Search Results (473)

Numerous studies have demonstrated that tooth-supported dental guides improve the accuracy of implant placement. However, current manufacturing procedures and available materials are not yet optimal and may still lead to deviations from the planned implant position. The influence of the surgeon’s manual force on the deformation of dental guides during implant placement has not yet been sufficiently investigated. Therefore, this study evaluates the mechanical behavior of dental guides using finite element analysis (FEA) in order to assess the influence of the surgeon’s hand force during clinical application. Finite element simulations of deformation and stress were performed for four types of tooth-supported dental guides, including cantilever dental guides with free ends and beam-type guides with a large span between the supporting teeth. The manual force applied by the surgeon was arbitrarily set to 30 N. Simulations were conducted for five commonly used biocompatible polymer materials: Stratasys MED610, VeroGlaze MED620, EOS PA2200, Formlabs FLSGAM01, and Stratasys ULTEM 1010. The numerical results quantified the deformation of dental guides caused by the applied manual force during surgical manipulation. For all analyzed guide designs, the deflection was primarily influenced by the arm length, i.e., the distance between the support and the point of force application. Based on the obtained results, design diagrams were developed to provide guidelines for the design of beam-type (A and A1) and cantilever-type (B and B1) tooth-supported dental guides. Full article

Background/Objectives: This finite element analysis (FEA) assessed stress distribution in the tooth and dentin within an intact periodontium under 4 N of force and five orthodontic movements (intrusion, extrusion, rotation, tipping, and translation), using four failure criteria commonly used in numerical dental studies. Secondly, differences between brittle- and ductile-like failure criteria were found, and the most accurate criterion was determined. Additionally, movements more prone to inducing external orthodontic root resorption were assessed. Methods: Using nine 3D models of the second lower premolar, 180 numerical simulations were performed. The models were anatomically accurate based on CBCT scans. FEA employed the brittle-like Maximum Principal (MaxP), Minimum Principal (MinP), and ductile-like Von Mises (VM) and Tresca (T). Results: The results showed that tipping was less prone to external orthodontic root resorption than translation, extrusion, intrusion, and rotation, which showed areas of high stress concentration in the cervical third of the root. High-stress areas were visible only when the dentin-pulp-NVB components were separately analyzed, and not when the entire tooth structure was assessed. Only by correlating the qualitative with the quantitative results could the difference between brittle-like and ductile-like failure criteria be seen. Conclusions: In total, 4 N of applied orthodontic force can induce limited islands of external orthodontic root resorption (intrusion–extrusion on the vestibular side, rotation–translation on the lingual and distal–lingual sides). The ductile-like failure criteria maintained the accuracy of the results across all FEA simulations, while the brittle-like criteria showed various quantitative and qualitative inconsistencies. Full article

The fatigue pitting model based on the minimum oil film thickness does not consider the influence of tooth surface roughness and residual stress, which limits the accuracy of predicting the fatigue pitting of the model. Micro pitting often initiates on the surface due to large external loads. Therefore, it is urgent to propose a new-micro pitting bearing capacity model based on gear surface integrity parameters. This paper studied a new fatigue pitting model considering surface integrity subjected to polishing processes. This model thoroughly analyzes the effects of teeth surface roughness dynamically on the oil film pressure and explores the complex mechanism of residual stress in the near-surface stress field of the gear teeth. The new model can more accurately simulate the micro-pitting bearing capacity under actual operating conditions by introducing teeth surface roughness and residual stress, and the prediction reliability of gear steel is greatly improved. This improved model provides a solid theoretical basis and technical support for optimizing gear transmission systems, accurate diagnosis of micro-pitting defects, and in-depth theoretical research in related fields. Full article

