The present investigation enrolled 20 dental students, aged 19 to 28 years. All participants were school of dentistry students. All researchers were staff members of the school of oral health sciences. As such, the students did not depend on the researchers for their grades. The experiment was explained to all participants prior to its commencement, and both verbal and written consent to participate were provided. This study was conducted with the approval of the ethics review board of Kyushu Dental University (No.: 18-8).
This was a one-week, single-centre, randomised, two-treatment, examiner-blind, parallel group study (Figure 1). This randomised controlled trial was performed in accordance with the CONSORT (Consolidated Standards of Reporting Trials) checklist . The trial participants were randomly assigned either 1) an electric toothbrush with a monitor (monitor-usage group; n = 10) or 2) an electric toothbrush without a monitor (monitor-non-use group; n = 10). Eligible participants were adults aged 18 years or over with healthy gingiva. Exclusion criteria were gingivitis or periodontitis, current antibiotic therapy, smoking and ongoing dental treatment. The study was conducted at Kitakyushu, Japan, in October 2018.
An independent researcher (S. A., who was not the examiner) assigned the participants randomly to either the monitor-usage group or the monitor-non-use group to ensure that the examiner was blinded to both group sampling and assignment. All participants were examined initially and then attended a follow-up examination after one week. Oral examinations were performed from 4 pm to 6 pm. Both groups brushed their teeth with the same dentifrice (Butler Dental Liquid Gel, Sunstar, Osaka, Japan).
The primary outcome was difference in the amount of dental plaque between baseline and follow-up as assessed by personal hygiene performance (PHP, see section 2.4). The secondary outcome was the amount of change in dental plaque from baseline to one week.
QLR-applied electric toothbrush visualisation system
The newly developed electric toothbrush used in the present experiment is a device incorporating an image sensor with a λ > 520-nm filter and 400-nm wavelength light source with a microcomputer in the head and handle, respectively, in an oscillating-rotating brush (Figure 2). The electric toothbrush can be connected to a display device, such as a tablet or smartphone, to visualise red-autofluorescent plaque. To classify captured image data as teeth, plaque, or gingiva, each pixel of image data was assigned three elements of colour: hue, saturation, and brightness. The plaque was then visualised as red fluorescence on the display. In addition, users could see the pixel numbers that featured the red-fluorescent plaque.
Quantitative evaluation of dental plaque
To quantitatively evaluate the dental plaque, the present study used the personal hygiene performance (PHP) . After applying the disclosing agent, surfaces of six teeth (i.e. 16, 11, 26, 36, 31, and 46) were divided into five areas (i.e., three longitudinal thirds, distal, middle, and mesial; the middle third was subdivided horizontally into incisal, middle, and gingival thirds). Two teeth (36 and 46) were examined on their lingual sides, while the other teeth (16, 11, 26, and 31) were examined on their facial sides. The score assigned to each tooth ranged from 0 to 5. Individual scores were obtained by totalling six teeth, and so ranged from 0 to 30.
Assessment of gingival status
Evaluation of the gingival state was performed with the Gingival Index (GI) according to Löe and Silness on the facial, lingual, distal, and mesial surfaces of six teeth (16, 12, 24, and 36, 32, 44) . The GI of each surface was scored from 0 to 3 according to the severity of the gingival state: 0 indicated normal gingiva; 1, mild inflammation, a slight change in colour, mild alteration of gingival surface structure, and no bleeding on probing (BOP); 2, moderate inflammation, redness, oedema and swelling, and BOP; and 3, severe inflammation, marked redness and oedema, ulceration, and a tendency towards spontaneous bleeding. The mean of the values from all the examined surfaces was calculated. The score of personal GI thus ranged from 0 to 3.
Questionnaire for self-efficacy of oral health
Self-efficacy of the oral health of participants was assessed using a self-efficacy scale for oral health behaviour (SEOH) . The SEOH questionnaire consisted of 25 items, which were assessed using a five-point Likert scale that addressed four domains: ‘self-efficacy for brushing behaviour’, ‘self-efficacy for daily life habits’, ‘self-efficacy for psychological control’, and ‘self-efficacy for dental check-up’. The score of SEOH ranged from 0 to 125, where a lower score indicated a more positive self-efficacy.
Initially, the PHP, GI, and SEOH of all participants were assessed. Participants in the two study groups were instructed on the use of the electric toothbrush, and the monitor-usage group received an additional explanation concerning the operation of the monitor. To ensure blinding with regard to monitor usage, the monitor-non-use group first performed the procedures for 1 week, followed by the monitor-usage group. Participants were informed that the toothbrush was newly developed and that the aim of this study was to evaluate the plaque-removable effect of this toothbrush. Neither group was aware of the toothbrush used in the other group. Each group was assessed at the end of the one-week trial. Participants used the toothbrush at home.
All values are presented as median with upper and lower limits. The internal consistency of SEOH was assessed with Cronbach’s α coefficients. The Mann-Whitney U test was used to compare variables or extent of change in PHP between groups. The Kruskal-Wallis test was used to compare both groups before and after examination. The statistical analyses were performed using SPSS (version 22; IBM Inc., Armonk, NY, USA). Two-tailed p-values were calculated in all analyses. The alpha level for significance was set at 0.05.