Irrigant flow in the root canal during ultrasonic activation: A numerical fluid-structure interaction model and its validation.

AIM: The aim of the study was (a) to develop a three-dimensional numerical model combining the oscillation of a tapered ultrasonic file and the induced irrigant flow along with their two-way interaction in the confinement of a root canal. (b) To validate this model through comparison with experiments and theoretical (analytical) solutions of the flow. METHODOLOGY: Two partial numerical models, one for the oscillation of the ultrasonic file and another one for the irrigant flow inside the root canal around the file, were created and coupled in order to take into account the two-way coupled fluid-structure interaction. Simulations were carried out for ultrasonic K-files and for smooth wires driven at four different amplitudes in air or inside an irrigant-filled straight root canal. The oscillation pattern of the K-files was determined experimentally by Scanning Laser Vibrometry, and the flow pattern inside an artificial root canal was analysed using high-speed imaging together with Particle Image Velocimetry. Analytical solutions were obtained from an earlier study. Numerical, experimental and analytical results were compared to assess the validity of the model. RESULTS: The comparison of the oscillation amplitude and node location of the ultrasonic files and of the irrigant flow field showed a close agreement between the simulations, experiments and theoretical solutions. CONCLUSIONS: The model is able to predict reliably the file oscillation and irrigant flow inside root canals during ultrasonic activation under similar conditions.

Is reproducibility inside the bag? Special issue fundamentals and applications of sonochemistry ESS-15.

In this paper we report our most recent attempts to tackle a notorious problem across several scientific activities from the ultrasonics sonochemical perspective: reproducibility of results. We provide experimental results carried out in three different laboratories, using the same ingredients: ultrasound and a novel cavitation reactor bag. The main difference between the experiments is that they are aimed at different applications, KI liberation and MB degradation; and exfoliation of two nanomaterials: graphene and molybdenum disulfide. Iodine liberation rates and methylene blue degradation were higher for the cases where a cavitation intensification bag was used. Similarly, improved dispersion and more polydisperse exfoliated layers of nanomaterials were observed in the intensified bags compared to plain ones. The reproducibility of these new experiments is compared to previous experimental results under similar conditions. Our main conclusion is that despite knowing and understanding most physicochemical phenomena related to the origins and effects of cavitation, there is still a long path towards reproducibility, both in one laboratory, and compared across different laboratories. As emphasized in the sonochemical literature, the latter clearly illustrates the complexity of cavitation as nonlinear phenomenon, whose quantitative estimation represents a challenging aspect. We also provide a list of procedural steps that can help improving reproducibility and scale-up efforts.

Temperature evolution of preheated irrigant injected into a root canal ex vivo.

OBJECTIVES: The aim of this study is to test the influence of the temperature of the surrounding medium, flow rate, duration of irrigation, and apical patency on the evolution of the temperature of irrigants injected in a root canal. MATERIALS AND METHODS: Thermocouples were inserted into an incisor at different positions to monitor irrigant temperature during and after injection at 21, 45, or 60 °C. The tooth was immersed in a water bath at 21 and 37 °C. RESULTS: Preheated syringes were used for up to 2.5 min before being cooled down from 60 to below 45 °C. The irrigant temperature was higher apically than at coronal levels (P ≤ 0.028). The duration of irrigation had no influence on the average temperatures during delivery (P ≥ 0.337), but the apical patency lowered the intracanal temperature (P = 0.004). The highest temperature measured on the outside of the tooth was 39 °C. CONCLUSIONS: Preheating the irrigant at 60 °C resulted in temperatures higher than 45 °C throughout the root canal, during irrigant delivery. After completion, the temperature dropped rapidly. CLINICAL RELEVANCE: These results contribute to a better understanding of the optimum irrigant delivery time at given temperature, the cooling rate of irrigant in the syringe, and the influence of heated irrigant temperature in the periodontium, which should guide the preheated syringe turnover.

