Search Results (158)

This study aims to address the problem that traditional helical gears generate significant axial forces during transmission and innovatively proposes a design scheme of double helical face gears (DHFG). An accurate mathematical model of the tooth surface is established using spatial meshing theory and coordinate transformation. A systematic investigation using the orthogonal test method is then conducted to analyze the influence of key parameters, such as the pinion tooth number, transmission ratio, and helix angle, on gear performance. The finite element analysis results show that the overlap degree of this double helical tooth surface gear pair in actual transmission can reach 2–3, demonstrating excellent transmission smoothness. More importantly, its unique symmetrical tooth surface structure successfully achieves the self-balancing effect of axial force. Simulation verification shows that the axial force is reduced by approximately 70% compared to traditional helical tooth surface gears, significantly reducing the load on the bearing. Finally, the prototype gear is successfully trial-produced through a five-axis machining center. Experimental tests confirmed that the contact impressions are highly consistent with the simulation results, verifying the feasibility of the design theory and manufacturing process. Full article

Aim: This retrospective observational clinical cohort study evaluated 84-month clinical and radiographic outcomes of a regenerative protocol combining autologous dentin grafts processed with the Tooth Transformer^® device and Concentrated Growth Factors (CGFs) in patients with severe maxillary atrophy undergoing sinus augmentation with simultaneous implant placement. Materials and Methods: Thirty-one patients (30–75 years) with residual crestal bone height ≥ 5 mm and requiring extraction of ≥2 molars were included. Extracted teeth were processed with the Tooth Transformer^® to obtain demineralized dentin granules (500–1000 µm), which were combined with CGFs prepared using the Medifuge MF200^® to form “sticky bone.” All patients underwent sinus lift via a lateral window approach (Hilt Tatum technique) with simultaneous placement of 98 implants (12–14 mm), which were loaded after six months. Results: At the 84-month follow-up, no implant failures or peri-implantitis were recorded. CBCT and clinical evaluations showed stable regenerated bone volume and absence of peri-implant bone resorption. All patients received fixed prostheses within six months without complications. Conclusions: The combined use of processed autologous dentin and CGFs proved to be a safe, predictable, and effective regenerative technique in cases of severe maxillary atrophy, with a 100% implant survival rate at five years. Full article

Background: The addition of chlorhexidine in dental restorative materials is a promising strategy to reduce the recurrence of tooth decay lesions. However, the main challenge is to develop materials with antimicrobial activity in the long term. Objective: This study analyses the effect of filler type and concentration of resin composites supplemented with chlorhexidine loaded in carrier montmorillonite particles (MMT/CHX) regarding their chemical, physical, and short- and long-term antimicrobial proprieties. Materials: Experimental composites were synthesized with 0, 30, or 60% filler in two ratios, 70/30 and 80/20, of barium glass/colloidal silica, respectively, and 5 wt% MMT/CHX. Conversion was measured using near Fourier-transform infrared spectrometry. Sorption and solubility were determined by specimen weight before and after drying and immersing in water. Flexural strength (FS) and elastic modulus (E) were determined by three bending tests using a universal test machine. Chlorhexidine release was monitored for 50 days. Streptococcus mutans UA159 was used in all microbiological assays. Inhibition halo assay was performed for 12 months and, also, biofilm growth for the specimens and colony-forming unit (CFU). Remineralization assay was used on restored teeth using measurements of microhardness Knoop and CFUs. Results: Conversion, sorption, and solubility were not affected by filler type and concentration. FS and E increase with the filler concentration, independent from filler type. Chlorhexidine was significantly released for 15 days for all experimental materials, and the increase in filler concentration decreased its release. Halo inhibition was observed for a longer time (12 months) in materials with 60 wt% filler at 70/30 proportion. Also, 60 wt% filler materials, independent from the filler ratio, reduced the CFU in relation to the control group from 8 to 12 months. In the remineralization assay, besides the absence of differences in hardness among the groups, after biofilm growth, the CFU was also significantly lower in materials with 60 wt% filler. Conclusions: Materials with 60% filler, preferentially with 70% barium glass and 30% silica, and 5% MMT/CHX particles demonstrated long-term antimicrobial activity, reaching 12 months of effectiveness. Also, this formulation was associated with higher mechanical properties and similar conversion, sorption, and solubility compared to the other materials. Full article

