Microcrack Evaluation Research Articles

Unveiling the correlation between in vivo endodontic reciprocate instrumentation and crack formation

IntroductionDentinal microcracks have been supposedly associated with unrestorable vertical root fractures and consequently long-term treatment failure. This study aimed to investigate whether in vivo root canal instrumentation in mandibular incisors with vital pulps causes dentinal microcracks using two different irrigating solutions. MethodsFive patients with four vital mandibular incisors indicated for extraction were included. In vivo root canal preparation was performed using Reciproc R40 (tip #40 and taper 0.06). From these, two teeth were randomly assigned for root canal instrumentation irrigated with 5.25 % sodium hypochlorite irrigation (n = 10) or 2 % chlorhexidine gel with saline solution irrigation (n = 10). In sequence, all teeth were carefully extracted, stored in saline solution until microtomography (µCT) scan. Images were reconstructed and assessed for the presence or absence of dentinal microcracks where microcracks originating from the root canal lumen would be considered. All reconstructed samples were analysed dynamically and rendered in videos through the entire extension of the teeth, evaluating the axial cuts considering each third separately from the apex to the enamel-dentinal junction. Teeth were analysed using the DataViewer software at 100 % magnification without filters by three examiners blinded to the condition allocation. ResultsNo complete dentinal microcracks were observed after root canal instrumentation of mandibular incisors with vital pulps using Reciproc R40 regardless the irrigating solutions, 5.25 % sodium hypochlorite or 2 % chlorhexidine gel. ConclusionsIn vivo root canal instrumentation of mandibular incisors with vital pulps and bone/periodontal insertion does not cause dentinal microcracks and the irrigating solutions tested did not influence this occurrence. Microcrack evaluation must be performed in vivo conditions of dental tissue moist and periodontal support to avoid dryness dentinal alterations after extraction provoking false positive results. Clinical relevanceReciprocating instrumentation performed in vivo is safe and do not induce dentinal microcracks in mandibular incisors.

Experimental study on opto-acoustic nonlinear frequency-mixing technique with separated basic temperature

Different from the traditional frequency-mixing technique which employs a contacting transducer, the laser-induced acoustic nonlinear frequency-mixing detection technique utilizes a laser source to instigate crack motion and generate acoustic waves. Thus, apart from the temperature oscillation induced by the pump laser, the “basic temperature” originating from the probe laser can also influence the crack. This additional variable complicates the contact state of the crack, yielding a more diverse range of nonlinear acoustic signal attributes. In light of this, our study enhances the conventional opto-acoustic nonlinear frequency mixing experimental setup by integrating an independent heating laser beam. This modification isolates the impact of the “basic temperature” on crack width while also dialing down the probe laser power to mitigate its thermal effects. To amplify the sensitivity of crack detection, we deliberated on the optimal laser source parameters for this setup. Consequently, our revamped system, paired with fine-tuned parameters, captures nonlinear acoustic signals with an enriched feature set. This investigation can provide support for the non-contact opto-acoustic nonlinear frequency mixing technique in the detection and evaluation of micro-cracks.

7 - Evaluation of microcracks formed by grinding in machinable lithium silicate

7 - Evaluation of microcracks formed by grinding in machinable lithium silicate

Comparative Evaluation of TruNatomy, XP Endoshaper and Hand K File Systems on Dentinal Microcrack Formation and Vertical Root Fracture Resistance – An In Vitro Study

Background Vertical root fracture VRF accounts for 11 of failures in endodontically treated teeth. Microcracks can occur during instrumentation of root canal system with NiTi rotary files as it exerts forces increasing strain on dentinal wall which may progress to VRF. Newer file systems have been developed to reduce the risk of microcrack formation.Aim The aim of the present study was to evaluate the effect of TruNatomy XP Endoshaper and Hand K files on dentin microcrack formation and vertical root fracture resistance of root canals.Methods One hundred twenty-five extracted teeth were used in the study with 40 samples each in the experimental groups and five samples in the control group. Following instrumentation Group TRN-Trunatomy Group XPS ndash XP Endoshaper Group HF ndash Hand K File 50 of the samples were subjected to stereomicroscopic study for dentinal microcrack evaluation. The remaining samples were obturated and were subjected to Universal testing machine for vertical root fracture resistance assessment. Kruskal Wallis and Post hoc Bonferroni tests were used for statistical analysis.Results Statistically significant difference was observed between XP Endoshaper and other groups in terms of dentinal microcrack formation and vertical root fracture resistance. Significantly higher value was observed for Hand K file and TruNatomy against XP Endoshaper File p lt0.05.Conclusion TruNatomy serves as a file system causing least dentinal damage comparable to Hand K file system while XP Endoshaper caused more cracks.

