Tooth Contact Research Articles

The Effect of Some Parameters on Natural Occlusion in Different Ethnicities

Natural occlusion is the resultant of many components, such as muscles, temporomandibular joints, teeth, and neuromuscular systems, and thus plays an essential role in any dental treatment. This research aims to analyze some important features of occlusion in Malaysians. A clinical examination was conducted on 120 students at MAHSA University. The sample was equally divided by gender and ethnicity (Malays, Chineses, and Indians), their age ranged between 18 to 25 years. Results showed that the incidence of canine guidance and group function occlusions was 36% and 64% respectively. Angle’s classification analysis revealed that Class I included the highest ratio of group function, class II, division 1 incorporated more group function than canine protection, while class II division 2 had more canine protection. In Class III, the occurrence for both occlusal patterns was almost equal. Other findings were that subjects with reduced horizontal overlap (0-0.9mm.) showed a 45% group function occlusal pattern, while subjects with increased (7-8.9 mm.) horizontal overlap all had group function. On the other hand, when vertical overlap exceeds 3mm., the percentage of canine protection spikes sharply and it reaches more than 80% of the cases when vertical overlap stands out at 5mm. During edge-to-edge protrusion, 45 % of individuals had anterior and posterior teeth contact, while 55% had anterior teeth contact with posterior teeth disocclusion. Class II division 2 had only anterior teeth contact with posterior teeth disocclusion, while Class III had nearly only anterior teeth contact with posterior teeth contact. There was no statistical difference in types of occlusion among ethnic groups and genders. In conclusion, Angle’s Classification, horizontal and vertical overlaps affect the occlusal pattern types during lateral excursion and protrusion. A simple formula is presented to predict the vertical and horizontal overlaps.

Real time evaluation of awake bruxism behaviors in young asymptomatic students and its impact on the masticatory muscles

Statement of problemThe relationship of awake bruxism with pain is still unclear. PurposeThe purpose of this clinical study was to evaluate awake bruxism behavior for 1 week in healthy young adults with ecological momentary assessment, assess its relationship with masticatory muscle tenderness, and the participation of endogenous analgesia. Material and methodsA total of 150 healthy participants were provided with a smartphone application that sent 10 alerts at random intervals every day. The participants were instructed to report in real time which of the following awake bruxism behaviors best represented their current condition: relaxed jaw muscles, tooth contact, tooth clenching, tooth grinding, or jaw bracing. At baseline, participants underwent recordings of the pressure pain threshold and conditioned pain modulation of the masticatory muscles. Pressure pain threshold recording was also repeated on the last day of the study. A t test was used to compare the first and the last pressure pain threshold recording after 1 week with an ecological momentary assessment evaluation. The Pearson correlation test was performed to evaluate the correlation between variables (α=.05). ResultsOverall compliance was 75.9%. The average frequency of relaxed jaw muscles was 54.5%, tooth contact 29.4%, jaw bracing 5.8%, tooth clenching 9.7%, and tooth grinding 0.6%. The average frequency of a distinct awake bruxism behavior was 45.5%. A statistically significant increase in pressure pain threshold values was found (P=.001; P=.001; P=.045 for right and left anterior temporalis and left masseter, respectively). No significant correlation was found between the frequency of awake bruxism behaviors, the pressure pain threshold, and conditioned pain modulation (P>.05). ConclusionsThe most prevalent behavior was tooth contact (29.4%). No relationship was found between awake bruxism behaviors and masticatory muscle tenderness or endogenous analgesia.

Study on meshing performance of a novel point-contact hourglass worm drive based on modified involute

In this paper, a novel point-contact hourglass worm drive based on modified involute is proposed, it is composed of a modified involute gear and an hourglass worm enveloped by a standard involute gear. The involute modification method and criterion of the standard involute gear are proposed, four representative modification functions are established, and the mathematical model of this novel transmission pair is derived. The tooth contact analysis (TCA) is simulated by numerical analysis and finite element analysis (FEA); the effect of the modification position and modification amount on the contact stress is studied by transient structural analysis; the error sensitivity to center distance error, shaft angle error, and comprehensive error was studied by FEA. All these results of the analysis demonstrated that the tangible contact areas are in line with the theoretical contact points, the average stress value and variance are less affected by the modification position, and the novel worm pair has good error adaptability. This study aims to provide a new idea for the configuration of an hourglass worm drive with local conjugate meshing.

