Search Results (50)

In a planetary gear system, the planet phasing depends on the number of teeth in the sun and the ring and the number of planets. When the tooth numbers are both multiples of the number of planets, all planets mesh at the same relative position—which is called synchronous configuration—and the input torque is shared evenly among them. Otherwise, the configuration is asynchronous, or sequentially phased, and the torque sharing is uneven. This directly influences the instantaneous load sharing between the external planet–sun and internal planet–ring meshes, consequently altering both load-induced tooth deflections and the resulting transmission error. The profile relief, frequently used to avoid the mesh-in impact, influences the teeth contact along the interval of relief, which also affects the load distribution, mesh stiffness, and transmission error. Since the transmission error is a source of dynamic load, noise, and vibrations, its peak-to-peak amplitude should be controlled, and the geometry of the profile modification provides an efficient tool. In this paper, the transmission error of spur planetary gears is studied with an analytical model previously developed, based on the minimum elastic potential energy. The study also assesses the influence of the depth and length of the tip relief and compares the behavior of synchronous and asynchronous configurations. As a result of this analysis, it has been found that the variation in the amplitude of transmission error is significantly lower in sequentially phased configurations and reaches the minimum variation for the adjusted depth of relief and medium length of relief. Furthermore, an odd number of teeth on the planets results in a higher mesh stiffness than an even number, which induces a slightly lower peak-to-peak transmission error. Full article

The present study provides a comprehensive analysis of the grinding process of spiroid worm shafts, focusing on the combined application of lathe center displacement and lead angle correction on a conventional cylindrical grinding machine. The objective is to generate accurate tooth profiles for spiroid worms and spiroid hobs while minimizing lead errors and angular velocity fluctuations inherent in the worm grinding process. The implementation of lathe center displacement alters the kinematics of the workpiece, transforming the nominal circular path into an elliptical path. This kinematic modification introduces manufacturing deviations due to the continuously varying radius along the elliptical path. To address these effects, a novel mathematical model is developed, enabling the determination of an optimal grinding wheel profile for both spiroid worms and hobs under these non-ideal motion conditions. The simultaneous application of the optimized grinding wheel profile and lead angle correction is shown to significantly enhance the profile accuracy of the generated tooth geometry. Furthermore, a detailed manufacturing analysis is carried out to investigate the influence of variations in the half-taper angle on key process parameters. Based on the analytical and computational results, a methodological solution is proposed to effectively mitigate lead errors and angular velocity fluctuations in spiroid worm grinding. Full article

To reduce the time and computational cost of vibro-acoustic simulations in gear reducer noise evaluation, this study develops a simulation-driven surrogate modeling framework for a three-stage helical gear reducer. A high-fidelity “vibration–acoustic radiation” simulation chain is established, where the housing vibration responses computed in Romax Designer are mapped into ACTRAN to obtain the radiated noise. Using Optimal Latin Hypercube Sampling, 300 designs are generated by varying the first-stage pinion micro-modification parameters (tooth drum, tooth slope, and tooth profile), and the average RMS sound pressure level over six field points is adopted as the noise metric. A BP neural network (BPNN) surrogate is then constructed, in which Bayesian Optimization (BOA) is used to tune hidden layer nodes and learning rate, and an improved Sparrow Search Algorithm (ISSA) is employed to optimize the initial weights and biases, forming the proposed BOA-ISSA-BPNN model. On the test set, the proposed model achieves R² = 0.97499, RMSE = 0.91385, and MAE = 0.6547, with an average prediction time of 32.35s. Meanwhile, comparisons with SVM, BPNN, BOA-BPNN, SSA-BPNN, and ISSA-BPNN demonstrate superior prediction accuracy; moreover, relative to the hour-level computational cost of high-fidelity simulations, the proposed surrogate enables rapid noise evaluation on the order of tens of seconds, enabling fast micro-modification design iteration and practical engineering decision-making. Full article

Periodontal disease is a chronic inflammatory condition that destroys tooth-supporting tissues, particularly the alveolar bone and the periodontal ligament, and effective regenerative therapies remain limited. While the role of metabolic–epigenomic crosstalk in determining cell fate is well established, the specific mechanism by which a tricarboxylic acid (TCA) cycle metabolite can modulate chromatin regulation to promote periodontal regeneration remains to be elucidated. The impact of one TCA cycle metabolite, alpha-ketoglutarate (α-KG), was examined in human periodontal ligament fibroblasts cultured under osteogenic induction and profiled by ALP assays, RT-qPCR, analyses of multiple histone modifications, ATAC-seq, and RNA-seq. α-KG increased ALP activity and upregulated genes associated with osteogenesis and the extracellular matrix (ECM). ATAC-seq revealed minimal genome-wide accessibility changes, whereas histone analyses showed reduced H3K27me3, consistent with an epigenetic mechanism that does not require extensive chromatin opening. The RNA-seq identified 14 upregulated α-KG-induced genes, including multiple components of the OGN-OMD-PLAP1/ASPN-ECM2 loci, supporting an osteogenic/ECM transcriptional program. In a mouse periodontal regeneration model, oral administration of α-KG enhanced alveolar bone regeneration and reduced H3K27me3 signals and collagen-rich tissue organization within the periodontal ligament space. These findings identify α-KG as a metabolite-driven epigenetic modulator that alleviates H3K27me3-mediated repression and supports periodontal regeneration. Full article

