Thread Pitch Research Articles

Mechanical Design and Stress Analysis of Threaded Dental Implants along the Implant-Bone Interface

In this following work, distribution of stresses along the implant-bone interface is computed by performing 3D finite element analysis on commercially available dental implant system. The analysis of stresses is mainly focused at the implant-bone interface specifically at the neck region i.e. proximal zone. The effect of various thread parameters like thread pitch, and depth were studied on the stress distribution along the implant- bone interface

Influence of the accumulated error in thread pitch on the stress–strain state and cyclic strength of threaded joints

Using the finite element method, the analysis of influence of errors in pitch during the thread production on the behavior of stress distribution in stud–nut joints is performed. The value of maximum local stresses in studs of a threaded joint is shown to substantially depend on errors in thread pitch of a stud and a nut. On the basis of the analyses of stresses and strains under cyclic loading, fatigue curves are plotted for the threaded joints having deviations in thread pitch. It is shown that, with a rational selection of the deviation in pitch, the cyclic strength of threaded joints can be considerably increased. The results of analysis agree satisfactorily with the data of fatigue tests of the M39 × 3 threaded joints.

Load distribution in threads of porous metal–ceramic functionally graded composite joints subjected to thermomechanical loading

Metal–ceramic functionally graded materials (FGMs) have been extensively used in aerospace engineering where high strength and excellent heat insulation materials are desired. In this paper, load distribution in threads of the Thermal Protection System used bolted joint made up of porous ZrO2/(ZrO2+Ni) FGMs is investigated by ABAQUS codes. The bolted joint is subjected to reentry heating corresponding to the Access to Space Vehicle. Effects of bolt–nut parameters including thread tooth profile, thread pitch, and modulus ratio of bolt to nut on load distribution in threads are analyzed in detail. It is found that uneven load distribution in threads occurs at elevated temperature, which mainly focuses on the first two threads closest to the nut bearing surface, with the first thread carrying 74% of the total load. Bolt–nut parameters have great effects on load distribution in threads, with trapezoidal thread, extra fine thread and greater modulus ratio of bolt to nut leading to more evenly distributed load. Further studies show that nut shape has significant effects on load distribution in threads, the optimized nut is designed to make the maximum load bearing ratio of the thread decrease to 30.21%, and thus the service reliability of the bolted joint is greatly improved.

Application of uniform design to improve dental implant system.

This paper introduces the application of uniform experimental design to improve dental implant systems subjected to dynamic loads. The dynamic micromotion of the Zimmer dental implant system is calculated and illustrated by explicit dynamic finite element analysis. Endogenous and exogenous factors influence the success rate of dental implant systems. Endogenous factors include: bone density, cortical bone thickness and osseointegration. Exogenous factors include: thread pitch, thread depth, diameter of implant neck and body size. A dental implant system with a crest module was selected to simulate micromotion distribution and stress behavior under dynamic loads using conventional and proposed methods. Finally, the design which caused minimum micromotion was chosen as the optimal design model. The micromotion of the improved model is 36.42 μm, with an improvement is 15.34% as compared to the original model.

A SIMPLE AND EFFICIENT METHODOLOGY TO IMPROVE DESIGN PROPOSALS OF DENTAL IMPLANTS — A DESIGN CASE STUDY

Objective: To propose a methodology based on virtual simulation to assist in the design proposals of dental implants. Methods: The finite element method (FEM) was used to analyze the biomechanical dental implant system behavior, determining von Mises stress distribution induced by functional loads, varying parameter as load direction and geometric characteristic of the implant (taper, length, abutment angulation, thread pitch and width pitch). A final design was obtained by considering the parameters that showed improved performance. The estimated lifetime of the final design was calculated by reproducing in a virtual way the experimental fatigue test required by the ISO:14801 standards. Results: For all the studied cases, the maximum stresses were obtained in the connecting screw under oblique loads (OLs). The estimated lifetime for this critical part is at least 5 × 106 cycles, which meets the requirement of the ISO:14801. In bone tissue, the largest stresses were concentrated in cortical bone, in the zone surrounding the implant, in good agreement with previous reports. Conclusions: A dental implant design was obtained and validated through a simple and efficient methodology based on the application of numerical methods and computer simulations.

