How does ultrasonic cavitation remove dental bacterial biofilm?

Exploring viscosity influence mechanisms on coating removal: Insights from single cavitation bubble behaviours in low-frequency ultrasonic settings

The role of acoustic cavitation in various surface cleaning disciplines is important. However, the physical mechanisms underlying acoustic cavitation-induced surface cleansing are poorly understood. This is due to the combination of microscopic and ultrashort timescales associated with the dynamics of acoustic cavitation bubbles. Here, we have precisely controlled single-bubble cavitation in both space and time. Ultrasonic excitation leads to the cavitation of generated single bubbles. A synchronous ultrafast photomicrographic system simultaneously records the dynamics of single acoustic cavitation bubbles (SACBs) and the cleaning process of the nearby surface in liquids with varying viscosities. Finally, we analysed the correlation between bubble dynamics and surface cleaning situations. The differences in the typical dynamic characteristics of the bubbles during collapse in liquids with varying viscosities reveal two main mechanisms underlying surface cleaning by acoustic cavitation, which are respective the Laplace pressure during the bubble's movement and liquid jets during bubble collapse. Our study provides a better physical understanding of the ultrasonic cleaning process based on acoustic cavitation, and will help to optimize and facilitate the applications of surface cleaning, especially for the cleaning of substrates with tightly attached dirt.

Numerical investigation of acoustic cavitation and viscoelastic tissue deformation

Acoustic cavitation and tissue deformation are studied by modifying a level-set method for compressible two-phase flows to consider viscoelastic tissue deformation. The numerical simulations performed using different shear moduli and bubble-tissue distances demonstrate various interactions between bubble and viscoelastic tissue, including inverted cone-shape bubbles, bubble migration, liquid jet formation, compressive and expansive tissue deformation, and tissue perforation. The bubble is observed to grow larger with increasing tissue bulk modulus and density. The maximum tissue deformation generally increases with decreasing initial bubble-tissue distance and with increasing tissue bulk modulus and density. The tissue shear modulus conditions that maximize tissue deformation are in the range of 1-10 MPa, unless the tissue density is very large.

Evaluation of Antibacterial Efficacy of High-Intensity Focused Ultrasound Versus Photodynamic Therapy Against Enterococcus faecalis-Infected Root Canals

OBJECTIVE

The high incidence of endodontic failure is associated with the remnants of Enterococcus faecalis present within the intricate anatomies of the root canal system (RCS), often inaccessible by the current endodontic practices. This study was aimed at evaluating the effect of high-intensity focused ultrasound (HIFU) and photodynamic therapy (PDT) on E. faecalis biofilms in artificially infected root canals for the potential application in current endodontic practices.

METHODS

Forty-five single-rooted extracted teeth were instrumented using hand files, sterilized in an autoclave, infected with E. faecalis and incubated for 4 wk. The specimens were treated and identified as follows: Control, 4% sodium hypochlorite (NaOCl); riboflavin (1 mg/mL); light only; HIFU (250 kHz, 20 W, 60s); PDT; riboflavin/HIFU; light/HIFU; and riboflavin/HIFU/light. Bactericidal efficacy was determined by colony-forming units (CFU), (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) (MTT) assay, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM).

RESULTS

Enterococcus faecalis biofilm exhibited significantly lower metabolic activity when treated with HIFU (250 kHz, 20 W, 60 s) compared with the control (4% NaOCl) and PDT groups. A similar phenomenon was observed with the CFU assay. HIFU remained the most effective treatment modality, with consistent results in CLSM and SEM.

CONCLUSION

This study highlighted the potential application of HIFU as an adjunct drug-free, non-destructive root canal disinfection method for endodontic treatment, suggesting an alternative to the current gold standard of 4% NaOCl and PDT.

Intraoperative Direct Sonication of Implants and Soft Tissue for the Diagnosis of Periprosthetic Joint Infection

BACKGROUND

Sonication is very efficacious for the microbiological diagnosis of periprosthetic joint infection (PJI), but it involves many steps and multiple workplaces and personnel and therefore carries a potential contamination risk. We present an innovative version of the sonication culture method that involves direct sonication of the retrieved implant and soft tissue, without a sonication tube, intraoperatively and incubation using a BACT/ALERT 3D blood culture system to enhance the efficacy of microbiological diagnosis of PJI.