Emulsification in novel ultrasonic cavitation intensifying bag reactors.

Cavitation Intensifying Bags (CIBs), a novel reactor type for use with ultrasound, have been recently proposed as a scaled-up microreactor with increased energy efficiencies. We now report on the use of the CIBs for the preparation of emulsions out of hexadecane and an SDS aqueous solution. The CIBs have been designed in such a way that cavitation effects created by the ultrasound are increased. It was found that the CIBs were 60 times more effective in breaking up droplets than conventional bags, therewith showing a proof of principle for the CIBs for the preparation of emulsions. Droplets of 0.2µm could easily be obtained. To our knowledge, no other technology results in the same droplet size more easily in terms of energy usage. Without depending on the wettability changes of the membrane, the CIBs score similarly as membrane emulsification, which is the most energy friendly emulsification method known in literature. Out of the frequencies used, 37kHz was found to require the lowest treatment time. The treatment time decreased at higher temperatures. While the energy usage in the current non-optimised experiments was on the order of 107-109J/m3, which is comparable to that of a high-pressure homogenizer, we expect that the use of CIBs for the preparation of fine emulsions can still be improved considerably. The process presented can be applied for other uses such as water treatment, synthesis of nanomaterials and food processing.

Measuring cavitation and its cleaning effect.

The advantages and limitations of techniques for measuring the presence and amount of cavitation, and for quantifying the removal of contaminants, are provided. After reviewing chemical, physical, and biological studies, a universal cause for the cleaning effects of bubbles cannot yet be concluded. An "ideal sensor" with high spatial and temporal resolution is proposed. Such sensor could be used to investigate bubble jetting, shockwaves, streaming, and even chemical effects, by correlating cleaning processes with cavitation effects, generated by hydrodynamics, lasers or ultrasound.

Cavitation measurement during sonic and ultrasonic activated irrigation.

INTRODUCTION: The aims of this study were to quantify and to visualize the possible occurrence of transient cavitation (bubble formation and implosion) during sonic and ultrasonic (UAI) activated irrigation. METHODS: The amount of cavitation generated around several endodontic instruments was measured by sonochemiluminescence dosimetry inside 4 root canal models of human dimensions and varying complexity. Furthermore, the spatial distribution of the sonochemiluminescence in the root canal was visualized with long-exposure photography. RESULTS: Instrument oscillation frequency, ultrasonic power, and file taper influenced the occurrence and amount of cavitation. In UAI, cavitation was distributed between the file and the wall extending beyond the file and inside lateral canals/isthmuses. In sonic activated irrigation, no cavitation was detected. CONCLUSIONS: Cavitation was shown to occur in UAI at clinically relevant ultrasonic power settings in both straight and curved canals but not around sonically oscillating instruments, driven at their highest frequency.

Oscillation characteristics of endodontic files: numerical model and its validation.

During a root canal treatment, an antimicrobial fluid is injected into the root canal to eradicate all bacteria from the root canal system. Agitation of the fluid using an ultrasonically vibrating miniature file results in a significant improvement in the cleaning efficacy over conventional syringe irrigation. Numerical analysis of the oscillation characteristics of the file, modeled as a tapered, driven rod, shows a sinusoidal wave pattern with an increase in amplitude and decrease in wavelength toward the free end of the file. Measurements of the file oscillation with a scanning laser vibrometer show good agreement with the numerical simulation. The numerical model of endodontic file oscillation has the potential for predicting the oscillation pattern and fracture likeliness of various file types and the acoustic streaming they induce during passive ultrasonic irrigation.

Irrigant flow beyond the insertion depth of an ultrasonically oscillating file in straight and curved root canals: visualization and cleaning efficacy.

