Search Results (86)

Background/Objectives: Prosthodontic restoration design plays a key role in the long-term success of implant-supported treatments and in maintaining peri-implant tissue health. Inadequate emergence angles and profiles can compromise tissue stability and negatively influence clinical outcomes. Generative design, as an algorithm-driven optimization approach, requires the definition of key parameters in advance to guide the process and determine the final shape of the hybrid implant abutment. Methods: A detailed literature review of the PubMed and Scopus databases was performed to find appropriate studies published up to 1 December 2025. Studies that investigated the emergence angle and emergence profile of implant-supported restorations were included. Seventeen studies fulfilled criteria and were included in the final analysis. Results: While the optimal emergence angle is still debatable, the literature suggests that an angle less than 30° may be beneficial. However, a concave emergence profile of implant-supported restoration has a significant role in improving stability and maintaining peri-implant health. Conclusions: Careful characterization and evaluation of the included parameters provide useful insights for generative design workflows, enabling the creation of implant abutment designs that maintain a balance between mechanical performance and biological compatibility. Full article

During coal mining, parallel voids ahead of an advancing working face often trigger intense dynamic loading and structural instability, posing significant risks to operational safety. Using the 43,201 working face of the Shiyangou Coal Mine as a case study, this research investigates the mechanisms of surrounding rock instability and proposes an integrated synergistic control strategy. Based on voussoir beam theory, a mechanical model of the roof structure—incorporating the nonlinear coupling between the gangue and immediate roof—was developed to establish the critical thresholds for the rotational instability of key blocks. Analytical results indicate that the limit breaking distance for “Key Block B” in the main roof is 24.49 m, which defines the primary zone for advanced reinforcement and hazard prevention. Furthermore, applying short-arm beam theory, this study clarifies how pre-split roof cutting disrupts the transmission of advance abutment pressure, identifying 8° as the optimal cutting angle. Building on these insights, a multi-faceted control system was implemented, combining hydraulic fracturing for pressure relief, pumpable backfill pillars, and an artificial false roof (utilizing a suspended I-beam structure 1.2 m above the floor). Field monitoring confirms that this collaborative approach effectively stabilizes the surrounding rock, ensuring the safe and continuous passage of the working face through parallel void areas. Full article

Rock bursts frequently occur in the fault group area in China, seriously restricting the safe and efficient production of coal mines. Based on field investigation, physical experiments, and numerical simulation, this study investigates the rupture types and spatial evolution of microseismic events during the excavation of working face through fault group areas in the TB Coal Mine, where the hard roof asymmetric is cut by faults. It reveals the cooperative instability mechanism of faults and hard roof, as well as the mechanisms of rock burst. Targeted rock burst prevention measures are proposed, including “roof blasting to cut off dynamic and static load transfer” and “coal blasting to reduce abutment stress”. The results demonstrate the following: (1) during mining in fault group areas, the synchronous activation of faults induces shear-type and high-energy microseismic events and the subsequent movement of hard roof, which has been cut by faults, forms asymmetric parallelograms and symmetric inverted trapezoids, and induces tensile-type and high-energy microseismic events. The synchronous activation of faults and the breaking of the hard roof are identified as the primary reason for high-energy microseismic events. (2) As the fault dip angle approaches 90º, the compressive strength of the fault-segmented hard roof strata decreases. Under synchronous activation of faults, roof failure concentrates in the central, right, and left sections for fault combinations with dip angles of 70° + 70°, 90° + 70°, and 110° + 70°, respectively. (3) Numerical simulations reveal two rock burst mechanisms in faults—hard roof systems: a forward “high dynamic stress and high static stress” type and a rear “low dynamic stress and high static stress “ type, which is consistent with in situ monitoring data. (4) For the three stages in which the 502 working face approaches, passes through, and mines away from the fault group area, a stress relief scheme combining roof blasting and coal blasting is proposed. Compared with the 501 working face, during the mining of the 502 working face, the total microseismic frequency and energy decreased by 71.9% and 87.9%, respectively, and the effectiveness of these measures is verified. Full article

