## 4 Discussion
The Hawthorne effect [34] was attributed to the considerable importance of these positive effects. Test subjects changed their natural behavior [35] due to the awareness that they were under observation. In the present study, regular recall appointments and dental care contributed to these positive effects. The use of a soft toothbrush, the instructions regarding an adequate brushing technique (Stillmann technique), and the recommendation of a moderate brush contact pressure [36] had a further positive effect on CDH and consequently on the OHRQoL. The Schiff score and the VAS were used to evaluate dentine hypersensitivity [24] in the present study. Both are suitable for measuring CDH [37] in clinical trials. Patients in the present study showed a higher sensitivity for air blast stimuli than for probing [38,39], which is consistent with previous literature. Therefore, only the stimulus response with a Schiff score of 2 or 3 after a one-second air blast on the cervical area of the tooth was considered an inclusion criterion for this clinical investigation. The investigators were trained before patient recruitment measurement variability. In each study center, only the calibrated dentists (only one or two per center) examined all patients. Measurement errors were eliminated by the small number of examiners and their calibration. Thus, the Schiff score became a reliable and reproducible clinical parameter and was used as the stratification feature. Randomization ensured a random distribution of the patients among the trial groups in order to eliminate potential disruptive factors. These factors (confounders) such as age or body weight of the subjects might have had a positive or negative impact on the therapeutic effect. Therapeutic efficacy based on the sole effect [40] of the intervention can be determined by structural equality. Block randomization was performed for all patients in the KKS Halle/Saale. Randomization was planned for 300 patients (150 per treatment arm). The Schiff score (2/3) and the number of the study center (01/02/03) were used as stratification criteria. Using SAS version 9.1.3 (SAS Institute, Cary, NC, USA), a randomization list was compiled for each of the resulting six strata. The randomization algorithm assigned the patients to the therapy arms in a block-by-block manner. The blocks had a variable length of 6 or 10 subjects. At the end of the study, there was a group distribution of 136 control subjects and 137 test subjects. Systematic errors (bias) should be avoided by blinding [41] a scientific study. The randomization lists remained in the KKS until the end of the study. Thus, blinding was ensured for the entire duration of the study. The present clinical study was double-blind, implying that the investigator and the patient were not involved in the group distribution. The statistician, the sponsor, and the monitor were blinded to the data until the end of the therapy. A major limitation of the present study was the absence of positive control, as recommended by [PERSON] et al. [42]. The following trial could be used as a positive control. [PERSON] et al. [43] compared the effect of Pro-Argin with two positive controls, Gluma(2-hydroxyethyl methacrylate and glutaraldehyde) and NovaMin(5% calcium sodium phosphosilicate), after a single application and after 30 days. All three desensitizers led to a reduction in CDH, and Pro-Argin exhibited a significant reduction in the CDH values (\(p<0.016\)). In addition, in further studies, the GOHAI questionnaire could be replaced by the DHEQ questionnaire to address the CDH more specifically and compare the results with the present findings. The selection criteria in the present study were defined precisely. This made recruitment of the study population more difficult. The inclusion of molars and an increase in the age limit (>70 years) could have facilitated the recruitment process. Most of the excluded patients showed dentine hypersensitivity only in the molars. In Germany, 11 subjects (9%) fell into this category and had to be excluded.