METHODS

We performed a prospective study of consecutive patients requiring implant removal and classified them as having PJI or aseptic failure according to standard criteria. The removed prosthetic components and adjacent soft tissue were directly sonicated in a small metal container, without a sonication tube, during the operation. The sonication fluid was immediately incubated in blood culture bottles in the operating room and cultured in the BACT/ALERT 3D blood culture system. The synovial fluid was also cultured in the BACT/ALERT 3D system to serve as a comparison.

RESULTS

Of the 64 included patients, 36 had PJI and 28 had aseptic failure. Fluid from direct sonication and conventional synovial fluid showed sensitivities of 91.7% and 55.6% (p < 0.001) and specificities of 82.1% and 92.9%, respectively. Fourteen cases of PJI were detected by culture of fluid from direct sonication but not by culture of synovial fluid. Higher sensitivity was obtained by direct sonication of only tissue than by direct sonication of only the implant (88.9% versus 75.0%). No significant difference in detection time was found between Staphylococcus aureus and coagulase-negative Staphylococcus.

CONCLUSIONS

When combined with incubation in BACT/ALERT bottles, direct intraoperative sonication of implants and soft tissues without a sonication tube was more sensitive than conventional synovial fluid culture and could reliably and rapidly detect the bacteria commonly found in PJI.

LEVEL OF EVIDENCE

Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

On the Photo-Eradication of Methicillin-Resistant Staphylococcus aureus Biofilm Using Methylene Blue

This work compared the effectiveness of several Methylene Blue (MB)-based protocols for photo-eradication of biofilms formed on the surface of the glass and stainless steel discs by S. aureus MRSA isolates using a diode laser (λ = 665 nm; output power 40 mW; energy fluence was 189 J cm^-2). The results obtained showed that MB alone, up to a concentration of 62.5 mgL^-1, had limited photo-bactericidal activity. It was possible to enhance the activity of MB using two types of spherical gold nanoparticles of similar sizes, 15 ± 3 nm/20 ± 3 nm, but differing in the method of their synthesis and stabilization. The enhancement of the photodestruction effect was related to the increased production of hydroxyl radicals by the MB+gold nanoparticles mixture, and this mixture showed dark cytotoxicity against the cocci studied. Effective destruction (mortality above 99.9%) of the biofilms formed by MRSA isolates was also possible without the use of gold nanoparticles, but the concentration of MB had to be at least 125 mgL^-1. A highly efficient protocol of photodestruction of biofilms, consisting of triple exposure of biofilms to laser light in the presence of MB alone, combined with the removal of dead bacteria protecting deep layers of pathogens against photosensitization, was also described.

Fusobacterium nucleatum Subspecies Differ in Biofilm Forming Ability in vitro

Development of dysbiosis in complex multispecies bacterial biofilms forming on teeth, known as dental plaque, is one of the factors causing periodontitis. Fusobacterium nucleatum (F. nucleatum) is recognised as a key microorganism in subgingival dental plaque, and is linked to periodontitis as well as colorectal cancer and systemic diseases. Five subspecies of F. nucleatum have been identified: animalis, fusiforme, nucleatum, polymorphum, and vincentii. Differential integration of subspecies into multispecies biofilm models has been reported, however, biofilm forming ability of individual F. nucleatum subspecies is largely unknown. The aim of this study was to determine the single-subspecies biofilm forming abilities of F. nucleatum ATCC type strains. Static single subspecies F. nucleatum biofilms were grown anaerobically for 3 days on untreated or surface-modified (sandblasting, artificial saliva, fibronectin, gelatin, or poly-L-lysine coating) plastic and glass coverslips. Biofilm mass was quantified using crystal violet (CV) staining. Biofilm architecture and thickness were analysed by scanning electron microscopy and confocal laser scanning microscopy. Bioinformatic analysis was performed to identify orthologues of known adhesion proteins in F. nucleatum subspecies. Surface type and treatment significantly influenced single-subspecies biofilm formation. Biofilm formation was overall highest on poly-L-lysine coated surfaces and sandblasted glass surfaces. Biofilm thickness and stability, as well as architecture, varied amongst the subspecies. Interestingly, F. nucleatum ssp. polymorphum did not form a detectable, continuous layer of biofilm on any of the tested substrates. Consistent with limited biofilm forming ability in vitro, F. nucleatum ssp. polymorphum showed the least conservation of the adhesion proteins CmpA and Fap2 in silico. Here, we show that biofilm formation by F. nucleatum in vitro is subspecies- and substrate-specific. Additionally, F. nucleatum ssp. polymorphum does not appear to form stable single-subspecies continuous layers of biofilm in vitro. Understanding the differences in F. nucleatum single-subspecies biofilm formation may shed light on multi-species biofilm formation mechanisms and may reveal new virulence factors as novel therapeutic targets for prevention and treatment of F. nucleatum-mediated infections and diseases.

