OBJECTIVE:Dental biofilms are responsible for the majority of oral cavity diseases (e.g., caries, periodontitis and gingivitis). In this work, we evaluate the effects of therapeutic ultrasound on a Streptococcus mutans biofilm model. The research aim is to assess whether therapeutic ultrasound can be implemented in standard practice for the treatment and prevention of oral infections. METHODS:Streptococcus mutans biofilms were grown on a tooth-mimicking substrate and subsequently exposed to chlorhexidine (CHX) and therapeutic ultrasound treatments. We examined the effects of low duty cycle (1%) 0.5 MHz ultrasound treatment at varying peak negative pressures (0.75-3.00 MPa) and CHX concentrations (0.025, 0.050 and 0.100 % w/V), both in the presence and absence of lipid-coated gas microbubbles. RESULTS:Ultrasound treatment was effective at removing biofilm, particularly at peak negative pressures exceeding 2.25 MPa and in the presence of lipid-coated microbubbles as cavitation nuclei. Ultrasound exposure also resulted in improved bactericidal action of low-concentration CHX (0.050% w/V). CONCLUSION:We demonstrated that 0.5 MHz therapeutic ultrasound treatment can be used for the mechanical removal of a fully formed and mechanically robust Streptococcus biofilm model. Although the ultrasound treatment alone did not reduce bacterial cell viability, its combination with low concentrations of CHX improved the antimicrobial treatment outcomes.

The Philips® Sonicare® Power Flosser (PSPF) is highly effective in reducing gum disease. Next to effective supragingival cleaning, this may be partially driven by subgingival cleaning. This in vitro study aimed to assess the effectiveness of the PSPF in removing biofilm from a model periodontal pocket up to 6 mm deep and to investigate the taxonomic composition of biofilm regrown after use of the PSPF.

The objective of this in vitro study was to compare the area of oral biofilm removal by the Philips Sonicare Quad Stream (PSQS) nozzle (used on a Philips® Sonicare® Power Flosser) and a traditional oral irrigator with a standard nozzle (TOIS) when used per the directions for use (DFU) instructions for both devices.

The objective of this in vitro study was to quantify the removal of dental biofilm from human enamel surfaces after treatment with the Philips® Sonicare® Power Flosser. Dental biofilms were grown from pooled human saliva on human enamel disks for 4 days, according to an established academic model.* The biofilms (n = 6) were treated with the Philips Sonicare Power Flosser for 3 seconds using the Quad Stream nozzle. To quantify the number of bacteria before treatment, the biofilm volume was measured using optical coherence tomography (OCT) and the bacterial cell density was determined from untreated control samples (n = 6) using confocal laser scanning microscopy (CLSM). After treatment the number of remaining bacteria were counted using CLSM. Additionally, scanning electron microscope (SEM) images were recorded. While before treatment 0.2-mm thick dense biofilms were present, after treatment only scattered groups of bacteria remained (Figure 1 through Figure 4). Quantitative analysis showed 99.96% removal for the Quad Stream nozzle. The Philips Sonicare Power Flosser oral irrigator with Quad Stream nozzle removed over 99.9% of the bacteria in this established laboratory model of dental biofilm.

OBJECTIVE:To test the hypotheses that blue light accelerates whitening through either (1) direct photobleaching or (2) photon-assisted oxidation using sequential longitudinal bleaching.METHODS:Thirty extracted human tooth samples having natural life accumulated color were divided over five groups: A. 9h light + 10h 6% H2O2 gel + 6h light & 6% H2O2 combined; B. 9h 6% H2O2 gel + 10h light + 6h light & 6% H2O2 combined; C. 11 h light & 6% H2O2 combined; D. 8.45h 25 %H2O2 gel + 10h of light only + 6h light & 25% H2O2 combined E. 10.45 h light & 25 %H2O2 combined. Blue light (456nm) was used at 190 mW/cm2. Color change (ΔE) was measured over time, and reported after 48h color stabilization.RESULTS:Groups A, B and D reached saturation in the first phase (at 9h) at a ΔE of 4.3 ± 0.7, 4.9 ± 1.3 and 10.9 ± 2.2, respectively. Groups C and E achieved in the same time a significantly higher ΔE of 14.2 ± 1.7 and 15.6 ± 1.9, respectively. Subsequently adding the opposite single modality to groups A, B and D for 10h did reach an end stage at 8.1 ± 1.3, 8.8 ± 1.8 and 10.8 ± 1.4 ΔE, respectively. The final 6h treatment combining light and H2O2 showed in these groups a statistically significant step in ΔE reaching 12.9 ± 1.4, 10.7 ± 2.5 and 15.3 ± 1.7, respectively.CONCLUSIONS:Blue light significantly increases bleaching rate and final achievable ΔE.This sequential whitening study provides a first indication that this enhanced bleaching is the result of the hypothesized light mechanisms acting in parallel to hydrogen peroxide bleaching.CLINICAL SIGNIFICANCE:This study shows that blue light can accelerate whitening, within the limits of an in-vitro model. The findings help the clinician explain to their patients that in light accelerated whitening the light not merely accelerates the bleaching process, but that it attacks more stain compounds than peroxide alone does.

