Cantilever Length Research Articles

Utility of measuring anterior-posterior spread to determine distal cantilever length off a fixed implant-supported full-arch prosthesis: A review of the literature

BackgroundHistorically, anterior-posterior (AP) spread assessments were often used to determine the length that a distal cantilever could be extended off an implant-supported fixed full-arch prosthesis. Types of Studies ReviewedThe authors searched the literature for articles that used AP spread to calculate cantilever size to be constructed off implants bearing a fixed implant-supported full-arch rehabilitation. ResultsThe data indicate that the relationship between AP spread and cantilever length is not linear and many influences (such as beam theory, cantilever size differences in the mandible versus maxilla, number and distribution of placed implants, prosthetic materials, and framework design) need to be considered when computing cantilever length with respect to fixed implant-supported prostheses. Practical ImplicationsRecommendations using AP spread assessments to compute cantilever lengths have not been validated by means of prospective scientific evaluations. Therefore, AP spread evaluation is just one of many issues that need to be considered when determining distal cantilever length associated with a fixed full-arch implant-bearing prosthesis.

The effect of the design of a mandibular implant-supported zirconia prosthesis on stress distribution

Statement of problemProsthetic complications have been frequently reported in implant-supported complete-arch prosthesis. Prosthetic restorations designed with an all-on-four treatment concept and fabricated from zirconia ceramic may be used to overcome these problems. PurposeThe purpose of this biomechanical study was to evaluate the effects of cantilever length and inclination of implant on the stress distribution in bone tissue, implant, and a monolithic zirconia ceramic-lithium disilicate glass-ceramic superstructure for all-on-four prosthesis. Material and methodsAll-on-four mandibular prosthesis fabricated from a zirconia and lithium disilicate glass-ceramic (LDGC) superstructure was designed with cantilever lengths of either 5 mm or 9 mm and posterior implants with a distal tilt of either 15 or 30 degrees. Stresses were evaluated with a simulated application of a static load of 600 N. ResultsIncreasing implant inclination from 15 to 30 degrees led to a decrease in maximum principal stress (MaxPS) values of approximately 4 to 7 MPa in cortical bone around all implants except the right anterior implant in the designs with short cantilevers and an increase in MaxPS values (approximately 3 to 19 MPa) in the same places in the designs with the long cantilevers. Increasing cantilever length from 5 to 9 mm resulted in an increase in minimum principal stress (MinPS) values of approximately 3 to 13 MPa in the cortical bone surrounding all posterior implants. In the designs with the long cantilever, MaxPS values increased approximately 3 to 4 MPa in spongy bone adjacent to the right posterior implant. An increase in cantilever length also led to higher vMS values at the first and second implant grooves in the right posterior implant in the design with the 15-degree implant tilt. An increase in implant inclination in the design with the short cantilever resulted in lower vMS values at the apex and all grooves of the left posterior implant, whereas in the design with the long cantilever, an increase in implant inclination resulted in lower stress values in the first and second grooves of the same implant. An increase in implant inclination led to in an increase in vMS values in the core structure. ConclusionsIn zirconia ceramic restorations by using an all-on-four design with an LDGC superstructure, short cantilevers may be preferable because they result in a more favorable distribution of stress than long cantilevers. An increase in implant angulation from 15 to 30 degrees decreased MaxPS values in cortical bone.

Dynamic trajectory and parametric resonance in coupled pendulum-beam system

The azimuthal-radial pendulum is a coupled pendulum-beam system where a pendulum and a supporting string are attached to the free end of a cantilever beam with its other end clamped. Conversion between radial (parallel to cantilever) and azimuthal (perpendicular to cantilever) modes of oscillations is observed when the radial frequency is twice the azimuthal frequency. A theoretical Lagrangian formulation of the system is presented and numerical predictions are compared to experimental data, showing good agreement. A non-linear coupling term arising from the inextensibility of the cantilever beam is shown, via simplifying assumptions that reduce the equations of motion to the Mathieu equation for parametric oscillators, which is responsible for the parametric resonance observed in the system. Experimental work involved measurements of the dynamic trajectory of the pendulum bob in the lab frame, and systematic investigation into the maximum conversion amplitude, beat frequency, and parametric resonance regime boundaries as a function of bob mass, string length, cantilever length, initial release amplitude, and other relevant parameters, shows good agreement with numerical results.

