Performance simulation study of a modified root canal irrigation needle based on computational fluid dynamics

To compare using computational fluid dynamics (CFD) the flow pattern, irrigant velocity, apical pressure and shear stress produced by negative (MiC) and positive pressure with different types of needles (side-vented (SV), front-vented (FV) and notched (N)) at two insertion depths in the apical ramification of oval root canals. The micro-CT of a mandibular molar with an oval root canal with an apical ramification was used for computational analysis after preparation and geometric reconstruction. Geometries with the needles in two positions (1 and 3mm from WL) were created to run the simulations. Key parameters of irrigation were displayed with CFD and compared. The penetration depth of the needle in the root canal strongly influenced shear stress and apical pressure. The three needles revealed that the highest shear stress, velocity and apical pressure were 1mm from the WL and generated medium velocities. In N simulations, the fluid flow did not reach the apical ramification and the lowest shear stress values for positive pressure needles were found. The predominant axial component for FV revealed a different pattern of irrigation with high shear stress values and higher apical pressures than those exerted by other needles. SV simulations had generalized fluid flow in most of the main canal, the highest shear stress values and lower apical pressure than the threshold determined for risk of extrusion. MiC was associated with low velocity, shear stress and apical pressure. The SV needle demonstrated a combination of low positive pressure and high shear stress; while N had the lowest shear stress and FV the highest apical pressure. MiC generated fluid flow in part of the apical ramification with negative apical pressure values but low shear stress and velocity.

This study aimed to investigate the irrigation dynamics of the positive pressure side-vented (SV) needle, EndoVac (micropores) needle and modified apical negative pressure (mANP) open-ended needle using computational fluid dynamics (CFD). A simulation of a prepared root canal (conical frustum) of 15 mm length with an apical diameter of 0.40 mm following Protaper F4 apical preparation was created using three-dimensional (3D) CAD software. The 3D simulated needle of SV 30G needle, EndoVac with micropores needle and mANP, 30G flat open-ended needle were also created. The irrigation dynamics were evaluated through transient CFD simulations. In addition, the irrigation dynamics of mANP at 0.2 mm, 0.5 mm, and 1.0 mm short from the working length were also assessed. The EndoVac and mANP showed negative apical static pressure and streamline patterns able to reach the apical region, thus indicating negligible extrusion. Meanwhile, SV showed positive apical static pressure and almost nonexistent streamlines beyond the needle tip. The SV showed the highest wall shear stress (WSS) magnitude of 1030Pa whereas Endovac (161 Pa) and mANP1 (258 Pa). However, SV revealed lower average WSS (10 Pa) compared to mANP1 (13 Pa) and mANP2 (11 Pa). This is due to SV developed a localised maximum WSS opposite the open vent area only therefore, uneven distribution of WSS. The EndoVac system developed a localised maximum WSS in the pair of micropores furthest away from the apical. CFD analysis of the EndoVac, mANP and SV showed different technique approach, needle design and needle depths insertion affect the irrigation dynamics pattern and magnitude.

This study evaluated different irrigation methods in smear layer removal from the root canal walls using maleic acid (MA). Maxillary anterior teeth (N=30, n=10 per group) were decoronated, canals were enlarged with Protaper (size F4) and allocated to three groups: EndoUltra: 2.5 ml of 7% MA was irrigated for 30 s, followed by EndoUltra activation for 30 s; EndoSafe: EndoSafe irrigation system was used for 1 minute using 5 ml of 7% MA; Side-vented needle: 30 gauge needle irrigation was performed for 1 min using 5 ml of 7% MA. After SEM analysis, the inter-examiner reliability was verified using Kendall's Co-efficient and data were analyzed using Pearson Chi-Square test. No statistical significant differences were found between the two examiners (p⟩0.05). In intra-group comparison, needle and EndoSafe irrigation demonstrated significantly better smear layer removal at middle third of the root canal system (p⟨0.05) when compared to apical third. In inter-group comparison, smear layer was minimally removed with needle irrigation. In the apical third, EndoUltra group removed smear layer more effectively. Endosafe needle irrigation in combination with 7% MA removed the smear layer in the root canal at best, while the EndoUltra performed the best at the apical third of the root.

