Tooth Errors Research Articles

Accuracy Evaluation of an Estimation System for Dental Treatment Sites by Using Image Recognition.

In dentistry, misidentification of the treatment site may occur an adverse event with irreversible consequences. Among these, the left-right tooth error is the second most common site misidentification. In this study, we developed a treatment site estimation system using image recognition, and the accuracy rate of the left and right teeth was more than 85%. The results suggest that this system can be used to prevent the misidentification of the left and right teeth.

Identification of the error excitation in gear systems: A mediator algorithm between simulation and experiment

There are three primary sources of internal excitation in gear systems: time-varying mesh stiffness, meshing damping and tooth error. Compared with the first two excitations, it is more difficult to evaluate or measure the error excitation. The error excitation is usually assumed empirically or even neglected in the majority of dynamic models. To address this issue, we desired to propose a mediator algorithm between the simulation and the experiment to identify the error excitation of gear systems. Based on the second-order cyclostationarity of gear signals, a signal processing procedure is proposed to acquire the mediator signal with a high signal-to-noise ratio. The mediator signal is served as the “media” between the simulation and experiment. The error parameter is updated repeatedly in the iterative optimization until the optimal matching is found between the simulation and the experiment. Simultaneously, the pre-decomposition technique is proposed to accelerate the solution of the simulation dynamic model. The performance of the proposed identification algorithm is verified both numerically and experimentally. Moreover, noise immunity analysis shows that the proposed identification algorithm is robust to noise, damping and phase differences between the experiment and simulation. The proposed identification algorithm provides an indirect approach to estimating the error excitation when the direct measurement is unavailable.

Cone-Beam Computed Tomography Assessment of Prevalence of Procedural Errors in Maxillary Posterior Teeth.

A range of procedural errors can occur when performing endodontic treatment on posterior teeth. These errors may decrease the success rate in endodontic practice. This study assessed the prevalence of procedural errors and the quality of endodontic treatments in maxillary molars and premolars using cone-beam computed tomography (CBCT). CBCT scans from two private radiology centers were assessed retrospectively to ensure the same calculated sample size of 327 teeth for each of the four maxillary posterior tooth types (a total of 1,308 endodontically treated teeth). Image sets were evaluated for procedural errors categorized as follows: obturation length (overfilling or underfilling by >2 mm short of the root apex), missed canals, perforations, strip perforations (with extrusion of material into the furcation area), separated instruments in the root canal space, and root fracture. Data were analyzed with SPSS version 20 (SPSS Inc., Chicago, IL, USA), and frequency data was assessed using the Monte Carlo test at the 0.05 level of significance. The procedural errors most commonly reported in the present study were from most frequent to least frequent: underfilled canals (50.0%), missed canals (27.5%), overfilled canals (12.5%), apical perforations (5.0%), separated instruments (3.1%), and root fractures (1.9%). No strip perforations (with extrusion of material into the furcation area) were seen in the study (0%). Underfilled and missed root canals were the most frequent procedural errors identified in the present study. These findings underline the importance of more consideration of critical working length management during all stages of root canal treatment, greater awareness of root canal anatomy, and the use of imaging and diagnostic devices that enhance the ability to identify and treat root canals both safely and effectively.

Simulation and Compensation of Axial Geometric Errors for Cycloidal Gears Based on Form Grinding

To increase quality, reduce cycloidal gear noise, and avoid unnecessary vibration and shock, a compensation of axial geometric errors method is proposed based on the cycloidal gear form grinding. In the process of machining cycloidal gears, the relative position relationship between the grinding wheel and workpiece is affected by geometric errors of the motion axes, which has serious effects on the surface accuracy of the cycloidal gears. Combined with cycloidal gear form grinding kinematic principles, a geometric error model for each axis of a four-axis computer numerical control form grinding machine is established. By changing the compensation value of the geometrical errors on six degrees of freedom, the error of the cycloid gear tooth surface machined is obtained. Based on a sensitivity analysis of geometrical errors of each axis, the corrections are determined through an optimization process that targets the minimization of the tooth flank errors. The geometric errors of each axis of the cycloid gear grinding machine are compensated, and then, the cycloid gears produced by the machine are processed. Through the processing experiment, the error data of the actual processing before and after the compensation are compared, which indicates that the machining accuracy of the cycloid gear grinding machine is obviously improved. It has an important guiding significance in improving the precision and performance of large CNC form gear grinding machines.

