Study 1 – Mechanical testing of toothbrush deflection
During mechanical testing, the test toothbrushes and the control toothbrushes behaved differently. For the test toothbrushes with flexible necks, at the starting position, the head of the toothbrush was straight, although following the start of deflection, the brush head flexed at both pivot points (thumb position and flexible neck, see Figure 2a/2b). This flexing was slightly larger at the flexible neck. At maximum deflection, the brush head was significantly bent. The bending occurred mainly through deformation at the flexible neck. For the control toothbrush, at the starting position, the head of the toothbrush was unchanged with a small angle at the end of the head. After the deflection started, the toothbrush head was bent at both pivot points (thumb position and start of head). The bending was slightly larger at the toothbrush head. At maximum deflection, the toothbrush head was significantly bent due to deformation of the smallest cross section at the end of the toothbrush head.When force was further exerted on a test toothbrush, the bending occurred mainly at the flex zone, whereas the entire neck and head were deflected for the control toothbrush. At an applied force of 2.5 N, a mean deflection of 3.9±0.1 mm was measured for the test toothbrush, and 1.6±0.1 mm for the control toothbrush (Figure 4). The entire force-deflection progression showed that the test toothbrush is deflected 2–2.5 times more than the control toothbrush when the same bending force was applied (Figure 4).
Study 2 – Cleaning efficacy by plaque planimetry
After a pre-test assessment of two different brushing forces (2.5 N vs 3.5 N) it was decided to test all the toothbrushes at the lower brushing force of 2.5 N only, which a bending assessment indicated was associated with 75% bending of the test toothbrushes. All of the five test toothbrushes were statistically superior in performance in terms of artificial plaque removal (%) compared to the control toothbrush (p < 0.001 for most comparisons). The superior performance of the test toothbrushes was maintained at all crown risk areas, including ABCDF next to the gumline, mesial and distal inbetween fields. This is shown in the WMW U statistics and associated probabilities for total cleaning effects of the five test toothbrushes versus the control toothbrush in Table 1 and in Supplementary Tables 4–6.
A comparison of interdental and gumline cleaning for the test toothbrushes versus the control toothbrush is given in Figure 5. The plots show means and standard deviations (as error bars) for plaque removal by the six toothbrushes using horizontal, rotating and vertical brushing movements. In each case, the superiority in performance by the flexible-neck designs compared to the control toothbrush was shown. This difference was most apparent for mesial, distal and ABCDF buccal locations for all three types of brushing action.
For horizontal, rotating and vertical cleaning efficacy parameters, the ComPro toothbrush showed the best overall plaque removal performance. The next best-performing test toothbrushes were the RepPro and the RapRe. These three toothbrushes tended to perform better when compared to the other test toothbrush counterparts (TrueWhi and SensGu) but the differences between them were quite small (Figure 5, Table 1, and Supplementary Figure 3). However, all of the test toothbrushes performed significantly better than the rigid control toothbrush, which was the poorest-performing toothbrush (Figure 5, Table 1, and Supplementary Figure 3).
The average cleaning score across three movements for the ComPro test toothbrush was 64.12% compared to the control toothbrush, which was 43.11%. The brushing efficacy was generally greater for the five test toothbrushes in terms of access to interdental spaces, exposed root surfaces and differing tooth types, compared to the control toothbrush. Horizontal and rotating brush movements with the test toothbrushes were significantly more effective in removing simulated plaque than for the control toothbrush. Vertical brushing movements were also more effective with the test toothbrushes, although only for 3 out of 5 test toothbrushes.
An analysis of single replicated human teeth showed that there was optimum plaque control at incisors (up to 99.75%) after horizontal brushing in interdental risk areas, followed by wisdom teeth (up to 64.06%) then canines, premolars and molars (up to 45.72%) (See Supplementary Tables 1–6).