Protein-conjugated microbubbles for the selective targeting of S. aureus biofilms

Staphylococcus aureus (S. aureus) is an important human pathogen and a common cause of bloodstream infection. The ability of S. aureus to form biofilms, particularly on medical devices, makes treatment difficult, as does its tendency to spread within the body and cause secondary foci of infection. Prolonged courses of intravenous antimicrobial treatment are usually required for serious S. aureus infections. This work investigates the in vitro attachment of microbubbles to S. aureus biofilms via a novel Affimer protein, AClfA1, which targets the clumping factor A (ClfA) virulence factor – a cell-wall anchored protein associated with surface attachment. Microbubbles (MBs) are micron-sized gas-filled bubbles encapsulated by a lipid, polymer, or protein monolayer or other surfactant-based material. Affimers are small (∼12 kDa) heat-stable binding proteins developed as replacements for antibodies. The binding kinetics of AClfA1 against S. aureus ClfA showed strong binding affinity (K_D = 62 ± 3 nM). AClfA1 was then shown to bind S. aureus biofilms under flow conditions both as a free ligand and when bound to microparticles (polymer beads or microbubbles). Microbubbles functionalized with AClfA1 demonstrated an 8-fold increase in binding compared to microbubbles functionalized with an identical Affimer scaffold but lacking the recognition groups. Bound MBs were able to withstand flow rates of 250 μL/min. Finally, ultrasound was applied to burst the biofilm bound MBs to determine whether this would lead to biofilm biomass loss or cell death. Application of a 2.25 MHz ultrasound profile (with a peak negative pressure of 0.8 MPa and consisting of a 22-cycle sine wave, at a pulse repetition rate of 10 kHz) for 2 s to a biofilm decorated with targeted MBs, led to a 25% increase in biomass loss and a concomitant 8% increase in dead cell count. The results of this work show that Affimers can be developed to target S. aureus biofilms and that such Affimers can be attached to contrast agents such as microbubbles or polymer beads and offer potential, with some optimization, for drug-free biofilm treatment.

Numerical modelling of acoustic cavitation threshold in water with non-condensable bubble nuclei

Numerical modelling of acoustic cavitation threshold in water is presented taking into account non-condensable bubble nuclei, which are composed of water vapor and non-condensable air. The cavitation bubble growth and collapse dynamics are modeled by solving the Rayleigh-Plesset or Keller-Miksis equation, which is combined with the energy equations for both the bubble and liquid domains, and directly evaluating the phase-change rate from the liquid and bubble side temperature gradients. The present work focuses on elucidating acoustic cavitation in water with a wide range of cavitation thresholds (0.02-30 MPa) reported in the literature. Computations for different nucleus sizes and acoustic frequencies are performed to investigate their effects on bubble growth and cavitation threshold. The numerical predictions are observed to be comparable to the experimental data in the previous works and show that the cavitation threshold in water has a wide range depending on the bubble nucleus size.

Microtensile bond strength to sealer-contaminated dentin after using different cleaning protocols

Background/purpose

Sealer residues on dentin may affect bonding to restorative materials. This study aimed to evaluate the bond strength to sealer-contaminated dentin after using different cleaning protocols.