Experimental investigation and numerical analysis of axle spline shaft analysis for different materials

This paper presentsan investigation of numerical analysis of splined shafts made of various materials. These axle spline shafts are subjected to torsional stress to determine if they can withstand the load without failing. The investigation aims to identify the best material type that can withstand high torsional stress levels. Additionally, a Calyx simulation has been used to examine the effects of tooth error. The experiment was conducted to determine the effect of the spline axle shaft's mechanical and chemical endurance strength. The troptometer is used to determine the angular distortion of a bar or piece that has been subjected to torsion. Torsion tests are conducted using a torsion testing machine, and numerical simulation is performed using Ansys software. The result indicates that AISI 1040 torqued between 2800 and 3000 lb-in until it reached a breaking point. AISI 1050 produced between 5700 and 6000 lb-in of torque until it reached its limit. AISI 1340 reached a maximum torque of approximately 8000–8500 until it reached a breaking point.

Identification method for the dynamic cutting force variation of a high energy efficiency milling cutter

The dynamic cutting force of a high energy efficiency milling cutter is an important indicator for evaluating the stability of the cutting energy efficiency. The existing cutting force analysis focuses on the main characteristics and influencing factors of the cutting force variation in the cutting process, ignoring the influence of the variation of the cutting layer parameters with the cutter tooth error in different cutting stages, and the dynamic cutting force variation is uncertain. In this research, the analytical model of the instantaneous cutting volume of a milling cutter was developed in order to obtain the time-frequency characteristics of the instantaneous cutting volume with the cutter tooth error. According to the sudden changes of the cutting force and the milling vibration, the variations were studied in different cutting stages. The dynamic cutting behavior sequences such as the instantaneous cutting volume, milling vibration, and dynamic cutting force were constructed to characterize the mapping relationship between the dynamic cutting behavior of a milling cutter. Based on these approaches, the identification method for the dynamic cutting force variation of a high energy efficiency milling cutter was proposed. The effectiveness of the method was verified by the results of the milling experiment and the dynamic cutting behavior response analysis. The results showed that the proposed method could effectively identify the variation and its control variables for the dynamic cutting force in the cutting process, and the method could provide a scientific basis for constructing the dynamic cutting force model of a high energy efficiency milling cutter.

Hybrid Dynamic Modeling and Analysis of High-Speed Thin-Rimmed Gears

Abstract In this study, a hybrid dynamic model of high-speed thin-rimmed gears is developed. In this model, the translational and angular displacements (including the rigid and vibration displacements) with a total of six degrees-of-freedom (DOFs) are selected as the generalized coordinates for each gear, and the meshing force distributions along the contact line and between the teeth are considered. Thus, the model can be implemented under stationary and nonstationary conditions. The condensed finite element models (FEMs) are developed with the centrifugal and inertia forces for gear bodies. This paper proposes a novel method to couple the lumped-parameter model and condensed finite element model for the hybrid dynamic model system, which considers the variation of the meshing tooth during the gear operation, namely, the variations of the acting point of meshing force. Based on the model, the dynamic analysis of high-speed thin-rimmed gears is conducted under stationary speed and acceleration processes. The effects of the flexible gear body, high speed, and tooth errors on the system dynamics and tooth load distribution are investigated. The analysis results are also compared with the current reference and pure finite element method to validate the proposed model.

Estimation of a Planetary Gear Mesh Stiffness: An Approach Based on Minimising Error Function

The mesh stiffness of gear teeth is one of the major sources of excitation in gear systems. Many analytical and finite element methods have been proposed in order to determine the mesh stiffness of gears especially parallel axis spur gears. Most of these methods are not trivial because they involve complicated analyses which incorporate parameters like gear tooth error, gear spalling sizes and shapes, nonlinear contact stiffness and sliding friction before mesh stiffness can be determined. In this work, a method is proposed to determine the sun-planet and ring-planet mesh stiffnesses of a planetary gear system. This approach involves fitting a relationship between the measured natural frequencies from an experimental modal test and natural frequencies predicted using an analytical model of a planetary gear. This method is relatively easier compared to the existing methods which involve complicated analyses. For this study, the average mesh stiffness estimated is 12.5 MN/m.