Background: Endodontic irrigation with 5.25% sodium hypochlorite (NaOCl) solution using single side-vented and double side-vented needles is commonly used. Surfactant is added to reduce high surface tension of the NaOCl solution. Apical vapor lock, or air entrapment inside closed-end root canal system, lowers the efficacy of irrigants. Thus, the irrigants are hindered in penetrating the root canal system and can lead to risk of reinfection. Objective: The objective is to analyze the difference of 5.25% NaOCl solution with and without surfactant using two types of irrigation needle in the formation of apical vapor lock. Methods: Forty lower premolars were prepared and randomly divided into four groups (n = 10 per group) then irrigated with 5.25% NaOCl solution with and without surfactant using a single side-vented or double side-vented needle. Contrast medium was added so that the measurement of the apical vapor lock could be performed using a digital radiograph. Analysis was done with two-way analysis of variance and the Tukey method. Results: 5.25% NaOCl solution with a single side-vented needle showed a significant difference from 5.25% NaOCl solution with a double side-vented needle. 5.25% NaOCl solution with a surfactant using a single side-vented needle showed a significant difference from 5.25% NaOCl solution using a double side-vented needle, likewise NaOCl 5.25% using double side-vented needle group from NaOCl 5.25% with surfactant using single side-vented needle group. Conclusion: Minimal formation of an apical vapor lock resulted from the use of 5.25% NaOCl solution with a surfactant using a single side-vented needle.

Root canal irrigation is an important step in root canal preparation procedures and has a great impact on the success rate of root canal treatment. Computational fluid dynamics (CFD) is a new method to study root canal irrigation. It can be used to simulate and visualize the process of root canal irrigation, and quantitatively evaluate the effect of root canal irrigation through parameters such as flow velocity and wall shear stress. In recent years, researchers have conducted extensive studies on the factors that influence root canal irrigation efficiency, such as the position of the irrigation needle, the size of root canal preparation, the types of irrigation needles, and so on. This article reviewed the development of root canal irrigation research methods, the steps of CFD simulation in root canal irrigation, and the application of CFD in root canal irrigation in recent years. It aimed to provide new research ideas for the application of CFD to root canal irrigation and to provide a reference for the clinical application of CFD simulation results.

A digital holographic microscope is used to simultaneously measure the instantaneous 3D flow structure in the inner part of a turbulent boundary layer over a smooth wall, and the spatial distribution of wall shear stresses. The measurements are performed in a fully developed turbulent channel flow within square duct, at a moderately high Reynolds number. The sample volume size is 90 × 145 × 90 wall units, and the spatial resolution of the measurements is 3–8 wall units in streamwise and spanwise directions and one wall unit in the wall-normal direction. The paper describes the data acquisition and analysis procedures, including the particle tracking method and associated method for matching of particle pairs. The uncertainty in velocity is estimated to be better than 1 mm/s, less than 0.05% of the free stream velocity, by comparing the statistics of the normalized velocity divergence to divergence obtained by randomly adding an error of 1 mm/s to the data. Spatial distributions of wall shear stresses are approximated with the least square fit of velocity measurements in the viscous sublayer. Mean flow profiles and statistics of velocity fluctuations agree very well with expectations. Joint probability density distributions of instantaneous spanwise and streamwise wall shear stresses demonstrate the significance of near-wall coherent structures. The near wall 3D flow structures are classified into three groups, the first containing a pair of counter-rotating, quasi streamwise vortices and high streak-like shear stresses; the second group is characterized by multiple streamwise vortices and little variations in wall stress; and the third group has no buffer layer structures.

