Search Results (982)

Background: Stabilization of surgical guides in fully edentulous patients remains a clinical challenge due to mucosal resilience and potential micromovement, even when fixation pins are used. Guide instability may affect drilling accuracy and overall workflow predictability. This proof-of-concept case series describes a stabilization approach based on pre-placed tripod reference implants with multi-unit coupling, designed to create a mechanically defined prosthetic docking platform for fully guided implant surgery. Methods: Three fully edentulous patients requiring implant-supported rehabilitation were treated using a two-stage protocol. Three temporary reference implants were inserted in a tripod configuration 7–10 days prior to definitive surgery. Multi-unit abutments were mounted on the reference implants, and intraoral scanning was performed to design a surgical guide indexed to the prosthetic interfaces. During implant placement, the guide was screw-retained to the reference implants via the multi-unit connections. Postoperative implant positions were evaluated radiographically by superimposing postoperative datasets onto the preoperative planning model. Intraoperative guide stability, surgical events, and early postoperative outcomes were recorded. Results: Stable guide fixation was achieved in all three cases without detectable intraoperative displacement. Implant placement was completed as planned in each patient, and removal of the temporary reference implants was uneventful. No intraoperative or early postoperative complications were observed. Mean coronal, apical, and angular deviations between planned and achieved implant positions were 0.70 ± 0.16 mm, 0.39 ± 0.13 mm, and 3.30 ± 0.59°, respectively. These preliminary findings, derived from four treated arches, were comparable to ranges reported in selected studies on fully guided implant surgery; however, no direct statistical comparison with previously published datasets was performed. Conclusions: Within the limitations of this proof-of-concept case series, temporary reference implants arranged in a tripod configuration provided a stable and reproducible prosthetic indexing platform for guided implant surgery in fully edentulous patients. Further prospective studies involving larger patient cohorts and controlled comparative designs with conventional mucosa-supported or fixation-pin-supported surgical guides are required to evaluate the reproducibility, clinical performance, and long-term applicability of this stabilization concept. Full article

Implant screw loosening remains among the most frequently reported technical complications in implant-supported prostheses and may compromise prosthetic stability, maintenance requirements, and long-term clinical outcomes. Etiology is multifactorial and involves biomechanical, prosthetic, occlusal, and patient-related factors. This narrative review aimed to synthesize medium- and long-term clinical evidence (>5 years whenever available) regarding mechanisms, prevalence, and risk factors associated with screw loosening in implant-supported restorations. A structured literature search was conducted in PubMed, Web of Science, Cochrane Library, and EBSCOhost to identify clinical studies, randomized controlled trials, systematic reviews, and meta-analyses. Evidence regarding preload, implant–abutment connection design, retention type, implant splinting, framework fit, abutment angulation, implant dimensions, occlusal loading, parafunction, full-arch restorations, and torque protocols was critically interpreted. Current evidence indicates that screw loosening is influenced by inadequate preload, unfavorable occlusal forces, cantilevers, angulated abutments, framework misfit, and parafunctional habits. Single-unit and screw-retained restorations appear to exhibit higher complication rates in several studies, although findings remain inconsistent. Internal connections and splinting may improve mechanical stability; however, superiority has not been conclusively demonstrated. Most screw loosening events occur during the early functional period, emphasizing the importance of preload optimization, occlusal control, maintenance, and follow-up. High-quality long-term comparative studies remain limited. Full article

