Loosening Process Research Articles

Analysis of relaxation characteristics of multi-bolted connections under the transverse cyclic load

A modeling method under lateral cyclic loading is proposed for the complex multi-bolt connection loosening problem. Firstly, the thread stress surface is divided into n small sectors, and the self-relaxation mechanical model of multi-bolt connection is established considering the interaction between bolts. Secondly, the self-relaxation model is solved by MATLAB software and compared with Nassar model to verify the correctness of the model. Finally, considering the influence of different bolt number, hole clearance and connection spacing, the relaxation characteristics of multi-bolt connection are studied. The results show that during the loosening process, the bolt head undergoes a bending-sliding-bending cycle process, and the bolt tension shows a wave downward trend. When multiple bolts are connected, the number of loosening cycles decreases linearly with the increase of hole clearance. With the equidistant increase of bolt connection spacing, the number of bolt loosening cycles shows a decreasing trend. Compared with the number of bolts, the change of bolt hole clearance and connection spacing is more likely to affect bolt loosening.

Study on Shear Failure Process and Zonal Disintegration Mechanism of Roadway under High Ground Stress: A Numerical Simulation via a Strain-Softening Plastic Model and the Discrete Element Method

Fracture expansion in rock masses can be observed by monitoring the break of contacts between the bounding particles via the discrete element method. The latter’s realization in this study via the PFC2D program tracked the evolution process of the zonal disintegration in an exemplary roadway-surrounding rock affected by mining. Besides, the damage evolution pattern in a high-stress soft rock roadway was simulated by the FLAC2D program using a strain-softening plastic model, revealing the effects of rock mass strength, stress state, and anchor support on the zonal disintegration of the roadway. Numerical simulation results show that in a roadway with high-level stress, the obvious fractures spread from the roadway surface to the depth of the surrounding rock along a series of geometric planes and cut the surrounding rock into rock mass blocks. Under high crustal stress, conjugate shear fractures occur near the roadway surfaces and form a closed-loop fractured zone after intersecting the conjugate fracture faces. The closed fractured zone becomes a free face, from which conjugate shear fractures develop, forming new closed fractured zones in the deep surrounding rock. By repeatedly generating the closed fracture zones, a fracture network appears in the roadway-surrounding rock. The development of zonal disintegration of roadway-surrounding rock mainly depends on the rock mass strength and its stress state. Zonal disintegration only occurs when the crustal stress of the roadway-surrounding rock exceeds its strength. When the horizontal stress is low and the vertical stress exceeds the rock mass strength, zonal disintegration only occurs on two sides of the roadway. When the vertical stress is low and the horizontal stress exceeds the rock’s mass strength, it only appears on the roof and floor. When the values of cohesion, internal friction angle, and tensile strength are reduced in the same proportion, cohesion has the greatest impact on the expansion of the zonal disintegration zone, followed by the internal friction angle, while the tensile strength effect is the least. In anchor-supported roadways undergoing zonal disintegration processes, the intact zone blocks slide relatively along the fracture surface during the process of loosening and deformation of the surrounding rock, making the anchor rods susceptible to tensile, shear, and bending actions.

SIMULATION OF SOIL LOOSENING PROCESSES WITH COMPRESSED AIR

A model for describing soil loosening when exposed to compressed air is considered. The model allows you to calculate, depending on the compressed air pressure, the diameter of the hole and the depth of the feed point, the dilatancy zone (the area within which the created stresses will exceed the threshold and the loosening process will begin). The developed model is also used to describe soil loosening at several air supply points and at different jet directions.

A prediction model of bolted joint loosening based on deep learning network

The Bolted joint loosening is challenging to describe with an accurate mathematical model. Therefore, a prediction model of bolted joint loosening was proposed based on a deep learning network. Firstly, the loosening experiments of the bolted joint were carried out with an orthogonal test. And the nonlinear and uncertain characteristics of bolted joint loosening process were further analyzed. Furthermore, a prediction model of bolted joint loosening based on a deep learning network was established. The proposed model was trained and verified using the experimental data. The results showed that compared with the traditional mathematical and regression models, the model could not only obtain the change of the mean value of preload but also describe the confidence interval of the change of preload in the sense of probability synchronously. The experiment data and prediction data are in good agreement, which can be used to validate the rationality of the model.