Identification of Geometric Parameters Influencing the Impedance Sensitivity of Piezoelectric Mass Sensors

For resonant mass sensors, a frequency sweeping procedure is usually required to identify the frequency shift in a relative frequency range, which is not suitable for detecting incremental mass. The impedance detection method can measure mass at a fixed frequency. To further explore such sensing mechanism, the main geometrical parameters influencing the impedance sensitivity have been carefully analyzed considering the electro-mechanical coupling effects, and a series of design rules have been proposed for improving sensitivity, e.g. increasing the cantilever length and piezoelectric thickness, which is contrary to the traditional method of minimizing the geometric size for frequency based sensors. Three macro-sized sensors with 21.0 mm, 26.0 mm and 30.0mm long cantilevers are fabricated, and the measured impedance sensitivities are $212.7\Omega $ /mg, $514.8\Omega $ /mg and $737.4\Omega $ /mg that are increasing with the cantilever length, thus validating the design rules on cantilever length. However, the frequency sensitivities are 14.0 Hz/mg, 9.2 Hz/mg, and 7.2 Hz/mg that are decreasing with the cantilever length. Furthermore, the impedance sensitivity is much higher than the frequency sensitivity, and the design map of the sensor is presented as an overall guideline for structure optimization.

Signal-to-noise ratio enhanced electrode configurations for magnetoelectric cantilever sensors

Magnetoelectric cantilevers consisting of strain-coupled magnetostrictive and piezoelectric (PE) layers are applicable to magnetic-field sensing. For the first bending mode, the magnetic field-induced stress distribution is of equal sign along the cantilever length. Thus, a plate-capacitor electrode configuration encompassing the complete PE layer may be used for collecting the strain-induced charge. For higher order modes, stress regions of the opposite sign occur in the cantilever length direction. To prevent charge cancellation and to harvest the piezoelectric induced charge efficiently, segmented electrodes are employed. This study investigates the effect of the electrode configuration on the signal-to-noise ratio (SNR) for higher order bending modes. The charges collected by the electrodes are calculated using a finite element method simulation considering the mechanical, electrical, and magnetic properties of the cantilever. By combination with an analytic noise model, taking into account the sensor and amplifier noise sources, the SNR is obtained. We analyze a 3 mm long, 1 mm wide, and 50 μm thick silicon cantilever with layers of 2 μm magnetostrictive soft amorphous metal (FeCoSiB) and 2 μm piezoelectric aluminum nitride. We demonstrate that an SNR-optimized electrode design yields an SNR improvement by 2.3 dB and 2.4 dB for the second and third bending modes compared to a signal optimized design.

Façade Components Optimization of Naturally Ventilated Building in Tropical Climates through Generative Processes. Case study: Sumatera Institute of Technology (ITERA), Lampung, Indonesia

Global warming and climate change have led to the world energy crisis. While it also leads to the crisis of energy consumption, the main reason is still debatable among the researchers. However, the released of carbon emission in construction field is generally believed has triggered the phenomena and become the primary cause of global warming. It is proven that the building sector contributes to the biggest causes of overheating in the environment. Based on previous research, residential and commercial has reached 20% to 40% of the total energy consumption and this growing trend is still happening. Moreover, the electricity consumption in the building and construction process is the main reason for the growth of carbon emission. Therefore, the stakeholder particularly architects and designer should take an early initiative to overcome the problems. One of the approaches is to predict building performance through simulation in the initial design phase. In line with this, rapid technology development has brought to an alarming situation concerning energy consumption. Passive design is considered as one of the strategies to moderate indoor temperature in a tropical climate. Some studies suggest that the use of natural ventilation is potentially reducing operating costs and produce better thermal and indoor air quality. This study will investigate the optimization process of daylight performace condition that driven by façade components such as balcony size, orientation, openings, layout and louver windows using generative and parametric tools through multi-objectives optimization and generative simulation. The methodology used in this research is generative simulation in parametric platform named Grasshopper sith plugin software ladybug + honey bee. From the simulation it is resulted that Preferred individuals have an illuminance value of 211 test points. The properties owned by these individuals are cantilevered as a canopy at the height of 3 meters, a cantilever or canopy length of 2 meters, the building’s orientation angle to the south is 21 °, and has 32% opening of the total façade surface.