Cylindrical gears are used extensively due to their significant advantages including high efficiency, high load-bearing capacity, and long lifespan. However, the machining accuracy of cylindrical gears is significantly affected by motion errors and force-induced errors of machine tools. In this study, a motion error model of the machine tools was established based on multi-body system theory and homogeneous coordinate transformation method, quantifying the contributions and variation patterns of 12 key errors in the A and B-axes to workpiece geometric errors. Then, by using the stiffness analytical model and the spatial meshing theory, the influence of the force-induced elastic deformation of the shaft of rolling wheel and the springback of the workpiece tooth flank on the geometric error was revealed. Finally, taking the through rolling of a spur cylindrical gear with a module of 1.75 mm, a pressure angle of 20°, and 46 teeth as an example, the force-induced elastic deformation model of the shaft was verified by the rolling tests. Results show that for 40CrNiMo steel, the total profile deviation, total helix deviation, and single pitch deviation in the X-direction caused by rolling forces are 32.48 μm, 32.13 μm, and 32.13 μm, respectively, with a maximum contact rebound is δ_c = 28.27 μm. The relative error between theoretical and measured X-direction spindle deformation is 8.26%. This study provides theoretical foundation and experimental support for improving the precision of rolling process. Full article

Introduction: Dental caries remains a public health concern, and early detection prevents its progression and complications. Panoramic radiographs are essential diagnostic tools, yet the interpretation of panoramic X-rays varies among practitioners. Artificial intelligence (AI) presents a promising approach to enhance diagnostic accuracy in detecting dental caries. This scoping review examines the current literature on the use of AI programs to analyze panoramic radiographs for the diagnosis of dental caries. Methods: This scoping review searched PubMed, Scopus, Web of Science, and Dentistry and Oral Sciences Source, adhering to PRISMA guidelines. The review included peer-reviewed, original research published in English that investigated the use of AI to diagnose dental caries. Data were extracted on the AI model characteristics, advantages, disadvantages, and diagnostic performance. Results: Seven studies met the inclusion criteria. The Deep Learning Model achieved the highest performance (specificity 0.9487, accuracy 0.9789, F1 score 0.9245), followed by Diagnocat and Tooth Type Enhanced Transformer. Models such as CranioCatch and CariSeg showed moderate performance, while the Dental Caries Detection Network demonstrated the lowest. Benefits included improved diagnostic support and workflow efficiency, while limitations involved dataset biases, interpretability challenges, and computational demands. Conclusions: Applying AI technologies to panoramic X-rays demonstrates the potential for enhancing caries diagnosis, with some models achieving near-expert performance. However, future research must address the generalizability, transparency, and integration of AI models into clinical practice. Future research should focus on diverse training datasets, explainable AI development, clinical validation, and incorporating AI training into dental education and training. Full article

To address the unclear coupling mechanism between thermal elastohydrodynamic lubrication (TEHL) and dynamic behaviors in planetary gear systems, a novel tribo-dynamic model for dual-star planetary gears considering TEHL effects is proposed. In this model, a TEHL surrogate model is first established to determine the oil film thickness and sliding friction force along the tooth meshing line. Subsequently, the dynamic model of the dual-star planetary gear transmission system is developed through coordinate transformations of the dual-star gear train. Finally, by integrating lubrication effects into both time-varying mesh stiffness and time-varying backlash, a tribo-dynamic model for the dual-star planetary gear transmission system is established. The study reveals that the lubricant film thickness is positively correlated with relative sliding velocity but negatively correlated with unit line load. Under high-speed conditions, a thickened oil film induces premature meshing contact, leading to meshing impacts. In contrast, under high-torque conditions, tooth deformation dominates meshing force fluctuations while lubrication influence diminishes. By establishing a test bench for the planetary gear transmission system, the obtained simulation conclusions are verified. This research provides theoretical and experimental support for the design of high-reliability planetary gear systems. Full article

For transmission systems with regular order excitation, the order vibration will be conducted to each component of the system and affect the stability and service life of the system. A method with a regular non-circular active pulley is proposed in this paper, which is used to counteract the regular order excitation and the regular load excitation. A toothed belt drive system with second-order excitation is taken as an example. According to the existing analytical model of the tooth belt drive system, the modeling process and analytical solution algorithm of the system are derived. Based on the coordinate transformation, the algorithms for any position of an elliptical pulley and the common tangent of the circular pulley are given. And the algorithm for the arc length of the elliptical pulley at any arc degree is proposed. The influence of the phase and eccentricity in the elliptical pulley on the dynamic performance of the system is analyzed. Then the experimental verification is carried out. This shows that this system can generate excitation opposite to the main order rotational vibration of the driving pulley and opposite to the load of the driven pulley. Under the combined effect of other load pulleys in the system, there will be an amplification phenomenon in its vibration response. Considering the decrease in the belt span tension and the decline in the performance of energy-absorbing components after long operation, the presented method can better maintain the stability of system performance. This method can provide new ideas for the vibration reduction optimization process of systems with first-order wave excitation. Full article