Cox Regression Analysis of Prognostic Factors in Full Crown Restoration of Premolars with Cervical Defect

Objective: To study the prognostic factors in Full crown restoration of Premolars with cervical defect by analyzing long-term survival. Methods: A total of 432 Premolars with cervical defect, selected from 2012 Jan to 2014 Dec, were restored by Full crown. According to different repair methods, they were divided into resin repair group and post core repair group. The effect was analyzed by Cox regression analysis in 5-year follow-up. Results: Different repair methods (RR=0.567, 95% CI: 0.355~0.907), Teeth contact (RR=0.033, 95% CI: 0.016~0.840), Abutment teeth (RR=0.494, 95% CI: 0.308~0.793), Dentin shoulder collar (RR=11.465, 95% CI: 6.653~19.759), Defect size RR=0.386, 95% CI: 0.187~0.798) were the isolated factor influencing the prognosis. Further subgroup analysis shows that, the survival rate of the affected teeth as abutments restored with single crown fixed dentures is higher than that restored with fixed bridge dentures (χ²=4.141, P =0.0419). The survival rate of reinforced abutments restored with fiber posts is higher than that of reinforced abutments restored with metal posts (χ²=18.12, P =0.0001)。The C-index of the nomogram for prognosis was 0.838. Conclusion: In order to improve the long-term preservation rate, different restoration methods for Premolars with cervical defect should be selected according to different situations.

Analytical model for meshing stiffness, load sharing, and transmission error for helical gears with profile modification

For the simulation of the tooth contact of helical gears, a precise determination of the length of the line of contact is required, which is variable throughout the meshing cycle. This variation is influenced not only by the inclination of the lines, but also by their elongation due to the sooner start of contact induced by the teeth deflections under load, as well as by the reduction in this length due to profile modification. These factors affect the mesh stiffness, transmission error, and load sharing, which have a decisive influence on the induced dynamic load and therefore on the dynamic behavior of the gear pair. In this paper, a simple and efficient, analytical model is presented for the simulation of the mesh stiffness, transmission error, and load sharing for helical gears with profile modification.

Transmission performance evaluation of non-circular spur bevel gear based on a novel isochronal measurement method

This paper aims to study the transmission performance evaluation of non-circular spur bevel gear (NCSB-gear) based on a novel isochronal measurement method. Firstly, the mathematical model of NCSB-gear is established. Then a novel isochronal measurement method is proposed, and the actual tooth surfaces are reconstructed by non-uniform rational B-spline interpolation. The advantages of the proposed method are discussed based on the geometric characteristics of tooth surface and measurement fitting error. A pair of forged NCSB-gears is measured through a coordinate measurement machine and the maximum tooth surface fitting error by the proposed method reduces 2μm compared with the traditional method. Moreover, deviation tooth contact analysis (DTCA) and load tooth contact analysis (LTCA) are conducted to evaluate the transmission performance. Finally, the transmission performance of measured NCSB-gear is obtained by a gear rolling tester. By comparing the TCA calculation of different measurement methods, it is found that the relative error of the maximum transmission error based on the isochronal measurement method reduces 4.719% compared with the traditional measurement method, thus verifying the validity of the proposed measurement method.