Estimation of a Planetary Gear Mesh Stiffness: An Approach Based on Minimising Error Function

The mesh stiffness of gear teeth is one of the major sources of excitation in gear systems. Many analytical and finite element methods have been proposed in order to determine the mesh stiffness of gears especially parallel axis spur gears. Most of these methods are not trivial because they involve complicated analyses which incorporate parameters like gear tooth error, gear spalling sizes and shapes, nonlinear contact stiffness and sliding friction before mesh stiffness can be determined. In this work, a method is proposed to determine the sun-planet and ring-planet mesh stiffnesses of a planetary gear system. This approach involves fitting a relationship between the measured natural frequencies from an experimental modal test and natural frequencies predicted using an analytical model of a planetary gear. This method is relatively easier compared to the existing methods which involve complicated analyses. For this study, the average mesh stiffness estimated is 12.5 MN/m.

РАЗРАБОТКА МЕТОДА ПРОГНОЗИРОВАНИЯ ТОЧНОСТИ СПИРОИДНЫХ КОЛЕС

The article considers the possible errors of the spiroid transmission based on mathematical modeling of the process of shaping the teeth of the spiroid wheel. Typical errors such as tooth profile error, tooth pitch error, tooth thickness error, tooth longitudinal line error are applicable to spiroid wheel tooth errors. Currently, the accuracy standards for spiroid transmissions are not standardized. It is shown that the mandrel of a cylindrical spiroid cutter for processing spiroid wheels has an increased length, which contributes to its greater squeezing from the spiroid wheel during the shaping process. Based on the components of the cutting forces, a graph of the vibrations of the milling cutter mandrel is presented. In the study of precision spiroid wheels on the basis of a comprehensive analysis of the formation of the tooth profile of spiroid wheel revealed that the geometric deviations of the lateral surfaces of the teeth of wheels due to the errors of gear cutting tools and technological factors.

Random missing tooth error detection in crankshaft function of an engine control unit

Automotive industry is migrating to electronic based control which has promoted the evaluation and enhancement of engine control performance using electronic components in the research field. Modern engines are controlled by Engine Control Unit (ECU) where not only functions and control systems are in placed, but also the fail-safe mechanisms must be integrated in the ECU to ensure user safety when an error occurred. This work focuses on developing a reliable crankshaft function in an ECU using field-programmable gate array (FPGA). ABa test is carried out and the number of occurrences at unintended location are being monitored in the system to detect the random missing tooth. The reliability of the function is tested by evaluating response of the crankshaft function in an ECU when an unexpected missing tooth occurs during its operation. The developed system is able to detect the random missing tooth on a crank trigger wheel at an accuracy of 100% when the wheel is on a run at a constant wheel rotational speed. It also flags error message for further processing in other functional units of the ECU as a safe-fail mechanism for the system. Implementation of the random missing tooth detection in the crankshaft function is shown to work in the system which is developed using Verilog code

Study on the quality and tooth root load carrying capacity of the high contact ratio asymmetrical gear tooth machined using WCEDM process

ABSTRACT This work aims to report the quality of the high contact ratio asymmetrical gear tooth manufactured through wire cut electrical discharge machining(WCEDM) process and static load capacity of the gear tooth. The effect of various process parameters such as peak current (IP), pulse on time (Ton), pulse off time (Toff) and servo voltage (SV) on the performance parameters such as Surface roughness (Ra) and Kerf width (Kf) has been examined on the regular shaped specimen. Taguchi method was used with process parameters at three levels and the significance of WCEDM process parameters was studied through analysis of variance (ANOVA). Based on the significant process parameter values, the gears were manufactured and gear tooth errors such as profile, lead and pitch errors were estimated based on DIN3962 Standard using the Gleason inspection system and found that the range of quality of the gear obtained through this process was from Q8-Q11. The experimental test results conducted to explore the tooth root load carrying capacity of the gear tooth revealed that the gear with lower pressure angle at the non-drive side (17º-20º) has a maximum load carrying capacity and maximum yielding when compared to symmetric (20º-20º) and asymmetric gears with higher pressure angle at the non-drive side (22º-20º).

Root canal configuration and its relation with endodontic technical errors in premolar teeth: a CBCT analysis.

