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Table of Contents   
ORIGINAL ARTICLE  
Year : 2021  |  Volume : 24  |  Issue : 1  |  Page : 94-99
To compare the continuous and intermittent irrigation method on the removal of dentin debris from root canals and to evaluate the dynamics of irrigant flow using computational fluid dynamics


1 Department of Conservative Dentistry and Endodontics, Subharti Dental College and Hospital, Swami Vivekanand Subharti University, Meerut, India
2 Department of Conservative Dentistry and Endodontics, Seema Dental College and Hospital, Rishikesh, Uttarakhand, India

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Date of Submission18-Dec-2020
Date of Decision24-Jan-2021
Date of Acceptance03-Feb-2021
Date of Web Publication05-Jul-2021
 

   Abstract 


Aim: This study aimed to compare the efficiency of continuous and intermittent irrigating methods on the removal of dentin debris from the simulated grooves and to evaluate the dynamics of irrigant using computational fluid dynamics (CFD).
Methodology: Seventy-five extracted human permanent maxillary canines were selected. Access cavities were made, working length was determined, and canals were prepared by crown down technique. The teeth were split longitudinally and standard groove 2.0 mm in length was made in split halves and each groove was filled with dentin debris and the images were taken under a microscope (E200). The halves were re-assembled and divided into five groups based on different irrigation methods. Group 1: ultrasonic Irrigation with continuous flow for 3.0 min; Group 2: ultrasonic irrigation with continuous flow for 1.5 min; Group 3: ultrasonic irrigation with intermittent flow for 3.0 min; Group 4: ultrasonic irrigation with the intermittent flow for 1.5 min; and Group 5: syringe irrigation for 1 min. The root halves were again separated and re-evaluated for debris elimination after the irrigation protocol for all the groups separately. The effect of time and method of passive ultrasonic irrigation were compared. For the computational fluid analysis, a GAMBIT 2.2 (Ansys) software was used for mesh construction. FLUENT 6.2 (Ansys) software was used to set the boundary conditions and reconstruction of the canal; flow patterns and turbulence were graphically constructed.
Results: The continuous irrigation methods were better at debris removal than intermittent irrigation flow methods. The CFD showed that the turbulence of flow of irrigant was dependent on the inlet velocity and pressure of the irrigant.
Conclusion: Debris removal from the simulated grooves was better with continuous irrigation compared with intermittent irrigation. CFD study revealed that the turbulence that was affected by the velocity and pressure of the irrigant introduced and is a variable entity.

Keywords: Computational fluid dynamics, continuous irrigation, dentin debris, intermittent irrigation, passive ultrasonic irrigation

How to cite this article:
Raj S, Dhingra A, Jha P, Nikhil V, Ravinder R, Mishra P. To compare the continuous and intermittent irrigation method on the removal of dentin debris from root canals and to evaluate the dynamics of irrigant flow using computational fluid dynamics. J Conserv Dent 2021;24:94-9

How to cite this URL:
Raj S, Dhingra A, Jha P, Nikhil V, Ravinder R, Mishra P. To compare the continuous and intermittent irrigation method on the removal of dentin debris from root canals and to evaluate the dynamics of irrigant flow using computational fluid dynamics. J Conserv Dent [serial online] 2021 [cited 2021 Aug 4];24:94-9. Available from: https://www.jcd.org.in/text.asp?2021/24/1/94/320682



   Introduction Top


Eliminating endodontic infections and healing of periapical infections require a disinfection regime, in which irrigation plays an important role.[1] The penetration of irrigation solution depends on several variables such as root canal configuration, volume, type, and temperature of the irrigation solution, and the most important is the type of irrigation agitation device used. The debris removing capability is enhanced by ultrasonic agitation as it generates both cavitation and acoustic streaming.[2],[3],[4],[5],[6] Various studies[2],[3] have been shown that passive ultrasonic irrigation along with sodium hypochlorite is effective in removing dentin debris from the root canals. Passive ultrasonic irrigation can be used in two different methods for irrigation, one being continuous and the second intermittent. In the continuous method, the irrigant is continuously delivered into the canal which helps in the continuous activation of the irrigant and also reduces the irrigation time. The intermittent flow method, in the debris removal and pulpal dissolution in a more effective manner.[2]

Computational fluid dynamics (CFD) is a method of mathematically modeling and computer simulation of various flow patterns and techniques. The fluid dynamics of an irrigant in the root canal involves the turbulent nature of the fluid. Various methods have been tried to measure the flow, pressure, and turbulence of the irrigants. However; the different methods have provided little insight on the effects and flow pattern of the irrigants. Fluid flow is commonly studied in one of three ways: experimental fluid dynamics, theoretic fluid dynamics, and CFD.