Deterioration of performances and structures of cement pastes under the action of thermal cycling fatigue

Concrete structures in the atmosphere are continuously subjected to thermal cycle (TC) inducedby varying environmental temperature. However, the influencing mechanism of thermal cycling fatigue on the mechanical properties and microstructure of cement-based materials has not been thoroughly documented. To address this issue, the relationship between the macro-properties and microstructure of cement paste under TC was analyzed using micro-properties measurement and quantitative microcrack evaluation. In this work, ordinary Poland cement pastes with three different water-to-cement (w/c) ratios (0.4, 0.5, and 0.6) were exposed to TC in the range of 5–45 °C. The mechanical properties, pore structures, and micromorphology of cement pastes after different cycle times were measured. The result indicated that as the number of cycles increased, TC negatively affected the macro-mechanical characteristics, pore structure, and micromorphology of cement pastes. Cement pastes with greater w/c ratios were more susceptible to TC-induced deterioration. In addition, thermal cycling fatigue caused the propagation of microcracks including crack width, length, and density. Thermal cycling fatigue also coarsened the pore structure of cement pastes, especially the large pores (i.e., diameter > 100 nm). The underlying damage mechanism caused by TCis the coupled actions of fluid flow, thermal deformation, and thermal fatigue. Moreover, a negative linear relationship was established between microcrack density and Vickers hardness of cement pastes.

Evaluation of Microcracks formed During Root Canal Preparation by Different File Systems Using Micro-computed Tomography: An In Vitro Study

The purpose of this study was to evaluate and compare the incidence of dentinal microcracks after instrumentation with various types of nickel-titanium (NiTi) files in rotary and reciprocating motion. Fifty human extracted mandibular molars were taken and divided into five groups (n = ten teeth per group). Group I included ProTaper Gold, group II included OneShape, group III included WaveOne Gold, group IV included Reciproc, and group V included hand K files. The teeth were desectioned at the cemento-enamel junction (CEJ) and dentinal microcracks were observed under Micro-computed tomography. Postoperative Micro-computed tomography analysis of the samples was conducted to inspect cracks in the images obtained before and after preparation. Results confirmed that there was a statistically significant difference between the study groups (p <0.05). The highest percentage of microcracks was seen in ProTaper Gold followed by OneShape. WaveOne Gold and Reciproc showed closely similar percentage of microcracks followed by hand K files that showed the least. Both rotary file systems showed higher number of microcracks than reciprocating file systems. Hand K files showed least microcracks formation among all studied groups. Among all the tested methods and systems, hand K files demonstrated least incidence of dentinal microcracks. However, these hand K files systems are not advanced and have certain practical limitations. Reciprocating systems usually exhibits clinically acceptable microcracks therefore they may be judiciously utilized. Rotary file systems showed excellent biomechanical outcomes with redundant microcrack formation. Hence, precise selection of a particular system must be solely dependent upon the clinical decision making and circumstantial requirements.

