Toward 1D Transport in 3D Materials: SOC-Induced Charge-Transport Anisotropy in Sm3ZrBi5.

1D charge transport offers great insight into strongly correlated physics, such as Luttinger liquids, electronic instabilities, and superconductivity. Although 1D charge transport is observed in nanomaterials and quantum wires, examples in bulk crystalline solids remain elusive. In this work, it is demonstrated that spin-orbit coupling (SOC) can act as a mechanism to induce quasi-1D charge transport in the Ln3MPn5 (Ln = lanthanide; M = transition metal; Pn = Pnictide) family. From three example compounds, La3ZrSb5, La3ZrBi5, and Sm3ZrBi5, density functional theory calculations with SOC included show a quasi-1D Fermi surface in the bismuthide compounds, but an anisotropic 3D Fermi surface in the antimonide structure. By performing anisotropic charge transport measurements on La3ZrSb5, La3ZrBi5, and Sm3ZrBi5, it is demonstrated that SOC starkly affects their anisotropic resistivity ratios (ARR) at low temperatures, with an ARR of ≈4 in the antimonide compared to ≈9.5 and ≈22 (≈32 after magnetic ordering) in La3ZrBi5 and Sm3ZrBi5, respectively. This report demonstrates the utility of spin-orbit coupling to induce quasi-low-dimensional Fermi surfaces in anisotropic crystal structures, and provides a template for examining other systems.

What are the common factors that lead to the failure to achieve minimal clinically important difference after shoulder surgery? A scoping review.

INTRODUCTION: The goal of this research is to identify the factors that negatively impact the achievement of the minimum clinically significant change (MCID) for the American Shoulder and Elbow Surgeons (ASES) score within the realm of various orthopedic shoulder procedures. METHODS: We conducted a comprehensive review of studies published from 2002 to 2023, utilizing OvidMedline and PubMed databases. Our search criteria included terms such as "minimal clinically important difference" or "MCID" along with associated MeSH terms, in addition to "American shoulder and elbow surgeon" or "ASES." We selectively included primary investigations that assessed factors linked to the failure to achieve MCID for the ASES score subsequent to orthopedic shoulder procedures, while excluding papers addressing anatomical, surgical, or injury-related aspects. RESULTS: Our analysis identified 149 full-text articles, leading to the inclusion of 12 studies for detailed analysis. The selected studies investigated outcomes following various orthopedic shoulder procedures, encompassing biceps tenodesis, total shoulder arthroplasty, and rotator cuff repair. Notably, factors, such as gender, body mass index, diabetes, smoking habits, opioid usage, depression, anxiety, workers' compensation, occupational satisfaction, and the preoperative ASES score, were all associated with the inability to attain MCID. CONCLUSION: In summary, numerous factors exert a negative influence on the attainment of MCID following shoulder procedures, and these factors appear to be irrespective of the specific surgical technique employed. Patients presenting with these factors may perceive their surgical outcomes as less successful when compared to those without these factors. Identifying these factors can enable healthcare providers to provide more effective counseling to patients regarding their expected outcomes and rehabilitation course. Furthermore, these findings can aid in the development of a screening tool to better identify these risk factors and optimize them before surgery.

A platform for far-infrared spectroscopy of quantum materials at millikelvin temperatures.

Optical spectroscopy of quantum materials at ultralow temperatures is rarely explored, yet it may provide critical characterizations of quantum phases not possible using other approaches. We describe the development of a novel experimental platform that enables optical spectroscopic studies, together with standard electronic transport, of materials at millikelvin temperatures inside a dilution refrigerator. The instrument is capable of measuring both bulk crystals and micrometer-sized two-dimensional van der Waals materials and devices. We demonstrate its performance by implementing photocurrent-based Fourier transform infrared spectroscopy on a monolayer WTe2 device and a multilayer 1T-TaS2 crystal, with a spectral range available from the near-infrared to the terahertz regime and in magnetic fields up to 5 T. In the far-infrared regime, we achieve spectroscopic measurements at a base temperature as low as ∼43 mK and a sample electron temperature of ∼450 mK. Possible experiments and potential future upgrades of this versatile instrumental platform are envisioned.

Synthesis of an aqueous, air-stable, superconducting 1T'-WS2 monolayer ink.