To evaluate the association between endodontic technical errors and the root canal configuration (RCC) of human premolars, as well as their relationship with periapical lesions through cone-beam computed tomography (CBCT) images. The sample consisted of CBCT scans belonging to 136 patients, totalling 152 root filled premolars (185 roots). CBCT images were evaluated by two oral radiologists. RCC was recorded according to Vertucci's classification, and the endodontic treatment quality was judged on the presence and type of technical endodontic errors (underfilling, overfilling, nonhomogeneous filling, nonfilled canal, fractured instruments, root deviation and absence of coronal restoration). In addition, the presence of periapical lesions associated with each RCC was recorded. Data were expressed by frequencies and percentages, and intraobserver agreement was calculated using the Kappa test. The most common RCC was type I (71%), followed by type IV (15%), type II (8%), type V (3%), type VI (1%) and type III (1%). Types VII and VIII were not observed in the sample. Underfilling was the most frequent endodontic technical error for most RCCs, except for types IV, V and 'other', whose most frequent error was a nonfilled canal. The presence of technical errors was greater with an increase in the proportion of the periapical lesions. The intraobserver agreement was excellent. There was an increase in the prevalence of endodontic technical errors and in the presence of periapical lesions as the anatomical complexity of the root canals increased. Underfilled and nonfilled canal were the most frequent endodontic technical errors.

Tooth friction force and transmission error of spur gears due to sliding friction

This study investigated the tooth friction force and transmission error (TE) of spur gears due to sliding friction under quasi-static condition. The sliding velocity and friction force of spur gears and mesh compliance during meshing were calculated. The load–deformation relations between the tooth normal load, tooth errors, and mesh compliance, and moment equilibrium equation, including friction force, were derived. The friction force, tooth load, and TE of unmodified and linear tip-relief modified spur gears were analyzed by using the derived equations. Results indicated that the friction force, tooth load, and TE increased during approach and decreased in recess regardless of tooth modification, particularly in the single-mesh region. Friction caused larger peak-to-peak change of TE than that without friction. Xu’s friction coefficient generated smooth TE and tooth load transitions near the pitch point, and BK’s friction coefficient remained approximately constant, except for the sharp increase in tooth load and TE near the pitch point.

Numerical and Experimental Investigations of Noise and Vibration Characteristics for a Dual-Motor Hybrid Electric Vehicle

This paper investigates the abnormal noise and vibration of a hybrid electric vehicle during the electric-only driving mode. The sources of the noise and vibration are first identified through the frequency analysis, and then several measures are implemented to reduce the noise and vibration level. The experimental results have identified the gear meshing in the compound planetary gear set is the main source of the noise and vibration. The theoretical analysis demonstrates that gear pairs of the short planet-small sun gear and short planet-long planet in the compound planetary gear set contribute to the main noise and vibration of the hybrid system in the electric-only driving mode. This research also shows that the gear-meshing noise level in the compound planetary gear set can be decreased significantly by matching the engagement parameters, such as meshing stiffness, tooth error, and pitch error. The observation results in this paper are able to provide a practical reference for improving the ride comfort of hybrid electric vehicles in the future study.

Accuracy of bracket positions with a CAD/CAM indirect bonding system in posterior teeth with different cusp heights.

Our objective was to evaluate the effect of cusp height of posterior teeth (first premolar, second premolar, first molar) on the accuracy of the computer-aided design and computer-aided manufacturing (CAD-CAM) indirect bonding system. Five kinds of maxillary arch models, without attrition, were divided into 2 groups: control group (with 0.5mm of grinding) and experimental group (with the addition of 0.5mm of wax to the cusp tip). Rapid prototype models were printed for both groups. Transfer jigs of the individual tooth brackets were designed using a digital model. 3-dimensional program to evaluate the differences between the intended digital bracket position and actual bracket position after indirect bonding. The differences were measured in the linear (mesiodistal, buccolingual, vertical) and angular (angulation, rotation, torque) dimensions. The Wilcoxon signed rank test was used for statistical analyses; significance was defined as P<0.05. Both groups had similar frequencies of errors between the intended and actual bracket positions. The frequencies of vertical errors over 0.5mm were 3.3% and 6.7% in the control and experimental groups, respectively. The frequencies of angulation, rotation, and torque errors over 1° were 53.3%, 43.3%, and 60%, respectively, for the control group; and 60%, 60%, and 73.3%, respectively, for the experimental group. A difference in cusp height of maxillary posterior teeth did not produce a statistically significant difference in the linear and angular dimensions of bracket placement with the CAD/CAM indirect bonding system. However, given the tendency for a higher frequency in bracket placement errors in posterior teeth with larger cusp tips, cusp height should be considered when using a CAD/CAM indirect bonding system.