Electromechanical Impedance Instrumented Wearable Piezoelectric Ring-Type Sensor for Bolted Connection Monitoring

Due to the loss of preload, structural failure caused by bolt loosening is common in engineering structures. Effective monitoring of bolted connections is of great importance in providing early warning to the structural maintenance department. In this study, a novel and reusable electromechanical impedance (EMI) instrumented wearable piezoelectric ring (WPR) was proposed to detect bolted connection loosening. In the experimental investigation, the EMI spectra of three identical WPRs during the bolt-loosening process were acquired and analyzed. It was concluded that bolt looseness changes can be qualitatively and quantitatively characterized by conductance spectra. Specifically, the resonance frequency and amplitude at certain frequencies were reduced correspondingly as bolts loosen. This was further validated by finite element model simulation results. Moreover, two statistical metrics including mean absolute percentage deviation (MAPD) and root mean square deviation (RMSD) were adopted to evaluate different degrees of bolted connections quantitatively. Both metrics showed an increasing tendency during the bolt loosening process in three different frequency bands. It was found that both metrics demonstrated a significant linear correlation with bolt torque variations. Both of them serve as reliable indicators to detect loose bolts in the bolted connection. The present work verifies the feasibility and applicability of using EMI-instrumented WPR to monitor bolted connections.

The effect of periprosthetic bone loss on the failure risk of tibial total knee arthroplasty.

The effect of long-term periprosthetic bone loss on the process of aseptic loosening of tibial total knee arthroplasty (TKA) is subject to debate. Contradicting studies can be found in literature, reporting either bone resorption or bone formation before failure of the tibial tray. The aim of the current study was to investigate the effects of bone resorption on failure of tibial TKA, by simulating clinical postoperative bone density changes in finite element analysis (FEA) models and FEA models were created of two tibiae representing cases with good and poor initial bone quality which were subjected to a walking configuration and subsequently to a traumatic stumbling load. Bone failure was simulated using a crushable foam model incorporating progressive yielding. Repetitive loading under a level walking load did not result in failure of the periprosthetic bone in neither the good nor poor bone quality tibia at the baseline bone densities. When applying a stumble load, a collapse of the tibial reconstruction was noticed in the poor bone quality model. Incorporating postoperative bone loss led to a significant increase of the failure risk, particularly for the poor bone quality model in which subsidence of the tibial component was substantial. Our results suggest bone loss can lead to an increased risk of a collapse of the tibial component, particularly in case of poor bone quality at the time of surgery. The study also examined the probability of medial or lateral subsidence of the implant and aimed to improve clinical implications. The FEA model simulated plastic deformation of the bone and implant subsidence, with further validation required via mechanical experiments.

Improvement of the machine for wool scutching for obtaining ecologically clean fiber

The article covers natural wastes emitted from wool in the loosening process. The results of experimental research of the amount of ecologically clean fiber are shown. Analytical research of scientific and technical information about technologies and technical means of primary processing of wool, as well as previous research in this area has been carried out. Improvement of the technological parameters of machines for loosening wool by adapting them to the characteristics of local wool has been studied. The dependence of the separation of contaminants from the composition of wool on the design of the fire bar of the fire grate of the column structure and the density of the product in the working chamber has been determined. Based on the results obtained, it has been determined that the use of an improved wool loosener improved cleaning efficiency. It has been determined that during the testing process, an experimental sample showed high performance. It was determined that after the peg drums, the porosity of the wool doubled, and the density of the wool decreased by half. The development of a new design of a loosening machine for loosening and cleaning wool fibers has been shown in technological schemes.

Prediction for Loosening Life of Bolted Joints Using IMUs With Dimensionality Reduction

Bolted joints are widely employed as fasteners, but the loosening of them leads to severe safety risks. Prediction for Remaining Bolt Loosening Life (RBLL) allows for more proactive management of equipment and can help to optimize maintenance schedules, which hence reduces maintenance costs. Due to the complex structure and various working conditions of bolted joints, it is difficult to describe the loosening process with an intrinsic mechanism. The lack of understanding on mechanism makes it difficult to predict RBLL using conventional approaches. This paper develops a passive monitoring system based on Inertial Measurement Units (IMUs) for monitoring multi bolts in complex structures. By analyzing the vibration signals obtained by bonded sensors around joints, the changes in structural properties caused by loosening can be detected and used to evaluate RBLL. A novel prediction algorithm for RBLL is presented in this paper: with a pipeline of preprocessing, signal feature extraction, dimensionality reduction, and regression, a mapping from vibration signals to RBLL are established. The dimensionality reduction methods compress original features into fewer but informative and non-redundant ones. The compression elimination undesirable noise and prevent overfitting, resulting in improvements in both prediction accuracy and training speed. Specifically, the number of features is compressed from 972 to 200, and Rooted Mean Squared Error (RMSE) is reduced to about 19.0% with Training Time Cost (TTC) to about 22.3%.