Materials and methods

Freshly extracted bovine incisors were prepared and exposed the buccal pulp chamber dentin, obtaining segments measuring 5 mm × 5 mm with a height of 3 mm. The segments were randomly distributed into 4 groups (n = 7) according to different protocols. Control group: no contamination was performed. In the three experimental groups, the segments were contaminated with epoxy resin-based sealer for 5 min, and different cleaning protocols were performed. Acetone group: acetone-saturated cotton pellets were used to wipe the sealer. Ultrasound group: ultrasonic ET-20D tip cleaning. Acetone combined with ultrasound group: cleaning with acetone-saturated cotton pellets and ultrasonic tip. All segments were bonded using a self-etch adhesive. Two samples in each group were scanned by swept-source optical coherence tomography (SS-OCT) to evaluate sealer residues. A microtensile test was performed on the remaining 5 samples, which were built up with composite resin.

Results

Sealer residues were observed in 3 of 14 (21.4%) sections of acetone group by SS-OCT. Compared to the control, ultrasound alone or in combination with acetone preserved the bond strength (P > .05). The ultrasound group exhibited the highest bond strength (39.38 MPa), which differed from that of the acetone group, which provided the lowest bond strength (32.88 MPa) (P < .05).

Conclusion

Cleaning epoxy resin-based sealer-contaminated dentin surfaces using ultrasound or combined with acetone could preserve the bond strength.

The promising shadow of microbubble over medical sciences: from fighting wide scope of prevalence disease to cancer eradication

Microbubbles are typically 0.5-10 μm in size. Their size tends to make it easier for medication delivery mechanisms to navigate the body by allowing them to be swallowed more easily. The gas included in the microbubble is surrounded by a membrane that may consist of biocompatible biopolymers, polymers, surfactants, proteins, lipids, or a combination thereof. One of the most effective implementation techniques for tiny bubbles is to apply them as a drug carrier that has the potential to activate ultrasound (US); this allows the drug to be released by US. Microbubbles are often designed to preserve and secure medicines or substances before they have reached a certain area of concern and, finally, US is used to disintegrate microbubbles, triggering site-specific leakage/release of biologically active drugs. They have excellent therapeutic potential in a wide range of common diseases. In this article, we discussed microbubbles and their advantageous medicinal uses in the treatment of certain prevalent disorders, including Parkinson's disease, Alzheimer's disease, cardiovascular disease, diabetic condition, renal defects, and finally, their use in the treatment of various forms of cancer as well as their incorporation with nanoparticles. Using microbubble technology as a novel carrier, the ability to prevent and eradicate prevalent diseases has strengthened the promise of effective care to improve patient well-being and life expectancy.

Biological and Physiochemical Methods of Biofilm Adhesion Resistance Control of Medical-Context Surface

The formation of biofilms on medical-context surfaces gives the EPS embedded bacterial community protection and additional advantages that planktonic cells would not have such as increased antibiotic resistance and horizontal gene transfer. Bacterial cells tend to attach to a conditioning layer after overcoming possible electrical barriers and go through two phases of attachments: reversible and irreversible. In the first, bacterial attachment to the surface is reversible and occurs quickly whilst the latter is permanent and takes place over a longer period of time. Upon reaching a certain density in the bacterial community, quorum sensing causes phenotypical changes leading to a loss in motility and the production of EPS. This position paper seeks to address the problem of bacterial adhesion and biofilm formation for the medical surfaces by comparing inhabiting physicochemical interactions and biological mechanisms. Several physiochemical methodologies (e.g. ultrasonication, alternating magnetic field and chemical surface coating) and utilizing biological mechanisms (e.g. quorum quenching and EPS degrading enzymes) were suggested. The possible strategical applications of each category were suggested and evaluated to a balanced position to possibly eliminate the adhesion and formation of biofilms on medical-context surfaces.