Streptococcus sanguinis (S. sanguinis) is an oral commensal and early colonizer of the tooth surface that contributes to dental biofilm homeostasis. Zinc oxide nanoparticles (ZnO NPs) are often incorporated into dental restorative materials to enhance mechanical performance and confer antibacterial properties; however, their effects on S. sanguinis have not been thoroughly studied. Here, we investigated the antimicrobial and antibiofilm efficacy of ZnO NPs against this bacterial species. ZnO NPs exhibited a minimal inhibitory concentration (MIC) of 100 µg/mL and caused rapid, dose-dependent suppression of intracellular ATP levels and overall metabolic activity within 2–4 h of exposure. ZnO NPs induced reactive oxygen species (ROS) production in a dose-dependent manner. The free radical scavenger α-tocopherol partly prevented the antibacterial effect of ZnO NPs, suggesting that lipid peroxidation contributes to ZnO NP-mediated toxicity, although it is not the sole mechanism involved. Short-term exposure (2 h) to ZnO NPs did not significantly affect membrane integrity or cellular morphology, whereas prolonged treatment (24 h) resulted in pronounced membrane permeabilization, membrane hyperpolarization, and cellular swelling. Computational morphometric analyses of high-resolution scanning electron microscopy (HR-SEM) images of planktonic growing bacteria after a 24 h treatment confirmed a significant, dose-dependent increase in cell surface area and surface roughness. Importantly, ZnO NPs also reduced the metabolic activity and compromised the structural integrity of mature, preformed biofilms. Collectively, these findings demonstrate that ZnO NPs exert antimicrobial and antibiofilm effects against S. sanguinis through early metabolic inhibition associated with oxidative stress followed by progressive membrane dysfunction. Full article

Periodontitis is a chronic infectious disease characterized by the destruction of the tooth-supporting tissues, including the gingiva, periodontal ligament, and alveolar bone, which may ultimately lead to tooth loss. However, blood-based biomarkers reflecting systemic inflammation in periodontitis remain poorly defined. We analyzed plasma proteomic data from the UK Biobank using Olink Explore proteomics to identify systemic protein signatures distinguishing chronic periodontitis patients (n = 90) from healthy controls (n = 2234). Among 2151 proteins passing quality control, 29 proteins showed significant differential expression (FDR < 1.0 × 10⁻⁵). Growth differentiation factor 15 (GDF15) exhibited the strongest upregulation (mean NPX: −0.183 to 0.157, effect size = 0.337, FDR = 2.82 × 10⁻¹²), followed by N-terminal pro-B-type natriuretic peptide (NT-proBNP) (effect size = 0.594), Interleukin-6 (IL-6) (effect size = 0.450), and Insulin-like growth factor binding protein-(4IGFBP4) (effect size = 0.269). Multiple TNF receptor superfamily members (TNFRSF1A/1B, TNFRSF10A/10B) and proteins involved in extracellular matrix remodeling (COL6A3, ADAM12) and vascular stress (ADM) were significantly elevated. In contrast, EGFR and DNER showed decreased expression. Protein–protein interaction network analysis revealed IL-6 as a central hub protein forming a tightly interconnected cluster with TNF receptor family members. These findings indicate systemic plasma protein profiles associated with chronic periodontitis within this population-based cohort. The identified proteins may provide a basis for future evaluation of blood-based biomarkers for chronic periodontitis, pending further validation. Full article

Dental hard tissues, through their remarkable resistance to degradation, represent one of the most durable biological materials available for postmortem investigation. The preparation of undecalcified or ground sections allows microscopic visualization of enamel, dentin and cementum structures, which can preserve chronological, physiological, or environmental information. This review provides a comprehensive overview of the forensic applications of dental hard tissue ground sections, focusing on methodological principles, interpretive potential and practical constraints. The literature in forensic odontology highlights their relevance for age estimation through tooth cementum annulation, identification of neonatal and accentuated stress lines, and the assessment of thermal or chemical alterations. While these methods have proven scientific validity in anthropology and histology, their forensic implementation remains limited by heterogeneity in protocols and interpretative subjectivity. Standardization of preparation techniques, digital imaging, and integration with complementary analyses such as micro-CT or SEM could enhance the reliability and medico-legal relevance of this classical but underused approach. Full article