Liquid-phase chemical exfoliation can achieve industry-scale production of two-dimensional (2D) materials for a wide range of applications. However, many 2D materials with potential applications in quantum technologies often fail to leave the laboratory setting because of their air sensitivity and depreciation of physical performance after chemical processing. We report a simple chemical exfoliation method to create a stable, aqueous, surfactant-free, superconducting ink containing phase-pure 1T'-WS2 monolayers that are isostructural to the air-sensitive topological insulator 1T'-WTe2. The printed film is metallic at room temperature and superconducting below 7.3 kelvin, shows strong anisotropic unconventional superconducting behavior with an in-plane and out-of-plane upper critical magnetic field of 30.1 and 5.3 tesla, and is stable at ambient conditions for at least 30 days. Our results show that chemical processing can make nontrivial 2D materials that were formerly only studied in laboratories commercially accessible.

A Class of Magnetic Topological Material Candidates with Hypervalent Bi Chains.

The link between crystal and electronic structure is crucial for understanding structure-property relations in solid-state chemistry. In particular, it has been instrumental in understanding topological materials, where electrons behave differently than they would in conventional solids. Herein, we identify 1D Bi chains as a structural motif of interest for topological materials. We focus on Sm3ZrBi5, a new quasi-one-dimensional (1D) compound in the Ln3MPn5 (Ln = lanthanide; M = metal; Pn = pnictide) family that crystallizes in the P63/mcm space group. Density functional theory calculations indicate a complex, topologically nontrivial electronic structure that changes significantly in the presence of spin-orbit coupling. Magnetic measurements show a quasi-1D antiferromagnetic structure with two magnetic transitions at 11.7 and 10.7 K that are invariant to applied field up to 9 T, indicating magnetically frustrated spins. Heat capacity, electrical, and thermoelectric measurements support this claim and suggest complex scattering behavior in Sm3ZrBi5. This work highlights 1D chains as an unexplored structural motif for identifying topological materials, as well as the potential for rich physical phenomena in the Ln3MPn5 family.

Evolving Devil's Staircase Magnetization from Tunable Charge Density Waves in Nonsymmorphic Dirac Semimetals.

While several magnetic topological semimetals have been discovered in recent years, their band structures are far from ideal, often obscured by trivial bands at the Fermi energy. Square-net materials with clean, linearly dispersing bands show potential to circumvent this issue. CeSbTe, a square-net material, features multiple magnetic-field-controllable topological phases. Here, it is shown that in this material, even higher degrees of tunability can be achieved by changing the electron count at the square-net motif. Increased electron filling results in structural distortion and formation of charge density waves (CDWs). The modulation wave-vector evolves continuously leading to a region of multiple discrete CDWs and a corresponding complex "Devil's staircase" magnetic ground state. A series of fractionally quantized magnetization plateaus is observed, which implies direct coupling between CDW and a collective spin-excitation. It is further shown that the CDW creates a robust idealized nonsymmorphic Dirac semimetal, thus providing access to topological systems with rich magnetism.

Artificial Intelligence in the Management of Anterior Cruciate Ligament Injuries.

BACKGROUND: Technological innovation is a key component of orthopaedic surgery. With the integration of powerful technologies in surgery and clinical practice, artificial intelligence (AI) may become an important tool for orthopaedic surgeons in the future. Through adaptive learning and problem solving that serve to constantly increase accuracy, machine learning algorithms show great promise in orthopaedics. PURPOSE: To investigate the current and potential uses of AI in the management of anterior cruciate ligament (ACL) injury. STUDY DESIGN: Systematic review; Level of evidence, 3. METHODS: A systematic review of the PubMed, MEDLINE, Embase, Web of Science, and SPORTDiscus databases between their start and August 12, 2020, was performed by 2 independent reviewers. Inclusion criteria included application of AI anywhere along the spectrum of predicting, diagnosing, and managing ACL injuries. Exclusion criteria included non-English publications, conference abstracts, review articles, and meta-analyses. Statistical analysis could not be performed because of data heterogeneity; therefore, a descriptive analysis was undertaken. RESULTS: A total of 19 publications were included after screening. Applications were divided based on the different stages of the clinical course in ACL injury: prediction (n = 2), diagnosis (n = 12), intraoperative application (n = 1), and postoperative care and rehabilitation (n = 4). AI-based technologies were used in a wide variety of applications, including image interpretation, automated chart review, assistance in the physical examination via optical tracking using infrared cameras or electromagnetic sensors, generation of predictive models, and optimization of postoperative care and rehabilitation. CONCLUSION: There is an increasing interest in AI among orthopaedic surgeons, as reflected by the applications for ACL injury presented in this review. Although some studies showed similar or better outcomes using AI compared with traditional techniques, many challenges need to be addressed before this technology is ready for widespread use.