INTRODUCTION: The purpose of this study was to evaluate the influence of the insertion depth of an ultrasonically oscillating file on the ability to remove dentin debris from simulated canal irregularities in an extracted tooth model of a straight root canal and its influence on the flow of irrigant in both straight and curved canals. METHODS: A tooth model with artificial depressions in 1 canal wall at 0.5, 2, 4, and 6 mm from the working length was used. Ultrasonic-activated irrigation was performed with the file inserted 1, 2, 3, 4, or 5 mm short of the working length. Dye penetration and high-speed recordings of the flow in straight and curved canals showed the static and dynamic behavior of the flow during ultrasonic activation. RESULTS: The overall cleaning efficacy decreased with increasing distance between the file and the apex, with the depressions next to the file and within 3 mm in front of the file being the cleanest. The flow observed from the visualization experiments matched this distance, suggesting a direct relation between flow and cleaning. The observed flow depth increased with increasing power setting; the curvature of the root canal had no influence on the flow depth. High-speed imaging showed a start-up phase with deeper fluid activation than in the steady phase afterward. CONCLUSIONS: The ultrasonically oscillating file could remove dentin debris up to 3 mm in front of the file tip, coinciding with the extent of the observed flow. The root canal curvature had no influence on the irrigant flow.

Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles.

We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip.

The influence of the ultrasonic intensity on the cleaning efficacy of passive ultrasonic irrigation.

INTRODUCTION: It is not clear whether increasing the ultrasonic intensity would enhance the cleaning efficacy of passive ultrasonic irrigation (PUI) inside a root canal. The aim of this study was to evaluate the effect of the ultrasonic intensity on PUI to remove dentin debris and whether there is any lateral effect beyond the ultrasonic tip. METHODS: Each of 15 in vitro root canal models with four standard depressions in the apical part of one canal wall were filled with dentin debris and received PUI repeatedly. The most apical depression was localized apically from the ultrasonic tip. The highest intensity was applied in group 1, the lowest intensity was applied in group 3, and syringe irrigation was performed in group 4 as a control. Before and after irrigation, images of the canal wall with depressions were taken and compared. The removal of dentin debris in the depression was categorized as clean or not clean. The data were analyzed by means of the chi-square test. The oscillation amplitude of the ultrasonic file at each intensity was recorded in vitro using time-resolved high-speed imaging. RESULTS: Group 1 (highest intensity) exhibited significantly better cleaning than all the other groups (P < .05); no significant difference was found between the four levels of the depressions within any of the four groups. High-speed imaging showed that the amplitude of the oscillating file increased as the intensity went up, which leads to a higher velocity of the irrigant around the file. CONCLUSIONS: Higher ultrasonic intensity resulted in a higher amplitude of the oscillating file and, consequently, enhanced the cleaning efficacy of PUI.

An evaluation of the effect of pulsed ultrasound on the cleaning efficacy of passive ultrasonic irrigation.

INTRODUCTION: Multiple activations of the irrigant by using pulsed ultrasound may enhance the removal of dentin debris because of repeated acceleration of the irrigant. The aim of this study was to evaluate the effect of pulsed ultrasound on passive ultrasonic irrigation (PUI) in its ability to remove artificially placed dentin debris from a simulated apical oval extension within standardized root canals. METHODS: Each of 20 in vitro root canal models with a standard groove in the apical portion of one canal wall filled with dentin debris received PUI repeatedly, either without pulsation (group 1) or with pulsation (730 milliseconds on/100 milliseconds off in group 2, 400 milliseconds on/400 milliseconds off in group 3, and 100 milliseconds on/670 milliseconds off in group 4), corresponding to duty cycles of 100%, 88%, 50%, and 13%, respectively. After each irrigation procedure, the amount of dentin debris in the groove was evaluated by taking photographs of the groove and scoring. The irrigation procedures were also visualized in vitro using high-speed imaging performed in glass root canal models. RESULTS: The debris score was significantly lower only in group 3 (p = 0.023). The in vitro visualization showed increased streaming and cavitation during the start-up phase of each pulse. CONCLUSIONS: PUI with a pulsation pattern of 400 milliseconds on/400 milliseconds off and a duty cycle of 50% is more effective in removing dentin debris from a simulated apical oval extension in standardized root canals than continuous ultrasonic activation. Duty cycles of 13% and 88% showed no difference compared with continuous oscillation.