Aim: To develop clear, evidence-based, and standardized guidelines for the design, selection, and clinical use of implant abutments and prosthetic components in order to optimize the biological, mechanical, and esthetic performance of the implant supracrestal complex. Methods: A panel of 10 expert clinicians and researchers in prosthodontics participated in the Osstem Global Consensus Meeting. For the present consensus meeting, a scoping review was performed in advance and discussed among the participants. A comprehensive search of the literature was performed up to June 2025. Two reviewers (M.T. and F.G.) independently conducted screening, data extraction, and quality assessment using the Newcastle–Ottawa Scale. The evidence was synthesized and discussed by the panel of expert clinicians during the consensus meeting. After that, guidelines were developed using a 14-question questionnaire to formulate consensus-based clinical recommendations. The participants answered structured questions and discussed discrepancies to achieve a consensus. Results: The panel of expert clinicians reached a consensus on several prosthetic key points. Concave abutment profiles and emergence angles <30° promoted peri-implant tissue stability, while convex designs and wider angles increased risks of bone loss and peri-implantitis. Titanium remains the reference abutment material in posterior sites, while zirconia provides superior esthetics anteriorly, and hybrid abutments balance strength and esthetics. Conclusions: Prosthetic design and abutment material selection critically affect peri-implant tissue stability and esthetic outcomes. The evidence supports screw-retained designs, platform switching, and the “one abutment–one time” approach for predictable long-term success. Full article

Stress evolution during overburden stabilization in non-pillar mining with roof-cutting and roadway formation (NMRRF) in inclined coal seams is highly complex due to the combined influence of seam dip angle and mining method. This study investigates the spatial stress evolution and structural stability of the overburden through numerical simulation and theoretical analysis. Results indicate that along the strike direction, the peak abutment pressure ahead of the working face decreases from the lower to the upper sections. As mining advances, the peak in the lower section shifts significantly forward, whereas changes in the middle and upper sections remain minimal. After advancing 150 m, upward expansion of the pressure-relief zone ceases, with the relief height in the lower goaf being smaller than that in the upper region. Along the dip direction, a pressure-relief zone forms in the roof and floor after 30 m of advancement, while stress concentration zones develop in the coal on both sides. With continued mining, the highest point of the pressure-relief zone gradually deviates from the central axis toward the upper section and eventually stabilizes within deeper strata at a certain distance from the axis. By 150 m of advancement, the relief zone peaks in the upper-middle section of the working face, and the height of the caved zone in the upper goaf exceeds that in the middle and lower parts. An asymmetric “inverted J-shaped” stress shell forms along the working face centerline, evolving into an overall asymmetric stress shell with its apex located in the upper goaf. A mechanical model of the overburden structure is established, yielding an expression for the three-dimensional stress shell morphology. Based on the stability mechanism of overburden movement and the failure modes of key block structures, support strategies for the mining face are proposed. The findings provide theoretical insights for non-pillar mining under similar geological conditions. Full article

The lateral abutment stress and damage range of the coal seam are prerequisites for the layout of gob-side entries and surrounding rock control. They are influenced by the structure and mechanical properties of the coal seam and the overlying strata. To address this issue, this study establishes a mechanical analysis model for the lateral abutment stress and damage range under coupled conditions between the coal seam and overlying strata. This model systematically investigates the influence of various factors, including the fracture height and break angle of the overlying strata, the rotation angle and subsidence of key blocks, the burial depth and thickness of the coal seam, as well as the cohesion and internal friction angle of the coal mass. The study reveals that the weight and overburden load of the triangular hanging roof zone, along with the subsidence and rotation of the key blocks, are the key factors influencing the lateral abutment stress and damage range. Meanwhile, the reliability of the mechanical model has been substantiated through a combination of numerical simulation and in situ monitoring results. Full article