Possibility of Usage of Aluminium Rivet Nuts Connections in Composite Materials

Development and application of composite materials in modern industry are very dynamic. Composite materials seem to be replacing steel and aluminium ones. Composites are a cheaper solution, with similar mechanical strengths. Generally, there are two types of joints in composite structures: mechanical and adhesively bonded ones. The aim of the study was to determine the feasibility of riveted joints in composites materials. Static tensile test method was used. In the test there was used one type of glass fabric (Interglas 92140) from which two types of composite samples were prepared. In each sample there was used the same type of fiber with the same fiber orientation – 3 layers. Samples had dimensions of 220x100 mm and thickness of approximately 1.5 mm. They were connected to each other with aluminium rivet nuts (from 1 to 3) and placed in a metal frame with a screw connection which was made of screws with nominal thread pitch M5. Screws were tightened with constant torque. It was to provide an axial force to the sample during the tensile test. The frame was placed between cross-bars of tensile machine INSTRON 8516. The samples were stretched at a speed of 0.05 mm/s at a distance up to 20 mm. During the tensile test displacement of the samples and pull force were registered. Depending on the fiber orientations and number of rivet nuts composite damage models were described. On the basis of the results the possibility of usage of aluminium rivet nuts connections in composite materials was determined.

Design of an innovative and simplified polar heliostat for integration in buildings and urban environments

The increasing improvement of energy sustainability entails an increase in the use of heliostats in small applications for urban environments. For these applications, smaller heliostats and lower distances traveled by reflected rays are proposed, and, consequently, higher tolerances in error are allowed.This paper describes a new simple heliostatic system suitable for small applications based on a polar heliostat which redirects the sun’s rays parallel to the earth polar axis. Additionally, these solar rays can be redirected towards a desired point by means of a fixed secondary mirror.The polar heliostat is composed of a polygon that is deformable due to the rotary movement of axis A–A′ parallel to the earth’s axis. Its astronomical and mechanical principles are described in the paper. The device is quite simple and it only needs a single action for its positioning, both in elevation and in azimuth, so that it is easily implemented by an electronic controller. Moreover, it is possible to associate and control different heliostats by a single engine.Finally, in this paper, the systematic pointing error of the polar heliostat, and its dependence on the dimensions of the device, has been analyzed, finding out that the average errors decrease as the ratio between the dimensions of the deformable polygon and the thread pitch of axis A–A′ increases. Particularly, for the dimensions of the polar heliostat presented, the average pointing error of the device proposed is ε¯=2.96mrad (with a standard deviation of σɛ=3.11mrad), which is acceptable for small urban applications.

Thread Pitch Variant in Orthodontic Mini-screws: A 3-D Finite Element Analysis

Orthodontic miniscrews are widely used as temporary anchorage devices to facilitate orthodontic movements. Miniscrew loosening is a common problem, which usually occurs during the first two weeks of treatment. Macrodesign can affect the stability of a miniscrew by changing its diameter, length, thread pitch, thread shape, tapering angle and so on. In this study, a 3-D finite element analysis was done to show the effect of thread pitch variant on the stress distribution pattern of the screw-cortical bone interface. While orthodontic forces were applied, stresses were usually concentrated at the first thread of the screw in contact with the cortical bone. The cortical bone provided a significant percentage of stability compared to the trabecular bone against orthodontic forces. Therefore, spongy bone was removed from the finite element analysis. The changes of maximum von Mises stresses were shown on the charts. The results showed that stresses decreased with decrease in thread pitch, but they increase when thread pitch becomes less than a certain value. The pattern of stress distribution differed when the stresses were increased. The results are beneficial for the design of an ergonomic dual miniscrew, with better properties than the commercially available miniscrews and based on the results, a new dual miniscrew is recommended.

