Search Results (179)

Molybdenum disulfide is more attractive and valuable at the molecular level due to its unique structure and exceptional properties. Here, new-type MoS₂-ring chains are constructed and theoretically investigated for relevant electronic properties influenced by the length of the chain and the bias. Different from traditional wires, our findings demonstrate that the conductance of such a new-type chain presents unusually non-exponential decay with the length of the chain, with a particularly anomalous length of seven rings, which shows stronger equilibrium conductance than a shorter four-ring chain. Multi-peaks of electron transmission and delocalized electronic states contribute such uniqueness. Mo atoms play a vital role in electron transport. Essentially, a narrower “HOMO-LUMO” (the two closest energy levels to the Fermi level of MoS₂-ring chain) gap compensates for the lower device density of states of new-type molybdenum disulfide-ring chains. The usual electronic structure of a seven-ring chain is derived from its slightly arched structure and mainly originates from interference, which is the resonance occurring between the electrodes. Noticeably, the bias could greatly enhance conductance, which could reach 1000 times more than the equilibrium conductance. At a certain bias, the conductance of a seven-ring chain even exceeds the shortest one- or two-ring chain. Furthermore, the threshold voltage (at which the maximum conductance appears) gradually decreases with the length of the chain and eventually remains at 0.7 V. The valuable negative differential resistance (NDR) effect could be found in such a molecular chain, which becomes more obvious as the length rises until the seven-ring chain reaches the peak. Our findings shed light on the relations between electronic properties and the length of a new-type molybdenum disulfide-ring chain, and provide support for such new-type chains in applications of innovative low-power and controllable electronics. Full article

Background: The aim of this retrospective study was to conduct an in vivo evaluation of the accuracy of surgical guides obtained via 3D printing technology that were used to transfer the 3D software-planned position and axis during palatal miniscrew placement. Methods: Twenty-four Caucasian subjects with permanent dentition underwent a CBCT examination to plan palatal skeletal anchorage using two miniscrews in the anterior palatal arch. A specific software function capable of identifying and displaying all CBCT scans passing through the planned miniscrew axis was used to identify the scan showing the maximum discrepancy between the planned and final miniscrew placement. The maximum insertion angle discrepancy and the maximum linear difference between the head and tip of the miniscrew were measured on the overlaid 3D STL models of the planned miniscrew position at CBCT with the final clinical position of the miniscrew. Results: Descriptive and inferential statistics were performed. On average, there was a discrepancy between the planned insertion axis and the final insertion axis of 2.95° (SD ± 1.13°), with a 10 mm miniscrew length. Conclusion: Three-dimensional I.-printed surgical guides for palatal miniscrew placement show a mean deviation of 2.95° from the planned position, indicating good but improvable accuracy in placement. Full article

Study design: The advent of the Matrix Wave^TM System (Depuy-Synthes)—a bone-anchored Mandibulo-Maxillary Fixation (MMF) System—merits closer consideration because of its peculiarities. Objective: This study alludes to two preliminary stages in the evolution of the Matrix Wave^TM MMF System and details its technical and functional features. Results: The Matrix Wave^TM System (MWS) is characterized by a smoothed square-shaped Titanium rod profile with a flexible undulating geometry distinct from the flat plate framework in Erich arch bars. Single MWS segments are Omega-shaped and carry a tie-up cleat for interarch linkage to the opposite jaw. The ends at the throughs of each MWS segment are equipped with threaded screw holes to receive locking screws for attachment to underlying mandibular or maxillary bone. An MWS can be partitioned into segments of various length from single Omega-shaped elements over incremental chains of interconnected units up to a horseshoe-shaped bracing of the dental arches. The sinus wave design of each segment allows for stretch, compression and torque movements. So, the entire MWS device can conform to distinctive spatial anatomic relationships. Displaced fragments can be reduced by in-situ-bending of the screw-fixated MWS/Omega segments to obtain accurate realignment of the jaw fragments for the best possible occlusion. Conclusion: The Matrix Wave^TM MMF System is an easy-to-apply modular MMF system that can be assembled according to individual demands. Its versatility allows to address most facial fracture scenarios in adults. The option of “omnidirectional” in-situ-bending provides a distinctive feature not found in alternate MMF solutions. Full article

