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

A novel ultrasonic cavitation enhancer

We introduce a Cavitation Intensifying Bag as a versatile tool for acoustic cavitation control. The cavitation activity is spatially controlled by the modification of the inner surface of the bag with patterned pits of microscopic dimensions. We report on different measurements such as the transmission of ultrasound, temperature increase inside the bag during sonication. Several applications of interest to other scientific activities are also demonstrated

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 ultrasoun

Ultrasonic cleaning of 3D printed objects and Cleaning Challenge Devices

We report our experiences in the evaluation of ultrasonic cleaning processes of objects made with additive manufacturing techniques, specifically three-dimensional (3D) printers. These objects need to be cleaned of support material added during the printing process. The support material can be removed by dissolution in liquids with or without ultrasonic cavitation. Distinctive stages in the cleaning processes were found for two different liquids (water and NaOH solutions). The combination of ultrasound and high concentration of NaOH has the best results for support material dissolution in the particular conditions studied. The sonication of cleaning processes in ultrasonic baths is typically a slow process. Here we show the advantages of using an ultrasonic horn to clean the surface of small parts and holes more effectively. We introduce a Cleaning Challenge Device design to be used for the universal evaluation of cleaning performance of different equipment or processes, and specifically for ultrasonic baths. The results and conclusions can be of use for different cleaning situations besides 3D printed parts, such as when deciding which protocol has a better performance or comparing different equipment

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 0.2 μm 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, 37 kHz 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.</p

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

Scaled–up sonochemical microreactor with increased efficiency and reproducibility

Bubbles created with ultrasound from artificial microscopic crevices can improve energy efficiency values for the creation of radicals; nevertheless it has been conducted so far only under special laboratory conditions. Limited reproducibility of results and poor energy efficiency are constraints for the sonochemistry and ultrasonics community to scale-up applied chemical processes. For the first time, using conventional ultrasonic bath technology, the numbering-up and scale-up of a microfluidic sonochemical reactor has been achieved. Sonochemical effects such as radical production and sonochemiluminescence were intensified by the modification of the inner walls of a novel Cavitation Intensification Bag. While 25 times bigger than the previous microreactor, a reduction of 22 % in standard deviation and an increase of 45.1 % in efficiency compared to bags without pits were obtained. Mechanical effects accompanying bubble collapse lead to two distinct types of erosion marks observed in the bags

Study on the Influence of Refreshment/Activation Cycles and Irrigants on Mechanical Cleaning Efficiency During Ultrasonic Activation of the Irrigant\ud

Introduction\ud 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.\ud \ud Methods\ud 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.\ud \ud Results and Conclusions\ud 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\u