Contrasting SnTe-NaSbTe2 and SnTe-NaBiTe2 Thermoelectric Alloys: High Performance Facilitated by Increased Cation Vacancies and Lattice Softening.

Defect chemistry is critical to designing high performance thermoelectric materials. In SnTe, the naturally large density of cation vacancies results in excessive hole doping and frustrates the ability to control the thermoelectric properties. Yet, recent work also associates the vacancies with suppressed sound velocities and low lattice thermal conductivity, underscoring the need to understand the interplay between alloying, vacancies, and the transport properties of SnTe. Here, we report solid solutions of SnTe with NaSbTe2 and NaBiTe2 (NaSnmSbTem+2 and NaSnmBiTem+2, respectively) and focus on the impact of the ternary alloys on the cation vacancies and thermoelectric properties. We find introduction of NaSbTe2, but not NaBiTe2, into SnTe nearly doubles the natural concentration of Sn vacancies. Furthermore, DFT calculations suggest that both NaSbTe2 and NaBiTe2 facilitate valence band convergence and simultaneously narrow the band gap. These effects improve the power factors but also make the alloys more prone to detrimental bipolar diffusion. Indeed, the performance of NaSnmBiTem+2 is limited by strong bipolar transport and only exhibits modest maximum ZTs ≈ 0.85 at 900 K. In NaSnmSbTem+2 however, the doubled vacancy concentration raises the charge carrier density and suppresses bipolar diffusion, resulting in superior power factors than those of the Bi-containing analogues. Lastly, NaSbTe2 incorporation lowers the sound velocity of SnTe to give glasslike lattice thermal conductivities. Facilitated by the favorable impacts of band convergence, vacancy-augmented hole concentration, and lattice softening, NaSnmSbTem+2 reaches high ZT ≈ 1.2 at 800-900 K and a competitive average ZTavg of 0.7 over 300-873 K. The difference in ZT between two chemically similar compounds underscores the importance of intrinsic defects in engineering high-performance thermoelectrics.

The Effect of Thoracolumbar Pedicle Isthmus on Pedicle Screw Accuracy.

STUDY DESIGN: Retrospective analysis. OBJECTIVES: Aberrant pedicle screws can cause serious neurovascular complications. We propose that a predominant factor of pedicle screw breach is the vertebral anatomy at a given spinal level. We aim to investigate the inverse correlation between breach incidence and vertebral isthmus width. METHODS: The computed tomography scans of patients undergoing thoracolumbar surgery were retrospectively reviewed. Breaches were categorized as minor (<2 mm) or major (>2 mm). Breach incidence was stratified by spinal level. Average isthmus width was then compared to the collected breach incidences. A regression analysis and Pearson's correlation were performed. RESULTS: A total of 656 pedicle screws were placed in 91 patients with 233 detected breaches. Incidence of major breach was 6.3%. Four patients developed post-operative radiculopathy due to breach. Breach incidence was higher in the thoracic than lumbar spine (Fisher's exact test, P < .0001). The 2 spinal levels with the thinnest isthmus width (T4 and T5) were breached most often (73.7% and 73.9%, respectively). The 2 spinal levels with the thickest isthmus width (L4 and L5) were breached least often (20.5% and 11.8%). Breach incidence and isthmus width were shown to have a significant inverse correlation (Pearson's correlation, R 2 = 0.7, P < .0001). CONCLUSIONS: Thinner vertebral isthmus width increases pedicle screw breach incidence. Image-guided assistance may be most useful where breach incidence is highest and isthmus width is lowest (T2 to T6). Despite high incidence of cortical bone violation, there was little correlation with clinical symptoms. A breach is not automatically a clinical problem, provided the screw is structurally sound and the patient is symptomless.

The Subchalcogenides Ir2In8Q (Q = S, Se, Te): Dirac Semimetal Candidates with Re-entrant Structural Modulation.