Background and Objectives: Patients with unilateral cleft lip and palate (UCLP) require a phase of infant orthopedic treatment prior to surgical cleft closure. Treatment planning in this phase necessitates a thorough understanding of maxillary growth dynamics in this period. The aim of the present study was to evaluate the quantitative and qualitative surface growth of maxillary segments in infants with UCLP. Materials and Methods: In total, 195 intraoral scans from 50 patients were obtained postnatal (T0), at monthly intervals (T1–5), and prior to surgical cleft closure at 6 months of age (T6). Surface, linear, and angle measurements of the maxillary segments were performed. Results: Significant increases in the total surface area and the surface areas of the small and large segments were observed at monthly intervals and over the overall duration. The large segment showed greater absolute growth (11.62 mm² per month, 46.57 mm² total), while the small segment had a higher percentage increase (1.49% monthly, 6.57% overall). A positive small correlation was observed between surface area growth changes in the small segment and its increase in length. Conclusions: Our results revealed distinct growth patterns of the large and small segments in amount and direction, underscoring the relevance of incorporating segment arch width in surface evaluations. Full article

Previous research on the jumping structures of insects with strong leaping abilities mainly focused on overall jumping mechanisms. Our study reveals that the unilateral jumping structures (UJSs) of L. delicatula has relative functional autonomy. The UJSs consist of three distinct but interconnected parts: (1) energy storage component: it comprises the pleural arch and trochanteral depressor muscles, with the deformation zone extending about two-thirds of the pleural arch from the V-notch to the U-notch; (2) coupling component: made up of the coxa and trochanter, it serves as a bridge between the energy and lever components, connecting them via protuberances and pivots; and (3) lever component: it encompasses the femur, tibia, and tarsus. A complete jumping action lasts from 2.4 ms to 4.6 ms. During a jump, the deformation length of the pleural arch is 0.96 ± 0.06 mm. The angles ∠ct (angle between coxa and trochanter), ∠fp (angle between femur and pleural arch), and ∠ft (angle between femur and tibia) change by 57.42 ± 1.60, 101.40 ± 1.59, and 36.06 ± 2.41 degrees, respectively. In this study, we abstracted the jumping structures of L. delicatula and identified its critical components. The insights obtained from this study are anticipated to provide valuable inspiration for the design and fabrication of biomimetic jumping mechanisms. Full article

Advancements in endovascular stent graft design have enabled the treatment of distal aortic arch pathologies. However, the length of the proximal landing zone remains a limitation, especially with vascular anomalies like an aberrant right subclavian artery (ARSA) posing additional challenges. A 78-year-old patient underwent computed tomography angiography (CTA), which revealed progressive enlargement of a distal aortic arch aneurysm located beyond an ARSA that coursed between the esophagus and trachea. Following evaluation by the multidisciplinary Aortic Team, a hybrid procedure was planned. A right carotid-to-ARSA bypass was performed and a Castor single-branched stent graft (CSBSG) was deployed in the aortic arch with its side branch directed into the left subclavian artery (LSA), thereby covering the origin of the ARSA. To prevent a type II endoleak, plug embolization of the ARSA origin was subsequently performed. CSBSG is a feasible treatment for distal aortic arch aneurysms, even in the presence of vascular anomalies such as ARSA. Full article