Severe floor heave in gate roadways under high-intensity longwall mining is primarily controlled by mining-induced stress redistribution. Abutment pressure is preferentially transferred through the coal pillar into the floor, accelerating floor instability. From the perspective of symmetry, mining disturbance breaks the original mechanical symmetry of the coal pillar–roadway system, resulting in asymmetric stress concentration and uneven floor heave. In this study, field monitoring and FLAC3D simulations were conducted for the 12 Upper 301 panel in the Buertai Coal Mine. The objectives were to quantify the sensitivity of coal-pillar loading and floor-heave response under stress redistribution, and to derive implications for pressure-relief design. Field monitoring indicates strong disturbance and large deformation: the maximum roof–floor and rib-to-rib convergences reached 1095 mm and 452 mm, respectively, accompanied by continuous growth of coal-pillar stress during mining. Numerical results show that increasing coal-pillar width enhances stress-bearing capacity and promotes a more symmetric stress distribution, thereby suppressing floor heave. In contrast, increasing the mining advance rate aggravates stress-field asymmetry and intensifies floor uplift. Greater burial depth further strengthens stress concentration and amplifies asymmetric deformation. Based on these findings, a roof-cutting pressure-relief scheme was optimized. This scheme aims to relieve and re-route the asymmetrically transmitted pillar loading. The optimal design adopts a roof-cutting length of 75 m and an angle of 30°, which reconstructs a more symmetric stress-transfer path; reduces the peak side abutment pressure to 8.72 MPa; and limits floor heave to 134.4 mm (control rate: 88.4%). Field application confirms the effectiveness of the proposed symmetry-based pressure-relief design. Full article

Uplift pressure is a major contributor to seismic instability in arch dam abutments, particularly where jointed rock masses form wedge-shaped failure blocks. This study develops an integrated numerical framework combining nonlinear finite element analysis, the Londe limit-equilibrium method, and Incremental Dynamic Analysis (IDA) to quantify the seismic stability of multiple abutment wedges in the Bakhtiari Arch Dam. A three-dimensional finite element model is used to compute dam–abutment thrust forces, while sixteen far-field ground motions are scaled to capture the progression of wedge instability with increasing spectral acceleration. Uplift pressures on joint planes are varied to represent different levels of grout curtain performance. The results indicate that uplift pressure is the dominant factor controlling wedge stability, substantially reducing effective normal stresses and shifting IDA and fragility curves toward lower acceleration demands. Deep wedges (WL4, WL5, WL6 located in the left abutment of the dam) exhibit the highest vulnerability, with instability probabilities exceeding 50% at spectral accelerations as low as 0.34 g under 50% uplift conditions, compared with values greater than 0.65 g for upper wedges. Parametric analyses further show that increasing the joint friction angle significantly enhances seismic resistance, whereas cohesion has a comparatively minor effect. The findings emphasize the necessity of accurate uplift characterization and wedge-specific seismic assessment, and they highlight the crucial role of grout-curtain effectiveness in ensuring the seismic safety of arch dam abutments. Full article

This study performed a finite element analysis to evaluate the biomechanical effects of implant connection geometry and bone quality (D2, D4) on stress distribution and structural stability. A mandibular model consisting of cortical and cancellous bone was generated, and implant components—including fixture, abutment, screw, and crown—were simulated. Two designs were analyzed based on Morse taper angle (11° or 15°) and the presence of an apical slot. A tightening torque of 32 N·cm and an occlusal load of 200 N were applied, with the lateral mandible constrained. The 11° taper with the non-slot design showed the highest von Mises stress (1048.81 MPa) in the fixture with D4 bone type and Tessera crown. In contrast, the 15° taper with the slot design improved stress distribution at the fixture–abutment interface, reducing fixture stress by 26.78% in D2 bone type. Localized stress near the slot was observed but did not compromise overall structural stability. Under oblique loading, stress concentrated primarily in the cortical bone, whereas D4 cancellous bone showed increased susceptibility to microdamage. Prosthetic materials demonstrated no significant differences in stress behavior. These findings suggest that connection design and bone density strongly influence biomechanical performance and should guide individualized implant selection. Full article