Finite Element Analysis of Displacement and Vibration Characteristics of Cantilevered Plate

The cantilever structure will produce a large dynamic response under the vertical load, which will cause the user’s discomfort. Therefore, the vibration characteristics of the structure caused by the vertical load are an important part of the comfort design of the cantilever structure in the normal use limit state. This article takes the vertical displacement of a cantilevered balcony slab on one side of a project under load as an example, and builds a model in the nonlinear finite element software to calculate the structural displacement and the factors of the cantilever length and the tensile reinforcement, and the corresponding comfort evaluation is carried out, which provides a reference for the vibration comfort evaluation of the house cantilever structure.

Analysis of Dynamic Behavior of V-Shaped Atomic Force Microscope Cantilever in Contact and Tapping Modes by Considering Various Immersion Surroundings

In atomic force microscope (AFM) as a powerful device for scanning the samples, a cantilever is used to sense the variations of its dynamic characteristics due to the tip–sample interaction. Theoretical models that can accurately simulate the surface-coupled dynamics of the cantilever are necessary for quantifiable and qualitative explanation and understanding of measured results. A good understanding of the dynamics of AFM cantilevers vibrating in liquid is needed for the interpretation of scanning images, selection of AFM operating conditions and evaluation of sample’s mechanical properties. In this paper, the amplitude of frequency response functions (FRF) of vertical and rotational movements for a V-shaped atomic force microscope beam immersed in various surroundings has been surveyed for the first time. For rising the precision of theoretical model, we have considered all needful details for the beam and sample. The amplitude of FRF of vertical and rotational movements and resonant frequency of beam have been surveyed by supposing cantilever thickness, breadth and length, the angle between cantilever and sample surface, tip height and normal and lateral tip–sample interaction force. In this study, carbon tetrachloride (CCL4), methanol, acetone, water and air have been considered as surroundings. The results show that an increase in the tip–sample interaction force considerably raises the amount of resonant frequency. By increasing the liquid viscosity, the amplitude of FRF for vertical and rotational movements and resonant frequency reduce. Moreover, the amplitude of FRF of vertical and rotational movements is reduced by raising the rectangular and tapered parts lengths, but increased by raising the rectangular part breadth and cantilever thickness. The resonant frequency goes down by increasing the rectangular and tapered parts lengths and rectangular part breadth, but increases by rising the cantilever thickness. In this paper, we have tried to model the realistic dynamic behavior of V-shaped AFM beam in contact and tapping modes with the most accuracy. Results show good agreement. Based on the experimental results, the present theoretical model can forestall better the realistic behavior of tapping mode than the contact mode for V-shaped AFM cantilever. Based on the complexity of the V-shaped AFM cantilever, this study has been done for the first time in both of the contact and tapping modes.

Size-dependent dynamic stability analysis of the cantilevered curved microtubule-associated proteins (MAPs)

A pathway to the design of even more effective versions of the powerful anti-cancer drug Taxol is opened with the most detailed look ever at the dynamic and static behaviors of MAPs. Regarding this issue, the dynamic stability analysis of cantilevered microtubules in axons with attention to different size effect parameters based on the generalized differential quadrature method is presented. Supporting the effects of MAP Tau proteins and surrounding cytoplasm are considered as an elastic foundation. The better understanding modeled as a moderately thick curved cylindrical nanoshell. The real property of the living biological cells is presented as the Kelvin-Voight viscoelastic properties. Hamilton’s principle is employed to establish the Clamped-Free boundary conditions and governing equations, which is finally solved by the Fourier-expansion based generalized differential quadrature method (FGDQM). Considering length scale and nonlocal parameters (l = 3h, =h/2) in nonlocal strain gradient theory (NSGT) leads to a better agreement with experimental results in comparison by other theories that in the results section is presented, in details. Based on presented semi-numerical results, for a specific value of the cantilevered microtubule length, the influence of the parameter on the amplitude of MAPs is much more considerable, that should be attention to this value. Another important consequence is that when the property of the MAPs is not considered viscoelastic, the relation between axial load and frequency of the living structure is nonlinear but by considering the time-dependent viscoelastic property the relation could be linear. Communicated by Ramaswamy H. Sarma