The instability of mine roadways is significantly influenced by the coupled effects of groundwater seepage and non-uniform loading. These interactions often induce localized plastic deformation and progressive failure, particularly in the roof and sidewall regions. Seepage elevates pore water pressure and deteriorates the mechanical properties of the rock mass, while non-uniform loading leads to stress concentration. The combined effect facilitates the propagation of microcracks and the formation of shear zones, ultimately resulting in localized instability. This initial damage disrupts the mechanical equilibrium and can evolve into severe geohazards, including roof collapse, water inrush, and rockburst. Therefore, understanding the damage and failure mechanisms of mine roadways at the mesoscale, under the combined influence of stress heterogeneity and hydraulic weakening, is of critical importance based on laboratory experiments and numerical simulations. However, the large scale of in situ roadway structures imposes significant constraints on full-scale physical modeling due to limitations in laboratory space and loading capacity. To address these challenges, a straight-wall circular arch roadway was adopted as the geometric prototype, with a total height of 4 m (2 m for the straight wall and 2 m for the arch), a base width of 4 m, and an arch radius of 2 m. Scaled physical models were fabricated based on geometric similarity principles, using defect-bearing sandstone specimens with dimensions of 100 mm × 30 mm × 100 mm (length × width × height) and pore-type defects measuring 40 mm × 20 mm × 20 mm (base × wall height × arch radius), to replicate the stress distribution and deformation behavior of the prototype. Uniaxial compression tests on water-saturated sandstone specimens were performed using a TAW-2000 electro-hydraulic servo testing system. The failure process was continuously monitored through acoustic emission (AE) techniques and static strain acquisition systems. Concurrently, FLAC^3D 6.0 numerical simulations were employed to analyze the evolution of internal stress fields and the spatial distribution of plastic zones in saturated sandstone containing pore defects. Experimental results indicate that under non-uniform loading, the stress–strain curves of saturated sandstone with pore-type defects typically exhibit four distinct deformation stages. The extent of crack initiation, propagation, and coalescence is strongly correlated with the magnitude and heterogeneity of localized stress concentrations. AE parameters, including ringing counts and peak frequencies, reveal pronounced spatial partitioning. The internal stress field exhibits an overall banded pattern, with localized variations induced by stress anisotropy. Numerical simulation results further show that shear failure zones tend to cluster regionally, while tensile failure zones are more evenly distributed. Additionally, the stress field configuration at the specimen crown significantly influences the dispersion characteristics of the stress–strain response. These findings offer valuable theoretical insights and practical guidance for surrounding rock control, early warning systems, and reinforcement strategies in water-infiltrated mine roadways subjected to non-uniform loading conditions. Full article

Double-arch tunnels in inclined layered jointed rock masses face risks of lining cracking and collapse under bedding-inclined asymmetric stress (BIAS); however, related studies remain limited. Based on a case study of an expressway tunnel case in Zhejiang Province, a three-dimensional discrete element model of a double-arch tunnel was developed using Three-Dimensional Distinct Element Code (3DEC) (version 7.0, Itasca Consulting Group, Inc., Minneapolis, MN, USA). The impacts of joint dip angle (0–90°) and spacing (0.5–6.5 m) on deformation, BIAS evolution, and middle partition wall stability were analyzed. Key findings reveal that joint presence significantly amplifies surrounding rock deformation, with pronounced displacement increases observed on the counter-dip side. The BIAS intensity follows a unimodal distribution with joint dip angles, peaking within the 30–60° range. Increasing joint spacing reduces BIAS effects, with a 57.1% decrease in asymmetric deformation observed when spacing increases from 0.5 m to 6.5 m. The implementation of dip-side pilot excavation with the main tunnel full-face method, combined with an optimized support strategy (installing dip-side bolts perpendicular to joints and extending counter-dip side bolt lengths from 4 m to 6 m), achieved a near-unity stress ratio between tunnel sides under equivalent overburden depths compared to conventional methods. These findings offer theoretical and technical insights for optimizing excavation and reinforcement in similar tunnel engineering contexts. Full article

