Divergent Walls Research Articles

Control effect on the divergent and convergent riblets in particle-laden turbulent boundary layer

Particle image velocimetry was employed to investigate the impact of convergent–divergent riblets on turbulent boundary layers in both clear water and liquid–solid two-phase flow fields containing 155 μm polystyrene particles. The turbulence statistics such as turbulence intensity and Reynolds stress were investigated. The spatial topology of spanwise vortex head and the development and evolution process of hairpin vortices were explored from Euler and Lagrange perspectives, respectively. Additionally, the particle distribution, concentration, and dispersion within the turbulent boundary layer were statistically analyzed. The results indicated that the boundary layer thickness, friction resistance, integrated turbulence intensity, and Reynolds stress were significantly lower on divergent riblet walls compared to convergent riblet walls. Notably, divergent riblets with a yaw angle of 30° exhibited the best drag reduction effect in both single-phase and two-phase flow fields. The addition of particles resulted in an increase in boundary layer thickness but effectively reduced turbulent fluctuations in the logarithmic region, enhancing drag reduction. This extended the drag reduction range of divergent riblets to a yaw angle of 45°, increasing the maximum drag reduction rate to 26.18%. Through spatial multi-scale local average structure function and finite-time Lyapunov exponent field analysis, it was found that the 30° divergent riblet wall significantly inhibited the development of vortex structures and reduced momentum exchange within the boundary layer. Conversely, the 30° convergent riblet wall had the opposite effect, while the particle phase inhibited the development of all wall turbulent structures. Analysis of particle concentration variations within different regions of the turbulent boundary layer revealed that as the normal height of the boundary layer increased, particle concentration gradually increased, and particle dispersion decreased accordingly. The analysis further showed that particle dispersion was mainly influenced by flow structures, whereas concentration was significantly affected by turbulence intensity. These findings elucidate the effect of the flow field on the particle phase and provide insights into the interaction mechanism between the flow field and particles.

The analogous intraoral judgement of the abutment preparation angle is almost impossible! At least avoid undercuts.

A total occlusal convergence (TOC) angle (ϕ) of 6 degrees is a typical crown preparation requirement. It has been shown that this is difficult to achieve clinically. The present study therefore aims to compare the ability of students to judge different steepnesses, including a -1-degree undercut of prepared canines and molars, under clinical conditions with different analog tools. The complete dentures of a patient were duplicated without denture teeth 16, 23, 33, and 46. For each of these gaps, six crown stumps were milled with ϕ/2 = -1, 3, 6, 9, 12, and 15 degrees, each of which was insertable using mini-magnets. A total of 144 dental students, 48 students each from the 1st, 6th, or 9th semester, estimated these angles intraorally with various aiding tools: In addition to basic dental instruments, they used a parallelometer mirror, an analog clock dial with a 6-degree visualization, and a scale of tooth stumps with ϕ/2 between -1 and 15 degrees. The widely demanded 3 degrees were hardly recognized, but assumed to be steeper or even undercut. In contrast, the -1-degree divergent stump walls were predominantly estimated as parallel-walled or slightly conical. With increasing taper, the stumps tended to be classified as steeper, ie, "better." The additional tools did not result in a general improvement of the estimation performance. Students from higher semesters did not achieve better results. The present authors question the objectivity of an exclusively visual assessment of crown stump taper. It appears that dental training should at least focus on avoiding undercuts as the minimal prerequisite for an accurate intraoral scanning procedure. Digital control of the preparation angle by an intraoral scan and immediate clinical implementation of these results could help to produce appropriate preparations.