Advances in nonlinear ultrasonic detection of microcracks

<p indent="0mm">A large number of key components are widely operated under extreme conditions of high temperature and high pressure in power, nuclear energy, aerospace and other important industrial fields. Microdefects are inevitably generated in these key components during the process of manufacturing. Due to the periodic loading and thermal stress, microcracks are generally initiated from these microdefects at the location with stress concentration. It has been found that the initiation and propagation of fatigue microcracks usually occur prior to 70%–90% of fatigue life. It is difficult to observe the evidence before the formation of macrocracks, which may result in catastrophic accidents. Thus, the risk of sudden failure of key components increases greatly. Therefore, the accurate detection of microcracks is crucial for guaranteeing the safe operation of key components. Based on the diffraction, reflection and transmission, traditional ultrasonic testing method is merely validated to effectively detect macroscopic defects within half a wavelength. The nonlinear ultrasonic testing method is found to be sensitive to microcracks, as high order harmonics, sub-harmonics, DC components and frequency mixing waves can be generated due to the strong nonlinear interaction microcracks and ultrasonic waves. With the outstanding effectiveness to detect microcracks, the nonlinear ultrasonic testing method has attracted much attention in recent years. In this work, the research on detection of microcracks using nonlinear ultrasonic testing method is systematically reviewed in terms of theoretical models, numerical simulations and experimental measurements. Firstly, according to the breathing effect and sliding mechanism of microcrack surfaces, we present several theoretical models of nonlinear interaction between ultrasonic waves and microcracks, namely contact acoustic nonlinearity (CAN), bi-linear stiffness model, nonlinear spring model, Hertz contact theory, and rough contact surface model. The advantages and disadvantages of these theoretical models are discussed comparatively. Two mechanisms are mainly considered for the nonlinear interaction of microcracks and ultrasonic waves, namely the macroscopic opening and closing of crack surfaces and the microscopic contact of rough microcracks surfaces. Secondly, we introduce numerical simulation studies on the nonlinear ultrasonic generation induced by microcracks. The applicability is analyzed for several simulation methods, such as finite element method, spectral finite element method, finite difference method, boundary element method and local interaction simulation approach, and the generation and propagation of nonlinear ultrasonic waves are analyzed as well. The effect of microcrack geometries on the nonlinear ultrasonic waves is then summarized. The microcrack geometries are considered mainly clouding the microcrack length, width, depth, density and direction. Furthermore, we present the experimental measurements on the generation of nonlinear ultrasonic waves induced by microcracks and on the localization and imaging of microcracks based on the nonlinear ultrasonic waves. The generation of high order harmonics, sub-harmonics, DC components and frequency mixing waves was observed in the specimens with microcracks. The nonlinear ultrasonic detection is presented to evaluate fatigue microcracks with various microcrack length, width, depth, density and direction. Based on this phenomenon, nonlinear ultrasonic mixing method, transducer array imaging method and nonlinear ultrasonic phased array method are introduced to localize the microcracks. Finally, further studies on evaluation of microcracks using nonlinear ultrasonic waves are proposed, including the comprehensive physical model for actual microcracks in engineering components, robust detection method, and quantitative evaluation of microcracks and service life.

Influence of Root Canal Preparation on Formation of Dentinal Microcracks: A Systematic Review.

The effect of root canal preparation technique on microcrack initiation is a controversial issue. This systematic review aimed to assess the role of root canal preparation techniques with different kinematics (manual, rotary, reciprocating, adaptive, self-adjusting file) on microcrack initiation. In vitro and in situ studies comparing the influence of at least two different root canal preparation techniques on the initiation of dentin microcracks were searched in PubMed/MEDLINE and SCOPUS up to June 5, 2018 without language and period restriction. Two authors independently reviewed all identified titles and abstracts for eligibility. Tables were generated to summarize the included studies, and the included studies were assessed for bias. Fifty-four (n=54) articles met the eligibility criteria. The results were classified according to the method used for microcrack evaluation, and most studies that used micro-computed tomography showed no formation of new cracks after root canal preparation. In general, the instrumentation techniques induced microcrack formation when the methods were destructive, irrespective of kinematics. In relation to the apex region, when the preparation working length was set as the root canal length subtracted of 1 mm, the risk of microcrack initiation reduces. The majority of the included studies had low risk of bias for all assessed domains. Our results seem to indicate that the various root canal preparation techniques considered in this study will not cause damage to the dental structure when adequately employed and the proper methodology is applied.