Subchalcogenides are uncommon compounds where the metal atoms are in unusually low formal oxidation states. They bridge the gap between intermetallics and semiconductors and can have unexpected structures and properties because of the exotic nature of their chemical bonding as they contain both metal-metal and metal-main group (e.g., halide, chalcogenide) interactions. Finding new members of this class of materials presents synthetic challenges as attempts to make them often result in phase separation into binary compounds. We overcome this difficulty by utilizing indium as a metal flux to synthesize large (millimeter scale) single crystals of novel subchalcogenide materials. Herein, we report two new compounds Ir2In8Q (Q = Se, Te) and compare their structural and electrical properties to the previously reported Ir2In8S analogue. Ir2In8Se and Ir2In8Te crystallize in the P42/mnm space group and are isostructural to Ir2In8S, but also have commensurately modulated (with q vectors q = 1/6a* + 1/6b* and q = 1/10a* + 1/10b* for Ir2In8Se and Ir2In8Te, respectively) low-temperature phase transitions, where the chalcogenide anions in the channels experience a distortion in the form of In-Q bond alternation along the ab plane. Both compounds display re-entrant structural behavior, where the supercells appear on cooling but revert to the original subcell below 100 K, suggesting competing structural and electronic interactions dictate the overall structure. Notably, these materials are topological semimetal candidates with symmetry-protected Dirac crossings near the Fermi level and exhibit high electron mobilities (∼1500 cm2 V-1 s-1 at 1.8 K) and moderate carrier concentrations (∼1020 cm-3) from charge transport measurements. This work highlights metal flux as a synthetic route to high quality single crystals of novel intermetallic subchalcogenides with Dirac semimetal behavior.

Augmented reality in orthopaedics: a systematic review and a window on future possibilities.

AIMS: Computer-based applications are increasingly being used by orthopaedic surgeons in their clinical practice. With the integration of technology in surgery, augmented reality (AR) may become an important tool for surgeons in the future. By superimposing a digital image on a user's view of the physical world, this technology shows great promise in orthopaedics. The aim of this review is to investigate the current and potential uses of AR in orthopaedics. MATERIALS AND METHODS: A systematic review of the PubMed, MEDLINE, and Embase databases up to January 2019 using the keywords 'orthopaedic' OR 'orthopedic AND augmented reality' was performed by two independent reviewers. RESULTS: A total of 41 publications were included after screening. Applications were divided by subspecialty: spine (n = 15), trauma (n = 16), arthroplasty (n = 3), oncology (n = 3), and sports (n = 4). Out of these, 12 were clinical in nature. AR-based technologies have a wide variety of applications, including direct visualization of radiological images by overlaying them on the patient and intraoperative guidance using preoperative plans projected onto real anatomy, enabling hands-free real-time access to operating room resources, and promoting telemedicine and education. CONCLUSION: There is an increasing interest in AR among orthopaedic surgeons. Although studies show similar or better outcomes with AR compared with traditional techniques, many challenges need to be addressed before this technology is ready for widespread use. Cite this article: Bone Joint J 2019;101-B:1479-1488.

A New Three-Dimensional Subsulfide Ir2In8S with Dirac Semimetal Behavior.

Dirac and Weyl semimetals host exotic quasiparticles with unconventional transport properties, such as high magnetoresistance and carrier mobility. Recent years have witnessed a huge number of newly predicted topological semimetals from existing databases; however, experimental verification often lags behind such predictions. Common reasons are synthetic difficulties or the stability of predicted phases. Here, we report the synthesis of the type-II Dirac semimetal Ir2In8S, an air-stable compound with a new structure type. This material has two Dirac crossings in its electronic structure along the Γ-Z direction of the Brillouin zone. We further show that Ir2In8S has a high electron carrier mobility of ∼10 000 cm2/(V s) at 1.8 K and a large, nonsaturating transverse magnetoresistance of ∼6000% at 3.34 K in a 14 T applied field. Shubnikov de-Haas oscillations reveal several small Fermi pockets and the possibility of a nontrivial Berry phase. With its facile crystal growth, novel structure type, and striking electronic structure, Ir2In8S introduces a new material system to study topological semimetals and enable advances in the field of topological materials.

Ir6In32S21, a polar, metal-rich semiconducting subchalcogenide.