Nanotomographic Analysis of Orthodontic Molar Tubes for Direct Bonding

(1) Background: The most important part of an orthodontic attachment (bracket or tube) is the tube or slot for the insertion of the orthodontic wire. Aligning teeth along the archwire according to angular values preadjusted in the bracket slots (or tubes) requires a very precise size accordance between the archwires and slots. The aim of this study was to perform a nanotomographic analysis of the geometric features of molar tubes for direct bonding in terms of their dimensions and angles of their inner walls and analyze the presence of metallurgic imperfections. (2) Methods: Orthodontic tubes (n = 100) for upper right first molars from five different manufacturers (3M-Victory Series, Adenta-Bond Sing, Dentaurum-Ortho Cast M, GC-L LP, and ORMCO-Accent), 20 tubes each, were subjected to nanotomographic analysis. Measurements of the inner channel of the tubes, angles between the walls, and analysis of metallurgic imperfections were performed using high-resolution computed tomography. (3) Results: height measurements differed by 4–14% from ideal values declared by manufacturers, whereas the angles ranged from reducing by a maximum 1% comparing to values declared (hypodivergent walls) to increasing by a maximum 4.5% (divergent walls). (4) Conclusions: 1. The sizes of channels measured were slightly larger than those declared by manufacturers. 2. Slight deviations in wall parallelism and angles between the walls were found. 3. Some tubes were characterized by manufacturing defects of the metal. 4. Efforts should be made to further improve the production process of orthodontic attachments.

Influence of Different Apical Foramen Morphologies on the Accuracy of Four Electronic Foramen Locators.

The aim of this study was to evaluate the accuracy of the Root ZX II (RZX), Raypex 6 (RAY), EPex Pro (EPEX), and CanalPro (CNP) electronic foramen locators (EFLs) in different foraminal morphologies (fully formed foramen, immature foramen with parallel walls, and immature foramen with divergent walls); this article also evaluated the influence of different penetration levels (0.0 mm and -1.0 mm). Thirty single-rooted human premolars were accessed and had their cervical/middle thirds prepared with SX ProTaper files. The apical foramens (AF) were standardized to 250 µm and the initial root canal length (RCL1) was measured under 16x magnification with aid of a digital caliper. Using the alginate model, electronic measurements (EM) were taken 1.0 mm up to AF (EM1/-1) and at AF (EM1/0), always using adjusted hand K-files. The root apexes were then cross-sectioned 3.0 mm from the foramen; then, new RCL (RCL2) and electronic measurements were performed (EM2/-1 and EM2/0.0). Finally, retropreparations were performed with instruments SX ProTaper files introduced 4.0 mm in the apicocervical direction. Then new RCL (RCL3) and electronic measurements (EM3/-1 and EM3/0) were performed. Values were tabulated and tested for normality using the Shapiro-Wilk test, which yielded nonparametric distributions of the data. Data were subjected to the Kruskal-Wallis and Dunn tests to estimate possible differences between devices as a function of foramen morphology and/or apical limit. The significance level was set at 5.0%. In general, the EFLs were accurate in determining the RCL. Statistically significant differences were observed between EPEX and RAY at 0.0, when measuring the divergent AF canals (p < 0.05). Regarding the different foramen morphologies in each EFL, RZX and EPEX showed no interference (p > 0.05), whereas RAY and CNP had lower accuracy levels at 0.0 with divergent AF (p < 0.05). The four devices evaluated are accurate to determine the RCL in the conditions tested. The apical limit of penetration did not have significant influence on their accuracy. Conversely, the presence of divergence in the AF walls negatively influenced de RAY and CNP precisions at the foraminal level.

A scanning electron microscopy investigation of the precision of three orthodontic bracket slot systems

ObjectiveOne of the most imprortant factors in achieving ideal teeth positions is the precision of the slot dimensions of orthodontic brackets into the archwires are inserted.This study aimed to assess the accuracy of the dimensions of orthodontic bracket slots and molar buccal tube apertures and to compare them with the specifications provided by the manufacturers.MethodA total of sixty brackets and ten molar buccal tubes with varying slot heights were examined using a scanning electron microscope from the mesial side. The dimensions and morphology of these bracket slots and buccal tubes apertures were assessed using the AutoCAD Software. A one-sample t-test was conducted to compare the measurements with the values provided by the manufacturer.ResultsThe findings of the present study indicated that the height of the measured bracket slots and buccal tube apertures dimensions were significantly larger than the actual dimensions and exhibiting divergent walls. On the other hand, the depth of the brackets slots showed significantly smaller values than the actual one.ConclusionA need for careful consideration when selecting a commercially accessible brand for everyday use is essential as certain materials may not meet acceptable standards.