Semi-analytical loaded tooth contact analysis method for spiral bevel gears

Loaded tooth contact analysis (LTCA) is an important tool for analyzing the meshing of spiral bevel gears. This paper presents a semi-analytical LTCA method, where the analytical formulas are used to calculate the tooth deformation and contact force, with partial coefficients corrected by finite element analysis (FEA) results. Based on Tredgold's Approximation, the tooth is sliced, of which the flank is determined by simulating the manufacturing process. In order to calculated the potential contact curves of a real gear pair, an optimization model is established to find the points more likely to be in contact within the range of contact curves obtained by the help of roll angle surfaces. The compliance of tooth is modeled as a combination of two contributions, where the deformation of cantilever beam under load is used to determine the global deformation, and the local contact deformation is obtained by Hertz line contact assumption. A contact judgement strategy is proposed to detect the contact of the slices at ends of contact curves, and the correction coefficients are introduced in the tooth deformation to consider the coupling effect among slices. In the end, a numerical instance of LTCA under different load torques is provided, which demonstrates the accuracy and efficiency of the presented LTCA method by comparisons with results of FEA. This method can be easily modified to analyze other gear pairs and has the ability to be extended to simulate the gears with local defects or cracks.

Optimising the Geometric Parameters of a Gear in a Tractor Transmission Under Constraints Using Kisssoft

Abstract We optimise the speed gears in a tractor transmission with KISSsoft software under three constraints: input power torque, transmission system volume and the gear ratio for each speed. This study aimed to optimise the module, face width, gear quality, centre distance, number of teeth, helix angle, addendum modification coefficient and pressure angle for each speed while considering the above constraints based on an optimisation chart. Tooth bending stress, tooth contact stress, contact ratio and specific sliding were considered during optimisation. Additionally, the effects of changes in a module on the gear profiles, overlap ratio, number of teeth and weight of the gear pair were examined. Strength calculations of gear pairs that were optimised and defined for all geometric parameters with KISSsoft were calculated with the mathematical model described in ISO 6336, and results were then compared. Finally, backlash was minimised for all gear pairs as defined with geometric parameters, and all dimensions and tolerances were determined for gear inspection after manufacturing. A concept design was also presented. We conclude that both the KISSsoft results and mathematical model results are within the range of the target value.

Nonlinear dynamic modeling and analysis of spur gears considering uncertain interval shaft misalignment with multiple degrees of freedom

Shaft misalignment is regarded as a deterministic parameter in traditional dynamics analysis of gear system, but due to design tolerance and assembly accuracy, shaft misalignment is unavoidably uncertain and this kind of uncertainty exhibits interval attribute. To evaluate the dynamic characteristics of gear system more reasonably, a new nonlinear dynamic model of spur gears considering the uncertainty of shaft misalignment with multiple degrees of freedom (DOFs) is proposed and studied in this paper. First, the meshing analysis of spur gears under shaft misalignment is completed based on tooth contact theory. Then a nonlinear interval dynamic model of gear system is established and an interval analysis approach based on Chebyshev inclusion function and optimization method is used to obtain the upper and lower bounds of the dynamic response. Afterwards, the effectiveness of proposed dynamic model and interval algorithm is validated by comparison with the existing experiments and simulations respectively. Finally, parameter studies are carried out in detail and the result shows that the uncertainty of shaft misalignment will significantly change the internal excitation of gear system and thus enormously enhancing the system vibration, this will bring valuable guidance for the tolerance allocation in gearbox design.

Straightening of the rollers of planetary roller screw — Design of straightening die and experimental validation

The roller of a Planetary Roller Screw (PRS) is prone to bending deformation and runout error after carburizing, which results in the uneven transmission performance, increased transmission friction, and decreased service life. Traditional grinding methods used to rectify these errors have high costs and low efficiency and furthermore reduce the thickness of the carbon layer of the roller. This paper proposed a new radial feed-in straightening method to correct the geometric errors of carburized PRS rollers. Trial tests are first performed to explore the feasibility of different straightening techniques, as well as to discover key factors for the rational design of a straightening die. Based on the trial tests, a new tooth profile model of the straightening die for the PRS roller is proposed. Finite element models are developed to analyze the material flow feature of the straightening process, as well as to verify the effectiveness of the proposed tooth profile model of the straightening die. For mass production needs, experimental tests are performed to further examine the performance of the proposed straightening method. It is found that reducing the tooth contact interference between the roller and die can effectively increase the quality of the straightened workpiece. Results show that the bending deformation and runout error of the carburized PRS roller are effectively corrected by the proposed straightening process. Furthermore, the smoothness of the tooth surface of the roller is significantly increased, and all the tested samples meet production quality standards after straightening. A comparison of transmission performance under 0.3 million cycles shows that the maximum friction torque (1.82 N·mm) of the PRS product with straightened rollers is much better than without straightening (105.70 N·mm).