Large-mining-height technology has been increasingly applied in thick seam mining to enhance productivity and resource recovery. However, it also intensifies strata pressure and complicates surrounding rock control, leading to greater overburden movement, stronger roof weighting, and severe coal wall spalling. Taking the 12306 working face of the Wangjialing Mine as a case, this study employs physical similarity experiments and UDEC numerical simulations to investigate the coupled mechanism of overburden migration and coal wall instability. Results show that abutment stress induces non-uniform deformation, while strata pressure changes directly govern spalling depth. Moreover, coal wall instability is strongly affected by multiple factors: greater burial depth intensifies crack propagation, larger mining height expands failure depth, larger mining step size extends the stress-affected zone, larger dip angle shifts failure upward, and lower support resistance weakens control capacity. These findings clarify the disaster mechanism of deep large-mining-height faces and provide theoretical and engineering guidance for optimizing support design and enhancing coal wall stability. Full article

Narrow-diameter implants (≤3.5 mm) have garnered significant attention due to their widespread application in areas with insufficient bone volume. However, their mechanical performance is limited. The cervical region, serving as a pivotal stress concentration zone, exhibits a thread form that directly modulates stress distribution and determines the long-term stability of the implant–bone interface. This study was designed to investigate the influence of varying thread forms and face angles on microstrain and stress distribution patterns in narrow-diameter implants (NDIs) and their adjacent cortical bone structures. Through systematic modification of implant thread forms and face angle parameters, finite element analysis (FEA) was employed to develop nine distinct implant models featuring varied geometric characteristics. Each model was implanted into Type III bone tissue, followed by the application of a 100 N occlusal force, including a vertical load and an oblique load deviated 30 degrees lingually from the long axis of the implants. Subsequent biomechanical evaluation quantified peak von Mises stress concentrations at the bone–implant interface, maximum equivalent elastic strain distributions in peri-implant bone tissue, and abutment stress profile characteristics. The results indicated that in the RB thread group, the optimal thread face angle parameter was 60 degrees; in the B thread group, this optimal thread face angle parameter was 45 degrees, whereas in the V thread group, the optimal thread face angle parameter was 30 degrees. Full article

Microbial colonization is a major factor contributing to peri-implantitis, and creating durable glassy surfaces with antimicrobial agents such as silver and copper may reduce microbial accumulation on dental abutments. This study aimed to develop antimicrobial thin-film glassy surfaces on Ti6Al4V alloy and to evaluate their surface and mechanical properties, antimicrobial effectiveness, and biocompatibility before and after thermal aging. A sol–gel-derived glassy matrix (G) was synthesized, and two antimicrobial coatings were prepared by incorporating ionic Ag (GAg) or a combination of Ag/Cu (GAgCu). Ti6Al4V specimens; these were either left uncoated or dip-coated with G, GAg, or GAgCu and cured at 450 °C. Half of the specimens underwent thermal aging between 5 °C and 55 °C for 3000 cycles. Surface roughness, contact angle, hardness, adhesion strength, scratch resistance, cytotoxicity (Agar diffusion and MTT assay on L929 fibroblasts), and microbial adhesion were evaluated using Streptococcus sanguinis, Porphyromonas gingivalis, and Candida albicans as representative oral microorganisms. Both coatings exhibited low surface roughness, hydrophilic surfaces, improved hardness, and significantly reduced microbial adhesion for all tested species. GAg showed superior mechanical properties, whereas GAgCu demonstrated a relatively stronger antimicrobial effect. Cytotoxicity tests indicated that all coatings were biocompatible at levels suitable for oral use. Overall, these coatings demonstrated strong adhesion, durability, and antimicrobial activity, suggesting their suitability for dental abutments made of Ti6Al4V. Full article