Background/Objectives: Clinical and scientific professionalization in orthodontics requires a comprehensive understanding of the biomechanical principles governing force generation and distribution produced by orthodontic appliances, beyond purely esthetic considerations. In this context, finite element analysis (FEA) has emerged as a fundamental computational tool for the detailed evaluation of the biomechanical behavior of the dentoalveolar system. The aim of this study was to map and synthesize the available scientific evidence on the application of FEA in the assessment of force distribution, tooth movement, and the mechanical response of periodontal tissues during orthodontic treatment. Methods: Original studies published between 2020 and 2025 that relied exclusively on computational simulations using FEA were included. Eligible studies addressed orthodontic biomechanics, including tooth movement, appliance–tooth–periodontium interactions, or the mechanical evaluation of orthodontic attachments. Clinical studies, narrative reviews, and articles without finite element modeling were excluded. A systematic literature search was conducted in the PubMed and ScienceDirect databases to answer the following question: Which FEA methodologies have been used to evaluate the biomechanical behavior of orthodontic appliances? Results: Data were categorized according to key biomechanical variables. The findings indicate an increasing use of FEA as a supportive tool in orthodontic research. However, significant limitations were identified, including lack of methodological standardization, limited model validation, and insufficient correlation between computational outcomes and clinical evidence. Conclusions: Currently, FEA in orthodontics is used predominantly for descriptive purposes, particularly for visualizing stress and strain distributions. Greater standardization and validation are required to enhance its translational applicability in clinical relevance. Full article

The gears of helicopter transmission system have strict requirements on machining accuracy, and the accurate prediction of tooth surface grinding force is the key to its manufacturing. The existing model simplifies the micro-contact behavior of the abrasive-workpiece, which limits the accuracy of the grinding load solution. In this paper, the stress state of single abrasive grain at different stages is refined from the micro level, and the grinding force mechanism model of contact area superposition is established. A mechanism-constrained data-driven grinding force prediction algorithm (MCDDP) is proposed. The algorithm integrates the microscopic force mechanism as a physical constraint into the neural network. The experimental results show that the R² of the model for predicting the normal and tangential grinding forces under multiple working conditions is higher than 0.98, and the average error is reduced by about 17% compared with the traditional model. This study reveals the non-uniform force mechanism of abrasive-workpiece, realizes the integration of mechanism model and data-driven method, and provides engineering theoretical and technical support for grinding force prediction and process parameter optimization of aviation precision gears. Full article

Polycrystalline diamond compact (PDC) bits often experience localized heating during impact rock breaking in complex formations, resulting in reduced service life and lower drilling efficiency. An optimized structural design of PDC cutters can significantly enhance bit performance, mitigate thermal concentration, and extend operational longevity. Inspired by previous work on PDC cutter surface topography, five saw-type tooth-shaped cutter designs—featuring one to five saw-type teeth were developed. To evaluate their rock-breaking effectiveness and identify the optimum design, the impact-induced rock fragmentation processes of these cutters were compared using the finite element method. Key indicators, including cutting force, mechanical specific energy (MSE), and cutter surface temperature, were analyzed to determine the superior tooth configuration. Among the five designs, the four-saw-tooth cutter induced the most pronounced stress concentration in the rock. Its optimized number of saw-type teeth ensured full participation of all teeth in rock cutting, enabling efficient rock removal and maximizing breakage performance. Compared with other designs, this cutter exhibited the smallest fluctuations and mean cutting force. The specific mechanical energy decreased initially and then increased with the number of saw-type teeth, reaching a minimum for the four saw-type tooth design. Moreover, it showed the lowest surface temperature and the mildest temperature variation, which helps alleviate localized heating and improve wear resistance. The cutting performance of the four saw-type tooth was further influenced by cutting depth and back rake angle, with optimal values identified as 1.5 mm and 20°, respectively. Compared with a conventional cutter, the four saw-type tooth design reduced the overall surface temperature by approximately 10.69%, with temperature rise confined mainly to the grooves between adjacent saw-type teeth and no widespread thermal concentration observed, confirming its design superiority. Full-scale rock-breaking simulations demonstrated that the bit equipped with four saw-type tooth achieved greater penetration depth and required lower torque than the conventional design, indicating enhanced rock-breaking ability and higher drilling efficiency. In conclusion, the four saw-type tooth PDC cutter design offers a promising approach for developing high-performance drill bits and reducing drilling costs. Full article