Surrogate model based prediction of transmission error characteristics based on generalized topography deviations

Simulation models of the tooth contact can provide valuable information of the gearbox operational behavior for deviated gears. It is therefore possible to gather geometry and deviation information of the two gears in contact and then estimate how they will perform in the assembled unit before even mounting them. This procedure could save time and costs used to disassemble gear boxes which fail the end of line tests because of acoustic reasons. The major challenge using sophisticated simulation models, which can describe the tooth contact is the tremendous amount of calculation time they need to produce suit-able results. In a productive gearbox manufacturing process this time is just not available. Therefore, a method to predict the operational behavior faster, than with the current used simulation models is needed. Firstly the size of the problem is downsized by introducing the sum deviation surface. It allows to reduce the number of necessary input parameters for a gear topography description to eighteen factors. With the help of that sum deviation surface, 3000 variants within a given variation space are calculated. The resulting training dataset is used to develop a deep neural network meta-model of the gear contact, which can predict the characteristics of the transmission error under load. With the help of that meta-model, the excitation of a gear pair can be predicted faster than real-time.

Investigation on the impact of electrical faults on the loads and exposures of wind turbine gears

For the design of a wind turbine, it is necessary that the design process takes into account the stresses of real operation to a high degree of detail so that targeted dimensioning can be carried out. Depending on its design, the drivetrain of a wind turbine includes a gearbox that connects the rotor to the generator. During operation of a wind turbine, transient load conditions can occur due to loopback from the power grid and faults in the frequency converter. The influence of the resulting stress and possible damage to the gears used in the gearbox is unclear in the design phase. While the stresses on the gears can often be simulated with a high degree of accuracy for constant operating conditions and can thus be integrated into the drivetrain design, this is not the state of the art for dynamic load conditions. The objective of this report is a method for considering dynamic loading events in the design of the cylindrical gear stage used in wind turbine gearboxes using a coupled multi-body simulation and a finite element based tooth contact analysis. Afterwards the method is used to quantify the stress on the tooth flank and tooth root due to special electrical events such as short circuits between the frequency converter and generator or power grid faults for various converter designs. The simulation analyses show that different converter concepts have different effects on the resulting gear load during electrical faults, but are not significantly decisive for the accumulated damage due to elastic material behavior between generator and gear.

Manufacturing Method for Large Cylindrical Worm Gear Set of ISO Type I on Universal CNC Machine Tools

Large cylindrical worm gear set of ISO type I are manufactured using endmill tools on universal CNC machine tools. This manufacturing method requires neither special gear-generating machines nor special tools. The tooth flank forms of ISO type I cylindrical worm gears are involute helicoids as a standard. The targeted theoretical tooth flanks of the worm and the mating worm wheel are determined based on a tooth contact analysis (TCA) of such worm gear set. The cutting conditions of the worm are determined after the offset distance between the worm axis, and the central axis of the endmill tool is calculated. Afterward, the worm is manufactured by controlling only two axes on machine tools using a swarf milling method by use of the side of the endmill tool under the determined conditions. Meanwhile, the targeted theoretical tooth flanks of the mating worm wheel are modeled in 3-dimensional computer-aided design software, and the worm wheel is manufactured by a swarf milling method in a computer-aided manufacturing process. The comparison of experimental and analytical tooth contact patterns indicates almost no difference between the two tooth contact patterns.