A Preliminary Numerical Study on the Interactions Between Nonlinear Ultrasonic Guided Waves and a Single Crack in Bone Materials With Motivation to the Evaluation of Micro Cracks in Long Bones

Fatigue damage in a bone occurs in the form of micro-scale cracks with the lengths as small as to a few microns. The evaluation of cracks in bones has recently been a hot topic. However, the current most frequently used method is based on traditional linear ultrasound, which is just sensitive to gross damages rather than micro cracks. Nonlinear ultrasonic technique, which is capable of detecting micro-scale damages, has been widely used in metallic structures. However, few study has been directed to employing second harmonic generation of nonlinear ultrasound to evaluate fatigue damages in bones. In this study, a preliminary study is conducted on the interactions between nonlinear guided waves and a single crack in bone materials motivating to the evaluation of micro cracks in long bones. Considering the symmetry, asymmetry, location, orientation, length and width of the crack in bone materials, their influences on second harmonic responses are discussed in detail. Our results are presented as follows. Firstly, not only the primary S0 but also A0 mode Lamb wave generates the second harmonic component of S0 mode after interacting with a symmetric crack. Secondly, along the thickness direction, the primary S0 mode Lamb wave possesses almost the same detection sensitivity, no matter where the crack is located. Thirdly, the amplitudes of S0 mode second harmonic component are increased slightly when the oblique angle of the crack is set from 0°to 45°, while the amplitudes increase dramatically when the oblique angle changes to 67.5° and 90°. Lastly, the second harmonic amplitude and the relative acoustical nonlinear parameter are increased with the length of the crack, while they possess a monotonically decreasing relationship with the width of the crack. Our preliminary studies will provide priori knowledge when using nonlinear ultrasonic guided waves for detecting micro-scale cracks in long bones in future clinical inspections.

Evaluation of microcracks in the interfacial transition zone of recycled rubber concrete

AbstractThis work focuses on the feasibility of recycling waste tire rubber aggregates into recycled concrete. The performance of interface transition zone (ITZ) is a key factor affecting the mechanical properties and durability of concrete. The influence of rubber particle size (5–10, 10–20, 20–50, and 50–90 mesh) and volume fraction of rubber aggregate (0, 10, and 20%) on the ITZ of common and rubber aggregate‐cement pastes was studied. Scanning electron microscopy was used to observe the microstructure of recycled rubber concrete cured at constant temperature and humidity for 28 days. Moreover, the size of microcracks in the ITZ area was evaluated. Results showed that the crack width of the ITZ between the rubber and cement paste (ITZ‐R) and between the ordinary aggregate and cement paste (ITZ‐S) showed similar variation patterns. The addition of 50–90 mesh rubber powder improved the ITZ micro‐crack structure of rubber concrete. Increasing the rubber content and particle size also increased the microcrack width of ITZ. The size of rubber aggregate was the key factor affecting the crack width in ITZ. Finally, the addition of rubber inhibited the hydration degree of cement, reduced the formation of hydration products in ITZ and substantially affected ITZ‐R.

Application and Evaluation of Micro-Cracking on Cement-Stabilized Bases at Field Projects in Louisiana

Cement stabilized soil bases have been used in flexible pavements in Louisiana for years. Soil cement has an excellent load carrying capacity and durability, but is also well-known for developing shrinkage cracks, which can reflect through asphalt concrete surfaces and accelerate the deterioration of asphalt pavements. Micro-cracking is a special reflective cracking mitigation technique used in cement-stabilized base construction. The objectives of the research were to determine the effectiveness and performance of micro-cracking on soil-cement pavements. Micro-cracking was applied on field projects, based on the experience of a previous micro-cracking research project at the Pavement Research Facility of the Louisiana Department of Transportation and Development. Two pavement sites were selected for the field pavement rehabilitation projects, LA 1003 and LA 599, to test the micro-cracking technique. In-situ tests were conducted and pavement performance was monitored for both sites. It was found that an 8.5-in. micro-cracked soil cement pavement showed a similar or better early performance as compared to a non-micro-cracked soil cement pavement with regards to the overall cracking performance. On the other hand, more cracks were found on the micro-cracked test sections than the control sections when micro-cracking was applied on a 12-in. cement treated soil base in Louisiana. Analysis of the structural numbers did not show a significant difference between the control and micro-cracked sections. Further monitoring is recommended for both of the field projects.