Surface treatments play a crucial role in modifying the surface properties and biological performance of dental ceramics. This study investigated the effects of surface conditions on the wettability, cytocompatibility, and bacterial resistance of 4 mol% Y₂O₃-stabilized tetragonal zirconia polycrystal (4Y–TZP) and two lithium disilicate (Li₂Si₂O₅) glass ceramics (Amber^® Mill (AM) and Amber^® Mill Abut-Crown (AC)). Human gingival fibroblast (HGF-1) responses and biofilm formation on the machined, polished, and glazed samples were evaluated. The polished 4Y–TZP sample exhibited the highest water contact angle (WCA; 71.3°), while that of the AC samples decreased as the sample was machined (58.4°), polished (46.8°), and glazed (14.0°). The wettability, cytocompatibility, and bacterial resistance of the dental ceramics were significantly influenced by material type and surface condition. Among the surface-treated samples, the glazed specimens exhibited the lowest WCA and bulk density; thus, wettability is an important factor for cell proliferation and bacterial resistance. Among all samples, HGF-1 cells adhered well to the glazed ceramics and significantly proliferated over time. Particularly, the 4Y–TZP and AC glazed samples exhibited the lowest biomass and strong resistance to biofilm formation and bacterial adhesion. Thus, the glaze dramatically affected HGF-1 cell growth and antibiofilm formation. Full article

Tailings dams are unique structures due to the materials they store and the methods applied in their construction, often resulting in complex three-dimensional (3D) problems. Most current slope-stability analyses neglect the 3D effects without significant consequences. However, certain conditions, such as the valley shape, the spatial variability of the tailings’ resistance, and the presence of internal dikes, may render the 2D simplification inadequate. For translational slides, the sliding-mass width-to-height ratio (W/H) is a reliable estimator of the 3D effects. However, it is unclear whether this geometric ratio is the most suitable for rotational slides, where the width of the sliding mass varies along its height. This paper presents a parametric study of the 3D effects of the dam’s height (H_M) and the valley shape, namely the abutments’ slope angle with the horizontal (β) and the thalweg width (L_M), on the overall stability of a tailings dam raised by the upstream method, by means of 2D and 3D Limit Equilibrium (LE) analyses. The study evaluates the dam stability using a straightforward and practical methodology, specifically the FS_3D to FS_2D ratio (R_3D/2D), to compare the results of the 3D and 2D analyses, adapting current state-of-the-art techniques originally for translational slides, focused on pre-defined, closed-form slip-surface geometry, to rotational ones where the main focus is the geometry of the whole structure as a physical constraint for the sliding mass. The results show that the model average width-to-height ratio (W_M,avr/H_M), developed in this study, may be a better estimator of the 3D effects for rotational slides than the W/H ratio. Full article

The aim of this pilot in vitro study is to investigate the fracture strength of hybrid abutment crowns (HACs) made of a 3D-printable, tooth-colored, ceramic-reinforced composite (CRC). Based on an upper first premolar, a crown was designed, and specimens were additively fabricated from a composite material (VarseoSmile Crown plus) (N = 32). The crowns were bonded to standard abutments using a universal resin cement. Half (n = 16) of the samples were subjected to artificial aging, during which three samples suffered minor damage. All specimens were mechanically loaded at an angle of 30° to the implant axis. In addition, an FEM simulation was computed. Statistical analysis was performed at a significance level of p < 0.05. The mean fracture load without aging was 389.04 N (SD: 101.60 N). Two HACs suffered screw fracture, while the crowns itself failed in all other specimens. In the aged specimens, the mean fracture load was 391.19 N (SD: 143.30 N). The failure mode was predominantly catastrophic crown fracture. FEM analysis showed a maximum compressive stress of 39.79 MPa, a maximum tensile stress of 173.37 MPa and a shear stress of 60.29 MPa when loaded with 389 N. Within the limitations of this pilot study, the tested 3D-printed hybrid abutment crowns demonstrated fracture resistance above a clinically acceptable threshold, suggesting promising potential for clinical application. However, further investigations with larger sample sizes, control groups, and clinical follow-up are required. Full article