Experimental investigations of three laser-induced synchronized bubbles

Herein, we investigated experimentally the dynamics of three laser-induced, same-sized, symmetrically aligned, and synchronized bubbles. Three synchronized laser beams split from the same beam using a Diffractive Optical Element splitter were focused on water, and then we obtained three bubbles. Another nanosecond laser pulse was used to probe the bubbles to obtain shadowgraphs. The exact delay of the excited and detected light was controlled using a delay generator. The results revealed that the maximum volumes of bubbles in arrays decrease as the normalized distance falls, while the lifetimes and translation increase. It was explained by the interaction between the acoustic radiation of bubbles and the surrounding bubbles. The shrinkage of linear bubble arrays exists an anomaly. The center bubbles were stretched, to ellipsoid, stick, even fractured, by the peripheral bubbles. The closer they are, the more distinct is the above phenomenon. However, when the normalized distance was sufficiently small, instead of being stretched, the center bubbles were compressed to disk shape and thus shrank with the whole array. Finally, the dependence of the distance on the energy transfer of the bubble system is also discussed.

Databases for the study of biofilms: current status and potential applications

Biofilms play an important role in health, being associated with >80% of all microbial infections in the body and in the development of antibiotic resistance. Research in this field has continuously produced large volumes of data. Being able to handle all this information will be paramount for progress in this field. However, this places a heavy burden on the development of strategies to gather, organize and make this information available in a way that can be readily and effectively used by those requiring it. Lately, efforts towards this goal have been reported, particularly with the development of Quorumpeps, BiofOmics, BaAMPs, QSPpred, dPABBs, aBiofilm and the Biofilms Structural Database. This work reviews these databases and highlights their applicability and potential, while stressing some of the challenges for the coming years in database development and usage brought about by the use of big data and machine learning.

Ways to control harmful biofilms: prevention, inhibition, and eradication

Biofilms are complex microbial architectures that encase microbial cells in a matrix comprising self-produced extracellular polymeric substances. Microorganisms living in biofilms are much more resistant to hostile environments than their planktonic counterparts and exhibit enhanced resistance against the microbicides. From the human perspective, biofilms can be classified into beneficial, neutral, and harmful. Harmful biofilms impact food safety, cause plant and animal diseases, and threaten medical fields, making it urgent to develop effective and robust strategies to control harmful biofilms. In this review, we discuss various strategies to control biofilm formation on infected tissues, implants, and medical devices. We classify the current strategies into three main categories: (i) changing the properties of susceptible surfaces to prevent biofilm formation; (ii) regulating signalling pathways to inhibit biofilm formation; (iii) applying external forces to eradicate the biofilm. We hope this review would motivate the development of innovative and effective strategies for controlling harmful biofilms.

A comparative questionnaire study of patient complaint levels between magnetostrictive ultrasonic scaler (Cavitron® ) and piezoelectric ultrasonic scalers

OBJECTIVES

Ultrasonic scalers often cause an uncomfortable feeling to patients during the procedure. This study was conducted to compare patient complaint levels between magnetostrictive (M-USSC) and piezoelectric ultrasonic scalers (P-USSC) during supragingival scaling.

METHODS

This study enrolled 82 subjects who received supportive periodontal therapy for at least 2 years. At each recall visit, probing pocket depth (PPD), bleeding on probing (BOP) and O'Leary plaque control record (O'PCR) were recorded. Then, supragingival scaling was performed using P-USSC (Varios or Petit Piezo) at the first visit and M-USSC (Cavitron) at the second visit. After each treatment, a questionnaire survey was performed using the Wong-Baker Faces Pain Scale for six items, which included the typical complaints occurring during ultrasonic scaling.

RESULTS

The scores for all the six items related to patient complaints were greater for P-USSC than for M-USSC (p < 0.001). Patient complaints such as discomfort, pain, sound, vibration, hyperesthesia and length of treatment time were ameliorated in 74%, 65%, 80%, 67%, 57% and 53% of subjects using M-USSC, respectively. On the other hand, only <5% of subjects showed deterioration in terms of each complaint.

CONCLUSION

This study suggested that M-USSC causes fewer patient complaints during supragingival scaling than P-USSC. M-USSC may improve patient motivation and compliance and may contribute towards achieving successful treatment outcomes. However, this result could differ depending on the shape of the tip and the insert and treatment site. Further research will be required under various conditions.