CFD has various advantages over other methods which are it is relatively inexpensive, gives better visualization, and can help in enhanced understanding of design. In addition, it can be used to evaluate and predict specific parameters such as the streamlining, velocity distribution of irrigant flow in the canal, flow pressure, and shear stress on the root canal wall, which are difficult to measure in vivo due to the microscopic size of the root canal.

The flow of irrigants with its velocity, turbulence was effectively measured by Boutsioukis et al.[7] using CFD model. They stated that the irrigant flow rate is highly significant in determining the flow pattern within the root canal system. The development of turbulent flow is desirable as it leads to more efficient irrigant replacement.

To the best of our knowledge, no study has evaluated the removal of dentin debris physically and correlated it with CFD. Hence, the aim of this study was to compare the efficiency of continuous and intermittent irrigating methods on the removal of dentin debris from the simulated grooves and to evaluate the dynamics of irrigants using CFD model.


   Methodology Top


Seventy-five freshly extracted human permanent single-rooted maxillary canines were selected, disinfected with 0.1% thymol solution, and stored in normal saline till the time of use. The teeth were sectioned horizontally at 15 mm from the apex; access cavity preparations were done using endo access bur (Dentsply, Maillefer Ballaigues, Switzerland).

The working length was established by using #10 K file into the root canal until the tip of the file was just visible at the apical foramen under magnification of ×2.5 and then 0.5 mm was deducted from this length. The root canals were prepared with Protaper Gold rotary (Dentsply, Maillefer, Ballaigues, Switzerland) finishing files up to F4.

After that, nonpenetrating grooves were made longitudinally on the buccal and lingual aspects of all the specimens. The teeth were then longitudinally split into two halves with the help of chisel and mallet and the half which had the greater part of the apex was selected as the representative sample for each group.

A standard groove 2.0 mm in length, 0.2 mm in width and 0.5 mm in depth was made in the split halves at a distance of 2.0–4.0 mm to simulate a noninstrumented canal extension in the apical half.

To prepare the dentin debris, dentin surface (decoronated crown of the samples) was scrubbed on arkansas stone, collected, and mixed for 10 min with 2% sodium hypochlorite. Each groove was filled with dentin debris to reproduce a noninstrumented canal extension and measured on an electronic weighing machine, with and without debris such that each tooth contained 0.5 mg of dentin debris. Images of the groove were taken using a Nikon microscope, E200 attached with a digital camera, Q Imagine Go-3, at ×40 magnification with and without the dentin debris.

The halves were re-assembled using orthodontic plastic bands and sticky wax. The teeth were divided into five groups based on different irrigation methods:

Group 1: Ultrasonic Irrigation with continuous flow for 3.0 min:

During ultrasonic activation, a 30-gauge side vent irrigation needle (Dentsply, Maillefer Ballaigues, Switzerland) was used instead of an endosonics. The irrigation needle was attached to the ultrasonic device with the help of a needle adaptor. The unique feature of this needle holding adapter is that the needle is simultaneously activated by the ultrasonic handpiece, while an irrigant was delivered from intravenous tubing connected via a Luer-Lok device to an irrigation delivering syringe. The irrigant thus can be delivered apically through the needle under a continuous flow for 3 min.

Group 2: Ultrasonic Irrigation with continuous flow for 1.5 min:

This is same as Group 1 except the time of irrigation which was 1.5 min.

Group 3: Ultrasonic Irrigation with intermittent flow for 3.0 min:

The sodium hypochlorite in the root canal was activated ultrasonically for 1 min and the root canal was flushed with 2 mL of 2% sodium hypochlorite with a 30 G needle 2 mm short of the working length. The total time of agitation was 3 min.

Group 4: Ultrasonic Irrigation with the intermittent flow for 1.5 min:

This is same as Group 1 except the time of irrigation which was 1.5 min.

