorne and Spoon-feeding effects to modify oral hygiene habits. A two-factorial randomized controlled trial.

PURPOSE. The aim of the study was to estimate the Hawthorne effect through the patients’ awareness of being observed regarding the detection of bacterial plaque with the use of a periodontal chart or the awareness of being observed in toothbrushing manoeuvres. MATERIALS AND METHODS. A randomized factorial trial with two-week follow-up was conducted. The factors investigated were: awareness of being observed in the detection of bacterial plaque accumulation and bleeding on probing (Factor Chart, FC), and awareness of being observed in toothbrushing manoeuvres (Factor Toothbrush, FT). Forty adult patients from a private dental practice were recruited, and divided into 4 groups of 10 patients each, which were randomly assigned to one, both or none of the study factors. Two weeks later, full-mouth plaque score (FMPS) and full-mouth bleeding score (FMBS) were evaluated by a blinded examiner. The randomization list was computer generated, and allocation was concealed by using opaque sealed numbered envelopes. RESULTS. Regarding FMPS, there was a positive Hawthorne effect in the case of FC, but it was not statistically significant [difference in FMPS: -4.5 95%CI from -14.5 to 5.4, P-value = 0.359], while a statistically significant negative Hawthorne effect was recorded in the case of FT [difference in FMPS: +10.0 95%CI from 0.1 to 19.9, P-value = 0.048]. Regarding FMBS, there was a positive, but not statistically significant, Hawthorne effect in the case of FC [difference in FMBS: -3.7 95%CI from -8.1 to 0.8, P-value = 0.103], while a statistically significant negative Hawthorne effect was recorded for FT [difference in FMBS: +5.2 95%CI from 0.8 to 14.8, P-value = 0.023]. CONCLUSIONS. The Hawthorne effect can take on a positive or negative value, depending on the indications given to the patient. The negative effect could be due to the expectation that others will tell us what to do (spoon-feeding effect). The intentional use of the Hawthorne effect to improve home oral hygiene habits is not supported by the results of this study.