Objectives: Anterior crowding in the lower jaw is a common orthodontic issue often managed through premolar extraction, which can affect facial profile development. This study aimed to evaluate skeletal and dental changes in moderate to severe crowding using a novel mandibular reference line—the Ramus Anterior Vertical (RaV)—to support treatment planning. Methods: A total of 140 patients (LII > 4 mm and < 9 mm; mean age ≈ 12.5 years) were divided into two groups (G1: extraction; G2: nonextraction; total n = 140; n = 70 per group). Skeletal and dental parameters were measured before (T0) and after (T1) orthodontic treatment using 280 lateral cephalograms. RaV was defined as a vertical line through the anterior ramus point, perpendicular to the occlusal plane. Results: Sagittal measurements relative to RaV were reproducible and unaffected by mandibular mobility. Significant vertical skeletal changes were observed in G2 females, with an increased anterior facial height (N–Sp′ and Sp′–Gn) but a stable Hasund Index. In G1, the dental arch length and distances from RaV to i5 and i6 were reduced, while second molars (i7) remained stable. Sagittal incisor axis changes (L1–NB°, SAi1°) and skeletal–dental correlations (ML–NSL, Gn–tGo–Ar) were present only in G1. Conclusions: RaV proved to be a stable mandibular reference for assessing treatment effects. In this study, premolar extraction vs. nonextraction was comparably effective, though some vertical skeletal adaptations, especially in G2 females, took place. Full article

Background/Objectives: Dental crowding and the premature loss of one or more deciduous teeth are common issues during the growth phase that accompanies the transition from mixed to permanent dentition. The aim of this systematic review is to examine the effectiveness of using a passive lingual arch in preserving the length of the lower arch and managing the leeway space, analyzing the effects on the linear and angular positions of the permanent teeth. Methods: A systematic review of the literature was conducted using the PubMed, Web of Science, Scopus, and Cochrane Library database. After an initial selection of 306 articles, seven studies that met the defined selection criteria were included. These articles were used to compile the PICO table. Results: The studies examined agree that the application of the passive lingual arch is useful in preserving the length of the lower arch during the transition from mixed to permanent dentition. The observed changes in the linear and angular positions of the permanent teeth, particularly the distoinclination of the permanent molars and the proclination of the incisors, were considered indicative of the effectiveness of this technique. However, one author did not observe these changes, noting only a prevention of mesioinclination and lingualization of the molars and incisors. Conclusions: The use of the passive lingual arch in the transition from mixed to permanent dentition proves to be advantageous for correcting mild anterior crowding, maintaining residual spaces after the premature loss of deciduous molars, and preventing the impaction of permanent premolars. This simple and effective orthodontic device can be applied in clinical practice, always based on an accurate diagnosis and a well-defined treatment plan. Full article

Background: The objective of this study is to investigate the cone beam computed tomography (CBCT) features of the coronoid process in patients without limitations in mouth opening and to develop a functional classification of the coronoid process, considering its relationship with the zygomatic bone. Methods: This cross-sectional retrospective study analyzed the CBCT features of 408 coronoid processes. Volume rendered and axial images were evaluated to assess the shape, surface configuration, length of the coronoid process, the coronoid/condyle ratio, the distance of the coronoid process from the posteromedial surface of the zygoma, and its vertical level. The coronoid process was considered hyperplastic when the coronoid/condyle ratio was >1. Results: The maximum coronoid processes had a triangular shape (221). The mean length of the coronoid process was 13.85 mm. The mean coronoid/condyle ratio was 0.84. A total of 85 coronoid processes were hyperplastic. The mean distance from the coronoid process to the posteromedial surface of the zygoma was 15.99 mm, ranging from 5.8–27.9 mm. The mean vertical level of the coronoid process in the study sample was 9.6 mm. A novel functional radiographic classification was developed. The coronoid processes were classified as Type I, II, III (a,b,c), and IV (a,b,c). Type IIIa was the most common (45.83%), followed by Type II (29.68%), Type I (16.17%), Type IIIc (4.41%), Type IIIb (3.18%), Type IVa (0.49%), and Type IV b (0.24%). Conclusions: The vertical extension of the coronoid process beyond the lower border of the zygomatic bone/arch and its distance from the posterior surface of the body of the zygoma could play a significant role in impacting the mandibular movements. Full article

It is well established that the proper functioning of dams plays an important role in society. Therefore, as a fundamental part of their safety, the identification of anomalies by monitoring their deformations must be given special consideration. The ability to detect cracks based on monitoring device records depends largely on the number of devices included in the dam’s original design, their arrangement, and their accuracy. This paper aims to help determine the appropriate spacing and accuracy of the devices for detecting a given crack. For this purpose, numerical simulations of cracks that match the most likely cracks in arch dams are performed based on a real dam, ensuring that such cracks result in an opening wide enough to be of concern. Afterward, the study analyzes the impact of the length and depth of the crack and the accuracy and position of the monitoring device on the ability of the system to detect the crack. Full article