Subchalcogenides are uncommon, and their chemical bonding results from an interplay between metal-metal and metal-chalcogenide interactions. Herein, we present Ir6In32S21, a novel semiconducting subchalcogenide compound that crystallizes in a new structure type in the polar P31m space group, with unit cell parameters a = 13.9378(12) Å, c = 8.2316(8) Å, α = ß = 90°, γ = 120°. The compound has a large band gap of 1.48(2) eV, and photoemission and Kelvin probe measurements corroborate this semiconducting behavior with a valence band maximum (VBM) of -4.95(5) eV, conduction band minimum of -3.47(5) eV, and a photoresponse shift of the Fermi level by ∼0.2 eV in the presence of white light. X-ray absorption spectroscopy shows absorption edges for In and Ir do not indicate clear oxidation states, suggesting that the numerous coordination environments of Ir6In32S21 make such assignments ambiguous. Electronic structure calculations confirm the semiconducting character with a nearly direct band gap, and electron localization function (ELF) analysis suggests that the origin of the gap is the result of electron transfer from the In atoms to the S 3p and Ir 5d orbitals. DFT calculations indicate that the average hole effective masses near the VBM (1.19m e) are substantially smaller than the average electron masses near the CBM (2.51m e), an unusual feature for most semiconductors. The crystal and electronic structure of Ir6In32S21, along with spectroscopic data, suggest that it is neither a true intermetallic nor a classical semiconductor, but somewhere in between those two extremes.

Quaternary Pavonites A1+xSn2-xBi5+xS10 (A+ = Li+, Na+): Site Occupancy Disorder Defines Electronic Structure.

The field of mineralogy represents an area of untapped potential for the synthetic chemist, as there are numerous structure types that can be utilized to form analogues of mineral structures with useful optoelectronic properties. In this work, we describe the synthesis and characterization of two novel quaternary sulfides A1+xSn2-xBi5+xS10 (A = Li+, Na+). Though not natural minerals themselves, both compounds adopt the pavonite structure, which crystallizes in the C2/m space group and consists of two connected, alternating defect rock-salt slabs of varying thicknesses to create a three-dimensional lattice. Despite their commonalities in structure, their crystallography is noticeably different, as both structures have a heavy degree of site occupancy disorder that affects the actual positions of the atoms. The differences in site occupancy alter their electronic structures, with band gap values of 0.31(2) eV and 0.07(2) eV for the lithium and sodium analogues, respectively. LiSn2Bi5S10 exhibits ultralow thermal conductivity of 0.62 W m-1 K-1 at 723 K, and this result is corroborated by phonon dispersion calculations. This structure type is a promising host candidate for future thermoelectric materials investigation, as these materials have narrow band gaps and intrinsically low thermal conductivities.

Nonsurgical management of an extensive spontaneous spinal epidural hematoma causing quadriplegia and respiratory distress in a choledocholithiasis patient: A case report.

RATIONALE: Spontaneous spinal epidural hematoma (SSEH) manifests from blood accumulating in the epidural space, compressing the spinal cord, and leading to acute neurological deficits. The disease's cloudy etiology and rarity contribute to dangerously suboptimal therapeutic principles. These neural deficits can be permanent, even fatal, if the SSEH is not treated in a timely and appropriate manner. Standard therapy is decompressive laminectomy, though nonsurgical management is a viable course of action for patients who meet a criterion that is continuously being refined. PATIENT CONCERNS: A 76-year-old woman on warfarin for a past pulmonary embolism presented to the emergency room with jaundice, myalgia, hematuria, neck pain, and an International Normalized Ratio (INR) of 14. Upon admission, she rapidly developed quadriplegia and respiratory distress that necessitated intubation. DIAGNOSES: T2-weighted magnetic resonance imaging (MRI) revealed an epidural space-occupying hyperintensity from C2 to S5 consistent with a spinal epidural hematoma. An incidental finding of dilated intrahepatic and common bile ducts prompted an endoscopic retrograde cholangiopancreatography, which demonstrated choledocholithiasis. INTERVENTIONS: The patient's INR was normalized with Vitamin K and Beriplex. Upon transfer to the surgical spine team for assessment of a possible intervention, the patient began to demonstrate recovery of neural functions. The ensuing sustained motor improvement motivated the team's preference for close neurologic monitoring and continued medical therapy over surgery. Thirteen hours after the onset of her symptoms, the patient was extubated. A sphincterotomy was later performed, removing 81 common bile duct stones. OUTCOMES: MRI demonstrated complete resorption of the SSEH and the patient maintained full neurological function at final follow-up. LESSONS: Nonsurgical management of SSEH should be considered in the context of early and sustained recovery. Severe initial neural deficit does not necessitate surgical decompression. Choledocholithiasis and subsequent Vitamin K deficiency, particularly when coupled with anticoagulant use, can increase INR and is a novel proposed risk factor for SSEH. Furthermore, coagulopathies should be medically corrected before surgical intervention within a given timeframe, as spontaneous recovery may manifest. This should be favored over surgery in patients demonstrating early and sustained recovery, as nonsurgical management is 25% more effective in achieving full recovery.