Bioreactor systems, for example, spinner flask and perfusion bioreactors, and cell-seeded three-dimensional (3D)-printed scaffolds are used in bone tissue engineering strategies to stimulate cells and produce bone tissue suitable for implantation into the patient. The construction of functional and clinically relevant bone graft using cell-seeded 3D-printed scaffolds within bioreactor systems is still a challenge. Bioreactor parameters, for example, fluid shear stress and nutrient transport, will crucially affect cell function on 3D-printed scaffolds. Therefore, fluid shear stress induced by spinner flask and perfusion bioreactors might differentially affect osteogenic responsiveness of pre-osteoblasts inside 3D-printed scaffolds. We designed and fabricated surface-modified 3D-printed poly-ɛ-caprolactone (PCL) scaffolds, as well as static, spinner flask, and perfusion bioreactors to determine fluid shear stress and osteogenic responsiveness of MC3T3-E1 pre-osteoblasts seeded on the scaffolds in the bioreactors using finite element (FE)-modeling and experiments. FE-modeling was used to quantify wall shear stress (WSS) distribution and magnitude inside 3D-printed PCL scaffolds within spinner flask and perfusion bioreactors. MC3T3-E1 pre-osteoblasts were seeded on NaOH surface-modified 3D-printed PCL scaffolds, and cultured in customized static, spinner flask, and perfusion bioreactors up to 7 days. The scaffolds' physicochemical properties and pre-osteoblast function were assessed experimentally. FE-modeling showed that spinner flask and perfusion bioreactors locally affected WSS distribution and magnitude inside the scaffolds. The WSS distribution was more homogeneous inside scaffolds in perfusion than in spinner flask bioreactors. The average WSS on scaffold-strand surfaces ranged from 0 to 6.5 mPa for spinner flask bioreactors, and from 0 to 4.1 mPa for perfusion bioreactors. Surface modification of scaffolds by NaOH resulted in a surface with a honeycomb-like pattern and increased surface roughness (1.6-fold), but decreased water contact angle (0.3-fold). Both spinner flask and perfusion bioreactors increased cell spreading, proliferation, and distribution throughout the scaffolds. Perfusion, but not spinner flask bioreactors more strongly enhanced collagen (2.2-fold) and calcium deposition (2.1-fold) throughout the scaffolds after 7 days compared with static bioreactors, likely due to uniform WSS-induced mechanical stimulation of the cells revealed by FE-modeling. In conclusion, our findings indicate the importance of using accurate FE models to estimate WSS and determine experimental conditions for designing cell-seeded 3D-printed scaffolds in bioreactor systems. Impact Statement The success of cell-seeded three-dimensional (3D)-printed scaffolds depends on cell stimulation by biomechanical/biochemical factors to produce bone tissue suitable for implantation into the patient. We designed and fabricated surface-modified 3D-printed poly-ɛ-caprolactone (PCL) scaffolds, as well as static, spinner flask, and perfusion bioreactors to determine wall shear stress (WSS) and osteogenic responsiveness of pre-osteoblasts seeded on the scaffolds using finite element (FE)-modeling and experiments. We found that cell-seeded 3D-printed PCL scaffolds within perfusion bioreactors more strongly enhanced osteogenic activity than within spinner flask bioreactors. Our results indicate the importance of using accurate FE-models to estimate WSS and determine experimental conditions for designing cell-seeded 3D-printed scaffolds in bioreactor systems.

We compared differences in the hemodynamic parameters of multiple surgical techniques for supravalvular aortic stenosis (SVAS). A three-dimensional model was reconstructed based on a patient's CT scan. Virtual McGoon, Doty, and Brom repairs were completed using computer-aided design (CAD). Hemodynamic parameters were calculated through computational fluid dynamics (CFD). The velocity profile and wall shear stress (WSS) showed the blood flow pattern. Energy loss (EL) and energy efficiency (EE) were calculated to estimate the cardiac workload. The perioperative blood flow ratio (BFR) of brachiocephalic vessels and coronary arteries was calculated. The preoperative flow velocity was abnormally high (> 5.0m/s). High WSS was detected at the sinotubular junction (STJ), and its preoperative distribution in the aorta was uneven. High-speed flow disappeared after each of the three operations. The WSS distribution at the aortic root was consistent with the postoperative STJ structure of each operation. EL in the systolic phase decreased postoperatively (Original: 634 mW, McGoon: 218 mW, Doty: 278 mW, Brom: 255 mW). No significant difference in brachiocephalic BFR was detected among the different techniques. A slightly increased coronary BFR (Original: 7.56%, McGoon: 7.99%, Doty: 8.55%, Brom: 8.89%) was detected. McGoon, Doty, and Brom repair each effectively restored stable blood flow and greatly improved EE. The best WSS distribution and coronary blood supply were achieved after Brom repair due to its ability to reconstruct the symmetrical aortic root structure. CFD combined with a virtual operation is a promising method in surgical planning and optimization for SVAS.