Autogenous tooth transplantation offers a biologically favorable approach to tooth replacement, preserving the periodontal ligament, promoting alveolar development, and maintaining proprioception. Background/Objectives: Its broader clinical applicability is limited by variability in techniques and outcome definitions. This systematic review and meta-analysis evaluated the clinical success of autogenous tooth transplantation across donor tooth types, developmental stages, surgical techniques, and fixation methods. Methods: Following PRISMA 2020 guidelines and a PROSPERO-registered protocol (CRD42024625550), five databases and the gray literature were searched through July 2025. Eligible studies reported clinical outcomes for autogenous tooth transplantation. Risk of bias was assessed using the Newcastle–Ottawa Scale. A random-effects meta-analysis of logit-transformed proportions was conducted, with subgroup and sensitivity analyses by tooth type, root development stage, surgical technique, and fixation method. Results: Twenty studies involving 1366 transplanted teeth were included. The pooled success rate was 94.0% (95% CI: 22.5–99.9%) across follow-up periods ranging from one month to twenty-nine years. However, interpretation is limited by distinct heterogeneity (I² = 99.8%) and the wide confidence interval. Subgroup analyses by tooth type, root maturity, surgical technique, and fixation method are, therefore, emphasized to support clinical interpretation. Conclusions: Autogenous tooth transplantation achieves consistently high success across clinical contexts when biologic handling is respected. These findings support its broader use in dental and orthodontic practice and underscore the need for standardized outcome reporting and prospective research. Interpretation is limited by heterogeneity and variation in reporting standards. Full article

Stylolites are a common mineral dissolution feature in rocks that develop during compression and form distinct tooth structures. On a tectonic plate scale, mid-ocean ridges (MORs) and transform faults are a significant feature of the Earth’s surface that develop due to accretion of new material in an extensional regime. We present a comparison between the two features and argue that transform faults in MOR are similar to the sides of stylolite teeth, with both features representing kinematic faults (KFs). First, we present a numerical model of both stylolite and MOR growth and show that in both cases, KFs nucleate and grow spontaneously. In addition, we use a well-established technique (Family–Vicsek scaling) of describing fractal self-affine interfaces, which has been used for stylolites, to characterize the pattern of MOR systems in both simulations and natural examples. Our results show that stylolites and MOR have self-affine scaling characteristics with similar scaling regimes. They both show a larger roughness exponent at the small scale, a smaller exponent at the intermediate scale, followed by a flattening of the system at the largest scale. For stylolites, the physical forces behind the scaling are the surface energy at the small mineral scale, the elastic energy at the intermediate scale, followed by the system reaching the correlation length where growth stops. For MORs, the physical forces behind the scaling are not yet clear; however, the self-affine scaling shows that transform faults at MORs do not have a preferred spacing, but that the spacing is fractal. Our study offers a new perspective on the study of natural roughening phenomena on various scales, from minerals to tectonic plates, and a new view on the development of MORs. Full article

To address the widespread challenges of significant multi-category dental morphological variations and interference from overlapping anatomical structures in panoramic dental X-ray images, this paper proposes a dual-stream dental segmentation model based on Transformer heterogeneous feature complementarity. Firstly, we construct a parallel architecture comprising a Transformer semantic parsing branch and a Convolutional Neural Network (CNN) detail capturing pathway, achieving collaborative optimization of global context modeling and local feature extraction. Furthermore, a Pooling-Cooperative Convolutional Module was designed, which enhances the model’s capability in detail extraction and boundary localization through weighted centroid features of dental structures and a latent edge extraction module. Finally, a Semantic Transformation Module and Interactive Fusion Module are constructed. The Semantic Transformation Module converts geometric detail features extracted from the CNN branch into high-order semantic representations compatible with Transformer sequential processing paradigms, while the Interactive Fusion Module applies attention mechanisms to progressively fuse dual-stream features, thereby enhancing the model’s capability in holistic dental feature extraction. Experimental results demonstrate that the proposed method achieves an IoU of 91.49% and a Dice coefficient of 94.54%, outperforming current segmentation methods across multiple evaluation metrics. 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