The release of osteoclast-stimulating factors on supraphysiological loading by osteoprogenitors coincides with expression of genes associated with inflammation and cytoskeletal arrangement

Supraphysiological loading induced by unstable orthopedic implants initiates osteoclast formation, which results in bone degradation. We aimed to investigate which mechanosensitive cells in the peri-implant environment produce osteoclast-stimulating factors and how the production of these factors is stimulated by supraphysiological loading. The release of osteoclast-stimulating factors by different types of isolated bone marrow-derived hematopoietic and mesenchymal stem cells from six osteoarthritic patients was analyzed after one hour of supraphysiological loading (3.0 ± 0.2 Pa, 1 Hz) by adding their conditioned medium to osteoclast precursors. Monocytes produced factors that enhanced osteoclastogenesis by 1.6 ± 0.07-fold and mesenchymal stem cells by 1.4 ± 0.07-fold. Medium from osteoprogenitors and pre-osteoblasts enhanced osteoclastogenesis by 1.3 ± 0.09-fold and 1.4 ± 0.03-fold, respectively, where medium from four patients elicited a response and two did not. Next generation sequencing analysis of osteoprogenitors revealed that genes encoding for inflammation-related pathways and cytoskeletal rearrangements were regulated differently between responders and non-responders. Our data suggest that released osteoclast-stimulating soluble factors by progenitor cells in the bone marrow after supraphysiological loading may be related to cytoskeletal arrangement in an inflammatory environment. This connection could be relevant to better understand the aseptic loosening process of orthopedic implants.

Does stem profile have an impact on the failure patterns in revision total knee arthroplasty?

IntroductionRevision total knee arthroplasty (RTKA) has been increasing continuously. The results of RTKA still remain unsatisfactory. Failure patterns and risk factors in RTKA were thoroughly analyzed, with periprosthetic joint infections (PJI) and aseptic loosening remaining at the forefront of re-revision (ReRTKA) causes. While there is evidence that stem profile impacts the revisability of cemented implants, its association with the modes of RTKA failure is unknown.Methods50 consecutive ReRTKA performed in a single orthopedic center during 2016–2017 were retrospectively analyzed. The cases were stratified according to age, sex, number of preexisting revisions, fixation technique, stem design and causes of re-revision. All explanted implants with conical vs. cylindrical stem profiles were compared.ResultsMean age was 67 ± 11.5, and 54% were females. 72% of the cases had ≥ 3 previous revisions. 88% were full-cemented, 3% hybrid and 9% press-fit stems. 36% of the RTKA had conical, 58% cylindrical and 6% combined stem profiles. 92% of the RTKA components were removed. Removal causes were: PJI (52.2%), aseptic loosening (34.8%), implant malposition (9.8%), painful knee (1.1%) and instability (2.2%). While the overall RTKA failure patterns were equally distributed between conical and cylindrical stems, subgroup analysis of only cemented ReRTKA revealed a higher incidence of aseptic loosening within cylindrical stem profiles (46.7% vs. 25.7%, P = 0.05).ConclusionStem profile may have an impact on the process of aseptic loosening in cemented non-metaphyseal engaging RTKA, with cylindrical designs tending to worse outcomes than conical designs. Large cohort studies could provide more clarity on current observation.

Determination of parameters of a trepanning machine for cleaning wool fibers

This article provides information about the technology of primary processing of wool and the feeding part of the baking machine. It analyzes the operating principle and types of baking machines at the enterprise of primary processing of wool. The disadvantages of baking machines affecting the product are considered. The principle of work and the design of new baking machines for the manufacture of quality products are proposed. The article provides information about the technology of primary processing of wool. Studied the mechanisms of machines for the production of wool and identified their design flaws. The designs and sizes of the pegs of the peg drum are analyzed. The designs of the loosening machines used in the loosening process were studied. The types and principles of baking machines working at the enterprises of primary processing of wool are analyzed. The technical characteristics of the machines are given. The negative aspects of the details of the mechanical impact on the product are noted. Defects of baking machines and their effect on the product are explained. The design and operational principle of a new spraying machine for the preparation of high-quality products is proposed. The proposed characteristics of the machine have high performance, structural design, impact on the product, low energy consumption, energy efficiency and effective loosening. In this machine, the optimal version of parts that have a positive effect on the natural characteristics of the product is selected. The designs of the loosening machines used in the loosening process were studied. The types and principles of baking machines working at the enterprises of primary processing of wool are analyzed. The technical characteristics of the machines are given. The negative aspects of the details of the mechanical impact on the product are noted. Defects of baking machines and their effect on the product are explained. The design and operational principle of a new spraying machine for the preparation of high-quality products is proposed. The proposed characteristics of the machine have high performance, structural design, impact on the product, low energy consumption, energy efficiency and effective loosening. In this machine, the optimal version of parts that have a positive effect on the natural characteristics of the product is selected.