The tooth flank distortion error occurring during the form-grinding (FG) of an involute helical gear can significantly compromise transmission performance. Conventional research approaches often focus on single-parameter optimization—either the grinding wheel installation angle (GWIA) or the contact line (CL)—without adequately accounting for the coupling relationships among GWIA, CL, and the modification curve (MC). To address this limitation, this study proposes an innovative joint optimization approach that simultaneously optimizes GWIA, CL, and MC to effectively minimize tooth flank distortion in FG. Based on the principles of form-grinding, a mathematical model is established for the contact line of the target gear and the cross-sectional profile of the grinding wheel. The relationship between GWIA and tooth flank deviation is investigated using a proprietary virtual prototype. A multi-objective artificial bee colony (ABC) optimization algorithm is employed to determine the optimal values of GWIA and CL. For the axial modification curve, this paper introduces a novel three-segment quadratic curve optimization scheme as an improvement over conventional modification methods. To validate the proposed optimization technique, form-grinding experiments are conducted on the L300G gear grinding machine. Simulation outcomes indicate that, pre-optimization, the maximum tooth flank distortion errors primarily occur at the tooth root and tip regions on both ends of the gear. After optimization, the simulated distortion error on the left tooth flank is reduced by 48.5%, while the right flank shows a reduction of 29.4%. These simulation outcomes exhibit a deviation of approximately 10% compared with the experimental results. This study provides valuable insights for enhancing the transmission performance of helical gears. Full article

Reducing noise in electric multiple-unit (EMU) gearboxes demands prediction tools that are both rapid and reliable. Gear sound pressure levels vary sharply with micrometre-scale changes such as tooth repair, inclination, or profile relief, yet traditional estimates depend on hours-long CAE simulations. We present a data-driven hybrid surrogate that combines k-means clustering and inverse distance weighting (CLS-IDW) within the ODYSSEE A-Eye platform to map geometry modifications directly to broadband noise. Trained on the open 200-case Romax dataset, the model returns predictions within milliseconds and reproduces unseen operating points, with R² = 0.75 and a mean absolute error of 2.33 dB, matching solver repeatability. Sensitivity analysis identifies a −7° tooth inclination coupled with a 10 µm repair depth as the most effective combination, lowering noise by 3–5 dB. Eliminating costly CAE loops, the surrogate supports acoustics-aware optimisation at the concept stage, compressing development cycles and enhancing passenger comfort while maintaining transparency for regulatory review. Full article

Background and Objectives: Adequate peri-implant soft tissue dimensions are essential for health, hygiene, and esthetics. When ridge volume is sufficient, phenotype modification may avoid bone grafting. This case report describes a pedicled roll flap performed concurrently with single-stage implant placement after spontaneous socket healing, without bone substitute, and assesses soft-tissue stability with serial intraoral scans. Clinical case: A single-tooth edentulous site underwent prosthetically driven, fully guided implant placement. A modified roll flap with vertical and palatal incisions was prepared; the de-epithelialized crestal connective tissue was elevated and rolled into a buccal envelope to augment thickness. No graft material was used. A provisional crown conditioned the emergence profile. Follow-up included photographs, radiographs, and intraoral scan superimpositions at 2 weeks, 3–4 months, 8 months, and 14 months after implant treatment. Healing was uneventful. Buccal soft-tissue thickness increased, keratinized mucosa was preserved, and midfacial levels remained stable. Emergence profile and papillae integrated harmoniously. Crestal bone levels were stable radiographically. Digital scans corroborated soft-tissue thickness maintenance. No donor-site morbidity occurred. Conclusions: In healed sockets with adequate bone, a modified pedicled roll flap at implant placement can thicken the peri-implant phenotype and achieve stable esthetic integration without bone substitutes. Full article

