Interproximal biofilm removal by intervallic use of a sonic toothbrush compared to an oral irrigation system

Background: The purpose of this in-vitro study was to investigate the potential of biofilm removal in interproximal tooth regions using intervallic cleaning with an oral irrigator or a sonic toothbrush. Methods: Three-species biofilms (Streptococcus mutans (OMZ 918), Streptococcus oralis SK 248 (OMZ 60), Actinomyces naeslundii (OMZ 745)) were grown on hydroxyapatite discs for 3 days in culture media. Every 24 h, specimens were incubated for 15 min in resazurin solution (i.e., culture medium and 10 % v/v alamarBlue (R)) to measure the metabolic activity with a fluorescence spectrophotometer in relative fluorescence units (rfu) at baseline. Then, specimens were fixed in interproximal holding devices and underwent treatment with an oral irrigator (WF; Waterpik (R) Sensonic WP-100E), an active sonic toothbrush (WPa), or an inactive sonic toothbrush (WPi; Waterpik (R) Sensonic SR-3000E) for 10 s (n = 18/group). Untreated biofilms served as controls (CO). After treatment, bacterial activity was re-measured, and specimens were re-grown in fresh medium for 24 h until next cleaning procedure. Altogether, cleaning was repeated in intervals of three treatment days (d1, d2, d3). After d3, SEM images were taken (n = 8) and CFU was measured (n = 3). Metabolic activity was analyzed for each disc separately, rfu values were averaged for d1 to compare initial biofilm stability, and ratios of baseline and post-treatment values were compared. Results were analyzed using ANOVA with the post-hoc Scheffe test, or Kruskal-Wallis with post-hoc Mann-Whitney test. Results: Median baseline rfu-values of d1 resulted in 7821.8 rfu (interquartile range = 5114.5). Highest reduction in metabolic activity was recorded significantly for the oral irrigator used for 10 s (residual activity per day d1: WF 17.9 %, WPa 58.8 %, WPi 82.5 %, CO 89.6 %; d2: WF 36.8 %, WPa 85.2 %, WPi 82.5 %, CO 90.0 %; d3: WF 17.2.%, WPa 79.6 %, WPi 96.3 %, CO 116.3 %). SEM images of untreated specimens (CO) and specimens treated with the sonic toothbrush (WPa and WPi) showed huge amounts of biofilm, while oral irrigator-treated specimens (WF) revealed barely any bacteria. CFU data confirmed the graduations between the groups. Conclusions: Cleaning of interproximal regions achieved better success with an oral irrigator as compared to the use of a sonic toothbrush. (350/350 words)