Моделирование технологических параметров процесса фрезерования заготовок деталей из поликарбоната при различных режимах обработки

Computer simulation of technological parameters in the milling process of polycarbonate workpieces under various processing modes is realized. The parameters are recorded at various points in the contact time of the milling cutter tooth with the workpiece. The regularities of changes in the parameters of the milling process, including forces and temperatures in the contact zones of the facing with the cutter tooth or in case of tooth contact with the workpiece, depending on the elements of the milling mode, are found. It’s also found that the temperatures in the contact zone of the tooth with the workpiece are higher than in the contact zone of the tooth with the facing. The pattern of temperature distribution in the surface layer of the workpiece is distilled. Mathematical dependences describing the relationship of temperatures with the elements of the milling mode, are obtained

Study on nonlinear dynamic characteristics of power six-branch herringbone gear transmission system with 3D modification

The power six-branch herringbone gear transmission system has the advantages of large power transmission and transmission ratio. Because of its multi-way transmission and over-constraint structure, to prevent loaded tooth interference, there are large backlashes between teeth. The system shows complex nonlinear dynamic characteristics under the influence of backlashes, which seriously affects meshing performance. The modification technology can effectively improve gear meshing performance. Hence, on the basis of optimizing meshing performance of the active pair of the six-branch herringbone gear transmission system, this article will combine 3D modification with system nonlinear vibration characteristics and propose an analysis method of the system nonlinear vibration characteristics under 3D modification to reduce vibration and noise. First, the 3D modified tooth surface equation is determined by forming grinding, the loaded transmission error (LTE) of the system's active pair is obtained by tooth contact analysis (TCA) and loaded tooth contact analysis (LTCA) technology, and the optimal modification parameters are obtained by Ant Lion Optimizer (ALO) with the minimum error amplitude as optimization objective. Then, the time-varying meshing stiffness of system under the optimal modification is calculated, and the pure torsional nonlinear dynamic model with backlashes, meshing stiffness, and static transmission error (STE) is established. Finally, the global vibration characteristics in parameter field are studied through time domain and bifurcation diagram of system. Results show that the 3D modification can eliminate edge contact of tooth and improve tooth contact performance. With the increase of input power, the root mean square (RMS) values of acceleration increase and the RMS values and jump decrease after 3D modification. With the increase of input speed, the RMS curves appear multiple resonance peaks and jumps at low input speed. After 3D modification, the RMS, jump, and resonance peak values decrease. Compared with level І, the backlashes and STEs of level II and phase difference ϛsII have great influence on system dynamic characteristics and easily make system in chaotic motion, while the 3D modification reduces their influence and makes system motion periodic.

An efficient process for macro geometry optimization of helical gear pairs considering static transmission error

Loaded tooth contact analysis (LTCA) adopted to obtain the static transmission error for the gear optimization affects significantly the computation time and results. This paper is to study an efficient process of macro geometry optimization of helical gear pairs with LTCA. An analytical LTCA model was proposed and verified with the measured transmission error. To find an efficient LTCA method, the proposed model was divided into three types (based on whether the slice stiffness and extended contact were included) by adjusting the fidelity. When extended contact was included in LTCA, the increased computation time was very short, but the accuracy of the results improved significantly. Optimization processes were designed based on the analysis results, and it was most efficient when starting with the model considering only the extended contact and ending 5%−10% of the entire generation with the highest fidelity model. In the process, the computational effort was significantly reduced compared to when the optimization process was configured with only the highest fidelity model, and the level of optimization was almost equal.

Numerical-experimental analysis of highly crowned spherical gear couplings working at high misalignment angles

Spherical gear couplings are characterized by their high capacity to transfer power between rotating shafts in highly misaligned conditions. They are usually small because of space restrictions and require a high amount of longitudinal crowning, which sometimes leads to undercutting profiles. These issues have been solved recently with analytical models for the generation of tooth surfaces that consider the hob thread surface, however, they are not experimentally validated. Likewise, it has been numerically concluded that the number of teeth in contact in high misalignment conditions decreases, and thus may fail by tooth root breakage. Nevertheless, published experimental tests for such high misalignment angles are scarce. This paper presents test techniques to study highly crowned spherical gear couplings, together with a test rig design adapted to high misalignment angles. The tooth surface geometry, maximum misalignment, stiffness, and contact pattern are compared. The results demonstrate that the analytical and numerical models employed accurately represent the mechanical behavior of spherical gear couplings working at high misalignment applications.