Forced convective heat transfer for Stokes flow including viscous dissipation in arbitrary corrugated channels

AbstractThe forced convective heat transfer for Stokes flow, including viscous dissipation in arbitrary corrugated channels, is studied using both an asymptotic method and a numerical solution. The aim is to specify the range of shape parameters for which the validity of the asymptotic approach is ensured, particularly regarding the characteristics of heat transfer. The axial velocity, transversal velocity, pressure, and temperature, for small corrugation's slope compared with unity, are sought as an asymptotic expansion in terms of a parameter that represents the corrugation's slope. The numerical solution is obtained by using ANSYS Fluent solver. Additionally, Python scripting is integrated to automate several parts of the simulations, including the creation of the geometry and a parametric study. Three different types of corrugations are investigated including zigzag, sinusoidal, and arbitrary corrugations defined using a function given by a particular case of the Fourier series. The Nusselt number is calculated to evaluate convective heat transfer. It is found that the asymptotic and numerical solutions for small corrugation's slope, are in good agreement with negligible quantitative differences. However, as the corrugation's slope increases (approaches unity), these quantitative differences increase up to cases where a change in the behavior of the local Nusselt number is observed. The results show that the local Nusselt number decreases in the channel's region with divergent walls due to the decrease in the average velocity. In contrast, it increases in the channel's region with convergent walls due to the increase in the average velocity.

Jeffery–Hamel flow of a shear-thinning fluid that mimics the response of viscoplastic materials

The flow between two divergent plane walls with a source at the vertex (Jeffery–Hamel flow) of a shear-thinning fluid, that mimics the response of a class of seemingly viscoplastic materials, is studied. The semi-inverse approach is used to obtain the governing equations for the velocity profile. The third-order non-linear ordinary differential equation governing the flow is solved numerically, and the effects of the material moduli that characterize the fluid, the angle between plane walls, and the inertial term, on the velocity are reported and discussed. Results show that there is a critical angle beyond which flow reversal occurs, and the number and angular extent of inflow regions varies based on the material moduli and the inertial term.

Numerical Investigation of a Designed-Inlet Optofluidic Beam Splitter for Split-Angle and Transmission Improvement.

The beam splitter is one of the important elements in optical waveguide circuits. To improve the performance of an optofluidic beam splitter, a microchannel including a two-stage main channel with divergent side walls and two pairs of inlet channels is proposed. Besides, the height of the inlets injected with cladding fluid is set to be less than the height of other parts of the microchannel. When we inject calcium chloride solution (cladding fluid) and deionized water (core fluid) into the inlet channels, the gradient refractive index (GRIN) developed in fluids flowing through the microchannel splits the incident light beam into two beams with a larger split angle. Moreover, the designed inlets yield a GRIN distribution which increases the light collected around the middle horizontal line on the objective plane, and so enhances the transmission efficiency of the device. To demonstrate the performance of the proposed beam splitter, we use polydimethylsiloxane to fabricate the microchannel. The results obtained by simulation and experiment are compared to show the effectiveness of the device and the validity of numerical simulation. The influence of the microchannel geometry and the flow rate ratio on the performance of the proposed beam splitter is investigated.

Comparison of conventional and Lorentz transmission electron microscopy in magnetic imaging of permanent magnets

Magnetization structures in magnetic materials are usually imaged in dedicated Lorentz transmission electron microscopes. Compared to conventional transmission electron microscopes, the magnetic field of the objective lens at the sample is removed by replacing the objective lens with a Lorentz lens below the sample. While this modification is critical for soft-magnetic materials whose magnetic state is affected by the strong magnetic field of the objective lens, we propose that this is not necessary for permanent magnets such as Sm–Co and Nd–Fe–B. Conventional and Lorentz microscopes are compared for imaging divergent and convergent domain walls in a Sm(Co,Fe,Cu,Zr)7.7 magnet. Both techniques provide an almost identical resolution and accuracy in the measurement of the domain-wall width parameter using focal-series imaging of divergent domain walls. It is further demonstrated that both techniques can be utilized to analyze the intensity profile of convergent domain walls. From this, the product of sample thickness and magnetic induction is extracted. These results illustrate that conventional microscopes can be used to image the magnetic state of permanent magnets with a resolution comparable to dedicated Lorentz microscopes, which make magnetic imaging experiments significantly more accessible to a wider scientific community.