УПРАВЛЕНИЕ СОЗНАНИЕМ СО СТОРОНЫ ЭКСТРЕМИСТСКИХ ОРГАНИЗАЦИЙ СРЕДСТВАМИ ИНТЕРНЕТ-КОММУНИКАЦИИ

Oblective of the study is to determine how extremist organizations manage the consciousness of individuals they recruit into their activities using mass communication media.     The methodological basis of the research consists of a systematic methodological approach used to analyze the cognitive-ideological matrices of individual consciousness, an information and communication methodological approach that allows us to consider the process of loosening and replacing nuclear ideologies of political consciousness with activated borderline ideologies that were previously in a de-actualized state, a subjective-personal methodological approach applied to reveal the process of the impact of extremist propaganda in recruiting new members.     Research results are presented by the conclusion about the role of activation of borderline ideologies by extremist propaganda in the process of reformatting the political consciousness of the individual, the conclusion about the role of Internet communication in the management of extremist organizations by the consciousness of social individuals, the conclusion about the radicalization of the political consciousness of the individual under the influence of extremist propaganda by means of Internet communication and its involvement in extremist and terrorist activities.     Prospects of the study unfold in the form of an analysis of the activities of specific extremist organizations, the development of methods to counter the propaganda of extremism and terrorism, the rehabilitation of a person subjected to the propaganda of extremism.

Morpho-Physiological and Transcriptome Analyses Provide Insights into the Wizened Bud Formation in Pear Trees

Wizened buds are frequently observed in pear (Pyrus spp.) trees, which greatly reduces the yield. However, little is known about the mechanism of wizened bud formation. Here, we analyzed physiological and transcriptomic differences between normal buds and wizened buds of ‘710’ pear trees. The results indicated that the sorbitol and boron (B) contents, during bud differentiation, were significantly reduced in wizened buds. The microscopic observation and transcriptome analysis revealed that the collapse of the organ structure and cell wall loosening process may have a close relation with wizened bud formation. Moreover, reduced transcript levels of PpyMYB39.1 and its downstream genes (PpyHT1, PpyHT2, PpyPMEI1 and PpyPMEI2) were found in wizened buds. However, the transcript levels of pentose and glucuronate interconversion pathway genes (PpyPME3, PpyPL18.1, PpyPL18.2, PpyPG1 and PpyPG2) and the concentration of pectin-degradation-related enzymes were increased in wizened buds. Correspondingly, the pectin concentration was significantly reduced in wizened buds. Taken together, PpyMYB39.1 may promote pectin degradation and decrease carbohydrate transport by regulating its downstream genes and is supposed to play a vital role in the wizened bud formation resulting from the cell wall loosening process. Our study provides fundamental insights into wizened bud formation and strategies to reduce the wizened bud occurrence in pear trees.

Structural behavior of large anchor bolts used for sign-support structures

Anchor bolts are commonly used to tie sign-support structures to their concrete base through a double-nut moment connection. Over the past decade, loose anchor rod nuts have proven to need frequent attention, incurring significant cost, while endangering the safety of sign-support structures. In particular, connections tightened with the current pre-tensioning specifications are found to have been loosened within only a year (if not sooner) after installation. Considering this long-standing issue, the objective of this study is to investigate the structural behavior of large anchor bolts used at the base of sign-support structures and evaluate the parameters that influence the rod tightening and loosening process most. For this purpose, a set of Skidmore-Wilhelm bolt tension calibrator tests were performed on different sizes of bolt that had been lubricated with various methods. The tests were to evaluate the effects of the lubrication method on the tightening process. In addition, a sign-post structure removed from the field was tested in the laboratory to study the bolt behavior when it was subjected to the lateral load. Finite-element models were then developed and calibrated using the data collected form the laboratory test. A parametric study was conducted on the calibrated model to understand the effects of key contributing factors, such as level of tightening preload, variation of preload level, washer size, and grip length, on the tightening and loosening process. The investigations determined that the current tightening process can generate a stress concentration in the rod in the range of 30 ksi, which was 55% of the rod's yield strength. The clamping force was also noted to experience a significant reduction during the first few cycles of loading (i.e., up to 20 cycles), beyond which further reduction was minimal. The outcome of this study directly helps choose a preload level that ensures adequate tightening, while avoiding permanent damage to the rod. This is critical for preventing or alleviating the issue of nut loosening.