Effect of Surface Roughness on Ultrasonic Testing of Back-Surface Micro-Cracks

Surface roughness is one of the main factors that affect the ultrasonic testing of micro-cracks. This article theoretically analyzes the relationship between the changes in the energy intensity of crack echo waves and roughness-modified transmission coefficients. A series of simulations are carried out using two-dimensional sinusoidal curves as rough surface. Then, parallel experiments are performed on sample surfaces with different arithmetic average heights (Ra). The signal amplitude ratio factor (SARF) is defined to assess the ultrasonic detection capacity for micro-cracks. Both finite element analysis and experimental results show that signal amplitude decreases with an increase in Ra, resulting in signal-to-noise ratio loss. Amplitude attenuation caused by the rough back surface is less than that caused by the rough front surface. It is difficult to identify the signal of micro-cracks with a depth less than 400 μm when the Ra of the front surface is larger than 15 μm. Cracks with depths of more than 200 μm can be distinguished when the back-surface roughness is less than 24 μm. Furthermore, the amplitude of the micro-crack signal increases slightly with variation in the horizontal parameter (Rsm). This study provides a valuable reference for the precision evaluation of micro-cracks using ultrasonic inspection.

Evaluation of cortical mandibular bone in patients with oral squamous cell carcinoma.

The aim of the study was to evaluate the mandible cortical bone changes in patients with oral squamous cell carcinoma (OSCC). Twenty patients who underwent some mandibular bone removal as part of the treatment of OSCC had bone samples collected in two parts: in the proximity of the tumor (BPT) and in the surgical margin (BEP). Cortical microarchitecture was analyzed trough micro-computed tomography, together with texture analysis, followed by microcrack evaluation in histological sections and gene expression of RANK, RANKL, OPG, and sclerostin by quantitative polymerase chain reaction. Bone surface was higher in BPT (0.005±0.002 vs 0.004±0.002, p=0.01) compared with BEP. In BPT, the subset of patients without bone invasion presented higher anisotropy (0.83±0.07) compared with the ones with bone invasion (0.70±0.14) (p=0.04). RANK, RANKL, OPG, and sclerostin were found to be downregulated in the majority of cases in both parts. There were significant correlations between the parameters of microarchitecture and gene expression analysis (p<0.001 to p<0.05), most of them related with OPG levels. The cortex in the mandible in the proximity of the tumor reveals more bone surface than the bone in the surgical margin, and the tumor invasion causes a decrease in anisotropy. RANK, RANKL, OPG, and sclerostin are downregulated in mandible, in both parts analyzed. Correlation tests revealed the association between cortical thickness, bone surface, anisotropy, porosity, bone mineral density, and OPG levels. The mandible cortical bone microarchitecture changes in the proximity of the squamous cell carcinoma lesion.

Characterization of stress-dependent ultrasonic nonlinearity variation in concrete under cyclic loading using nonlinear resonant ultrasonic method

In this work, an experimental study was carried out to investigate the stress-dependent characteristics of concrete under cyclic loading, based on a nonlinear resonant ultrasonic method. Since concrete subjected to cyclic loading accompanies variations in the elastic and plastic characteristics of concrete in relation to microstructural changes, the adoption of a nonlinear ultrasonic approach is required, which has advantages for the evaluation of micro-cracks in concrete. In this experimental study, two types of loading were considered, namely, continuously increased and cyclic repeated, to identify their effects on the ultrasonic nonlinearity of concrete and the load-induced damage. An additional experiment on the exposure of concrete samples to high temperature was conducted to further investigate the effects of cyclic loading accompanied by an increased occurrence of micro-cracking. A comparison analysis was also performed on the experimental results, and the potential to monitor the stress history of concrete by using the nonlinear resonant ultrasonic method was evaluated.

Retracted: Evaluation of the incidence of microcracks caused by Mtwo and ProTaper NEXT rotary file systems versus the Self Adjusting File: a scanning electron microscopic study.

The following article from International Endodontic Journal, 'Evaluation of the incidence of microcracks caused by Mtwo and ProTaper NEXT rotary file systems versus the Self Adjusting File: a scanning electron microscopic study' by S. G. Saha, N. Vijaywargiya, S. Dubey, D. Saxena & S. Kala, published online on 24 November 2015 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the authors, the journal Editor in Chief, Prof. Paul Dummer, and John Wiley & Sons Ltd. The retraction has been agreed due to the consideration that the SEM methodology used by the authors has the potential to cause cracks and is thus is not suitable for the evaluation of micro-cracks in roots.

