Endodontology

ORIGINAL ARTICLE
Year
: 2022  |  Volume : 34  |  Issue : 4  |  Page : 242--247

Evaluation of irrigant flow in the root canal isthmus region using a computational fluid dynamics model


Anchu Rachel Thomas1, Dhanasekaran Sihivahanan2, Ranjith Kumar Sivarajan2,  
1 Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Manipal University College Malaysia, Melaka, Malaysia
2 Department of Conservative Dentistry and Endodontics, SRM Kattankulathur Dental College, Kanchipuram, Tamil Nadu, India

Correspondence Address:
Dr. Anchu Rachel Thomas
Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Manipal University College Malaysia, Jalan Batu Hamper, Bukit Baru, Melaka 75150
Malaysia

Abstract

Aim: The aim of this study was to evaluate the irrigation dynamics of irrigant delivery systems and irrigating solutions in the root canal isthmus region of a mandibular premolar using computational fluid dynamics (CFD). Methods: A CFD model of the mandibular premolar with the root canal isthmus was created using scanned microcomputed tomography images. Using this CFD model, the irrigant flow in the root canal isthmus region was visualized. The irrigation dynamics of three irrigant delivery systems – Group 1: syringe irrigation (open-ended), Group 2: EndoVac irrigation system, and Group 3: modified EndoVac system were studied and compared to assess the efficiency. Following which, the wall shear stress, streamline of irrigant in the isthmus region, and irrigant velocity were evaluated. Results: Group 1 (open-ended needle) presented with the highest wall shear stress as compared to other groups, restricted to the apical third. All groups exhibited maximum velocity at the region of irrigant exit followed by a gradual decline in the isthmus and coronal region. It was observed that only Group III (Modified EndoVac) displayed a flow of irrigant in the isthmus region. Conclusions: The modified EndoVac system was efficient in delivering the irrigating solutions to the isthmus region.



How to cite this article:
Thomas AR, Sihivahanan D, Sivarajan RK. Evaluation of irrigant flow in the root canal isthmus region using a computational fluid dynamics model.Endodontology 2022;34:242-247


How to cite this URL:
Thomas AR, Sihivahanan D, Sivarajan RK. Evaluation of irrigant flow in the root canal isthmus region using a computational fluid dynamics model. Endodontology [serial online] 2022 [cited 2023 Jan 28 ];34:242-247
Available from: https://www.endodontologyonweb.org/text.asp?2022/34/4/242/365813


Full Text



 Introduction



The success of endodontic therapy is contingent on the efficient removal of pulp tissue, microorganisms, and microbial toxins from the root canal system.[1],[2],[3] However, the intricate nature of the root canal system renders it impossible to completely clean and shape the canal.[4] Even after complete instrumentation with nickel–titanium instruments, the canal fins, isthmus, and cul-de-sacs remain untouched.[5] These regions foster tissue debris and microbial by-products resulting in persistent periradicular inflammation.[6]

Irrigation plays a pertinent role in improving canal debridement as it allows for cleaning beyond what might be obtained by instrumentation alone.[7] Commonly used irrigating solutions include sodium hypochlorite (NaOCl), chlorhexidine, and ethylenediaminetetraacetic acid have been used with varying concentrations for canal disinfection.

Syringe-needle irrigation being the commonly used irrigation method has various limitations which include the inability to completely flush the debris, vapor lock effect, and periapical extrusion. To overcome these limitations, apical negative pressure system (EndoVac) was introduced. However, both the EndoVac and the conventional syringe-needle irrigation were found to be ineffectual in the disinfection of the root canal isthmus region.[8],[9] It was reported that the modified EndoVac technique was found to be effective in the debridement of the isthmus region.[10]

The number of factors influence the effectiveness of the irrigating solution and irrigant delivery system.[11] Effective irrigation depends on the exchange of irrigants along the entire length of the root canal, including lateral canals and canal isthmuses.[12] Several studies have highlighted the importance of direct contact of the irrigant solution on the entire canal wall for effective action, the isthmus region, particularly the apical portion of the canal.[13] However, no research has been conducted to check the flow pattern of irrigants in the root canal isthmus region.