The effect of needle-insertion depth on the irrigant flow in the root canal: evaluation using an unsteady computational fluid dynamics model.

INTRODUCTION: The aim of this study was to evaluate the effect of needle-insertion depth on the irrigant flow inside a prepared root canal during final irrigation with a syringe and two different needle types using a Computational Fluid Dynamics (CFD) model. METHODS: A validated CFD model was used to simulate irrigant flow from either a side-vented or an open-ended flat 30-G needle positioned inside a prepared root canal (45 .06) at 1, 2, 3, 4, or 5 mm short of the working length (WL). Velocity, pressure, and shear stress in the root canal were evaluated. RESULTS: The flow pattern in the apical part of the root canal was similar among different needle positions. Major differences were observed between the two needle types. The side-vented needle achieved irrigant replacement to the WL only at the 1-mm position, whereas the open-ended flat needle was able to achieve complete replacement even when positioned at 2 mm short of the WL. The maximum shear stress decreased as needles moved away from the WL. The flat needle led to higher mean pressure at the apical foramen. Both needles showed a similar gradual decrease in apical pressure as the distance from the WL increased. CONCLUSIONS: Needle-insertion depth was found to affect the extent of irrigant replacement, the shear stress on the canal wall, and the pressure at the apical foramen for both needle types.

Influence of the oscillation direction of an ultrasonic file on the cleaning efficacy of passive ultrasonic irrigation.

INTRODUCTION: The cleaning mechanisms and characteristics of passive ultrasonic irrigation (PUI) are not yet completely understood. The aim of this study was to investigate whether the oscillatory direction of the ultrasonically driven file had an influence on dentin debris removal from artificially made grooves in standardized root canals. METHODS: Each of 20 ex vivo root canal models with a standard groove in the apical portion of one canal wall filled with dentin debris received PUI repeatedly, either with file oscillation toward the groove or with file oscillation perpendicular to the groove. After each irrigation procedure, the amount of dentin debris in the groove was evaluated by photographs of the groove and by scoring. The oscillations of the ultrasonic file were also visualized in vitro by using high-speed imaging at a time scale relevant to the cleaning process, order 10 microseconds. RESULTS: A nonparametric analysis showed significantly more dentin debris reduction when the file oscillated toward the groove (P = .002). High-speed imaging showed that the oscillation of the file is in a single plane, resulting in high-velocity jets emanating from the file tip in the direction of the oscillations. CONCLUSIONS: Oscillation of the ultrasonically driven file toward the groove is more effective in removing dentin debris from the groove than oscillation perpendicular to the groove, which can be related to the fact that there is a high-velocity jet from the file tip in a single direction following the file oscillation and a relatively slow inflow in the perpendicular direction.

Evaluation of irrigant flow in the root canal using different needle types by an unsteady computational fluid dynamics model.

INTRODUCTION: The aim of this study was to evaluate the effect of needle tip design on the irrigant flow inside a prepared root canal during final irrigation with a syringe using a validated Computational Fluid Dynamics (CFD) model. METHODS: A CFD model was created to simulate the irrigant flow inside a prepared root canal. Six different types of 30-G needles, three open-ended needles and three close-ended needles, were tested. Using this CFD model, the irrigant flow in the apical root canal was calculated and visualized. As a result, the streaming velocity, the apical pressure, and the shear stress on the root canal wall were evaluated. RESULTS: The open-ended needles created a jet toward the apex and maximum irrigant replacement. Within this group, the notched needle appeared less efficient in terms of irrigant replacement than the other two types. Within the close-ended group, the side-vented and double side-vented needle created a series of vortices and a less efficient irrigant replacement; the side-vented needle was slightly more efficient. The multi-vented needle created almost no flow apically to its tip, and wall shear stress was concentrated on a limited area, but the apical pressure was significantly lower than the other types. CONCLUSIONS: The flow pattern of the open-ended needles was different from the close-ended needles, resulting in more irrigant replacement in front of the open-ended needles but also higher apical pressure.