Quality of root canal treatment of molar teeth provided by Saudi dental students using hand and rotary preparation techniques: Pilot study

Aim: To compare the quality of root canal treatment provided by dental students in relation to different root canal preparation techniques. Materials and Methods: A pilot study was conducted at King Saud University. Root canal treatments of 46 molar teeth performed by 23 female dental students were included in this study. Each student prepared two molars teeth, first molar prepared with stainless steel (SS) hand K-files using step-back technique and the other molar prepared with ProFile rotary nickel-titanium (NiTi) files in a crown-down manner. Preoperative, working and postoperative periapical radiographs were assessed to evaluate the quality of root canal treatment based on the following criteria; obturation length, density, taper and presence of procedural errors. The data were statistically analyzed using exact conditional logistic regression test and the level of significance was set at 0.05. Results: The percentage of root canal treatment with adequate length was better with the use of NiTi rotary instruments (65.5%) compared to SS hand files (34.5%). No difference between the obturation density and taper in both techniques (P = 1.000) (P = 0.6875). The incidence of procedural errors in teeth prepared with SS hand files (68.2%) was significantly more frequent compared with NiTi rotary group (31.8%). There was a statistically significant relationship between overall quality of root canal treatment and endodontic preparation techniques (P = 0.0386). Conclusion: The quality of root canal treatment performed by King Saud University undergraduate dental student was significantly better in teeth prepared by NiTi rotary filing technique than teeth instrumented with SS hand file.

Radiographic Quality of Single vs. Multiple-Visit Root Canal Treatment Performed by Dental Students: A Case Control Study.

Introduction:The aim of this study was to compare the quality of root canal treatment provided by undergraduate dental students in relation to the number of dental visits. Methods and Materials:Root canal treatments done by 77 dental students were observed. For each student, one tooth treated in a single visit was matched and compared with a tooth treated in multiple visits. The effect of preoperative conditions on the quality of root canal treatment and the number of visits were analyzed. The quality of root canal treatment was determined by the following criteria: obturation length, density, taper, and presence of procedural errors. The data were statistically analyzed using an exact conditional logistic regression test, and the level of significance was set at 0.05. Results:There was no statistically significant association between single- and multiple-visit root canal treatment in terms of obturation length (P=0.263), obturation density (P=0.625), and obturation taper (P=1.00). The incidence of procedural errors in teeth which required a single visit (7.8%) was less but not significantly different from those treated in multiple visits (16.9%). The presence of preoperative conditions was not significantly associated with multiple-visit treatment. Conclusion:Within the limitations of the study, multiple-visit treatment was not associated with a better quality of root canal treatment compared to single-visit treatment.

Closed-Loop Feedback Flank Errors Correction of Topographic Modification of Helical Gears Based on Form Grinding

To increase quality, reduce heavy-duty gear noise, and avoid edge contact in manufacturing helical gears, a closed-loop feedback correction method in topographic modification tooth flank is proposed based on the gear form grinding. Equations of grinding wheel profile and grinding wheel additional radial motion are derived according to tooth segmented profile modification and longitudinal modification. Combined with gear form grinding kinematics principles, the equations of motion for each axis of five-axis computer numerical control forming grinding machine are established. Such topographical modification is achieved in gear form grinding with on-machine measurement. Based on a sensitivity analysis of polynomial coefficients of axis motion and the topographic flank errors by on-machine measuring, the corrections are determined through an optimization process that targets minimization of the tooth flank errors. A numerical example of gear grinding, including on-machine measurement and closed-loop feedback correction completing process, is presented. The validity of this flank correction method is demonstrated for tooth flank errors that are reduced. The approach is useful to precision manufacturing of spiral bevel and hypoid gears, too.

Mathematical Model of Helical Gear Topography Measurements and Tooth Flank Errors Separation

During large-size gear topological modification by form grinding, the helical gear tooth surface geometrical shape will be complex and it is difficult for the traditional scanning measurement to characterize the whole tooth surface. Therefore, in order to characterize the actual tooth surfaces, an on-machine topography measurement approach is proposed for topological modification helical gears on the five-axis CNC gear form grinding machine that can measure the modified gear tooth deviations on the machine immediately after grinding. Combined with gear form grinding kinematics principles, the mathematical model of topography measurements is established based on the polar coordinate method. The mathematical models include calculating trajectory of the centre of measuring probe, defining gear flanks by grid of points, and solving coordinate values of topology measurement. Finally, a numerical example of on-machine topography measurement is presented. By establishing the topography diagram and the contour map of tooth error, the tooth surface modification amount and the tooth flank errors are separated, respectively. Research results can serve as foundation for topological modification and tooth surface errors closed-loop feedback correction.