Development of spiroid worm gear drive having arched profile in axial section and a new technology of spiroid worm manufacturing with lathe center displacement

With the knowledge of the advantageous characteristics of the cylindrical worm gear drives having arched profile in axial section and the conical worm gear drives having linear profile in axial section, a new geometric type spiroid worm gear drive has been designed and then manufactured, and that is the spiroid worm gear drive having arched profile in axial section [2, 7]. We have developed the production technology of this new gear drive using classical machine. During the classical manufacturing process of conical thread surfaces with lathe center displacement, the worm shaft is driven with the help of the driving pin through the lathe fork. As a result of the shifting of the worm shaft by half cone angle, the path curve of the driving pin will be an ellipse path instead of a circle on the perpendicular plane to axis. The peripheral speed of the spindle is constant, but due to the ellipse path, the radius is constantly changing as a function of time. That is why the angular velocity and the rotation angle are also changing, and these cause pitch fluctuation during the manufacturing process of spiroid worms. During the manufacturing process, we have examined pitch errors which are caused by angular velocity fluctuation. In favour of angular velocity fluctuation, we have to ensure equal thread pitch during the manufacturing process of spiroid worms. That is why we have to design the geometrical shaping of the driving pin to solve the thread pitch fluctuation problem.

基于二维轮廓点云的螺纹中径计算

The multi-parameter measurement of a thread based on profile points may show calculation errors for thread pitch diameters owing to the alignment deviations and inhomogeneous abrasion of thread work-pieces.Therefore,a new method for calculating the thread pitch diameters based on the2-dimensional profile point clouds was proposed.The cubic spline interpolation was used to increase the data point densification uniformly,and the robust Gauss regression filter was adopted to get the midline of contour.Then,an objective function was put forward to minimize the mean square error of the distance between two adjacent flank segments,and the complex simulated annealing algorithm was adopted to solve the function to get the pitch line.Finally,the pitch diameter parameters were calculated with the obtained pitch line.The experimental results show that the measurement error ofpitch diameter obtained by the proposed method is reduced by 17.23% and 96.93% respectively compared with the methods from FAN Y B and TONG Qet al,when the alignment deviation along axes directions of X,Y,Zis 1mm and the rotation deviation of each axis is 2°.The proposed method effectively reduces the influence of alignment deviations on the thread pitch diameters,and can be used for two dimensional point cloud data by both contact and non-contact 2-dimensional scannings.

Final report on EURAMET.L-S21: `Supplementary comparison of parallel thread gauges'

The results of the comparison of parallel thread gauges between ten European countries are presented. Three thread plugs and three thread rings were calibrated in one loop. Croatian National Laboratory for Length (HMI/FSB-LPMD) acted as the coordinator and pilot laboratory of the comparison. Thread angle, thread pitch, simple pitch diameter and pitch diameter were measured. Pitch diameters were calibrated within 1a, 2a, 1b and 2b calibration categories in accordance with the EURAMET cg-10 calibration guide. A good agreement between the measurement results and differences due to different calibration categories are analysed in this paper. This comparison was a first EURAMET comparison of parallel thread gauges based on the EURAMET ctg-10 calibration guide, and has made a step towards the harmonization of future comparisons with the registration of CMC values for thread gauges. Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

PRELIMINARY STUDIES OF RIVETED JOINTS AT FEED FORCE

The aim of the study was to determine the feasibility of riveted joints in composites materials. Static tensile test method was used. In the test one type of glass fabric was used (Interglas 92140) from which two types of composite samples were prepared. In each sample the same type of fiber with the same fiber orientation – 3 layers - was used. The samples had dimensions of 100×100 mm and thickness of approximately 1 mm. The composite probes were located in a metal frame with a screw connection which was made of screws with nominal thread pitch M5. Screws were tightened with constant torque. It was to provide an axial force to the sample during the tensile test. The frame was placed between cross-bars of tensile machine INSTRON 8516. The samples were stretched at a speed of 0.05 mm/s at a distance up to 15 mm. During the tensile test displacement of the samples and pull force were registered. Depending on the fibre orientations and the value of feed force, damage models were described. On the basis of the results the possibility of usage of aluminium rivet nuts connections in composite materials was determined.

A New Compensation Method for Measurement of Thread Pitch Diameter by Profile Scanning

Abstract For measurement of existing thread parameters using profile scanning, system error increases as pitch diameter, difference between the calibrating thread and measuring thread increases with the single gauge calibration method. There are several alignment deviations affecting the measurement of pitch diameter. To reduce the system error, a compensation method using two standard thread gauges to calculate the alignment deviations is proposed here. Finally, the theoretical and experimental comparisons between the single gauge calibration method and the proposed method are presented. The results demonstrate that the two gauges calibration method can effectively reduce the system error.