To investigate the three-dimensional seepage response and safety implications of high concrete-face rockfill dams (CFRDs) under waterstop failure scenarios, this study establishes a refined three-dimensional finite element model for a high CFRD at the JD Hydropower Station using COMSOL (version 6.1) Multiphysics. A comparative analysis is conducted for six representative scenarios, including peripheral joint failure, single vertical joint failure, overall vertical joint failure, and combined failures. The seepage safety assessment is based on the phreatic surface, seepage discharge, hydraulic gradients in key zones, and left- and right-bank abutment bypass seepage. The results show that waterstop failure significantly changes the seepage field, phreatic surface, leakage discharge, and hydraulic gradients. Among the six scenarios, S5, representing overall vertical joint failure with an aperture of 0.5 mm for each of the 41 vertical joints, produces the most unfavorable leakage response, with the total seepage discharge reaching 3010.46 L/s and the water level behind the face slab reaching 3888.23 m. In contrast, peripheral joint failure mainly induces local hydraulic-gradient concentration in the special cushion zone. Under S1, the maximum hydraulic gradient in the special cushion zone reaches 2.72, exceeding the allowable value of 0.72. The results also reveal asymmetric bypass seepage around the dam abutments, with the right-bank foundation leakage being 90.4–137.7% higher than that on the left bank. These findings clarify the distinct seepage risk mechanisms of different waterstop failures and provide support for waterstop design, construction quality control, targeted monitoring, and operation-stage safety assessment of high CFRDs. Full article

In the face of the raw materials crisis and environmental concerns, sustainable waste management has become a priority for current and future generations. Recycling waste from wastewater treatment plants in a closed loop protects natural resources, reduces landfill volumes, and lowers disposal costs. This paper presents the results of tests on the physical, filtration, and mechanical properties of mixtures of washed mineral waste (WMW) from grit chambers with fly ash from the thermal treatment of municipal sewage sludge (SSA) in a fluidized bed furnace. Additionally, radiological tests of the mixture components were conducted. Based on the conducted tests, the possibility of sustainable use in civil engineering, such as soil backfills and embankment construction materials, was assessed. The possibility of safely using waste materials in the indicated construction solutions was demonstrated for mixtures with dominant WMW content (90% and 70% by total weight). The waste mixtures correspond to poorly or medium-grade sands with a small amount of silt (uniformity coefficients of 3.33, 3.50, and 8.00). They are characterized by maximum dry densities of 1.542, 1.770, and 1.780 g/cm³; optimal moisture contents of 12.54, 12.86, and 20.25%; permeability coefficients of 0.08, 0.22, and 0.39 m/d; and internal friction angles of 38.4, 39.5, and 40.1°. The values of the determined parameters of some mixtures are similar to those of natural sands used as construction aggregates. All mixtures meet the geotechnical criteria for use in road embankments, below frost depth, and in flood embankment bodies. Mixtures with a 90% mass fraction of WMW were also approved for application as backfill for installation trenches. However, none of the mixtures met the hydraulic conductivity threshold required for the upper layers of embankments nor for backfill of abutments and retaining structures without the use of an additional binder (cement or lime), which is considered a prerequisite for these applications. Full article

Implant-Supported Fixed Prostheses (ISFPs) have become a common option for the rehabilitation of fully edentulous arches and have traditionally incorporated metallic substructures with ceramic or acrylic veneering. The rapid expansion of CAD/CAM technologies has introduced not only a range of polymer-based materials as alternatives to conventional metallic frameworks but also the possibility of the fabrication of monolithic rehabilitations. However, the evidence regarding the mechanical behavior of monolithic polymer-based full-arch rehabilitations remains limited. This study aimed to evaluate and compare the mechanical performance of monolithic polymer-based complete prostheses under static loading using Digital Image Correlation (DIC). A total of 12 specimens (3 per group) simulating an FP3 maxillary full-arch ISFP supported by four implants were milled from four materials: poly(ether ether ketone) (G1-PEEK), poly(ether ketone ketone) (G2-PEKK), poly(methyl methacrylate) (G3-PMMA), and fiber-reinforced composite (G4-FRC). All specimens were subjected to static loading up to 200 N at the incisors region, corresponding to the anterior unsupported span, and at the occlusal surface of the molars, corresponding to the most distal portion of the cantilever, using a universal testing machine. Full-field vertical displacement and strain distributions (principal tensile, compressive, and von Mises) were acquired through a stereo DIC system and analyzed using a Linear Mixed-Effects Model with Tukey’s HSD post hoc comparisons (α = 0.05). All prostheses withstood the applied load without macroscopic failure. G3-PMMA exhibited the highest vertical displacement, exceeding 1000 µm in the anterior span and 1500 µm in the cantilever region, along with the greatest strain concentrations, particularly at the interproximal embrasures distal to the terminal abutment. G1-PEEK provided the lowest displacement in the anterior span. G4-FRC presented displacements similar to G1-PEEK and G2-PEKK at the distal cantilever, but the lowest tensile strains and the most homogeneous strain dissipation in both loading at the anterior unsupported span and distal cantilever. This indicated that the biomechanical performance of full-arch ISFPs is highly influenced by the polymer used. PEEK, PEKK, and FRC appear as promising alternatives to PMMA for monolithic full-arch rehabilitations. Full article