Optimization Design Analysis of Large Span Cantilevered Cross Bracing Truss of Tai’an Tourism Distribution Center

The main structure of Tai’an Tourism Distribution Center is a steel frame structure system. On its west side, there is a large span cantilever structure with a maximum cantilever length of 22 meters, which adopts a space steel truss structure. The cantilever structure has great visual impact and excellent ornamental value, but it also has irregular items such as irregular torsion, irregular vertical lateral stiffness, and sudden change of floor bearing capacity. The overall stress of the structure is complex, and the design and construction of seismic performance are highly required. The seismic performance of the structure is calculated and analyzed by performance-based seismic design method, and the cantilever structure is modeled and analyzed by 3D3S, a space steel structure design software. The results show that cross support is more reasonable for cantilever structure. In view of the difficulties in the design analysis, this paper also proposes effective strengthening measures to ensure the safety of the structure, and makes technical reserves for later construction of the project, which is also of certain reference significance for similar projects.

Survival rates and prosthetic complications of implant fixed complete dental prostheses: An up to 5-year retrospective study

Statement of problemImplant fixed complete dental prostheses (IFCDPs) are widely used in the rehabilitation of completely edentulous patients, yet limited information is available on the relationship between prosthetic complications and patient-associated and prosthesis-associated risk factors. PurposeThe purpose of this retrospective study was to assess the prosthetic complication and survival rates of IFCDPs after a mean observational period of 3.5 years. Material and methodsEligible participants were identified by an electronic health record review. The study consisted of a review of the dental record and a single-visit study appointment when a comprehensive examination was performed, including a review of the medical and dental history, clinical and radiographic examination, intraoral photographs, patient satisfaction questionnaire, and occlusal analysis. Prosthodontic parameters and risk factors were assessed, including time with the prosthesis in place, bruxism, occlusal device use, prosthesis material, number of implants, cantilever length, and mode of prosthesis retention. Association between these prosthodontic parameters and risk factors and the observed prosthetic complications was assessed. ResultsA total of 37 participants (mean age 62.35 ±10.39 years) with 48 IFCDPs were included. Thirty-eight prostheses were metal-acrylic resin (MR group), whereas 10 were metal-ceramic (MC group). Five of the 48 prostheses failed during the follow-up period, a cumulative prosthesis survival rate of 88%. Minor complications were more frequent than major complications. The most frequent minor complication was loss of screw access hole material (5.18%/year), whereas the most frequently observed major complication was major wear of the prosthetic material (5.85%/year). A significant association was found between not wearing an occlusal device and minor chipping, loss of access hole material, and framework fracture. Minor chipping was significantly associated with bruxism, whereas the opposing dentition significantly affected the total number of prosthetic complications. ConclusionsHigh survival rates were observed with both MR and MC IFCDPs. No significant difference was found between MR and MC groups in terms of patient satisfaction, as well as total number of prosthetic complications.

Effects of Cantilever Length and Implant Inclination on the Stress Distribution of Mandibular Prosthetic Restorations Constructed from Monolithic Zirconia Ceramic.

This study aimed to biomechanically evaluate the effects of cantilever length and implant inclination on the stress distribution of mandibular prosthetic restorations constructed from monolithic zirconia ceramic. Mandibular full-arch prostheses supported by four implants constructed from monolithic zirconia were designed using either a 5-mm or 9-mm cantilever length and a 15-degree or 30-degree distal tilt for the posterior implants. A simulated static load of 600 N was applied from the right side at a 45-degree angle. Von Mises and principal stress values in superstructures were analyzed using the Mesh VR Studio program. When the effects of cantilever length were examined, in the models with the 15-degree implant tilt, stress values for posterior implants, porcelain, and cortical bone were lower when the cantilever length was shorter (5 mm). In the models with the 30-degree implant tilt, stress values in all implants (except for the anterior implant on the right) and in the porcelain superstructure were lower when the cantilever length was shorter; however, stress values for cortical and spongious bone were lower with the longer (9 mm) cantilever. When the effects of implant inclination were examined, in the models with a 5-mm cantilever, stress values for posterior implants and cortical bone were lower when the implant tilt was more severe (30 degrees). In the models with a 9-mm cantilever length, stress values for the right anterior implant, posterior implants, and cortical bone were lower when the implant tilt was less severe (15 degrees). Cantilever length and posterior implant inclination affected the distribution of force. Increasing the cantilever length led to a reduction in stress values in distally tilted posterior implants. Moreover, increasing the distal inclination led to a reduction in stress values in both the distally tilted posterior implants and cortical bone tissue in the model with a short cantilever. The monolithic zirconia full-arch porcelain superstructure was not affected by implant angulation, but was affected by cantilever length, with lower stress values observed with a longer cantilever.