Assessment on the Precision of the Orthodontic Bracket Slot Dimensions Using Micro-computed Tomography (Micro-CT)

To evaluate the precision of the orthodontic bracket slot dimensions of 0.022 inch and to compare them with those of the manufacturers' specifications. The slots of upper-right central incisor brackets (n = 5) from 11 commercial bracket systems of three different manufacturers (3M Unitek: Victory Mini Metal, Clarity, SmartClip, Clarity SL; ORMCO/SYBRON: Mini Diamond Twin, Damon Q, Damon Clear; Dentsply/GAC: Ovation, Mystique, In-Ovation R, In-Ovation C) were measured. The orthodontic brackets were scanned using micro-computed tomography (micro-CT), and the bracket slots were measured using micro-CT images. The slot was measured at four different surfaces (occlusal, gingival, base, and face) for both mesial and distal sites. Data were subjected to ANOVA and unpaired t-tests. A p-value of ≤0.05 was considered statistically significant. All brackets had slot dimensions that were significantly larger (p < 0.05) than the stated 0.022 inch. 3M-victory were 11.99% larger (0.02509 inch) and the closest to the stated dimension and the ORM-Damon C were 24.07% larger (0.02948 inch) than the quoted slot size of 0.022 inch. Comparison between mesial and distal sides showed that 91% of the bracket slots were asymmetrical at their bases and 100% asymmetrical at their faces. All of the bracket system showed divergent walls from base to face with values ranging from 1.96 (3M-SmartClip) to 26.58% (ORM-Damon C). The actual measurements of 11 bracket systems from three different manufacturers were more substantial than the manufacturers' specifications, and the walls of the slots diverged from the bracket bases in all of the tested bracket system. Orthodontic bracket slots vary significantly from that of the manufacturers' specification. The orthodontist should anticipate such shortcomings and be able to modify treatment mechanics through additional wire bending in three spatial planes.

Comparison of slot sizes and parallelism of metal brackets manufactured through metal injection molding and computerized numerical control.

ObjectiveTo investigate and compare the slot sizes and parallelism of metal injection molding (MIM) and computerized numerical control (CNC) brackets.MethodsThe following four MIM bracket series with 0.022-inch (in) slots were selected for investigation Di MIM mini Twin (Ortho Organizers), Mini Diamond Roth (Ormco), Gemini MBT (3M Unitek), and Formula R Roth (Tomy). The following four CNC bracket series with 0.022-in slots were selected for investigation Econoline MBT (Adenta), Legend mini MBT (GC Orthodontics), Crown mini MBT (Adenta), and Evolve MBT (DB Orthodontics). The slot dimensions were measured using an optical microscope (XTCam-D310M; Mitutoyo) with a resolution of 1 μm. The results were statistically analyzed using one-way analysis of variance and the Tukey post-hoc test with a significance level of 0.05.ResultsThe results indicated that all the investigated slot sizes were oversized with respect to the manufacturers’ specifications (0.022 in). Among the eight bracket series, the Di MIM bracket (MIM) was the most oversized by 10.4%, whereas the Evolve bracket (CNC) was the least oversized by 2.6%. The slots in seven of the bracket series had divergent walls instead of parallel ones. The Evolve bracket alone had parallel slot walls.ConclusionsRegardless of the manufacturing method, all the slot sizes of the brackets investigated in this study were significantly oversized; most of the slot walls were nonparallel, except for those of the Evolve bracket. This study could not establish that the CNC method was more accurate than the MIM method in manufacturing bracket slots.

Trueness of intraoral scanners in digitizing specific locations at the margin and intaglio surfaces of intracoronal preparations

Statement of problemStudies evaluating the trueness of intraoral scanners (IOSs) at anatomic locations within an intracoronal preparation are lacking. PurposeThe purpose of this in vitro study was to evaluate the trueness of digital scans obtained by IOSs at the margin and intaglio surfaces of intracoronal preparations. Material and methodsSix IOSs (CEREC Omnicam, E4D, FastScan, iTero, TRIOS, Zfx IntraScan) were used to obtain digital scans of various intracoronal preparations. Standard tessellation language (STL) data sets obtained from a reference scanner and each IOS were superimposed, and the deviation of the digital casts was assessed at multiple measuring points along the margin and intaglio surfaces of each preparation. The Kruskal–Wallis test and multiple Mann–Whitney tests were used to detect differences in trueness (α=.05). ResultsThe overall median trueness values were lowest for TRIOS (23.9 μm), followed by Zfx IntraScan (24.6 μm), iTero (25.4 μm), FastScan (26.1 μm), CEREC Omnicam (26.9 μm), and E4D (77.5 μm). The greatest deviation was generally observed at the line angles between the preparation surfaces. The axiogingival line angle was the most error-prone location in the cavity preparations. An increased tendency to produce a more accurate impression was observed when the cavity had a greater width and more divergent walls. ConclusionsThe trueness of digital scans was influenced by the type of IOS and the location within a prepared cavity. The trueness decreased at the line angles between the preparation surfaces, particularly at the axiogingival line angle. Among the tested IOSs, E4D produced the least accurate digital scans.