Group 5: Syringe irrigation with 2 mL of 2% sodium hypochlorite with a 30G needle 1–2 mm short of the working length for 1 min:

After the irrigation protocol, the root halves were separated and images of the groove were again taken using a Nikon microscope, E200 attached with a digital camera, Q Imagine Go-3, at ×40 magnification.

The quantity of debris in the groove before and after irrigation procedure was scored independently as per Mayer et al:[8]

  1. No debris or only isolated small particles were present
  2. Minimal debris particles present in small clumps
  3. Clumps of debris particles covered <50% of the canal wall
  4. Clumps of debris particles covered more than 50% of the canal wall
  5. Clumps of debris particles covered the canal wall.


Computational fluid dynamics analysis

Analysis of model geometry

The needle dimensions were measured using a precision caliper and shape was obtained through a stereomicroscope. The root canal was simulated as a geometrical frustum of cone 19 mm in length with a diameter of 0.45 mm at full working length and a diameter of 1.59 mm at the canal orifice, 19 mm coronally. The diameter of apical constriction was 0.3 mm and the diameter of apical foramen was 0.35 mm and the needle was constructed to be placed 2 mm short of the working length and centered within the root canal [Figure 1]a.
Figure 1: (a) The root canal and needle assembly in Gambit software (b) The root canal and needle assembly as used in fluent software (c) The turbulent flow pattern of the irrigant at the needle outlet

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Mesh generation

The preprocessor software Gambit 2.2 was used. A structural hexagonal mesh was constructed, with 1,279,856 cells.

Boundary conditions

The fluid was made to flow from the distal end of the needle and out from the orifice of the root canal. The velocity at inlet was 1, 6, 12, 24, and 36 m/s. The irrigant flow rate was 0.02, 0.14, 0.26, 0.53, and 0.79 mL/s and Reynolds number was 177, 1063, 2126, 4253, and 6379, respectively. Turbulence intensity at the inlet was set to 5% and hydraulic diameter was defined as equal to the actual needle diameter. A pressure outlet boundary condition was imposed at the root canal orifice to allow flow of the irrigant, and the atmospheric pressure was assumed at the outlet.

Sodium hypochlorite 2% aqueous solution was modeled as an incompressible Newtonian fluid, with a density equal to 1.04 am/cm cube and viscosity 0.986 10–3.

Initial conditions

The domain was initialized with the irrigant at 50% of the inlet z-velocity, while x-velocity, y-velocity, and gauge pressure were set to zero. Initial values for the turbulence kinetic energy and turbulence dissipation rate were calculated from the corresponding values at the needle inlet [Figure 1]b.

Solver setup

The commercial CFD code FLUENT 6.2 was used to set up and solve the problem and analyze the results. The numerical solution method uses a finite volume approach applied to an unconstructed mesh. A steady and isothermal flow was assumed. The governing time was averaged, and three-dimensional, incompressible Reynolds-averaged-Navier-Equations were solved by a segregated implicit iterative solver.

The inlet flow rate of the needle was set at 0.1 g/s and the turbulent intensity at 0%, which was identical to the in vitro model. At the orifice of the simulated canal, natural outflow boundary conditions were applied. The canal walls and apical foramen were considered rigid and impermeable, and a no-slip condition was applied at the walls. The computation dynamics for different flow rates were compared. The turbulence kinetic energy and turbulence were calculated from the corresponding inlet values for each case. The flow patterns and turbulence were graphically constructed [Figure 1]c.


   Results Top


Within the limitations of this study's experimental conditions, the passive ultrasonic irrigation (mean value: 2.12) and activation of sodium hypochlorite inside the root canal exhibited better debris removal than syringe irrigation (mean value: 3.73). However, the continuous irrigation method (mean value: 1.7) was better at debris removal than the intermittent irrigation flow method (mean value: 2.53). The time used for the various irrigation regimens had a slight difference in the efficacy which did not exhibit any statistical significance.

The one-way ANOVA F-test shows a highly significant difference among the different groups at a 1% level of significance [Table 1].
Table 1: One-way ANOVA F table for significant difference among five groups

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Further, Karl Pearson correlation coefficient shows a strong positive and significant correlation between Group 1 and Group 5, respectively, at a 0.1% level of significance [Table 2].
Table 2: Karl-Pearson correlation coefficient among five groups

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Computational fluid dynamics

The CFD flow model exhibited maximum turbulence at the apical one-third, implying that the displacement magnitude of the tip was maximum at the apical third and that the flow of irrigant is from apical to the coronal end.