A finite element analysis to study the stress distribution on distal implants in an all-on-four situation in atrophic maxilla as affected by the tilt of the implants and varying cantilever lengths.

Aim:The aim of this work was to evaluate stress distribution on implants in All-on-Four situation with varying distal implant angulations (30°,40°,45°) and varying cantilever lengths (4 mm, 8 mm, 12 mm, 16 mm) in atrophic maxilla using finite element analysis.Setting and Design:A in vitro study, finite element analysis.Materials and Methodology:Three-dimensional finite element model of an edentulous maxilla restored with a prosthesis supported by four implants was reconstructed to carry out the analysis. Three different configurations, corresponding to 3 tilt degrees of the distal implants (30°, 40°, and 45°) were subjected to 4 loading simulations.Statistical Analysis Used:The results of the simulations obtained were evaluated in terms of Von Mises equivalent stress levels at the bone-implant interface.Result:From a stress-level viewpoint, the 45° model was revealed to be the most critical for peri-implant bone. In all the loading simulations, the maximum stress values were always found at the neck of the distal implants. With increasing distal implant tilt, cantilever length reduces depending on the quality of bone. At 30° angulation of distal implant a maximum cantilever length of 16 mm may be given if the quality of bone is D3 but only 8 mm cantilever may be recommended if bone quality is D4. At 40° angulation, 16 mm in D3 bone and 0 mm in D4 bone whereas at 45° angulation, it reduces to 12 mm in D3 bone and no cantilever is recommended with D4 bone.Conclusion:The 45° tilt induced higher stress values at the bone-implant interface, especially in the distal aspect, than the other 2 tilts analyzed. Stress values increased with increased cantilever length which was further influenced by the distal implant tilt and the quality of the bone.

Distortional response of doubly symmetric laminated composite box girder

Analysis for longitudinal bending and pure torsion of box girder can be made by means of elementary theories while distortional effects in the box girder cannot be predicted by these theories. Due to thinness of the laminated composite box walls, generalized loads applied to this structure give rise to warping and distortion of the cross-section. The phenomenon distortion is undesirable as it alters the geometry of the box cross-section and generates some additional stresses thereby reducing the bearing capability of the box girder. The objective of this paper is to understand distortional response of doubly symmetric i.e. rectangular laminated composite box girder for various geometrical parameters. In this study, distortional performance of a single span single cell simply supported laminated composite FRP rectangular straight box girder section is studied for 0°, ±45°, 90° fiber orientations using BEF analogy method for different geometrical parameters. A procedure is derived for warping and distortion of FRP box-girder using BEF analogy method considering a 4th order differential equation. The orthotropic nature of FRP has to be taken into consideration in this analysis. It is observed that from distortional considerations, the box girder section should be proportioned to have large span to depth ratio and increase in the web thickness, the distortion stresses will decreases. There is not significant increase in the distortional stresses and warping stresses with increment of length of side cantilever for lower span to depth ratios. It is also be observed that the distortion stress increases and warping stresses decreases with span for same span to depth ratio.