Gear systems operate under high mechanical and tribological loads, making their surfaces vulnerable to wear and fatigue. Improving surface durability requires finishing processes that improve near-surface properties and extend service life. Since machine hammer peening (MHP) offers such potential, this study investigates its influence on the performance of case-hardened spur gears and evaluates its suitability as an alternative to shot peening as a conventional finishing method. Analog specimens with simplified geometries were treated using various MHP parameters to identify effective process settings. These optimized settings were then applied to real spur gears to assess performance under practical conditions. The experiments showed that MHP can significantly modify surface integrity, achieving surface roughness reductions of up to 55%, surface hardness increases of up to 30%, and compressive residual stresses exceeding −1400 MPa with stability to depths of 200 µm. These modifications resulted in improved wear and fatigue performance, with increases in load cycle number in the tooth flank up to 99% and an increase in load amplitude in the tooth root of more than 5%. For comparison, specimens were also treated with shot peening. Although MHP induced stronger surface integrity modifications, shot peening achieved higher overall load-carrying capacity because several critical areas could not be fully accessed by MHP, limiting its effectiveness. Overall, MHP shows promise as a finishing process, but its full potential depends on overcoming accessibility limitations in complex gear geometries. Full article

Shear slip along structural planes in jointed rock masses is the primary trigger for rock slope instability, threatening geotechnical engineering safety. Direct shear tests were conducted on prefabricated granite specimens with regular sawtooth structural planes (undulation angles: 15°, 30°, 45°; tooth spacing: 10 mm) under 2, 4 and 6 MPa normal stresses, with synchronous acquisition of acoustic emission (AE) and infrasonic signals to explore shear failure characteristics, acoustic spectral features and instability precursors. Results show (1) peak shear stress and stiffness rise significantly with increasing undulation angle and normal stress, and failure modes evolve from sliding friction-dominated to asperity shearing-dominated, finally to composite asperity shearing and compressive crushing. (2) The spectral characteristics of both acoustic emission (AE) and infrasonic signals are closely related to the shear fracture mechanism. (3) Approaching peak shear stress, dominant frequency ratio correlation dimension drops to a minimum and the ib-value rises to a pre-sudden-drop critical point; higher undulation angles align these values with stress closer to the peak, valid as instability precursors. (4) A two-level early warning model (early to imminent warning) is proposed via cross-frequency band AE-infrasonic monitoring, providing a fundamental basis for rock slope stability monitoring using these signals. Full article

Mutations in the Mitofusin 2 (MFN2) gene cause Charcot–Marie–Tooth type 2A (CMT2A). Neurotrophin 3 (NT-3) is an autocrine factor that supports Schwann cell survival and differentiation, axon regeneration and myelination, neuromuscular junction (NMJ) integrity, and mitochondrial function. In this study, we assessed the efficacy of NT-3 gene therapy using the AAVrh74 serotype in the Mfn2^+/− mouse model for CMT2A. Although haploinsufficiency is not reported in CMT2A patients, our model shows some features of CMT2A, including axonal atrophy, muscle atrophy, length-dependent axon loss, and abnormal mitochondria, in muscle in the enzyme histochemistry. Eight-month-old Mfn2^+/− mice received a 3 × 10¹¹ vector genome dose of AAVrh74.tMCK.NT-3 intramuscularly, and functional, electrophysiological, and histological outcomes were assessed six months post-treatment. NT-3 gene therapy in Mfn2^+/− mice significantly improved grip strength and rotarod performance, and ameliorated electrophysiological abnormalities and NMJ denervation in lumbrical muscles. Additionally, our therapeutic approach improved muscle histopathology with reductions in mitochondrial abnormalities and oxidative stress. NT-3 further remodeled carbohydrate metabolism in muscle. Our study indicated that AAV.NT-3 gene therapy has a disease-modifying effect in the Mfn2^+/− model of CMT2A, providing further support for the translational potential of this surrogate gene therapy approach to CMT2A patients. Full article