Аналітичний огляд технічних рішень голчастих ротаційних знарядь для внесення рідких добрив у шар ґрунту

The purpose of the research is to identify trends in the technical development of needle rotary means for injecting liquid mixtures into the soil layer, taking into account the essence of the technological operation, as a control action to change the state of the soil. Research methods - analysis and generalization of essential features of technical solutions of needle tools for processing and applying liquid fertilizers to the soil layer. In order to develop criteria for evaluating technical solutions, scientific research on the classification of tools of this type and generalized interpretations of the essence of technological operations of tillage, application of chemicals, sowing, etc. were preliminary analyzed. Research results. An analysis from the point of view of the possibility of controlling the process and the degree of its implementation by a specific instrument allows to assess the place of a specific tool in the development stage. In accordance with the "System of properties and indicators of soil condition" [Vetokhin 2009], any introduction / extraction of matter, energy and / or information is considered a controlling factor in changing the state of the system, the ultimate goal of which is to change the level of metabolic processes and, as a result, to change the yield. An increase in the information component of processes is considered to be a tendency in the development of agricultural technologies and technical means aimed at a radical reduction in resource consumption [Vetokhin, Altybaev 2019]. One of the first technical solutions of needle tools for applying liquid to the soil layer is known from the American patent of 1898 [Morris, 1898]. The aim of the inventor is to provide a device adapted to form a hole in the soil for receiving a plant and supplying water to the hole. The current state of the development of technical means is illustrated by the invention, patented in the USA, RF and EU, "Systems, methods and devices for the introduction of agricultural liquids" [Stoller et al., 2020], [Radtke et al., 2020], [Levy et al., 2015]. A qualitatively new level is achieved by the inclusion of sensors of the current state of the soil in the process control system. Sensors come in contact with the soil to monitor its condition, in particular, density, temperature, humidity, percentage of carbon, organic matter, potassium, phosphorus, nitrogen, etc. In a fluid delivery system, each of the outlets is connected to separate sources of input material and may contain dissimilar fluid materials, for example, different types of fertilizers, liquid insecticides. Conclusions. It has been established that the technical solutions of needle tools have been developed from manual devices of periodic action to rotary needle tools of continuous action for dosed application of complex fertilizers and simultaneous loosening of the soil. The next step in technical development is to expect the creation of automated complexes with rotary needle working bodies, which are able to continuously assess the condition of the soil and control the process of loosening and applying agricultural materials with different doses along each row. A promising stage of technical and technological development is the creation of means that will directly control metabolic processes in a system with a layer of soil. In a scientific sense, the study of trends in the development of technical means confirmed the previously published theoretical generalization of soil properties in relation to the process of managing its condition with minimal resource costs.

Progressive loss of implant fixation in a preclinical rat model of cemented knee arthroplasty.

Aseptic loosening of total knee arthroplasty continues to be a challenging clinical problem. The progression of the loosening process, from the initial well-fixed component, is not fully understood. In this study, loss of fixation of cemented hemiarthroplasty was explored using 9-month-old Sprague-Dawley rats with 0, 2, 6, 12, 26 week end points. Morphological and cellular changes of cement-bone fixation were determined for regions directly below the tibial tray (epiphysis) and distal to the tray (metaphysis). Loss of fixation, with a progressive increase in cement-bone gap volume was found in the epiphysis (0.162 mm3 /week), but did not progress appreciably in the metaphysis (0.007 mm3 /week). In the epiphysis, there was an early and sustained elevation of osteoclasts adjacent to the cement border and development of a fibrous tissue layer between the cement and bone. There was early formation of bone around the cement in the metaphysis, resulting in a condensed bone layer without osteoclastic bone resorption or development of a fibrous tissue layer. Implant positioning was also an important factor in the cement-bone gap formation, with greater gap formation for implants that were placed medially on the tibial articular surface. Loss of fixation in the rat model mimicked patterns found in human arthroplasty where cement-bone gaps initiate under the tibial tray, at the periphery of the implant. This preclinical model could be used to study early biological response to cemented fixation and associated contributions of mechanical instability, component alignment, and periprosthetic inflammation.