Do Dual-Thread Orthodontic Mini-Implants Improve Bone/Tissue Mechanical Retention?

The aim of this study was to understand whether the pitch relationship between micro and macro thread designs with a parametrical relationship in a dual-thread mini-implant can improve primary stability. Three types of mini-implants consisting of single-thread (ST) (0.75 mm pitch in whole length), dual-thread A (DTA) with double-start 0.375 mm pitch, and dual-thread B (DTB) with single-start 0.2 mm pitch in upper 2-mm micro thread region for performing insertion and pull-out testing. Histomorphometric analysis was performed in these specimens in evaluating peri-implant bone defects using a non-contact vision measuring system. The maximum inserted torque (Tmax) in type DTA was found to be the smallest significantly, but corresponding values found no significant difference between ST and DTB. The largest pull-out strength (Fmax) in the DTA mini-implant was found significantly greater than that for the ST mini-implant regardless of implant insertion orientation. Mini-implant engaged the cortical bone well as observed in ST and DTA types. Dual-thread mini-implant with correct micro thread pitch (parametrical relationship with macro thread pitch) in the cortical bone region can improve primary stability and enhanced mechanical retention.

Optimized orthodontic palatal miniscrew implant insertion angulation: a finite element analysis.

There is a controversial body of evidence regarding optimal insertion angulation of an orthodontic miniscrew as a mean of skeletal anchorage. A bracket head-type 8-mm-long miniscrew (60-degree symmetrical trapezoid thread, 0.1-mm thread fillet, 0.2-mm thread height, with 0.5-mm thread pitch) was designed and monocortically inserted at 30, 45, 55, 70, 90, 110, 125, 135, and 150 degrees of inclination to the surface of bone. A bilayer cortical (1.6 mm) and cancellous (8.5 mm) bone model was constructed, adopted from a 22-year-old male patient's cone beam computed tomography (CBCT) image of his anterior hard palate area. A horizontal force of 2 N was applied parallel to the bone surface. Bone material was simulated as normal and osteoporotic bone. The maximum equivalent von Mises stress and microstrain values were separately calculated for the miniscrew, cortical bone, and cancellous bone. Deflections of the whole bone and miniscrew were also reported. A significant lower stress was found in the cancellous bone compared to the cortical bone. Osteoporotic bone displayed higher strain values. Overall, 30-degree models exhibited the lowest von Mises stress and strain values for the cortical layer and miniscrew in both normal and osteoporotic models. Meanwhile, 90-degree models displayed the lowest strain values in the osteoporotic and normal cancellous bones. Minimum bone and miniscrew deflection values were related to the model of 30-degree insertion angulation. These results showed that, within the limitations of the study, the 30-degree angulation of miniscrew insertion toward the direction of applied force could lower the cortical bone stress and strain.

Bivariate optimization of orthodontic mini-implant thread height and pitch.

Mini-implants have been used as anchorage for years, but failure is common in clinical practice. Mini-implant design is a critical factor affecting its stability. The aim of this study was to evaluate the effect of continuous and simultaneous variations of thread height and pitch on the biomechanical properties of an orthodontic mini-implant. A 3D finite element model, composed of a posterior maxilla section and an orthodontic mini-implant, was created. Mini-implant thread height ranged from 0.10 to 0.40 mm, and thread pitch ranged from 0.50 to 2.00 mm. Effects of the implant thread height and pitch on the maximum Von Mises stresses in maxilla and mini-implant, as well as maximum displacements in the mini-implant, were evaluated by a finite element method. Bivariate analysis was used to determine the optimal range of thread height and pitch. Variation of thread height and pitch decreased the maximum Von Mises stresses in cortical bone, cancellous bone and mini-implant by 54.9, 78.4 and 23.6 %, respectively. The maximum displacement in the mini-implant decreased by 21.8 %. Maxillary stress and mini-implant stability were influenced by mini-implant thread height and pitch. Increased thread height with a thread pitch of 1.20 mm was better for orthodontic mini-implant in the maxillary posterior region. Thread height played a more significant role than the thread pitch in reducing maxillary stress and enhancing orthodontic mini-implant stability.