Study on the influence of refreshment/activation cycles and irrigants on mechanical cleaning efficiency during ultrasonic activation of the irrigant.

INTRODUCTION: The aims of this study were to evaluate dentin debris removal from the root canal during ultrasonic activation of sodium hypochlorite (2% and 10%), carbonated water, and distilled water and to determine the influence of 3 ultrasonic refreshment/activation cycles of the irrigant by using the intermittent flush technique. METHODS: Root canals with a standardized groove in 1 canal wall, which was filled with dentin debris, were irrigated ultrasonically. The irrigant was refreshed and ultrasonically activated 3 times for 20 seconds. The quantity of dentin debris after irrigation was determined after each refreshment/activation cycle. RESULTS AND CONCLUSIONS: Ultrasonic activation of the irrigant combined with the intermittent flush method produces a cumulative effect over 3 refreshment/activation cycles. Sodium hypochlorite as an irrigant is significantly more effective than carbonated water, which is significantly more effective than distilled water, in removing dentin debris from the root canal during ultrasonic activation.

Evaluation of a sonic device designed to activate irrigant in the root canal.

INTRODUCTION: The aims of this study were to evaluate the removal of dentin debris from the root canal by sonic or ultrasonic activation of the irrigant and the physical mechanisms of sonic activation by visualizing the oscillations of the sonic tip, both inside and outside the confinement of the root canal. METHODS: Roots of 18 canines were embedded, split, and prepared into standardized root canals. A standard groove was cut on the wall of one half of each root canal and filled with the same amount of dentin debris before irrigation procedures. The removal of dentin debris was evaluated after different irrigation procedures. The oscillations of the sonic tip were visualized ex vivo by using high-speed imaging at a time scale relevant to the irrigation process, and the oscillation amplitude of the tip was determined under 20x magnification. RESULTS: After irrigation, there was a statistically significant difference between the experimental groups (P < .0001). Without irrigant activation, the grooves were still full of dentin debris. From the ultrasonic activated group, 89% of the canals were completely free of dentin debris, whereas from the sonic group, 5.5%-6.7% were (P = .0001). There was no significant difference between the sonic activation groups. CONCLUSIONS: Activation of the irrigant resulted in significantly more dentin debris removal; ultrasonic activation was significantly more efficient than sonic activation. The oscillation amplitude of the sonically driven tips is 1.2 +/- 0.1 mm, resulting in much wall contact and no cavitation of the irrigant.

Effect of molecular weight, crystallinity, and hydrophobicity on the acoustic activation of polymer-shelled ultrasound contrast agents.

Polymer-shelled microbubbles are applied as ultrasound contrast agents. To investigate the effect of the polymer on microbubble preparation and acoustic properties, polylactides with systematic variations in molecular weight, crystallinity, and end-group hydrophobicity were used. Polymer-shelled cyclodecane filled capsules were prepared by emulsification, and the cyclodecane was removed by lyophilization to obtain hollow capsules. Complete removal of cyclodecane from the microcapsules was only achieved for short chain (about M(w) 6000) crystalline polymers. The pressure threshold for acoustic destruction of the microbubbles was found to increase with molecular weight. Noncrystalline polymers showed a higher threshold for destruction than crystalline polymers. Hydrophobically modified short chain crystalline polymers showed the steepest increase in acoustic destruction after the threshold as a function of the applied pressure, which is a favorable characteristic for ultrasound mediated drug delivery. Microcapsules made with such polymers had an inhomogeneous surface including pores through which cyclodecane was lyophilized efficiently.