Seepage failure is a primary cause of reservoir dam breaches. Conventional monitoring cannot reveal leakage paths across the dam, and static surveys miss weak-zone evolution. To address these challenges, this study constructs a typical geoelectric numerical model of low-resistivity expansion at a dam abutment. It systematically analyzes the response characteristics of apparent resistivity, independently inverted resistivity, and time-lapse resistivity imaging to the seepage failure process and validates the method through physical model tests and field observations. Inverted resistivity delineates hazards better than apparent resistivity, especially for small targets. Using the initial non-leakage model as a baseline, the resistivity-change profile obtained by ratio processing reveals the development trend of the hazard. Time-lapse inversion suppresses spurious artifacts from independent inversions and images the gradual expansion of the seepage weak zone. The L1-norm-constrained differential inversion further improves the convergence of the low-resistivity region and the accuracy of the anomaly center. Physical tests show rising water level reduces resistivity, especially in leakage-prone areas. Field tests show that after grouting, deep resistivity increases while shallow resistivity decreases. The results demonstrate that the time-lapse differential inversion algorithm based on the L1 norm accurately captures the spatiotemporal evolution of leakage hazards in earth-rock dams, providing reliable technical support for reservoir safety monitoring and evaluation. Full article

Directional long-borehole hydraulic fracturing is an important technique for controlling rockbursts induced by hard roofs. Its effectiveness depends primarily on whether fracturing-induced damage can modify the roof-bearing structure and thereby regulate stress concentration and elastic strain energy accumulation in the coal-rock mass ahead of the working face. However, existing numerical simulations commonly rely on predefined weakened zones or empirical parameter reduction, which makes it difficult to represent the spatial heterogeneity and mechanical evolution of rock damage during field hydraulic fracturing. Taking the 2803 goaf-side working face in Hetaoyu Coal Mine as the engineering background, this study proposes a microseismic-data-driven method for characterizing hydraulic fracturing-induced damage and incorporates it into a FLAC3D finite-difference model. The stress field, elastic strain energy field, and damage distribution ahead of the working face are compared under non-fractured and hydraulically fractured conditions. In the proposed method, the energy of fracturing-induced microseismic events is converted into the Benioff strain of numerical zones according to the attenuation law of microseismic wave propagation, and the corresponding rock damage variable is then calculated using a Weibull damage model. The fracturing-damaged rock mass is further represented by weakening the elastic modulus, cohesion, and friction angle, together with the stochastic generation of strongly damaged zones. The results show that, without hydraulic fracturing, the hard roof maintains a strong, continuous bearing capacity, resulting in a continuous lateral abutment stress concentration zone and a high elastic strain energy accumulation zone ahead of the working face and near the goaf-side boundary. After hydraulic fracturing, a patchy and locally connected high-damage weakening zone forms in the target roof strata. This damaged zone cuts the original continuous load-transfer structure through which the hard roof concentrates load toward the goaf side, reduces the extent of high-stress and high-energy zones in the coal seam, and induces an asymmetric adjustment of the dominant mining-induced energy release zone from the goaf side toward the solid-coal side. These simulation results agree well with the field observation that microseismic activity is mainly concentrated near the roadway on the solid-coal side. The study indicates that the rockburst-control mechanism of directional long-borehole hydraulic fracturing is not limited to simple overall stress dissipation. A key finding is that the fracturing-induced heterogeneous damage zone effectively interrupts the continuous load-transfer and energy-storage paths on the goaf side. This induces an asymmetric spatial redistribution of the mining-induced energy field from the goaf side toward the solid-coal side, thereby mitigating the high static-load and high-energy-storage state ahead of the working face. Full article

