The protocol was reviewed and approved by the ethics committee of the State Medical Board of Rhineland-Palatinate, Mainz, Germany (Ref: 2020-14928) and registered as ISRCTN: https://www.isrctn.com/ISRCTN28649560. The study was conducted in accordance with applicable the International Conference on Harmonization’s Good Clinical Practice guidelines and the European Union’s Commission Directive 2005/28/EC. All subjects provided written, informed consent.
Study design and settings
This was a randomized, single-center, 2-treatment, 4-period crossover trial conducted at the University Medical Center of the Johannes Gutenberg-University. The objective of this study was to compare an O-R electric rechargeable toothbrush and a reference manual toothbrush with respect to adult users’ rate of overnight and daytime plaque regrowth during an 8-day period, as assessed by DPIA.
Sample size calculation
Based on previous data and using a 2-sided test with α = .05, it was determined that 40 subjects provided the study 80% power to detect a significant mean treatment difference of 1.44 for afternoon DPIA plaque over 5 days, with an estimated variability of 1.146. Due to COVID-related circumstances, we were able to recruit 34 subjects meeting inclusion criteria.
Patient recruitment and follow-up
Subjects were recruited by the University Medical Center of the Johannes Gutenberg-University from the Center’s patient population between July and August 2020. Subjects were asked to refrain from toothbrushing for 24 hours before the screening appointment, at which time they provided written, informed consent, personal medical history, and demographic information. Subjects meeting inclusion criteria received a comprehensive examination of hard and soft oral tissues, and then disclosed plaque according to the fluorescein plaque-disclosing procedure after which time a pre-brushing DPIA image was taken of the anterior teeth.
Eligibility criteria
Eligible subjects were adults in good general health with an estimated plaque coverage of at least 10% on the buccal surfaces of the anterior teeth, as assessed by DPIA approximately 24 hours after brushing. Eligible subjects had at least 10 natural anterior teeth with scorable facial surfaces (excluding crowns, excessive facial restorations, or severe staining from tetracycline, fluorosis, or hypocalcification). Exclusion criteria included participation in any other oral care study, use of non-study oral hygiene products, elective dentistry, caries lesions that required restoration, calculus on facial tooth surfaces, active treatment for periodontitis, fixed facial or lingual orthodontic appliances, use of an antibiotic or chlorhexidine mouth rinse within 2 weeks prior to screening visit, pregnancy, lactation, hypersensitivity to dyes, or any disease or condition that could be expected to interfere with study procedures. Subjects agreed to refrain from all oral hygiene procedures for 24 hours prior to each morning visit and between each morning on-site brushing and the afternoon imaging visit. Subjects also agreed to abstain from eating, drinking, chewing gum, and using tobacco for 2 hours prior to each morning appointment and for 1 hour prior to each afternoon appointment. Small sips of water were permitted up to 1 hour before each morning appointment and the use of dental floss was permitted between treatment periods.
Safety
Serious adverse events (AEs), oral-related AEs, and whole-body AEs that could possibly be related to the study products were recorded upon self-report.
Processes, interventions, and comparisons
Treatments were (A) an experimental electric toothbrush (Oral-B iO OP020-PS2.0) with accompanying brush head (Oral-B Ultimate Clean OR015-PS2.0) [Procter & Gamble, Cincinnati, OH, United States] and (B) a control manual toothbrush (Oral-B® Indicator 35 soft) [Procter & Gamble]. All products were used with a standard sodium fluoride dentifrice (Blend-a-Med Classic, 1450 ppm fluoride as sodium fluoride) [Procter & Gamble].
At the screening visit, enrolled subjects began an initial acclimation phase of 2 to 3 days to acclimate to the electric toothbrush. Subjects were provided with kit boxes containing instructions, the electric toothbrush handle and brush head, and one tube of toothpaste. After receiving product use instructions, subjects brushed on site and were then instructed to use the electric toothbrush for 2 minutes twice a day with the provided toothpaste during the acclimation phase. This was followed by a second phase, following a similar process, to acclimate subjects to the manual toothbrush. Subjects were instructed to use the manual toothbrush in their customary manner twice a day with the provided toothpaste. The manual toothbrush was also used as the washout product between treatment periods to prevent potential carry-over.