Energy assessment of intensive protective tillage

The study analyzes the traction resistance of chisel ploughs when working on light clayey chernozems, widespread in the arid southern part of Russia. This study allows concluding that in the theoretical description of the process of deep loosening of the soil, the influence of the square of the working speed of the machine-tractor unit could be neglected. The use of linear dependence not only provided an increase in the convergence of experimental and theoretical studies but also simplified the analysis of the results. So, for example, the use of a linear trim based on the results of experimental studies made it possible to derive the average values of the empirical coefficients for classic arrow-shaped plows: fp=0.4; k p=15.15 κN/m and εp=6.15 κN·s/m2, and for plows with a pair-block arrangement of working bodies: fp=0.4; kp=21.45 κN/m and εp = 1.61 κN·s/m2. The study found that the use of a pair-block arrangement of working bodies on subsoiler ploughs, in comparison with their arrow-shaped arrangement, helps to reduce the resistivity during chiselling by about 14%. At the same time, the share of energy consumption for useful soil deformation increases to values of more than 80%, while for classic subsoiler ploughs this figure is about 50%.

Effects of Friction Coefficient and Various Geometric Parameters on Loosening Phenomena of Bolted Joints under Shear Loads

There are two types of loosening phenomena of threaded fasteners which sometimes cause serious accidents involving a variety of machines, structures and electronic devices: rotational loosening and non-rotational loosening of threaded fasteners. The former pattern frequently occurs due to shear loads repeatedly applied perpendicular to the bolt axis. This paper aims to clarify quantitatively how friction coefficients at contact surfaces and the geometry of threaded fasteners affect rotational loosening by conducting three-dimensional finite element analyses with the use of helical thread models. Numerical results showed that friction coefficient at nut bearing surface largely influences the loosening process, and that the introduction of fine screw threads and longer grip length are effective in preventing or mitigating the progress of thread loosening. Based on the foregoing results, a practical proposal is made for the prevention of thread loosening.

Loosening of Bolted Connections under Transverse Loading in Timber Structures

Bolted joints are widely used in timber structures, and the loosening of bolt connections will reduce the structural performance. In this paper, a mechanical model of bolt connection for timber structures is established, and the process of bolt loosening under a transverse load is investigated. By using the finite element method to construct an accurate thread model with a helix angle, the thread contact state during the bolt loosening procedure was analyzed in detail, and the factors such as load amplitude, load frequency, load location, and different timber materials on bolt loosening are also studied. In the timber structure, the load amplitude is the main factor affecting the bolt loosening, the decay rate of the preload in the bolted joint is positively correlated with the amplitude of the cyclic transverse load. The frequency of the loading has a smaller effect on the looseness, the preload decreases as the frequency increases. When the load is applied to the smooth rod part of the bolt, the preload force will decrease rapidly, and the distance between the load position and the bolt has no effect on the change in looseness. The decreasing range of the preload is different with different timber material, but the decreasing law is the same. The model can be applied to analyze the loosening rule of bolted connections in timber structures.

Effect of dynamic cyclic loading on screw loosening of retightened versus new abutment screw in both narrow and standard implants (in-vitro study)

BackgroundThe purpose of this in-vitro study was to evaluate the effect of dynamic cyclic loading on screw loosening of retightened abutment screw versus new abutment screw in both narrow and standard implants.MethodsSeparate acrylic resin blocks containing implant assembly (fixture, abutment, abutment screw, metal tube capping the abutment). Samples were divided into two main groups according to the diameter of implant: group 1 (GI 4.5-mm diameter) and group 2 (GII 3-mm diameter). Each group is subdivided into two subgroups according to the suggested option to manage screw loosening either by retightening (GIA, GIIA) or using new screws (GIB, GIIB). One hundred thousand cycles of eccentric dynamic cyclic loading (DCL) were applied before and after retightening or replacing the screw; then, removal torque loss (RTL) ratio was calculated, tabulated, and analyzed by t-student, ANOVA, pair wise Tukey’s tests.ResultsThere were differences between GI and GII regarding the incidence of screw loosening process. Removal torque loss ratio was higher in GIB and GIIB where the old abutment screws were replaced by new screws for both standard implants (SIs) and narrow diameter implants (NDIs). There was significant effect of retightening and replacing the abutment screws after exposure to DCL.ConclusionsWithin the limitations of this in-vitro study, it can be conclude that screw loosening process occurred in both SIs and NDIs but with higher values in NDIs. It is better to retighten the screw of NDIs and SIs than replacing it with a new screw.