An Integrated Optofluidic Platform Enabling Total Phosphorus On-Chip Digestion and Online Real-Time Detection.

This paper presents a total phosphorus online real-time monitoring system integrated with on-chip digestion based on the merits of optofluidic technology. The integrated optofluidic device contains a hollow optical fiber employed for pretreatment and digestion of phosphorus solution samples, a polydimethylsiloxane (PDMS)-based micromixer with convergent–divergent walls designed to enable sufficient mixing and chromogenic reaction, and a couple of optical fiber collimators attached with a Z-shaped flow cell for optical detection. Details of system design and fabrication are introduced in this paper. In the experiment, on-chip digestion of four typical phosphates in aqueous solution including organophosphorus and inorganic phosphorus is investigated under different reaction conditions, such as digestion temperature, concentration of oxidant and pH value, and the optimal reaction parameters are explored under different conditions. Meanwhile, we demonstrate the online real-time monitoring function of the optofluidic device, and the digestion mechanisms of four different phosphates are analyzed and discussed. Compared with the national standard method, we find that the measurement accuracy and sensitivity are acceptable when the concentration of total phosphorus is between 0.005–0.9 mg/L (by weight of P) in aqueous solution, which covers the range defined in the national standard. The traditional digestion time of several hours is greatly reduced to less than 10 s, and the content of total phosphorus can be obtained in a few minutes. The integrated optofluidic device can significantly shorten the test time and reduce the sample amount, and also provides a versatile platform for the real-time detection and analysis of many biochemical samples.

Biomechanical behavior of maxillary premolars with conservative and traditional endodontic cavities.

The objective was to evaluate the effects of the configuration of endodontic cavities with parallel or divergent walls, versus traditional endodontic cavities, on stress distribution, fracture resistance, and fracture mode of maxillary premolars by using both fracture-strength and finite element tests. Thirty-two maxillary first premolars were divided into four groups (n = 8), according to the type of endodontic cavities: without endodontic cavities (control); conservative; conservative with diverging walls; and traditional. After performing root canal treatment and restoration, fracture resistance was evaluated by oblique compressive load. The stress distribution was evaluated by nonlinear finite element analysis by means of micro-computed tomography, operated at 50 kV and 800 mA. The fracture resistance data were analyzed by statistical software. Higher stress concentration was observed on the coronal portion of the palatal cusp and the palatal root dentin. Stress concentration on the palatal root dentin was similar for all groups. The stress level on the palatal cusp and at the proximal crests was slightly increased in the traditional endodontic cavities group compared with conservative endodontic cavities. Stress distribution in restored teeth was similar to that of intact teeth. No significant differences were observed in the fracture resistance among different endodontic cavities' design (P = .32). All groups had values similar to those of the control group (P > .05). Regardless of the cavity design, conservative endodontic cavities that preserve marginal ridge integrity did not affect the resistance to fracture, failure mode, or stress distribution in maxillary premolars restored with composite resin. Endodontically treated teeth displayed biomechanical behavior similar to sound teeth.

Optimization of pulsatile flow and geometry of a convergent–divergent micromixer

The geometry and operating conditions of a micromixer with convergent–divergent sinusoidal walls under pulsatile flow were optimized in this work to maximize the mixing performance. Flow and mixing analyses were performed using the three-dimensional unsteady Navier–Stokes equations with a convection–diffusion model for the species concentration. A time-averaged mixing index was used to evaluate the mixing performance of the micromixer with a pulsatile flow. The overall mixing index was selected as the objective function, and both geometric and flow variables were used as the design variables. The ratio of the amplitude to the wavelength of the sinusoidal walls and the throat width to depth of the convergent–divergent channel were selected as the geometric variables, and the Strouhal number and the ratio of the pulsing amplitude to the steady flow velocity of the pulsatile flow were selected as the flow variables. Three different surrogate models were tested for the optimization to approximate the objective function at a Reynolds number of 0.5. The results indicate that the Kriging model predicts the best optimum design with a mixing index of 92.35% at the outlet of the micromixer.