The long-term success of implant-supported prostheses (ISPs) is strongly influenced by material selection, which affects stress distribution within the implant system and surrounding cortical bone. This study aimed to assess the biomechanical behavior of a four-unit ISP supported by two implants in the posterior region, using different framework and superstructure material combinations through dynamic finite element analysis (FEA). Methods: A three-dimensional (3D) edentulous mandibular model was created using Mimics software, with two implants placed in the first premolar and second molar regions. Four framework materials—titanium (Ti), glass fiber–reinforced composite (GFRC), 3Y-TZP zirconia, and polyether ether ketone (PEEK)—were combined with two superstructure materials, 5Y-TZP zirconia and resin-matrix ceramic (RMC), forming eight groups. Dynamic loading simulated chewing forces, and stress distribution was analyzed using the von Mises criterion. Results: The results demonstrated that 3Y-TZP zirconia frameworks generated the highest stress values across implants, abutments, and cortical bone. RMC crowns consistently produced lower stress than 5Y-TZP zirconia across all the groups. PEEK showed the highest displacement, followed by GFRC, zirconia, and Ti. Conclusion: Materials with higher Young’s modulus tended to exhibit greater stress transfer to the implant, implant components, and cortical bone. In contrast, polymer-based materials may show a tendency toward greater deformation and displacement compared with metallic and ceramic materials. Full article

Background/Objectives: Peri-implantitis is a common complication affecting approximately 24% of dental implants and is characterized by progressive bone loss and reduced implant stability. Implantoplasty, an intraoral procedure used to remove biofilm by machining the titanium implant surface, has become increasingly common in clinical practice. However, this procedure may compromise the mechanical integrity of implants, especially when combined with peri-implant bone loss, potentially leading to premature fatigue failure. This study evaluated the effect of different marginal bone resection depths, with and without implantoplasty, on the cyclic mechanical behavior of dental implants. Methods: A total of 200 commercially pure grade 4 titanium implants were embedded in resin simulating human bone at depths of 3, 4, and 5 mm. A subset of implants underwent implantoplasty with a 0.4 mm surface reduction corresponding to the thread width. Finite element analysis was performed to evaluate von Mises stress distribution and predict fatigue behavior. Numerical results were experimentally validated using a servo-hydraulic MTS Bionix system under ISO 14801:2016 conditions. Fatigue limits were determined from the asymptotic region of the load–cycles-to-failure (S–N) curves, and fracture surfaces were examined by scanning electron microscopy. Results: Maximum von Mises stresses were concentrated at the thread–body transition and increased with greater marginal resection depth, with additional stress amplification observed after implantoplasty. Fatigue limits for untreated implants were approximately 351 N, 285 N, and 210 N for 3-, 4-, and 5 mm resections, respectively. Implants subjected to 0.4 mm implantoplasty showed fatigue limits of 311 N, 270 N, and 90 N, respectively. Failure patterns were load-dependent: higher loads produced coronal fractures, whereas lower loads resulted in failure at the implant–abutment connection. Finite element predictions showed strong agreement with the experimental results. Conclusions: Excessive marginal resection significantly decreases the fatigue resistance and long-term mechanical reliability of dental implants, particularly when combined with implantoplasty. The main limitations of this study include is in vitro design, the assumptions inherent to the numerical models, and the variability associated with implantoplasty procedures. Full article