Evaluation of the influence of inlet boundary conditions on computational fluid dynamics for intracranial aneurysms: A virtual experiment

Coronary artery bypass graft (CABG) operation for coronary artery disease with different types of grafts has a large clinical application world wide. Immediately after this operation patients are usually relieved of their chest pain and have improved cardiac function. However, after a while, these bypass grafts may fail due to for example, neointimal hyperplasia or thrombosis. One of the causes for this bypass graft failure is assumed to be the blood flow with low wall shear stress. The aim of this research is to estimate the wall shear stress in a graft and thus to locate areas were wall shear stress is low. This was done with the help of a blood flow computer model. Post-operative biplane angiograms of the graft were recorded, and from these the three-dimensional geometry of the graft was reconstructed and imported into the computational fluid dynamics (CFD) program FLUENT. The stationary diastolic flow through the grafts was calculated, and the wall shear stress distribution was estimated. This procedure was carried out for one native vessel and two different types of bypass grafts. One bypass graft was a saphenous vein and the other one was a varicose saphenous vein encased in a fine, flexible metal mesh. The mesh was attached to give the graft a defined diameter. The computational results show that each graft has distinct areas of low wall shear stress. The graft with the metal mesh has an area of low wall shear stress (< 1 Pa, stationary flow), which is four times smaller than the respective areas in the other graft and in the native vessel. This is thought to be caused by the smaller and more uniform diameter of the metal mesh-reinforced graft.

Introduction: Cerebral aneurysm is a cerebrovascular disease resulting to subarachnoid hemorrhage. The generation, development and finally rupture of cerebral aneurysm could be related to hemodynamic stimulate, especially wall shear stress (WSS). WSS have been considered to play a role on the expression of such enzymes as iNOS, MMP-2 and MMP-9 leading to weakening of the arterial wall. However, detailed WSS distribution contributing to the enzyme expression has not been clarified inside cerebral artery. The purpose of our study is to clarify the WSS distribution corresponding to the enzyme expressions. Materials and Methods: We tried to induce cerebral aneurysm on rabbits, and created the realistic silicone model of the induced aneurysm. The flow field and WSS were measured using PIV (particle image velocimetry) and LDV (laser Doppler velocimeter) inside the realistic model. Furthermore, histological structure and enzyme expression were evaluated on the image of elastica van Gieson stain and on the immunostaining images. Results: Induced cerebral aneurysms were found in posterior circulation; the arterial bifurcation at basilar artery or posterior communicating artery. The induced cerebral aneurysm had an arterial wall structure with thinned media and lacked IEL. The thinned media was observed at the bulge top area wth low WSS distribution. On the other hand, lacked IEL was observed near the aneurysm neck area. Although WSS was not so low at the area of lacked IEL, the WSS spatial gradient appeared with high value at this area. The lack of occurs before the thinning of media on the process of aneurysm formation. In addition, MMP-2 and MMP-9 showed similar trend as the WSS spatial gradient. From these findings, high WSS gradient seems to have an effect on the early stage of cerebral aneurysm generation, stimulating the enzymes expression which leads to the destruction of the IEL.

The significant progress in computer innovation technique, computational fluid dynamics (CFD) has been applied for real applications on patient-specific hemodynamics and extensively used to study cerebral aneurysm rupture. In addition, the computational study with representative blood vessel configuration has become a great tool in providing comprehensive information on geometry, the flow field of blood and wall shear stress (WSS). Generally, the numerical simulations have an expected problem on the specification of the exact boundary conditions which leads to unphysical numerical solutions. Therefore, this paper tends to find out whether CFD simulation manages to obtain precise and better predictions of hemodynamics patterns at present time especially for phase-contrast magnetic resonance imaging (PC-MRI) in terms of the velocity flow field and WSS distribution. Several research articles are included and their qualitative and quantitative results on hemodynamics have been compared. Both MRI measurement and CFD simulation have reasonably good agreement on velocity flow fields and a detailed spiral recirculating flow pattern can be observed in CFD simulation as compared to MRI measurement instead. However, CFD simulation has overestimated the WSS, especially at the maximum WSS location. The CFD simulation is capable to achieve good agreement on velocity flow fields with MRI measurement, yet the result for WSS distribution has to be further improved and justified with consistent assumptions and techniques.