The turbulence was dependent on the inlet velocity and pressure of the irrigant flown which is a variable entity. The higher the turbulence, the better will be the debris removal. In the present model, the inlet velocity was kept constant at 1 m/s to be able to evaluate the turbulence model. Hence accordingly, the turbulence was found maximum at the outlet [Graph 1].




   Discussion Top


In this study, the continuous and intermittent passive ultrasonic irrigation methods were compared along with the syringe method of irrigation. It has been seen that syringe irrigation methods are less effective than passive ultrasonic irrigation methods.[3],[4],[9],[10],[11],[12],[13]

The passive ultrasonic continuous and intermittent irrigation methods were compared and evaluated by various researchers.[2],[11],[14],[15] This study confirmed with the earlier found results and found continuous irrigation to be a more efficient method than the intermittent method of passive ultrasonic irrigation. However, the effect of time was insignificant in the present study which was in accordance with certain studies[2],[11] but varied from other studies.[16] This could be due to the amount of irrigant used in the specified time which was kept a variable entity here.

The continuous flow of irrigant helped in the activation of the sodium hypochlorite used and thus better debridement and disinfection of the canal. Sodium hypochlorite has proved over the ages its efficacy and was thus utilized as a standard in the present study. From a clinical point of view, the prevention of extrusion should precede the requirement for adequate irrigant replacement and wall shear stress.[17] In the present study, a thinner gauge needle was used because in various studies,[18],[19] it was observed that thinner gauge needle reached the maximum distance 2 mm short from the apical foramen to simulate a clinical scenario and remove the debris better during the syringe irrigation.

CFD is the science that focuses on predicting fluid flow and related phenomena by solving the mathematical equations that govern these processes; based on an shear stress transport k-u turbulence model, it has the potential to serve as a method for the study of root-canal irrigation.

Preprocessing requirements for CFD according to Cant[20] include that the geometry (physical bounds) of the problem should be defined. The volume occupied by the fluid was divided into discrete cells (the mesh). The mesh may be uniform or nonuniform. The physical modeling should defined, for example, the equations of motions + enthalpy + radiation + species conservation. Boundary conditions should be defined, that is specifying the fluid behavior, properties, and initial conditions at the boundaries of the problem. The simulation was started and equations solved iteratively as a steady state or transient. Finally, a postprocessor is used for the analysis and visualization of the resulting solution.[11],[21],[22]

The CFD model exhibited the turbulent flow of the irrigants in the root canal at various velocities and pressures. The turbulence was maximum at the apical one–third, thus proving the fact that the apical displacement of the irrigant at the apical one-third is of utmost importance for efficient cleaning and debris removal in the root canals. Boutsioukis et al.[23] observed that the root canal has smooth walls and the needle should be accurately placed in the center of the canal in the CFD model, which is inconsistent with real dentine anatomy. Boutsioukis et al.[7] also stated that for the irrigant to reach the working length, the side-vented needle should be placed at 1 mm.

In the present study, the side vented needle was chosen keeping in mind the studies[16],[23],[24] which prove their efficacy and less chances of extrusion of the debris periapically. The needles were kept at a distance of 2 mm from the working length for maximum efficacy of the turbulent flow and avoid extrusion of the debris. The inlet velocity was kept constant to measure the turbulence of the irrigation model which was found maximum at the outlet. This reinforces the already proven fact that the needle should be loose in the canal and kept short of the working length.