Background/Objectives: This narrative review aimed to critically assess the role of multi-unit abutments in implant dentistry, focusing on mechanical reliability and biological stability at the implant–abutment interface. Methods: A literature search was performed in PubMed/MEDLINE, Scopus, Web of Science and Google Scholar to identify clinical studies and experimental research from the past 20 years addressing implant–abutment connections, mechanical complications and biological integration of multi-unit abutments. Results: Dental implants demonstrate survival rates above 95%, yet complications, up to 35%, are primarily linked to the implant–abutment interface. Mechanical issues, especially screw loosening, may be mitigated with conical connections and adherence to evidence-based protocols. Biologically, multi-unit abutments with sufficient transmucosal height contribute to stable supracrestal tissue and preservation of marginal bone. Advances such as nanostructured surfaces and the concept of mucointegration represent a shift toward biologically active interfaces, enhancing peri-implant soft tissue health. Conclusions: Multi-unit abutments have evolved from simple angulation-correction tools to essential components across a wide range of clinical applications. Their success relies on strategic, protocol-driven use that integrates mechanical strength with biological harmony, enabling potentially favorable outcomes in modern implant dentistry, particularly in well-selected clinical scenarios. Full article

Part segmentation of industrial 3D models is often limited by the lack of sufficiently large and consistently labeled training datasets. This study proposes a workflow for generating synthetic segmentation datasets from robust parametric computer-aided design (CAD) models and evaluates its applicability on a dental abutment case. The workflow includes the definition of a modeling strategy, creation of a robust parametric CAD model, automated generation of valid geometry variants, and preparation of labeled training data for point-cloud-based segmentation. In the experimental part of the study, a synthetic dataset of segmented dental abutment geometries was generated from the developed parametric CAD model and used to train a PointNeXt-S part-segmentation model. The segmentation performance of the trained model was evaluated on manually labeled real-world abutments. Results show that the segmentation of industrial 3D models improved with increasing synthetic training-set size and further improved when data augmentation was applied. The best-performing augmented model achieved a mean Intersection over Union (IoU) of 89.2% on the real-world validation set, compared with 82.4% without augmentation. The findings indicate that parametric-CAD-based synthetic dataset generation can provide an effective basis for training segmentation models for complex industrial geometries. Full article

A clinically unresolved question in full-arch implant rehabilitation is whether early peri-implant bone adaptation is primarily a local (implant-level) phenomenon, a shared within-arch response, or a patient-level characteristic—information is unavailable from conventional mean-based outcome reporting. This prospective secondary analysis quantified the hierarchical distribution of peri-implant marginal bone level change (ΔMBL) in monolithic zirconia full-arch prostheses directly connected to multi-unit abutments during the first year of function. Unlike mean-based endpoints, this approach identifies whether early bone adaptation variability originates primarily at the implant, prosthetic-arch, or patient level. Of 308 implants placed in 40 completely edentulous patients rehabilitated with 49 prostheses, 2 implants failed before delivery of the definitive prosthesis and were excluded from radiographic analysis, leaving 306 implants available for multilevel analysis. Implant-level ΔMBL was analyzed using an unconditional three-level linear mixed-effects model. Implant survival was 99.2%, prosthetic survival was 100%, and mean ΔMBL at 12 months was 0.38 ± 0.27 mm. Variance partitioning showed that 60.8% of total variability occurred at the implant level, 28.4% occurred at the patient level, and 10.8% occurred at the prosthetic-arch level, providing a framework for identifying at which level of the restorative system future clinical interventions may have the greatest impact. Findings should be interpreted within the context of a secondary analysis with a 12-month follow-up and no explanatory covariates; longer-term comparative studies with explanatory multilevel designs are required to confirm and extend these observations. Full article