Computational fluid dynamics (CFD) is a branch of fluid dynamics that analyses problems concerning fluid flow using computer-based simulations.[14] CFD has been used as a powerful tool to study the irrigant flow by simulating the real-time flow of irrigants inside the root canal. Previous studies using CFD have examined the irrigation dynamics in a single canal and a C-shaped canal.[12],[15] However, no studies have been reported to assess the fluid dynamics in the canal irregularities and isthmus regions of a mandibular premolar using a closely simulated CFD model.

Thus, the aim of the study is to compare the wall shear stresses, streamline of irrigant in the isthmus region, and velocity of different irrigant delivery systems in the root canal isthmus region using a CFD model.

 Materials and Methods



Institutional ethical clearance was obtained for conducting this research. Thirty human mandibular premolar teeth extracted for orthodontic reasons were selected for the study. Teeth with immature apex, caries, and fractures were excluded from the study. Based on the inclusion criteria, the selected teeth were scanned using microcomputed tomography (CT) imaging (Bruker Singapore Pte. Ltd, Biopolis Street, Matrix, Singapore) device to check and confirm the presence of isthmus connecting the two canals. Based on this criterion, one mandibular premolar with an isthmus connecting the two canals was selected for the study.

Based on the preoperative images, access opening was done under a surgical operating microscope (EDI Dental Supply, Shah Alam, Selangor, Malaysia). Size 10-K file (NTC Dental Suppliers, Metro Prima, Kuala Lumpur, Malaysia) was used for canal negotiation, and the working length was determined by passing the file beyond the apex and subtracting 0.5 mm from the apex. Cleaning and shaping were done using proper universal rotary file system to size F3 #30/0.9% (Dentsply Sirona APAC, Petaling Jaya, Selangor, Malaysia). During the instrumentation, the debris was flushed out using 6 ml of saline.

Following instrumentation, the canals were rescanned by microCT imaging. From the cross-sectional slice, images are obtained; a three-dimensional root canal model is segmented, reconstructed, and exported in the standard template library format by Materialise Mimics software (Materialise, Petaling Jaya Selangor Darul Ehsan, Malaysia). Based on the postoperative microCT images, a CFD model of the mandibular premolar was created. The dimensions (length and diameter) of the open-ended needle, microcannula, side-vented needle, and macrocannula were taken from previous research.[12],[15] CFD models of the irrigation devices were generated based on the measurements and further divided into the following groups:

Group I: Open-ended needle

Group II: Microcannula (EndoVac needle)

Group III: Modified EndoVac (Macrocannula and side-vented needle).

For the Group I, open-ended needle, a cylindrical 30G needle was designed with an external diameter of 0.320 mm and an internal diameter of 0.196 mm. In Group 2, the microcannula comprised four rows of three opening vents measuring about 0.1 μm in diameter, the vents were positioned between 0.2 mm and 0.7 mm from the tip. The diameter of the microcannula was measured as 0.32 mm. The macrocannula for the modified EndoVac technique in Group IV had an external diameter of 0.55 mm, an internal diameter of 0.35 mm, and 0.02 taper.[16] The side-vented needle had a side vent with dimensions 0.2 mm × 0.1 mm to the needle designed for the open-ended needle.

Frequently used irrigating solution clinically, 5.25% of NaOCl was selected for the study. The density and viscosity of the irrigating solution were measured and modeled as an incompressible, Newtonian fluid. The viscosity of NaOCl was equal to 1.0 × 10−3 kg/m-s and the density was 998.2 kg m−3. To stimulate clinical irrigation conditions, the inlet flow rate of the needle was set at a flow inlet of 0.1 g/s (6 mL/min), consistent with a clinically realistic rate. The CFD model settings were based on the conditions given in the previous research.[12]

 Results



Wall shear stress distribution

Group I exhibited a region of flow extending approximately 1 mm apical to the tip of the needle, with the maximum wall shear stress observed at the apical region following a gradual decline toward the isthmus and coronal region [Figure 1]a.{Figure 1}

Group II exhibited a region of flow extending approximately 1 mm apical to the tip of the needle, with the maximum wall shear stress observed at a small region on the proximal wall adjacent to the microcannula vents following a gradual decline toward the apical and complete reduction in the isthmus and coronal regions. Several small jets were formed by the irrigant exiting from the six outlets proximal to the tip of the needle. The most intense jet of irrigant flow and wall stress was displayed by the outlets approximal to the wall [Figure 1]b.