Biomechanical evaluation of dental implants with three different designs: Removal torque and resonance frequency analysis in rabbits

The objective of this study was to investigate the effect of implant design on stability and resistance to reverse torque in the tibia of rabbits. Three test groups were prepared using the different characteristics of each implant model: square threads with progressive depth to the apex, a cervical portion without threads and a self-tapping system that is quite pronounced and aggressive (Group 1); triangular threads with flat tips with increasing thread depth from the cervical portion to the apex and a small self-tapping portion with a short thread pitch (Group 2); long thread pitch, progressive thread depth, an apical area with a small self-tapping portion (Group 3). For the two last groups, a final single-use drill was provided for each implant. Nine rabbits received 54 conical implants with a same surface treatment. The resonance frequency was analysed four times (0, 6, 8 and 12 weeks), and removal torque values were measured at three time intervals after the implantations (6, 8 and 12 weeks). In comparing the implant stability quotient at the four time points, highly significant statistic differences were found (p=1.29−10). The reverse torque at the three time points was also significantly different among the groups (p=0.00015). The implants of Group 2, with seemingly less aggressive design, more quickly reached high values of stability and removal torque. Under the limitations of this study, however, it is possible that in cases in which there may be low osseointegration response, the implant design should be evaluated.

The First Shot is Your Best Shot! Detrimental Biomechanical Effects of Revising Suboptimally Placed Pedicle Screws

everal factors affect the ultimate pullout strength of a pedicle screw. Features inherent to the screw design (its S format—conical or cylindrical, its thread width and pitch length, as well as its outer and inner diameter, just to mention a few) have a strong influence upon the distribution of forces on the metal/bone interface and, therefore, upon the overall pullout strength of the screw (Figure 1). As a general rule, a larger outer diameter (the most important factor), a smaller inner diameter, and a shorter pitch interval, by increasing the total contact area between the bone and the screw, improve its overall pullout strength (4). However, it has already been demonstrated that in osteoporotic patients a screw with larger diameter may not necessarily increase its ultimate pullout strength, and may even result in increased rates of pedicle fractures, as the outer cortex of osteoporotic pedicles has been shown to be significantly thinner than those of normal vertebrae (8).

FEA and microstructure characterization of a one-piece Y-TZP abutment

ObjectivesThe most important drawback of dental implant/abutment assemblies is the need for a fixing screw. This study aimed to develop an esthetic one-piece Y-TZP abutment to suppress the use of the screw. MethodsMaterial characterization was performed using a bar-shaped specimen obtained by slip-casting to validate the method prior to prototype abutment fabrication by the same process. The mechanical behavior of the prototype abutment was verified and compared with a conventional abutment by finite element analysis (FEA). The abutment was evaluated by micro-CT analysis and its density was measured. ResultsFEA showed stress concentration at the first thread pitch during installation and in the cervical region during oblique loading for both abutments. However, stress concentration was observed at the base of the screw head and stem in the conventional abutment. The relative density for the fabricated abutment was 95.68%. Micro-CT analysis revealed the presence of elongated cracks with sharp edges over the surface and porosity in the central region. SignificanceIn the light of these findings, the behavior of a one-piece abutment is expected to be better than that of the conventional model. New studies should be conducted to clarify the performance and longevity of this one-piece Y-TZP abutment.

STUDY ON TUBE SHELL TRANSVERSE DISPLACEMENTS UNDER ITS MACHINING BASED ON COMPUTER SIMULATION

The possibility to increase parameter accuracy (pitch of thread, pressure angle, external and internal thread diam eter) for various kinds of thread on the seamless casing is studied. As a means of achieving the targ et goal, the v ibration amplitude contraction arising in the system ‘machine — widget — tool — part’ is considered (MWTP). To solve the problem, a model which describes tube shell oscillations in the course of its processing a nd allows defining the impact on the work end of shell oscillations arising in its loose part is offered. The study is resulted in a math ematical model b ased on the initial parameters method. The calculations found the best (of the considered in the paper) support location diagram under which the arising oscillations are the lowest. The obtained re sults can be used at any enterprise dealing with thread cut ting on the casing tubes. The investigation results in the following: — optimum quantity of supports for the considered equipment is five; — expansion in the number of supports by no means always leads to the vibration amplitude contraction; — changing in the relative position of supports is an effective means of the vi bration amplitude contraction that acts to increa se thread parameters accuracy.