Background/Objectives: The aim of this study is to test different convolutional neural network (CNN) and Transformer-based models to detect and classify vertical misfit at the abutment-prosthesis interface on panoramic radiographs, and to develop a hybrid deep learning model enhanced with attention mechanisms. Methods: A dataset consisting of a total of 566 images, manually classified as 249 ‘fit’ and 317 ‘misfit’ cases by two experts, was created. Images were resized to 224 × 224 and divided into training, validation, and test groups. The deep learning model yielding the most successful results was determined as the backbone; a hybrid model was developed by integrating three different attention modules (SE, CBAM, and ECA) into this structure. Model performance was evaluated using accuracy, precision, sensitivity, and F1 score metrics. Results: CNN-based models (RegNetY-800MF, ConvNeXt-Tiny, EfficientNetV2-S, ResNet50) performed better than Transformer-based models (DeiT, Swin-Tiny) in all metrics. The proposed hybrid model exhibited the highest success among all tested models with a 99.12% accuracy rate. This model reached a 100% precision value in the misfit group and yielded no false positive results. The F1 scores of the hybrid model were recorded as 99.01% for the fit group and 99.21% for the misfit group. Conclusions: The findings of this study demonstrate that attention-enhancing deep learning frameworks have the potential to significantly improve the diagnostic utility of routine panoramic radiographs. It shows that panoramic imaging, when supported by advanced artificial intelligence, can provide valuable diagnostic support in detecting vertical misfit. The developed model has the potential to become a reliable clinical decision support system. Full article

Titanium base-free multi-unit abutment (MUA) restorations have been introduced to simplify implant prosthetic workflows by eliminating intermediate titanium bases and bonding interfaces. However, this approach modifies the biomechanical behavior of the prosthesis–abutment–implant complex and increases reliance on prosthetic screw performance. Despite growing clinical and commercial interest in these systems, the available evidence remains limited and fragmented, and the biomechanical consequences of removing the titanium base have not been clearly synthesized. Therefore, this critical review evaluated the influence of prosthetic screw design on the biomechanical behavior of titanium base-free MUA restorations, focusing on preload maintenance, load transfer, and mechanical stability. The evidence indicates that preload loss, screw loosening, and fatigue behavior are primary determinants of mechanical performance. Screw material, surface characteristics, and head geometry may affect preload generation, load distribution, and resistance to micromovement, although current evidence remains limited and heterogeneous. Short-term clinical outcomes appear acceptable when appropriate biomechanical and prosthetic protocols are followed; however, long-term comparative data are lacking. Titanium base-free MUA restorations should be considered a technique-sensitive approach requiring optimized screw selection, accurate prosthetic fit, and controlled occlusal loading. Further well-designed long-term studies are needed to establish their predictability. Full article

Context: Prosthetic rehabilitation of acquired maxillary defects with Maxillary Resection Prostheses (MRPs) remains biomechanically challenging, particularly in partially edentulous patients, where conventional clasp-retained designs often yield suboptimal retention, stability, and functional outcomes. Research Gap: The integration of telescopic crown systems with semi-precision attachments incorporating a rotational latching mechanism has not been previously described as a unified approach to optimise load distribution and prosthesis stability in maxillary defect rehabilitation. Objective: To describe and clinically evaluate a novel prosthetic design combining telescopic crowns and a semi-precision rotational latching attachment to enhance retention, stability, and functional performance of MRPs. Methodology: A 31-year-old patient with a unilateral maxillary defect following partial maxillectomy presented with an unstable interim prosthesis and impaired speech and mastication. A definitive MRP was designed using telescopic crowns on the remaining dentition to establish a controlled path of insertion and improved axial load transfer. A semi-precision attachment with a key–keyway rotational latching mechanism was incorporated into the secondary framework to engage specific undercuts while minimising lateral forces on abutment teeth. A provisional prosthesis was used for 3 months to evaluate base extension, phonetics, and functional parameters before fabrication of the definitive prosthesis. Results: Serial follow-up at 1, 3, and 6 months demonstrate consistent prosthesis stability, precise seating, and favourable retention. Marked improvements were observed in speech intelligibility, masticatory efficiency, and patient-reported comfort. Conclusions: This combined prosthetic strategy represents a novel and biomechanically optimised approach for the rehabilitation of partially edentulous maxillary defects, with promising clinical and functional outcomes. Full article