The Ethics committee of the Medical University of Innsbruck, Austria, approved the study (ID AN 5123). The study was conducted in accordance with the 1964 Helsinki declaration and its later amendments. All subjects signed an informed written consent prior to the study enrollment.
Twenty volunteers were recruited from the authors’ circle of acquaintances. Inclusion criteria were (1) age ≥ 14 years, (2) contractual capability, and (3) the presence of ≥ 5 teeth per quadrant. Exclusion criteria were (1) dental or medical students or professionals, (2) oral hygiene instructions prior to the study, (3) community periodontal index of treatment needs (CPITN) grade 3 or 4 , (4) pregnancy or breastfeeding, (5) systemic diseases or conditions that are associated with an increased risk of infection or necessitate concomitant antibiotic therapy with dental treatment, and (6) mental and behavioral disorders that impede (verbal) communication. Recruitment was performed from March 15 to April 14, 2019, and data collection was carried out from April 26 to May 13, 2019.
The cleansing efficacy of brushing with the amabrush® versus manual toothbrushing was evaluated in a randomized-controlled, examiner-blinded, two-period crossover study. Each subject was asked to attend four appointments. At day one, the probands were informed about the study procedure; they signed an informed consent, and inclusion and exclusion criteria were proofed. After plaque disclosing (2Tone, Young, Earth City, Mo, USA), professional tooth cleaning was accomplished with an air-polishing device (Airflow® prophylaxis master and Airflow® Plus powder; both EMS, Nyon, CH), and, if appropriate, with sonic scalers and rubber cups with polishing paste (Cleanic®, Kerr, Bioggo, CH). Each proband was instructed to refrain from oral hygiene, including toothbrushing, the use of dental floss or other interdental cleaning devices, and the use of mouth rinses or chewing gum for 3 days. According to a computer-generated randomization (Microsoft® Office Excel), probands were allocated either to group 1, designated to start with using the amabrush®, or group 2, determined to start with manual toothbrushing. After 3 days of undisturbed biofilm accumulation, plaque was disclosed and scored by two blinded investigators (DS and WS) using the Rustogi Modified Navy Plaque Index (RMPN)  before (baseline) and after brushing with the assigned device. Probands of group 1 were assisted with using the amabrush® according to the manufacturer’s instructions. Only one size (model “Amabrush Version 1.0”) was available at the time the study was conducted. The mouthpiece was wetted and attached to the handpiece, which was loaded with the pod containing the “fresh” toothpaste. The toothpaste button was pressed to inject the toothpaste. After insertion of the mouthpiece and adjustment between the dental arches so as to ensure maximum fit, the start button was pressed. After 10 s, the brushing automatically stopped. The mouthpiece was removed and the probands were instructed to rinse with water. The RMNPI was assessed and teeth were air-polished. Probands of the group 2 were told to brush their teeth with a manual toothbrush (Oral B Indicator Medium 35®, Procter & Gamble UK, Weybridge, Surrey, UK) that had been dipped once into the same (liquid) “fresh” toothpaste, which had been poured into a cup. Toothbrushing was performed without instruction and in the absence of a mirror to ensure that the probands had no visual control of the disclosed plaque. The respective brushing method was recorded and the brushing time was stopped and chosen freely up to a maximum of 4 min. After rinsing with water, the RMNPI was assessed and air-polishing was performed. After a wash out phase of 11 days when the probands were practicing their usual oral hygiene procedures, they presented for the third visit (day 15). Again, plaque was disclosed and teeth were cleaned by air-polishing. After abolishing oral hygiene for 3 days, the fourth visit (day 18) unfolded in analogy to the second visit, with group 1 using the manual brush and group 2 using the auto-cleaning device.
Alginate impressions of both jaws were taken to obtain stone plaster casts for the evaluation of the size and shape of the dental arches and the investigation of the auto-cleaning device’s fit.
Rustogi Modified Navy Plaque Index
The index divides buccal and lingual surfaces into nine areas (A to I) that are scored for the presence (score = 1) or absence (score = 2) of plaque. It assesses the amount of plaque on a whole-mouth basis (areas A–I), interdental basis (areas D and F), and the gingival margin basis (areas A–C). Third molars and deeply carious teeth were excluded from the evaluation, whereas teeth with fillings, inlays, onlays, or crowns were included. RMPNI is calculated as percentage of biofilm adhering sites to measured sites.
Examiner alignment and assessment was performed in five probands. The RMNPI was mutually assessed and agreed. Inter-examiner reliability was calculated with the Cohen’s kappa coefficient [9, 10] based on 9072 areas measured by both clinical investigators. Cohen’s kappa coefficient for RMPNI was κ = 0.768, reflecting a substantial inter-examiner reliability.
Due to lack of previous investigations, the pilot study was done on five participants. The reduction of the mean plaque score (RMNPI) applying conventional toothbrushing was RMNPI = 30.81 ± 5.17%, and for the auto-cleaning device it was RMNPI = 13.08 ± 2.96%. Sample size calculation for dependent samples, a power of 90% and α = 0.05 revealed a sample size of three. Sample size was increased to 20 to improve the validity of the study.
For descriptive analysis and if not stated otherwise, mean and standard deviation are given. On a proband level, RMNPI values were calculated as the total number of tooth areas with plaque present divided by the total number of tooth areas scored (for 28 teeth, there was a total of 504 sites for the whole mouth, 112 sites for the interdental, and 168 sites for the marginal areas). The amounts of plaque reduction (pre-minus post-plaque removal amounts) were calculated and mean reduction in the whole-mouth plaque, interdental, and marginal plaque scores were compared between the two toothbrushing procedures by Wilcoxon signed-rank test. The significance level was set at p ≤ 0.05.