Group III displayed a region of flow toward the proximal walls adjacent to the tip of the needle, with maximum wall shear stress observed on the proximal walls adjacent to the side vents of the needle followed by a reduction in the apical region and further decline in the isthmus and coronal regions [Figure 1]c.

Group I presented with maximum wall pressure in the apical third. The pattern of stress concentration on the canal walls was similar between Groups II and III with maximum stress concentrated on the proximal wall facing the outlet.

Velocity

Group I (open-ended) displayed maximum irrigant velocity at the exit of the needle and decreased in the isthmus and coronal region. Group II (EndoVac Microcannula) exhibited maximum irrigant velocity abutting the vents of the microcannula followed by a gradual decrease in the isthmus and coronal region. Group III (Modified EndoVac) showed similar irrigant velocity as Group II, with the maximum at the region proximal to the side vents of the needle and a gradual decline at the isthmus coronal region [Table 1].{Table 1}

Streamline of irrigant and accessibility to the isthmus region

Group I (open-ended): Following the discharge of irrigant in one canal, the flow is limited to the region surrounding the tip of the needle succeeded by a backward descent of irrigant through both the canals. The streamline backflow is unidirectional and uniform leaving the isthmus region untouched [Figure 2]a.{Figure 2}

Group II (Microcannula): The streamline patterns indicate two paths, one uniform backflow flow directed to the canal orifice from the region of the microcannula vents and another path of irrigant flow proceeding apically 1 mm and then backward to the canal orifice. The isthmus region was not covered in the irrigant backflow [Figure 2]b.

Group III (Modified EndoVac) showed uniform streamline backflow patterns with a significant flow observed in the isthmus region. The backflow had a turbulent flow pattern encompassing the macrocannula in a swirling turbulent motion up to the coronal portion [Figure 2]c.

 Discussion



CFD is an effective device which is used for studying the irrigant flow pattern inside the root canal system. CFD devices help in providing measurements of the velocity and the shear stress of fluids through mathematical modeling and computer simulations.[17],[18] Although CFD uses computer-based analysis, it provides fundamental information on the fluid dynamics within the root canal system.[15]

The current research studied the irrigant fluid dynamics in a mandibular premolar CFD model as the literature suggests that mandibular premolar exhibits a high degree of complexities in anatomy.[19] The management of the root canal isthmus is a challenge, as they serve as inaccessible regions for instruments, irrigation solutions, and medicaments and are potential reservoirs for microbes, often leading to the failure of a conventional root canal treatment.[20] These ribbon-shaped passages have circumscribed openings, with surface tension barriers[12] preventing efficient irrigant exchange in the isthmus region.

Previous studies using CFD models reported limitations associated with simulating canal irregularities, which in turn affected the irrigation dynamics. To overcome the limitation associated with the canal irregularities and to obtain exact clinical relevance and simulation, a CFD model was developed based on the preoperative and postoperative microCT images. Furthermore, the canals were instrumented till an apical size of 30 with 9% taper to provide better exchange and penetration of irrigants inside the root canals.[21] The irrigation devices were modeled based on measurements obtained from previous research[15],[16] and geared to evaluate the wall shear stress, velocity, irrigant streamline, and flow pattern of three irrigating solutions. Since, mathematical modeling gives a single value for each experimental setup, with no disparity between analogous experiments, statistical testing is seldom a part of CFD analysis in the literature.

It has been established that there is a strong correlation between wall shear stress and streamwise velocity,[22] in addition, the velocity of the irrigant has a direct effect on the exchange of irrigant in the root canal.[23] Irrigant streamlines allow qualitative examination of the flow field and represent the path taken by weightless particles released from the irrigant delivery system and their trajectories help in viewing the irrigant main flow in different dimensions.[24] The intensity of the irrigant streamline highlights the degree of irrigant penetration[23] and the backflow of irrigant to the orifice exhibits complete replacement irrespective of the irrigant delivery system.

Based on a previous CFD research, the needles were placed 3 mm short of the working length to evaluate the pattern of fluid flow apically[23] and the apical foramen was simulated as an impermeable wall for the purpose of evaluating the pressure applied in the apical region and the possibility of extrusion of irrigant by the irrigant delivery systems.