The tooth surface geometry of harmonic gears directly affects the transmission accuracy and service life. Traditional design methods may cause tooth profile distortion when changing the radial deformation coefficient, which limits their application. This paper proposes a comprehensive tooth surface modification method that changes the radial deformation coefficient on the basis of traditional design methods. Firstly, the meshing trajectories and corresponding tooth profiles of gear teeth under different radial deformation coefficients are calculated and analyzed based on the rack approximation method. Secondly, a calculation method is proposed to eliminate the tooth profile distortion caused by changing the radial deformation coefficient, which not only expands the application of the rack approximation method but also eliminates interference during the meshing process. Subsequently, a comprehensive tooth surface modification method is proposed with the aim of increasing contact area and contact ratio, as well as reducing contact stress. Compared to traditional modification, it requires less material removal, which is beneficial for increasing the tooth strength. Furthermore, a finite element simulation model of a harmonic drive is established, and the tooth surface and contact performance of harmonic gears under three different radial deformation coefficients are designed and analyzed, verifying the effectiveness of the proposed tooth surface design method. Full article

The design of cycloidal reducers requires a detailed knowledge of the intensity and character of load, as well as the maximum von Mises stresses on critical components. In the available literature, the load distribution and the stress–strain state of the cycloidal reducer elements are typically determined based on factors such as cycloidal disc tooth profile modifications, contact deformations, and internal clearances, whereas the influence of thermal stresses is most often neglected. To address this research gap, an innovative numerical–analytical methodology has been developed, which, for the first time, enables the prediction of the distribution of temperature fields and the quantification of the influence of temperature on the contact forces and the stress–strain state of key elements of the cycloidal reducer. Furthermore, the proposed methodology can be adapted for application within a broader context of mechanical engineering. From a practical perspective, it is expected to be beneficial to companies engaged in the design of power transmission gearboxes, as valuable practical guidelines for engineering applications are provided. This study also provides new insights into the dominant sources of heat generation and offers a clearer understanding of how thermal energy is transferred from internal heat sources to the outer surface of the housing. Full article

Photoacoustic tomography (PAT), which combines optical absorption and ultrasonic detection, enables the monitoring of dehydration-driven structural changes in extracted teeth over time. In this proof-of-concept study, 2D photoacoustic images of a wisdom tooth were generated on the same scanning plane at days 0, 1, 3, 6, 10, 15, 21, and 28 post-extraction, using day 0 as the reference. Measurements were performed in forward-detection mode with a single ultrasound transducer and a 532 nm pulsed laser. For the comparative analysis of variations between images, four metrics were used: Pearson correlation coefficient, Structural Similarity Index (SSIM), Mean Squared Error (MSE), and Peak Signal-to-Noise Ratio (PSNR). Structural changes were also examined through radial intensity profiles extracted from each image. The results revealed marked differences in the central region, evidencing progressive structural and acoustic modifications within the tooth. The most significant change occurred on day 1, followed by small but consistent variations on subsequent days. These differences are associated with dehydration-induced changes in tissue density, which affect sound propagation. This study highlights the value of PAT for noninvasive monitoring of post-extraction dental changes, with implications for diagnosis, treatment guidance, and biomaterials research in dentistry. Full article

Study design: Trends in the utilization of Mandibulo-Maxillary Fixation (MMF) are shifting nowadays from tooth-borne devices over specialized screws to hybrid MMF devices. Hybrid MMF devices come in self-made Erich arch bar modifications and commercial hybrid MMF systems (CHMMFSs). Objective: We survey the available technical/clinical data. Hypothetically, the risk of tooth root damage by transalveolar screws is diminished by a targeting function of the screw holes/slots. Methods: We utilize a literature review and graphic displays to disclose parallels and dissimilarities in design and functionality with an in-depth look at the targeting properties. Results: Self-made hybrid arch bars have limitations to meet low-risk interradicular screw insertion sites. Technical/clinical information on CHMMFSs is unevenly distributed in favor of the SMARTLock System: positive outcome variables are increased speed of application/removal, the possibility to eliminate wiring and stick injuries and screw fixation with standoff of the embodiment along the attached gingiva. Inferred from the SMARTLock System, all four CHMMFs possess potential to effectively prevent tooth root injuries but are subject to their design features and targeting with the screw-receiving holes. The height profile and geometry shape of a CHMMFS may restrict three-dimensional spatial orientation and reach during placement. To bridge between interradicular spaces and tooth equators, where hooks or tie-up-cleats for intermaxillary cerclages should be ideally positioned under biomechanical aspects, can be problematic. The movability of their screw-receiving holes according to all six degrees of freedom differs. Conclusion: CHMMFSs allow simple immobilization of facial fractures involving dental occlusion. The performance in avoiding tooth root damage is a matter of design subtleties. Full article