Arch beams are widely used in bridge construction due to their ability to withstand much greater loads than horizontal beams. The utilization of composite construction has also increased due to its tendency to optimize the utilization of construction materials, leading to significant savings in steel costs. In this research, a detailed experiment work on a simply supported arch composite beam under a positive moment was presented; then, a numerical model was created using ABAQUS to simulate its nonlinear behavior. The beams were formed from a concrete slab attached to steel beams by means of perfobond shear connectors (PSCs). A good agreement between the model and experiment was obtained. A parametric study was developed to identify the influence of the initial prestressing, rise to span ratio, and beam length on the behavior of the arch composite beam. It was found that the presence of tendons enhances the serviceability behavior, increases the ultimate load by 40% compared to the control beam, and equilibrates the horizontal thrust of the arch, even in the absence of initial prestressing. In addition, the beam exhibits a clear tied arch behavior due to the large eccentricity as the rise-to-depth ratio increases. Furthermore, the prestress force was found to be more effective in the longer span and the incremental stress in tendons more remarkable. Full article

Background and Objectives: The palate’s morphological characteristics are of great importance, especially in periodontology, where the palatine tissue represents a source of tissue graft for multiple mucogingival surgeries. This study aimed to estimate the amount of donor tissue available through the average palatal height and average location of the greater palatine artery in the Saudi population according to age and gender. Materials and Methods: Digital casts for adult Saudi patients at the age of 18–60 years old with a mean age of 37.76 ± 12.68 years were collected and analyzed using EXOCAD software. The digital casts were evaluated, and measurements of arch width at molars and canines, palatal vault height (PVH), palatal height index (PHI), and extension of the palatal rugae were registered. Finally, the amount available for soft tissue graft harvesting was calculated. Results: Overall, 109 maxillary casts for Saudi patients, 52 (47.7%) males and 57 (52.3%) females, were analyzed. The maxillary inter-molar arch width, inter-canine width, and palatal vault height significantly differed between males and females (p < 0.05). The mean PHI was 45.51% ± 8.12%, and 27.5% were classified as orthostaphyline, while 72.5% were categorized as hypsistaphyline, with no significant difference between the genders. The mean maximum graft width was 11.45 mm, and the graft width was significantly different between males and females (p < 0.005), while the mean maximum graft length was 17.78 mm, and the graft length showed no significant difference. Conclusions: The results of this study provide specific clinical guidelines for periodontal procedures by emphasizing the importance of gender-specific anatomical considerations. Data on graft dimensions and palatal measurements will enable the exact planning of soft tissue harvesting to minimize surgical risks and optimize mucogingival surgery outcomes in the Saudi population. Full article

Background: Obstructive sleep apnea is a sleep-related breathing disorder associated with craniofacial morphology and dental arches. The aim of this study was to evaluate the correlation between obstructive sleep apnea and the morphometry of dental arches and upper airways. Methods: Forty patients were enrolled in the study, and the polysomnographic parameters evaluated were the apnea hypopnea index (AHI) and the oxygen desaturation index (ODI). Dental measurements taken from the 3D models included anterior arch widths, posterior arch widths, maxillary and mandibular arch lengths, and palatal surface area. A cone beam computed tomography (CBCT) evaluation was also performed. Results: In patients with moderate OSA, posterior maxillary width was significantly correlated with both minimal airway area (rho = 0.65, p < 0.01) and its transverse diameter (rho = 0.68, p < 0.01). Similarly, in patients with severe OSA, posterior maxillary width showed a significant correlation with total airway volume (rho = 1, p < 0.01), minimal airway area (rho = 1, p < 0.01), and its transverse diameter (rho = 1, p < 0.01). Conclusions: Craniofacial morphology and malocclusion can contribute to obstructive sleep apnea syndrome. Full article