   Conclusion Top


Within the limitations of this study, the debris removal from the canals was better with passive ultrasonic irrigation than syringe irrigation. At the same time, it was exhibited that the passive continuous irrigation demonstrated better debris removal than the passive ultrasonic intermittent irrigation. In both continuous and intermittent regimens of irrigation, the effect of time did not have a statistically significant difference. CFD revealed that the turbulence was affected by the velocity and pressure of the irrigant introduced and is a variable entity.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Calberson FL, Deroose CA, Hommez GM, de Moor RJ. Shaping ability of ProTaper nickel-titanium files in simulated resin root canals. Int Endod J 2004;37:613-23.  Back to cited text no. 5
    
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Mayer BE, Peters OA, Barbakow F. Effects of rotary instruments and ultrasonic irrigation on debris and smear layer scores: A scanning electron microscopic study. Int Endod J 2002;35:582-9.  Back to cited text no. 8
    
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van der Sluis LW, Gambarini G, Wu MK, Wesselink PR. The influence of volume, type of irrigant and flushing method on removing artificially placed dentine debris from the apical root canal during passive ultrasonic irrigation. Int Endod J 2006;39:472-6.  Back to cited text no. 9
    
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Lee SJ, Wu MK, Wesselink PR. The efficacy of ultrasonic irrigation to remove artificially placed dentine debris from different-sized simulated plastic root canals. Int Endod J 2004;37:607-12.  Back to cited text no. 10
    
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Jensen SA, Walker TL, Hutter JW, Nicoll BK. Comparison of the cleaning efficacy of passive sonic activation and passive ultrasonic activation after hand instrumentation in molar root canals. J Endod 1999;25:735-8.  Back to cited text no. 11
    
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Rödig T, Sedghi M, Konietschke F, Lange K, Ziebolz D, Hülsmann M. Efficacy of syringe irrigation, RinsEndo and passive ultrasonic irrigation in removing debris from irregularities in root canals with different apical sizes. Int Endod J 2010;43:581-9.  Back to cited text no. 12
    
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Bhuva B, Patel S, Wilson R, Niazi S, Beighton D, Mannocci F. The effectiveness of passive ultrasonic irrigation on intraradicular Enterococcus faecalis biofilms in extracted single-rooted human teeth. Int Endod J 2010;43:241-50.  Back to cited text no. 13
    
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van der Sluis LW, Versluis M, Wu MK, Wesselink PR. Passive ultrasonic irrigation of the root canal: A review of the literature. Int Endod J 2007;40:415-26.  Back to cited text no. 14
    
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Souza CC, Bueno CE, Kato AS, Limoeiro AG, Fontana CE, Pelegrine RA. Efficacy of passive ultrasonic irrigation, continuous ultrasonic irrigation versus irrigation with reciprocating activation device in penetration into main and simulated lateral canals. J Conserv Dent 2019;22:155-9.  Back to cited text no. 15
[PUBMED]  [Full text]  
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Al-Jadaa A, Paqué F, Attin T, Zehnder M. Necrotic pulp tissue dissolution by passive ultrasonic irrigation in simulated accessory canals: Impact of canal location and angulation. Int Endod J 2009;42:59-65.  Back to cited text no. 16
    
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Boutsioukis C, Lambrianidis T, Vasiliadis L. Clinical relevance of standardization of endodontic irrigation needle dimensions according to the ISO 9,626:1991 and 9,626:1991/Amd 1:2001 specification. Int Endod J 2007;40:700-6.  Back to cited text no. 17
    
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Gopikrishna V, Sibi S, Archana D, Pradeep Kumar AR, Narayanan L. An in vivo assessment of the influence of needle gauges on endodontic irrigation flow rate. J Conserv Dent 2016;19:189-93.  Back to cited text no. 18
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Cant S. High-performance computing in computational fluid dynamics: Progress and challenges. Philos Trans A Math Phys Eng Sci 2002;360:1211-25.  Back to cited text no. 20
    
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Clarkson RM, Moule AJ. Sodium hypochlorite and its use as an endodontic irrigation. Int Endod J 1998;43:4.  Back to cited text no. 22
    
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Boutsioukis C, Lambrianidis T, Verhaagen B, Versluis M, Kastrinakis E, Wesselink PR, et al. The effect of needle-insertion depth on the irrigant flow in the root canal: Evaluation using an unsteady computational fluid dynamics model. J Endod 2010;36:1664-8.  Back to cited text no. 23
    
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Gu LS, Kim JR, Ling J, Choi KK, Pashley DH, Tay FR. Review of contemporary irrigant agitation techniques and devices. J Endod 2009;35:791-804.  Back to cited text no. 24
    

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Correspondence Address:
Dr. Preeti Mishra
Department of Conservative Dentistry and Endodontics, Subharti Dental College and Hospital, Swami Vivekanand Subharti University, Meerut, Uttarakhand
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcd.jcd_636_20

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