Performance Evaluation of Three Types of Passive Micromixer with Convergent-Divergent Sinusoidal Walls

A passive split-and-recombination micromixer with convergent- divergent channel walls of sinusoidal variation has been investigated using numerical simulations. With water and ethanol as working fluids, the analysis was performed using Navier-Stokes equations with convection-diffusion model in a Reynolds number range, 10 ≤ Re ≤ 70. Performances of three configurations with different split-and-recombination arrangements were evaluated in terms of mixing index and pressure drop. A parametric study was also conducted with two geometrical parameters, i.e., the ratios of throat-width to diameter of circular wall and diameter of circular wall to amplitude. The results showed a significant dependence of the mixing performance on the throat-width. But, mixing performance was insensitive to the diameter of circular wall over the chosen Reynolds number range.

Multiobjective Optimization of a Micromixer with Convergent–Divergent Sinusoidal Walls

A multiobjective optimization of a micromixer with convergent–divergent sinusoidal walls has been conducted using flow and mixing analyses, surrogate modeling, and multiobjective genetic algorithm. The ratios of amplitude to wavelength of the sinusoidal walls, throat width to depth of the convergent–divergent sections, and diameter of the inner circular wall to wavelength were chosen as the design variables for optimization. The full-factorial method was used to discretize the design space. The mixing index and nondimensional pressure loss were selected as objective functions. Radial basis neural network functions were used to train the objective functions. The optimization was carried out at a Reynolds number of 30. A concave Pareto-optimal front representing the trade-off between the two objective functions was obtained. The analysis of representative designs along the Pareto-optimal front showed significant variation in the ratio of throat width to depth of the convergent–divergent sections, whereas the ratio of amplitude to wavelength of the sinusoidal walls maintained a nearly constant value. The concept of mixing effectiveness was used to select the most efficient designs considering both the mixing performance and pressure drop.

Intraglottal pressure distribution computed from empirical velocity data in canine larynx

Intraglottal velocity measurements were taken using particle image velocimetry and the corresponding estimates for the intraglottal pressure were computed using the pressure Poisson equation. Results from five canine larynges showed that when the flow separated from the divergent glottal walls during closing, the vortices that were formed in the separated region of the glottis created negative pressure near the superior aspect of the folds. The magnitude of the negative pressure was directly proportional to the subglottal pressure. At low subglottal pressure, negative pressures at the superior edge were not observed when the divergence angle of the wall was minimal and the glottal flow did not separate from the wall.

Passive split and recombination micromixer with convergent–divergent walls

A passive micromixer featuring convergent–divergent channel walls with sinusoidal variations is proposed in this work. The main channel splits into two sub-channels that recombine at regular intervals along the microchannel’s length. To evaluate mixing performance, steady Navier–Stokes equations with a diffusion–convection model for species concentration are solved for Reynolds numbers in the range of 10⩽Re⩽70. A mixing index based on the variance of the mass fraction of the mixture is employed to evaluate the mixing performance of the micromixer. The effects of the Reynolds number, the amplitude of the sinusoidal walls, and the aspect ratio of the channel on mixing performance are investigated. The results indicate that a symmetric double vortex pair appeared at the throat of the convergent–divergent channel. And, secondary motions as a result of differential centrifugal forces originating in the sub-channels and throat of the convergent-divergent walls significantly affect mixing behavior. The proposed micromixer shows significantly improved mixing performance compared to a similar geometry based on the concept of unbalanced split and collisions for a wide range of Reynolds numbers. Also, the pressure drop is acceptable for a variety of lab-on-a-chip and micro-total analysis systems.

Avaliação da utilização de MTA como plug apical em dentes com ápices abertos

A young permanent non-vital teeth treatment requires special consideration due open apices and divergent thin dentinal walls. The apexification is defined as a method to induce a calcified barrier in an open apex root or the continued apical development of an incomplete root of teeth with necrotic pulp. An apical barrier placement with MTA at a single visit has been an alternative to the calcium hydroxide use. The non surgical condensation of mineral trioxide aggregate (MTA) in apex, provides an artificial barrier that allows immediate filling, enabling shorter treatment time,good apical seal and periradicular hard tissue deposition induction.