Piezoelectric layer length and thickness variation effects on displacement, von-Mises stress and electric potential generated by cantilever type piezoelectric energy harvester

Piezoelectric energy harvesters find applicability in remote area of application because of simple design and operation. Piezoelectric layer length and thickness are the key parameters for controlling the resonance frequency and optimal output. In this paper the effect of length and thickness of the piezoelectric layer on the von-Mises stress has been investigated. FEM results have been obtained for varying the length of piezoelectric layer from 50 to 200 µm for two different thicknesses of 2 and 5 µm. It has been observed the variation of the length of the piezoelectric layer has an effect on the von-Mises stress of the cantilever which affects the net potential generated. The base of the cantilever is Silicon; PZT piezoelectric material has been selected for the analysis. The length of the silicon cantilever has been fixed to 200 µm. The parameters for simulation are set as: Variation of Length of piezoelectric layer lpiezo as; 50, 75, 100, 125, 150, 175, and 200 µm. Variation of Thickness of the piezoelectric layer tpiezo as 2 and 5 µm. Thickness of beam Tcanti = 10 µm. Length of beam Lcanti = 200 µm. Displacement, von-Mises stress and electric potential has been obtained from FEM results for the piezoelectric layer length variation from 50 to 200 µm. The displacement of the cantilever increases from 0.0207 to 1.0462 µm, von-Mises stress of the cantilever increases from 6.6899 × 105 to 1.0728 × 108 N/m2 and the electric potential increases from 0.01 to 0.26 Volts when the length is increased from 50 to 200 µm. The results depicts that there is an effect of length and thickness of piezoelectric layer on the total displacement, net stress and electric potential generated by the cantilever.

Effect of seismic mass thickness on the resonance frequency of cantilever type piezoelectric energy harvester

Piezoelectric energy harvesters find applicability in remote area of application because of simple design and operation. Micro-electromechanical system (MEMS) process technology is utilized to fabricate these cantilever based structures. Piezoelectric layer length and thickness are the key parameters for controlling the resonance frequency. However, for further lowering the resonance frequency and having optimal output a seismic mass is introduced at the tip of the cantilever structure. In this paper, the effect of increasing the thickness of the seismic mass on the resonance frequency of the cantilever structure has been investigated. Finite Element Method (FEM) results have been obtained using Coventorware software by varying the thickness of the seismic mass 10–20 µm. It has been observed the variation of the thickness of the seismic mass has an effect on the resonance frequency of the cantilever. As the thickness increases, the volume of the seismic mass increases and the resonance frequency of the cantilever decreases. The base of the cantilever is Silicon; Aluminum Nitride (AlN) piezoelectric material has been selected of 3 µm thickness. The length of the silicon cantilever is varied from 1600 to 2500 µm and the resonance frequency is obtained. At a length of 1600 µm, variation of seismic mass thickness from 10 to 15 µm results in reduction in resonance frequency by 17.27% whereas when seismic mass is varied from 15 to 20 µm the resonance frequency is reduced by 12.63%.

Design of MEMS-based cantilever-type piezoelectric energy harvester for low frequency vibrations

Piezoelectric energy harvesters find applicability in remote area of application because of simple design and operation. Piezoelectric layer length and thickness are the key parameters for controlling the resonance frequency and optimal output. In this paper the effect of position of piezoelectric layer has been investigated. Finite element method (FEM) results have been obtained for varying the position of the piezoelectric layer from 50 to 200 µm for thicknesses of 5 µm. It has been observed the variation of the position of the piezoelectric layer has an effect on the displacement, von-Mises stress of the cantilever which affects the net potential generated. The base of the cantilever is Silicon; lead zirconate titanate (PZT) piezoelectric material has been selected for the analysis. The length of the silicon cantilever has been fixed to 200 µm. The parameters for simulation are set as: Variation of position of piezoelectric layer lpiezo as; 50, 100, 150, and 200 µm. Thickness of beam Tcanti = 10 µm. Length of beam Lcanti = 200 µm. Displacement, von-Mises stress and electric potential has been obtained from FEM results for the piezoelectric layer position variation from 50 to 200 µm. The displacement of the cantilever changes from 84.03 to 41.25 µm, von-Mises stress of the cantilever increases from 2.96 × 106 to 6.45 × 106 N/m2 and the electric potential increases from 0.3224 to 0.5446 V when the position is varied from 50 to 200 µm. The results depicts that there is an effect of variation of position of piezoelectric layer on the total displacement, net stress and electric potential generated by the cantilever.