Biofilms are thin layers of bacteria embedded within a slime matrix that live on surfaces. They are ubiquitous in nature and responsible for many medical and dental infections, industrial fouling and are also evident in ancient fossils. A biofilm structure is shaped by growth, detachment and response to mechanical forces acting on them. The main contribution to biofilm versatility in response to physical forces is the matrix that provides a platform for the bacteria to grow. The interaction between biofilm structure and hydrodynamics remains a fundamental question concerning biofilm dynamics. Here, we document the appearance of ripples and wrinkles in biofilms grown from three species of bacteria when subjected to high-velocity fluid flows. Linear stability analysis suggested that the ripples were Kelvin-Helmholtz Instabilities. The analysis also predicted a strong dependence of the instability formation on biofilm viscosity explaining the different surface corrugations observed. Turbulence through Kelvin-Helmholtz instabilities occurring at the interface demonstrated that the biofilm flows like a viscous liquid under high flow velocities applied within milliseconds. Biofilm fluid-like behavior may have important implications for our understanding of how fluid flow influences biofilm biology since turbulence will likely disrupt metabolite and signal gradients as well as community stratification.

Using high-speed imaging we assessed Streptococcus mutans biofilm–fluid interactions during exposure to a 60-ms microspray burst with a maximum exit velocity of 51 m/s. S. mutans UA159 biofilms were grown for 72 h on 10 mm-length glass slides pre-conditioned with porcine gastric mucin. Biofilm stiffness was measured by performing uniaxial-compression tests. We developed an in-vitro interproximal model which allowed the parallel insertion of two biofilm-colonized slides separated by a distance of 1 mm and enabled high-speed imaging of the removal process at the surface. S. mutans biofilms were exposed to either a water microspray or an air-only microburst. High-speed videos provided further insight into the mechanical behaviour of biofilms as complex liquids and into high-shear fluid–biofilm interaction. We documented biofilms extremely transient fluid behaviour when exposed to the high-velocity microsprays. The presence of time-dependent recoil and residual deformation confirmed the pivotal role of viscoelasticity in biofilm removal. The air-only microburst was effective enough to remove some of the biofilm but created a smaller clearance zone underlying the importance of water and the air–water interface of drops moving over the solid surface in the removal process. Confocal and COMSTAT analysis showed the high-velocity water microspray caused up to a 99.9% reduction in biofilm thickness, biomass and area coverage, within the impact area.

Streptococcus mutans in dental plaque biofilms play a role in caries development. The biofilm’s complex structure enhances the resistance to antimicrobial agents by limiting the transport of active agents inside the biofilm. The authors assessed the ability of high-velocity water microsprays to enhance delivery of antimicrobials into 3-d-old S. mutans biofilms. Biofilms were exposed to a 90° or 30° impact, first using a 1-µm tracer bead solution (109 beads/mL) and, second, a 0.2% chlorhexidine (CHX) or 0.085% cetylpyridinium chloride (CPC) solution. For comparison, a 30-s diffusive transport and simulated mouthwash were also performed. Confocal microscopy was used to determine number and relative bead penetration depth into the biofilm. Assessment of antimicrobial penetration was determined by calculating the killing depth detected by live/dead viability staining. The authors first demonstrated that the microspray was able to deliver significantly more microbeads deeper in the biofilm compared with diffusion and mouthwashing exposures. Next, these experiments revealed that the microspray yielded better antimicrobial penetration evidenced by deeper killing inside the biofilm and a wider killing zone around the zone of clearance than diffusion alone. Interestingly the 30° impact in the distal position delivered approximately 16 times more microbeads and yielded approximately 20% more bacteria killing (for both CHX and CPC) than the 90° impact. These data suggest that high-velocity water microsprays can be used as an effective mechanism to deliver microparticles and antimicrobials inside S. mutans biofilms. High shear stresses generated at the biofilm-burst interface might have enhanced bead and antimicrobial delivery inside the remaining biofilm by combining forced advection into the biofilm matrix and physical restructuring of the biofilm itself. Further, the impact angle has potential to be optimized both for biofilm removal and active agents’ delivery inside biofilm in those protected areas where some biofilm might remain.