After both acclimation phases, 34 subjects were each randomly assigned to 1 of the following 4 treatment sequences, each consisting of 4 treatment periods: ABBA, BAAB, AABB, or BBAA, with A and B representing the electric and manual toothbrush, respectively. Treatment periods lasted 8 days, including study visits on days 1, 3, and 8.
On day 1 of each period, continuance criteria were assessed, acclimation products were collected, and treatment kit boxes (consisting of instructions, the assigned toothbrush, and one tube of toothpaste) were distributed for use throughout the period.
On the morning of each visit (days 1, 3, and 8), each subject received an oral examination followed by plaque disclosure and pre-brushing DPIA plaque measurement of the anterior teeth. Brushing instructions were then reviewed, and subjects performed a supervised brushing (deemed their first brushing of the day) with their assigned brush. Subjects returned to the study site approximately 5 hours later for an afternoon assessment. At that time, plaque was again disclosed and a post-brushing DPIA plaque measurement was conducted of the anterior teeth. After the afternoon assessment of day 8 for treatment periods 1, 2, and 3, treatment products were collected, washout product kits (instructions, a manual toothbrush, and one tube of toothpaste) were distributed, and subjects were reminded to use the washout products twice daily during the 6-day washout period.
Continuance criteria were reviewed at each visit. Study procedures were repeated until all subjects had completed 4 treatment periods according to their randomly assigned treatment sequence.
DPIA imaging procedure
Prior to each imaging, subjects disclosed plaque by rinsing for 10 seconds with 25 ml phosphate buffer, then rinsing for 1 minute with 5.0 ml of 1240 ppm fluorescein in phosphate buffer, and finally rinsing 3 times for 10 seconds each with 25 ml phosphate buffer. The DPIA imaging system consisted of a high-resolution digital camera (Canon Corporation), 55 mm macro lens, and UV barrier filter, lit on each side by a compact flash unit with a long wave UV (365 nm peak) blue filter. A trained and validated operator captured images using validated image capture software. The system was initially calibrated to color standards values and then standardized daily with a calibrated color chart to ensure performance within calibration limits. The color chart was imaged every 30 minutes during use to ensure continued, standardized performance. Digital images were captured according to the procedure developed by Sagel et al.19 as described by Erbe et al21.
Primary and secondary outcome measures
The primary variable was afternoon plaque DPIA score, evaluated across 8 days. Secondary outcome measures included the morning pre-brushing DPIA measure. The null hypothesis was that the 2 toothbrush types would show no difference with respect to average DPIA after adjusting for baseline DPIA score. The alternative hypothesis was that the toothbrushes would show a difference with respect to average DPIA after adjusting for baseline DPIA score.
Statistical analysis
Summary statistics were calculated for the demographic variables and AEs were collected for each treatment group. Treatment effects were analyzed with 2-sided statistical tests and an α = .05 significance level. There were no adjustments for multiple comparisons.
Morning and Afternoon
For morning DPIA plaque coverage (days 3 and 8) and afternoon DPIA plaque coverage (on days 1, 3, and 8), an analysis of covariance (ANCOVA) for a crossover design was used. Assessment was conducted separately for each day, with the day 1 pre-brushing DPIA measurement used as the covariate. The model also included terms for subject as a random effect and treatment, period, and covariate by treatment interaction as fixed effects. Carryover effects were not significant at the 10% level, and thus were not included in the final model.
Weekly plaque reduction
An ANCOVA for a crossover design was used to assess the weekly reduction in pre-brushing plaque (day 1 pre-brushing minus day 8 pre-brushing DPIA measurements) with day 1 pre-brushing DPIA measurement as the covariate. The model also included terms for subject as a random effect and treatment, period, and covariate by treatment interaction as fixed effects. Carryover effects were not significant at the 10% level, and thus were not included in the final model.
Repeated measures
A repeated measures analysis across days was used to assess overall trends in morning pre-brushing (days 3 and 8) and afternoon post-brushing (days 1, 3, and 8) DPIA measurements. A repeated measures ANCOVA for a crossover design was used with the day 1 pre-brushing plaque as the covariate. The model also included terms for subject and subject by period interaction as random effects, and treatment, period, day, and baseline by treatment interaction as fixed effects. Carryover effects were not significant at the 10% level, and thus were not included in the final model.