Stress Evolution Law of Surrounding Rock with Gob‐Side Entry Retaining by Roof Cutting and Pressure Release in Composite Roof

The stress concentration of gob‐side entry surrounding rock is a hot topic in coal mining. In this paper, through theoretical analysis and numerical simulation, the pressure relief mechanism of the gob‐side entry retaining by roof cutting and pressure release (RCPR) and the spatiotemporal development law of surrounding rock stress of the gob‐side entry were analyzed. The studies showed that the gob‐side entry retaining by RCPR shortened the length of the lateral cantilever by directional roof cutting, which weakened the stress level of the gob‐side entry. In the meantime, the goaf gangues could play a good filling role by using their breaking and swelling characteristics under the action of gangue‐blocking supports and further optimized the stress environment along the roadway. Field industrial tests verified that the gob‐side entry retaining by RCPR had a significant effect on pressure relief, and the surrounding rock stress and deformation tended to stabilize after about 160 m of lagging working face. Numerical analysis reproduced the whole process of “mining‐retention‐using” of roof cutting roadway and revealed that surrounding rocks were always in the zone of relative stress reduction during the whole process. The peak value of mining‐induced lateral stress was about 10 m away from the middle point of the gob‐side entry. The change of surrounding rock stress could be divided into three stages: significant increase, dynamic adjustment, and stable stage. However, during the second mining, the stress connected zone would appear on the leading working face, and the stress concentration in this zone was significant. Based on the above analysis, we concluded that the new technology could be applied to the medium‐thickness coal seam in the composite roof.

Influence of metal bar lever-arm on screws detorque for dental prosthesis implant supported

Abstract Introduction The cantilever length of implant-supported fixed prosthesis metal structure has been considered an important factor to transfer occlusion forces to the dental implant. Objective This study evaluated the influence of different extensions of cantilevers of Branemark protocol implant prosthesis when submitted to mechanical thermocycling by screw loosening evaluation. Material and method The groups G10 (n = 5), G15 (n = 5) and G20 (n = 5) were formed according to the distance in millimeters between the force application site in the cantilever and the center of the last implant. All metal structures (n = 15) were submitted to a 120 N cyclic vertical load in a chewing simulation machine (MSM-Elquip, São Carlos-SP, Brazil) under controlled temperature and moisture conditions. Two hundred and fifty thousand mechanical cycles were performed with a frequency of 2 Hz that simulates a masticatory activity similar to 3 months. To compare the data obtained regarding the loosening of the metal structure screws, implant position and sites of load application, the analysis of variance with two factors and the Tukey test were performed. Result Statistical analysis showed that the G10 group presented greater torque loss, statistically different from G15 (p = 0.001) and G20 (p = 0.002), and there was no significant difference between groups G15 and G20. Conclusion It can be concluded from the results that all the screws presented torque loss after simulation of 3 month masticatory activity, suggesting the need for periodical evaluation to prevent failures in the treatment.

Effects of all-on-four implant designs in mandible on implants and the surrounding bone: A 3-D finite element analysis.

The purpose of this study was to observe the stresses of all-on-four implant designs in an edentulous mandible in the implant, surrounding bone, and monolithic ceramics. In mandibular all-on-four implant models, anterior implants were placed vertically, and posterior implants were differently inclined. On the full-arch fixed prosthetic restoration monolithic zirconia framework, monolithic lithium disilicate was prepared as the superstructure. Model 1M (1M-15.5); posterior implants angled at 15° to the occlusion plane and a cantilever length of 5 mm, Model 2M; (2M-15.9), Model 3M; (3M-30.5), and Model 4M; (4M-30.9) were prepared. A total of 300 N bilateral force was applied at an angle of 30° and oblique to the occlusion plane. Stress values on dental implants, abutments, the surrounding bone, and prosthetic restorations were calculated. The highest stress concentration was observed in the 2nd connector region between the canine and the 1st premolar tooth in the monolithic zirconia frameworks (457.21 MPa). Stress concentration in the cortical bone was 60.93 MPa in posterior implants. Stress was higher in posterior angled implants than straight implants. Stress at posterior angulation increased by 21 MPa in implants angled at 15°. In bilateral loading, the force applied to anterior implants does not have a significant effect on the bone structure. Stress concentration increases in posterior angled implants and surrounding bone. Moreover, stress concentration increases as the length of the cantilever, the weakest part in all-on-four implants, increases. As posterior implant angulation increases, stress concentration level and localization are affected.