Background: The pathophysiology of internal carotid artery (ICA) blister aneurysms is poorly understood. Our goal is to investigate the hemodynamic factors contributing to their formation and progression using computational fluid dynamics. Methods: We developed software allowing 3D reconstruction of type I and II blister aneurysms (Bojanowski et al., 2015) from ICA angiography. Kinematic blood flow data was obtained using a finite volume solver. We compared the wall shear stress distribution (WSS) of the healthy arterial wall under various blood pressure conditions. Results: WSS was maximal on the dorsal wall of the supraclinoid segment of the ICA at the distal part of the future site of the aneurysm sac, suggesting that the aneurysm sac initially develops in a retrograde fashion. The WSS gradient (WSSG) was maximal at both the proximal and distal boundaries of the bulging aneurysm. Hypertension exponentially exacerbates the WSS distribution. Very low WSS associated with a high WSSG at the proximal part of the aneurysm sac could explain the extension of the hemorrhage proximal to the forming blister. Conclusions: WSS and its gradient participate in the formation and progression of blister aneurysms of the supraclinoid segment of the ICA. Increasing blood pressure contributes exponentially to the formation of blister aneurysms.

Root canal system cleaning and disinfection is one of the most important steps to achieve endodontic treatment success. Mechanical preparation besides cleaning allows root canal irrigation to reach deeper and inaccessible areas to this mechanical preparation in the root canal system. Using chemical active substances, root canal irrigation tries to provide a chemical action along the root canal system but also a mechanical action where it removes the debris along it through the flow it creates. The effectiveness of this is quite related to the anatomy of the root canal system, the more complex it is the more difficult is to obtain this cleaning and disinfection. Mesial roots of lower molars are one of the examples where this kind of complex anatomy can be present in a high percentage, namely with the presence of isthmuses that aren’t most of the time mechanically prepared and are trusted to be disinfected and cleaned only by root canal irrigation. Side vented needles are used mainly for safety reasons, to avoid irrigant extrusion through the foramen, however, due to their lateral exit tip, they can be more prone to deliver the irrigant in complex anatomic areas of the root canal system, such as lateral canals or isthmuses compared to flat ended needles. The aim of this study was to evaluate the flow created with a 30G side vented and a 30G flat-ended needle in a Vertucci type II canal with the presence of an isthmus using computational fluid dynamics. Two domains were used and compared in terms of flow pattern. In both root canal was obtained from a mesial root of a mandibular molar, scanned by computed tomography (CT) providing a three-dimensional object that was exported to the computer-assisted design (CAD) software. A CAD model of a 30G side-vented irrigation needle and a 30G flat-ended needle were created, placed 3mm from the apical foramen and subtracted to the root canal providing two different domains for the two different needles but the same anatomy. The flow pattern obtained shows that flat ended needles provide a more favorable result in terms of what is expected from the mechanical objectives of irrigation.

Computational fluid dynamic analysis (CFD) is claimed to be a reliable tool for analysing the fluid flow and the generated apical pressures in the simulated root canal. The current study aimed to analyse the apical pressures in extracted teeth with single and joining canals. Forty-six freshly extracted teeth were collected for the present study. The power was set at 95%, with an effect size of 0.55 (1-β=95%, α=0.05). Once the root canal anatomy was confirmed with cone-beam computed tomography (CBCT), they were divided into two groups: group I: mandibular second premolars with Vertucci type-I (n=23), and group II: maxillary second premolars with Vertucci type-II (n=23). The instrumentation of the specimens was carried out to a 0.04-taper using rotary instruments. A post-instrumentation CBCT was obtained, and computer-aided design models were obtained. The CFD simulations were then con- ducted with simulated 30-gauge side vented needles at 25, 50, and 75% short of the working length (WL). Group I recorded significantly (p<0.05) higher apical pressures at needle positions 25% short of the WL. However, no significant differences were elicited in the groups at other needle positions. Single canal specimens recorded higher apical pressures at needle positions 25% short of the WL. However, no differences were elicited between single and joining canals at higher needle positions.