A computational simulation study on the acoustic pressure generated by a dental endosonic file: Effects of intensity, file shape and volume

doi:10.1016/j.ultsonch.2014.03.024

Ultrasonics Sonochemistry

Volume 21, Issue 5, September 2014, Pages 1858-1865

https://doi.org/10.1016/j.ultsonch.2014.03.024 Get rights and content

Highlights

•
Acoustic pressure generated is affected by the working volume.
•
Endosonic files were able to generate high acoustic pressures in a confined space.
•
The acoustic pressure generated contributes to the production of cavitation.
•
Decrease in size of the root canal model causes an increase in acoustic pressure.

Abstract

One of the uses of ultrasound in dentistry is in the field of endodontics (i.e. root canal treatment) in order to enhance cleaning efficiency during the treatment. The acoustic pressures generated by the oscillation of files in narrow channels has been calculated using the COMSOL simulation package. Acoustic pressures in excess of the cavitation threshold can be generated and higher values were found in narrower channels. This parallels experimental observations of sonochemiluminescence. The effect of varying the channel width and length and the dimensions and shape of the file are reported. As well as explaining experimental observations, the work provides a basis for the further development and optimisation of the design of endosonic files.

Introduction

Acoustic cavitation is a well-known phenomenon in the field of ultrasound [1]. It can increase mixing and fluid motion in a system, form reactive intermediates which accelerate chemical reactions and aid in cleaning processes [2], [3]. Ultrasound is used in dentistry to aid in cleaning. One of the most common applications of power ultrasound in dentistry is in periodontics where ultrasound with frequencies of 20–40 kHz is used in dental descalers to remove dental debris and plaque around the teeth and gums [4]. Apart from the mechanical cleaning effects, recent studies have shown that cavitation can be produced in water around the descalers [5], and the amount of cavitation and its distribution around the instrument has a strong correlation with the shape and design of the tip [6], [7], [8].

Another application of ultrasound in dentistry is in endodontics (root canal treatment). Here, ultrasound is applied to a narrow file which is placed within the root canal to improve the dissolution and removal of infected tissues and abscess from an infected root canal [9]. A number of researchers have shown that ultrasonically assisted irrigation improves the cleaning efficiency in root canal treatments [10], [11], [12]. Some argued that this was due to enhanced acoustic streaming [13], [14], [15] while others suggested that it could be due to the physical effects caused by cavitation [5], [8]. The oscillation profiles of endosonic files (i.e. files used during endodontic treatments that involve ultrasonic vibrations) have been measured to investigate correlations between the oscillation profiles and the cleaning effectiveness [16], [17]. The areas of cavitation activity around the instruments were assessed by the detection of sonochemiluminescence (SCL). Although it was reported that SCL tended to appear around the vibration antinodes of the oscillating files, there was no clear relation between the vibration amplitudes and the SCL emission [5], [6]. Furthermore, it was also reported that there was no correlation between the lengths of the endosonic files and the oscillation profiles [18].

Macedo and co-workers recently suggested that the production of SCL was greatly increased when an endosonic file was operated in a human-sized root canal model as compared with in a cuvette of 10 mm wide and claimed that it was due to higher acoustic intensities formed in a confined system [19]. Production of cavitation potentially plays an important role in root canal cleaning. The production of stable cavitation may enhance streaming and mixing in the canal [20], [21], while transient cavitation produces microjets [22] and radicals [23] upon collapse. Given this potential importance of acoustic cavitation in endodontics, there is a need for detailed information with which to optimize the operating parameters for endodontic instruments. In this work, we report computational simulation of the acoustic pressure generated by endosonic instruments with the aim of predicting the occurrence of cavitation since it will occur when the acoustic pressure exceeds a threshold value [1].

Several ultrasonic systems have been studied using computational modelling approaches such as computational fluid dynamics on the fluid flow of an ultrasonic system [24], [25] and finite element analyses to predict acoustic pressure fields [26], [27], [28]. The latter was shown to give results close to the experimental sonication systems. It was used to predict optimized conditions as it was found that slight changes in geometry of the sonicating system will significantly affect the acoustic pressure fields generated [28]. Studies on fluid dynamics for dental ultrasonic systems [29], [30] have been published although there is no clear data on the acoustic pressure fields around ultrasonically driven endosonic systems under different operating conditions.

This paper aims to provide insight into the acoustic pressures generated using a computational modelling approach. In this study, the effects of power supplied, dimensions of root canal model and the dimensions of the endosonic files were examined in order to provide information of the operating conditions for different root canal dimensions with endosonic files used in clinical practice.

Section snippets

Endosonic files

The dimensions of the endosonic files used in the models were based on the dimensions of a standard K-file #10, #15, #20 and #25 (Endosonor, Maillefer, Dentsply) which are 15 mm long and have diameters (d) of 0.10, 0.15, 0.20 and 0.25 mm respectively. In clinical use, these endosonic files operate on a MiniPiezon ultrasound generator (EMS, Nyon, Switzerland) at a driving frequency of 30 kHz [17]. Fig. 1 illustrates a standard K-file attached to a piezoelectric hand piece.

COMSOL simulation procedures

All simulations were

Effects of output power

Fig. 4 illustrates the simulated acoustic pressure fields generated around a vibrating file with dimensions of 0.25 mm (d) × 15 mm (l) contained in a cylinder of 1 mm (D) × 20 mm (L) at an output power of 6 W. Regions of high acoustic pressure are illustrated in red and low acoustic pressures are in blue. The areas of highest acoustic pressure are around the mid-length of the file, suggesting this to be where the highest tendency for cavitation to occur.

Table 1 collates reported values of the threshold

Conclusions

The acoustic pressure fields generated by endosonic files with varying dimensions have been calculated using the COMSOL simulation package. It was found that maximum acoustic pressures of 1.3 MPa, in excess of the cavitation threshold, can be achieved in a confined system of 1 mm (D) × 20 mm (L) at an output power of 6 W, comparable with conditions used in clinical proactice. This indicates the possibility of the generation of cavitation at high power settings in a root canal model.

Investigation on

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A computational simulation study on the acoustic pressure generated by a dental endosonic file: Effects of intensity, file shape and volume

Highlights

Abstract

Introduction

Section snippets

Endosonic files

COMSOL simulation procedures

Effects of output power

Conclusions

Ultrason. Sonochem.

Ultrason. Sonochem.

Med. Hypotheses

J. Endod.

J. Endod.

Ultrason. Sonochem.

J. Biomech.

Desalination

Ultrason. Sonochem.

Ultrason. Sonochem.

J. Endod.

J. Endod.

Comput. Math. Appl.

Ultrasound Med. Biol.

Ultrasonics

Med. Eng. Phys.

Cavitation

Cavitation microstreaming

J. Acoust. Soc. Am.

Applications of sonochemistry to materials synthesis

Advances in power driven pocket/root instrumentation

J. Clin. Periodontol.

Innovations in non-surgical periodontal therapy: Consensus Report of the Sixth European Workshop on Periodontology

J. Clin. Periodontol.

Ultrasound promoted reaction of Rhodamine B with sodium hypochlorite using sonochemical and dental ultrasonic instruments

Ultrason. Sonochem.

The efficacy of ultrasonic irrigation to remove artificially placed dentine debris from different-sized simulated plastic root canals

Int. Endod. J.

Passive ultrasonic irrigation of the root canal: a review of the literature

Int. Endod. J.