Assessment of local faults in helical geared system using vibro-acoustic signals based on higher order spectrum analysis

Geared transmission system plays an important role in modern technology to transmit both power and motion. The power transmission and control requirements in manufacturing, aviation, transportation, energy industries require uninterrupted operation under high efficiency.Increase in fatigue load cycles in a geared transmission system thereby leading to negative impact on contact surfaces of gear tooth, which result in non-unifor m power transmission, increase in dynamic response, and decrease in efficiency followed by catastrophic tooth failure.The wear propagated on gear teeth contact causes a variation in the dynamic response of geared system. It is widely acceptedthat the local/distributed faults developed on rolling/sliding contact elements can be detected by using vibration and/oracoustic monitoring and analysis techniques.This paper describes the results of experimental studies carried out to detect and diagnose the simulated faults in the helical gear tooth of a two stage helical gearbox.The helical gear was mounted in a two-stage gearbox operating under controlled speed and load conditions. The vibration and airborne sound signals obtained from the gearbox were considered to attain a reliable fault related information by using a higher-order spectrum analysis technique. The fault related features extracted from the vibration and the acoustic data post processed by using bispectrum analysis provided a better diagnostic information to detect progressive faulty operating conditions viz., 20%, 40%, 60%, 80% and 100% tooth removal cases in the gearbox.

Calculation of Drive-Related Structure-Borne Sound in Electric Driven Trains using Elastic Multi-Body Simulation

The structure-borne sound coming from the drive system defines especially for transient train manoeuvres the experienced interior noise of modern railway traction vehicles. A deeper look at the origin and the transmission of structure-borne sound is therefore of great importance to increase passenger comfort in newly developed trains. The possibility of modelling the vibration behaviour of an electric multiple unit train up to the acoustic frequency range using elastic multi-body simulation (EMBS) has been investigated in a joint research project of the Chair of Dynamics and Mechanism Design at TU Dresden and the company Alstom. Through usage of reduced order models of elastic bodies, the EMBS can be carried out in time domain in a computationally effi-cient way and non-linear system properties during motor run-up can be easily taken into account. Key research findings with regard to model structure and necessary level of detail of individual components (e.g. tooth contact, electric motor, roller bearings, elastic bodies, hydraulic dampers) of the elastic multi-body model can be shown. For validation purposes, measurements on individual parts, a motor-gear-unit test bench and the electric multiple unit on track have been carried out, results and comparison to simulation results can be presented.

Nonlinear Torsional Stiffness Analysis of Harmonic Drives Using Flexible Multibody Dynamics Simulation

Predicting the nonlinear torsional stiffness of harmonic drives is important not only for system control but also for the further development of the drive. However, it is difficult to predict the torsional stiffness because of the elastic deformation of the flexspline and the many contacts involved. Furthermore, nonlinear dynamic contact simulations between the elastic components of the harmonic drive are disadvantaged by high computational burden and convergence problems. To address these challenges, we establish a flexible multibody modeling process using augmented formulations of a floating reference frame to simulate the operation of the harmonic drive. The elastic deformation of the flexspline and the dynamic contacts between the main components are considered in the reproduction of the contact mechanism of the drive. Coordinate reduction techniques are used to properly replicate an elastic shaft, enabling the effective simulation of flexible multibody dynamics, including nonlinear elastic tooth contact analysis. The performance of the proposed modeling process is evaluated using catalog and experimental data on two types of standard harmonic drives (SHG-25-100-UH and SHG-40-100-UH). The hysteresis curve is predicted through flexible multibody dynamics simulation and the accuracy of parameters of torsional stiffness is approximately 91.7% on average. The proposed modeling method can be improved to predict other measures of performance and it remains a potential research topic.