Gear whine noise is governed not only by intentional microgeometry modifications but also by unavoidable pitch (indexing) deviation. This study presents a workflow that couples a tooth-resolved surface scan with a calibrated pitch-deviation table, both imported into a multibody dynamics (MBD) model built in MSC Adams View. Three operating scenarios were evaluated—ideal geometry, measured microgeometry without pitch error, and measured microgeometry with pitch error—at a nominal speed of 1000 r min⁻¹. Time domain analysis shows that integrating the pitch table increases the mean transmission error (TE) by almost an order of magnitude and introduces a distinct 16.66 Hz shaft order tone. When the measured tooth topologies are added, peak-to-peak TE nearly doubles, revealing a non-linear interaction between spacing deviation and local flank shape. Frequency domain results reproduce the expected mesh-frequency side bands, validating the mapping of the pitch table into the solver. The combined method therefore provides a more faithful digital twin for predicting tonal noise and demonstrates why indexing tolerances must be considered alongside profile relief during gear design optimization. Full article

Spiral bevel gears are used in a wide range of industries, such as automotive and aerospace, to transfer power between intersecting axes. However, a certain level of vibration is always present in the systems, primarily due to the complex dynamic forces generated during the meshing of the gear teeth affected by the tooth profile. To address these challenges, this research developed a comprehensive dynamic model with eight degrees of freedom, capturing both translational and rotational movements of the system’s components. The study focused on evaluating the effects of two different tooth profile modifications, namely topology and flank modifications, on the vibration characteristics of the system. The system comprised a spiral bevel gear pair with mesh stiffness in forward rotation. The results highlighted that optimizing the tooth profile and minimizing tooth surface deviation significantly reduce vibration amplitudes and improve dynamic stability. These findings not only enhance the performance and lifespan of spiral bevel gears but also provide a robust foundation for the design and optimization of advanced gear systems in industrial applications, ensuring higher efficiency and reliability. In this paper, it was observed that some modifications led to a 68% reduction in vibration levels. Additionally, three modifications helped improve the vibrational behavior of the system, preventing chaotic behavior, which can lead to system failure, and transforming the system’s behavior into periodic motion. Full article

Background: The behavior of soft tissues following recession type 1 (RT1) and/or non-carious cervical lesions (NCCLs) treated with class V restorations is not well understood. These conditions cause both functional and esthetic issues. Recent studies show that increased cervical thickness can influence gingival tissue response. This suggests that restoration design has a key impact. This study aims to evaluate the effect of tooth shape modification on gingival tissue response and periodontal health with 3D analysis. Methods: Seven patients with buccal gingival recession and NCCL were selected, resulting in 50 treated teeth. Patients underwent class V buccal restorations using the BOVR technique. Three-dimensional evaluation through scanned dental impressions was performed at baseline and at T1 to monitor tissue profile changes in the buccal zenith sagittal plane. The average observation period was 4 months. Following the assessment, linear measurements were calculated according to standard planes. These measurements aimed to monitor transverse and axial tissue modifications. Probing depth, plaque index, and bleeding index were also recorded. Results: Increased tooth thickness led to tissue alteration. Greater composite thickness was significantly associated with an increase in tissue thickness (p ≤ 0.001) and gingival creeping (p ≤ 0.001) at the free gingival margin. Periodontal health remained unaffected, and 50% of the teeth required no additional surgical treatment due to satisfactory outcomes. Conclusions: Class V restorations that increase cervical thickness may promote soft tissue volume gain over a 4-month period without compromising periodontal health. A 4-month observation period is recommended before considering the surgical correction. Full article

Due to its small size, high transmission ratio and precision, the harmonic reducer is widely used. The design of the flexspline tooth profile is crucial for the transmission accuracy and service life of harmonic reducers. However, the numerous design parameters and the lack of a unified design standard for the flexspline tooth profile make it challenging to accurately determine these parameters. This can lead to issues such as tooth profile interference and excessive stress on the gear teeth during transmission. To address these issues, we propose a novel rapid design framework for the tooth profile of a double-circular-arc common-tangent flexspline in harmonic reducers. Firstly, the mathematical formula for the flexspline tooth profile with a double-circular-arc common-tangent and its conjugate circular spline tooth profile is derived. Then, two-dimensional and three-dimensional parametric finite element models of the harmonic reducer are established, and radial and axial profile modifications of the flexspline are carried out. Based on the parametric two-dimensional finite element model of the harmonic reducer, the optimized Latin hypercube experimental design method is employed to determine the flexspline tooth profile parameters. The method proposed can be implemented using Python language code and integrated into the Abaqus 2019 software, offering the advantage of meeting the requirements for rapid engineering development. Finally, a case study is presented to verify the effectiveness of the proposed design method. Full article