To address the limitations in time–frequency feature representation of shearer arm gear faults and the issues of parameter redundancy and low training efficiency in standard convolutional neural networks (CNNs), this study proposes a diagnostic method based on an improved S-transform and a Depthwise Separable Convolutional Neural Network (DSCNN). First, the improved S-transform is employed to perform time–frequency analysis on the vibration signals, converting the original one-dimensional signals into two-dimensional time–frequency images to fully preserve the fault characteristics of the gear. Then, a neural network model combining standard convolution and depthwise separable convolution is constructed for fault identification. The experimental dataset includes five gear conditions: tooth deficiency, tooth breakage, tooth wear, tooth crack, and normal. The performance of various frequency-domain and time-frequency methods—Wavelet Transform, Fourier Transform, S-transform, and Gramian Angular Field (GAF)—is compared using the same network model. Furthermore, Grad-CAM is applied to visualize the responses of key convolutional layers, highlighting the regions of interest related to gear fault features. Finally, four typical CNN architectures are analyzed and compared: Deep Convolutional Neural Network (DCNN), InceptionV3, Residual Network (ResNet), and Pyramid Convolutional Neural Network (PCNN). Experimental results demonstrate that frequency–domain representations consistently outperform raw time-domain signals in fault diagnosis tasks. Grad-CAM effectively verifies the model’s accurate focus on critical fault features. Moreover, the proposed method achieves high classification accuracy while reducing both training time and the number of model parameters. Full article

Maintaining the cleanliness of orthodontic aligners is crucial for oral hygiene and preserving the optical properties of aligners. In this randomized clinical trial, we compared the effectiveness of different cleaning methods for the maintenance of Invisalign clear aligners. Twelve adult patients received five aligners, each worn for 10 days. The aligners were divided based on the cleaning method: tooth brushing with whitening toothpaste, vinegar, Fittydent Super Cleansing Tablets, Invisalign cleaning crystals, and only water. Scanning electron microscopy (SEM) was used to detect surface morphology changes; color changes (ΔE) were evaluated using a spectrophotometer. Fourier transform infrared spectroscopy (FTIR) with a diamond hemisphere was used to study the aligners’ chemical compositions. Nanoindentation testing was used to assess changes in the elastic modulus. SEM confirmed the effectiveness of Invisalign cleaning crystals in maintaining cleanliness, revealing a surface similar to that of the control group with no adverse effects. Color stability analysis revealed significant ΔE value differences; whitening toothpaste had significantly lower ΔE values than water and Invisalign cleaning crystals. The elastic modulus and FTIR analyses indicated no significant differences between the cleaning methods. Therefore, Invisalign cleaning crystals and whitening toothpaste are safe for aligner maintenance, showing successful and aesthetically pleasing results. Full article

Background: To reconstruct and maintain hard tissues over time, it is necessary to follow effective protocols and use appropriate materials. The selection of the graft material and its properties can also affect the final outcomes. For this purpose, numerous graft materials have been suggested. Among the valuable alternatives to these biomaterials, interest in using teeth as graft material has grown in recent years. Aim: The aim of the study was to investigate the histomorphometric outcomes of using tooth-derived materials when used as a bone substitute. Methods: We evaluated the histological results of autologous demineralized tooth graft material prepared using a Tooth Transformer device. A total of 187 histological samples from 186 subjects (52% male and 48% female, with an average age of 56.30 ± 12.97 years) were analyzed. The analysis focused on the total bone volume (BV%), residual tooth material (residual graft, TT%), and vital bone (VB%). The differences between the presence and absence of the resorbable membrane were also analyzed. Results: The amount of VB was 36.28 ± 19.09%, the residual graft TT was 9.6 ± 10.76%, and 46.96 ± 13.85% was the total bone volume (BV). The presence of membrane increased the amount of BV% and reduced the time to produce bone. Conclusions: The procedure using demineralized autologous tooth-derived biomaterial may be a predictable method for producing new vital bone capable of supporting dental implant rehabilitation and the use of membrane allow better results. Full article

Regenerative Endodontic Therapies (RETs) offer transformative potential by leveraging polymer-based scaffolds, stem cells, and growth factors to regenerate damaged dental pulp tissue, thereby restoring tooth vitality and prolonging tooth function. While conventional treatments focus on infection control, they often compromise the structural and biological integrity of the tooth. RETs, in contrast, aim to restore the natural function of the pulp–dentin complex by promoting cellular regeneration and immune modulation. In this context, biodegradable polymers—such as collagen, gelatin methacryloyl (GelMA), and synthetic alternatives—serve as scaffolding materials that mimic the extracellular matrix, support cell attachment and proliferation, and enable localized delivery of bioactive factors. Together, the tissue engineering triad—polymer-based scaffolds, stem cells, and signaling molecules—facilitates root development, apical closure, and increased fracture resistance. Recent innovations in polymeric scaffold design, including injectable hydrogels and 3D bioprinting technologies, have enhanced clinical translation by enabling minimally invasive and patient-specific RETs. Despite progress, challenges such as immune compatibility, scaffold degradation rates, and the standardization of clinical protocols remain. RETs, thus, represent a paradigm shift in dental care, aligning with the body’s intrinsic healing capacity and offering improved long-term outcomes for patients. Full article