Quantitative evaluation of micro-cracks using nonlinear ultrasonic modulation method

Nonlinear acoustic coefficients have a close relationship with structural cracks. A nonlinear ultrasonic modulation method for micro-crack quantitative evaluation is developed. The influence of phase threshold on the crack evaluation is discussed. Ultrasonic modulation using a unilateral incentive model is applied to the quantitative evaluation of micro-cracks for different specimens. The experimental results indicate that the method can be beneficially applied for micro-cracks detection. A proper phase threshold can improve the reliability of the method based on nonlinear ultrasonic modulation. The presented modulation factor can be used to quantitatively evaluate the structural cracks, and it is suitable for small-crack quantitative evaluation.

Investigation on surface micro-crack evaluation of engineering ceramics by rotary ultrasonic grinding machining

Rotary ultrasonic grinding machining (RUGM) is regarded as the most powerful machining method for engineering ceramic. However, there are micro-cracks on the machined surface inevitably for lower fracture roughness of material. As part of surface integrity, effective parameter and unified criterion are not proposed for micro-crack evaluation. In the paper, surface micro-crack evaluation of engineering ceramics by RUGM was investigated. Micro-crack generation area ratio calculation model and information dimension calculation model were established. On the basis of those, a new evaluation parameter, called micro-crack fractal density, was proposed to reveal the characteristics of micro-crack. The parameter was proved to evaluate micro-crack evolution rule effectively with the advantages of statistics and multi-scale. Meanwhile, the factors affecting micro-crack fractal density evaluation were investigated. It is found that the micro-crack fractal density increases with cutting force rising, while it decreases as fracture toughness rises. The results provide the support for surface integrity evaluation of engineering ceramics.

Study of Quantitative Evaluation of Micro Cracks in Extracted Concrete Core by Infrared Thermography Method

Study of Quantitative Evaluation of Micro Cracks in Extracted Concrete Core by Infrared Thermography Method

Sensitivity analysis of the non-destructive evaluation of micro-cracks using GMR sensors

Micro-cracks in a magnetized ferromagnetic material cause stray fields that can be observed using giant magnetoresistive (GMR) sensors. This work investigates the applicability of GMR sensors to the non-destructive evaluation of micro-cracks via the observation of stray fields. For this purpose, our measurement setup is assessed using a fast new sensitivity analysis based on adjoint states, employing the finite-element method. A model for the GMR sensor is developed and verified. We are able to resolve micro-cracks with an opening of 3μm and a depth of 30μm. GMR positioning inaccuracies are analyzed.

비선형 초음파 변조 기법을 이용한 열손상 콘크리트의 미세균열 평가

이번 연구에서는 비선형 음향효과를 기반으로 한 비선형 초음파 변조 기법을 통해 열손상 콘크리트의 미세균열 정도를 평가할 수 있는 방법을 제안하였다. 화재 시 콘크리트 구조물은 물리적, 화학적 변화에 따른 콘크리트 내 미세균열이 발생하므로, 기존 초음파 비파괴 기법의 민감도 한계를 극복한 비파괴 기법의 도입이 필요하다. 비선형 초음파 기법은 초음파와 저주파의 변조파로부터 열손상 평가 인자인 비선형인자를 측정하며, 이는 열손상 콘크리트의 미세균열에 적합한 민감도를 가진다. 이 연구에서는 SEM 관측, 열손상 전후 콘크리트의 투수공극량 변화 측정으로부터 수열온도에 따라 미세균열이 급격하게 발생함을 보였으며, 수열온도별 콘크리트의 초음파 전파속도 측정을 통해 제안된 방법의 민감도를 검증하였다. 추가적으로 열손상에 따른 미세균열이 콘크리트의 성능저하에 미치는 영향을 파악하고자 열손상 콘크리트 시편의 압축강도 측정을 수행하였다. 측정값 및 실험값의 연관성을 파악하여 비선형 초음파 변조 기법이 열손상 콘크리트의 미세균열 평가에 적합함을 보였으며, 향후 압축강도 추정에 대한 적용 가능성을 확인하였다.