The irrigant flow pattern depended on the mode of the irrigant delivery system. All the groups exhibited the highest irrigant velocity at the exit of the needle with a gradual decrease seen toward the isthmus and the least, as the fluid proceeded coronally. The open-ended needle exhibited significant flow, approximately 1 mm apical to the tip of the needle. The maximum stress was concentrated in the apical region followed by a decline in the isthmus and coronal region, expecting significant disruption of bacterial biofilm and dentin debris detachment in the apical region. These findings agree with a previous study reporting the efficient removal of collagen film[24] in the apical region in proximity to the needle outlet. It has also been reported that an increase in irrigant exchange in the apical area instinctively led to an increase in mean pressure in this region enhancing the risk of irrigant extrusion in the periapical region.[23]

In the EndoVac microcannula subgroups, maximum irrigant flow and wall pressure exerted by the irrigant were observed in small regions near the proximal walls adjacent to the irrigant exit followed by a gradual decrease toward the apical, isthmus, and coronal region. The apical negative pressure irrigation exhibited the lowest maximum wall shear stresses, which could imply that there was minimum mechanical interaction between the irrigant and the root canal wall, emphasizing the need for the placement of the needle close to the working length.[25]

The Modified EndoVac subgroups had irrigant flowing proximally, with maximum stress exerted in the proximal region adjacent to the irrigant exit. The rapid descent of the irrigant up the macrocannula could play an important role with respect to its ability to permit better penetration of the irrigant to the inaccessible areas of the root canal, and potentially enhance the interaction of irrigants with intracanal biofilms.

Previous research concluded that the distribution of shear stress along the root canal bestows light on the efficacy of each irrigant delivery system.[15] It has been reported that in pipe flow, the mean wall shear stress and increased flow rate influence the bacterial removal, which could conclude that the mean wall shear stress can be an important finding in terms of assessing the cleaning efficiency of an irrigant delivery systems.[26] Velocities greater than 0.1 m/s are considered clinically significant for sufficient irrigant replacement. Hence, higher the velocity of the irrigant, rapid and requisite replacement of irrigant takes place.[18]

The streamlined flow of the irrigant in the open-ended needle group showed two paths of the irrigant flow, laminar and unidirectional with the isthmus region being untouched. EndoVac microcannula group showed one uniform backflow flow to the coronal portion and other extending a little apically, with the isthmus region untouched. The modified EndoVac group exhibited uniform streamlines of the irrigant with significant flow traversing the isthmus region.

The prime objective of the study is to assess the flow pattern of the irrigant in the isthmus region. It was observed that only the Group III modified EndoVac system was able to deliver the irrigant across the isthmus region. The simultaneous delivery of the irrigant with the side-vented needle and the vacuum forces from the microcannula could have enabled the irrigant to be pulled across the isthmus region. The point of needle placement and the volume of irrigant delivered could also play an important part in the movement of irrigant across the isthmus region.

It has been studied that, in a rapid flow, a fine viscous underlying layer is formed next to the wall, where turbulent mixing is disrupted, and fluid movement occurs partially or completely by viscous diffusion.[27] In this research, a rapid swirl of irrigant backflow was observed in the modified EndoVac irrigation group, which could have aided the irrigant to flow into the inaccessible isthmus region.

It was also observed that the exchange of irrigant and the depth of the needle placement plays an important role in the efficient debridement of the root canal and its complex anatomy.

This research did not include the passive ultrasonic irrigation system, which is reported to be the most effective in root canal isthmus debridement, due to certain limitations while conducting the CFD analysis. Hence, further studies assessing the fluid dynamics of other irrigation systems should be carried out for more successful root canal therapy in teeth with canal isthmuses.

 Conclusions



The exchange of irrigant in the isthmus region was displayed only in the modified EndoVac group compared to the other groups, and additionally, it was observed that the irrigant penetration to the inaccessible areas of the root canal was entirely dependent on the irrigant delivery system and not the choice of the irrigant used.

Acknowledgment

The authors deny any potential conflict of interest.

Financial support and sponsorship

Self-funded.

Conflicts of interest

There are no conflicts of interest.

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