The management of dental caries has evolved from the traditional mechanical approach of “extension for prevention” to a biologically oriented philosophy centered on preserving natural tooth structures. Minimally invasive dentistry (MID) emphasizes early detection, risk assessment, prevention, and conservative intervention based on the lesion’s activity and depth. This review outlines current evidence on non-operative, micro-invasive, and minimally invasive strategies, including fluoride therapy, remineralizing agents such as casein phosphopeptide–amorphous calcium phosphate (CPP-ACP), self-assembling peptides that promote biomimetic enamel repair, sealants, and resin infiltration. Minimally invasive operative methods employ advanced technologies for selective tissue removal—chemomechanical systems (Carisolv, Papacarie, Brix3000), sono-and airabrasion, and new-generation polymeric and ceramic burs (SmartBur, Cerabur) designed to preserve sound dentin. Laser photoablation, particularly with erbium lasers (Er:YAG, Er,Cr:YSGG), enables precise cavity preparation with minimal thermal and mechanical stress. These approaches enhance patient comfort, reduce anesthesia requirements, and maintain tooth vitality. Despite limitations related to cost, equipment, and operator sensitivity, MID represents not only a set of refined clinical techniques but also a comprehensive, evidence-based treatment philosophy founded on biological principles, structural preservation, and the promotion of long-term oral health. Full article

Background: Periodontitis is a disease characterized by the destruction of periodontal tissue and tooth loss. The molecular mechanisms behind this disease, however, are not clearly understood. Ferroptosis is an iron-dependent, lipid peroxidation-driven form of regulated cell death that seems to play a role in periodontal pathogenesis by increasing oxidative stress and reducing tissue regeneration. Objective: The current narrative review aims to summarize current knowledge of the involvement of ferroptosis in periodontal tissue destruction and potentially to identify new targets of therapy. Methods: A comprehensive search of PubMed, Embase, and Web of Science databases was conducted. Original human, animal, and in vitro studies published in English were selected. Data on experimental models, molecular markers, and key outcomes were extracted and synthesized in the review. Results: After screening, four studies were identified and selected. Ferroptosis activation in periodontal ligament fibroblasts, stem cells, and gingival tissues was associated with increased ACSL4 and decreased GPX4 expression, iron accumulation, and oxidative stress. The administration of Ferrostatin-1 or antioxidants like curcumin seemed to reduce inflammation and alveolar bone loss in vivo. Transcriptomic analyses further revealed immune-related ferroptosis gene signatures in human periodontitis tissues. Conclusions: Ferroptosis represents a crucial mechanism in periodontal tissue destruction through not yet completely understood. Understanding these molecular pathways could be the key to developing new therapeutic strategies for periodontal treatment. Full article

The mitochondrial outer membrane (OMM) plays a crucial role in maintaining cellular homeostasis by regulating mitochondrial dynamics, organelle interactions, and stress responses. In peripheral neurons—cells with high metabolic demands and long axons—the OMM acts as a vital platform for coordinating bioenergetics, calcium signaling, and redox balance. Ganglioside-induced differentiation-associated protein 1 (GDAP1), an OMM-anchored protein, has emerged as a key regulator of mitochondrial fission and transport, redox homeostasis, and mitochondrial membrane contact sites (MCSs). Genetic variants in GDAP1 cause Charcot–Marie–Tooth disease (CMT), emphasizing its essential role in peripheral nerve function. This review highlights the multifaceted functions of GDAP1 in neuronal physiology and as a model protein that integrates organelle communication and mitochondrial biology. We further discuss how GDAP1 dysfunction leads to structural and functional impairments in peripheral neurons, proposing the OMM and its microenvironment as critical targets for therapeutic intervention in inherited neuropathies. Full article