Evaluating NaREMgWO6 (RE = La, Gd, Y) Doubly Ordered Double Perovskites as Eu3+ Phosphor Hosts.

Three doubly ordered double perovskites NaREMgWO6 (RE = La, Gd, Y) have been synthesized via traditional solid-state methods, doped with Eu3+, and characterized to evaluate their promise as Eu3+ phosphor hosts. NaYMgWO6, a new member of the family, was found to crystallize in the P21 space group and is isostructural with NaGdMgWO6. Emissions characteristic of Eu3+ ions (5D0 → 7F4,3,2,1,0) were observed, with the most intense transition being the 5D0 → 7F2 transition near 615 nm. Substitution of Eu3+ onto a more compressed RE site in the NaY1-xEuxMgWO6 and NaGd1-xEuxMgWO6 hosts results in a blue shift of the charge-transfer excitation band and an increase in the intensity of the 5D0 → 7F2 transition compared to NaLa1-xEuxMgWO6. All of the hosts can incorporate high concentrations of Eu3+ before concentration quenching is observed. When the rare-earth ion is either Gd3+ or Y3+, good energetic overlap between the Eu3+ charge-transfer band and the absorption of the host lattice results in sensitization and energy transfer from the perovskite host lattice to the Eu3+ activator sites. These hosts display comparable if not better luminescence than Y2O3:Eu3+, a commonly used commercial standard, demonstrating their promise as red phosphors.

Neural blockade anaesthesia of the mandibular nerve and its terminal branches: rationale for different anaesthetic techniques including their advantages and disadvantages.

Anaesthesia of structures innervated by the mandibular nerve is necessary to provide adequate pain control when performing dental and localised surgical procedures. To date, numerous techniques have been described and, although many of these methods are not used routinely, there are some situations where their application may be indicated. Patient factors as well as anatomical variability of the mandibular nerve and associated structures dictate that no one technique can be universally applied with a 100% success rate. This fact has led to a proliferation of alternative techniques that have appeared in the literature. This selective review of the literature provides a brief description of the different techniques available to the clinician as well as the underlying anatomy which is fundamental to successfully anaesthetising the mandibular nerve.

Endodontic essay.

"It has been said that Mineral Trioxide Aggregate is driving an endodontic revolution. Discuss this statement considering the biological and clinical attributes of this innovative material."

Anatomical relationships within the human pterygomandibular space: Relevance to local anesthesia.

A thorough understanding of the anatomy of the pterygomandibular space is fundamental to the successful administration of inferior alveolar nerve (IAN) blocks, which are frequently used in dentistry for mandibular anesthesia. However, the nature and extent of anatomical variations and relationships within this space are not well documented, and descriptions vary within the literature. This study analyzed the anatomical patterns and relationships of structures in the pterygomandibular space of 56 human cadaver hemi-heads, with both left and right sides from 10 individuals being available, and described the range of variability. In most cases, the IAN was anterior to the inferior alveolar vasculature with the inferior alveolar vein(s) being closest to the bone. On average, there were two veins per specimen. The position of the inferior alveolar neurovascular bundle expressed as the ratio of its distance from the anterior border of the ramus to the total anteroposterior length of the ramus was 0.60 (standard deviation [SD] = 0.07). The distance of anterior and medial displacement of the lingual nerve to the IAN was 7.3 mm (SD = 2.4 mm) and 3.9 mm (SD = 1.6 mm), respectively. The direct distance between the IAN and lingual nerve was 8.5 mm (SD = 2.4 mm). The sphenomandibular ligament always appeared dense and fibrous, medial to the neurovascular bundle. This anatomical study highlights the extent of variations in the positioning of anatomical structures directly relevant to IAN blocks, and reassesses the rationale for the direct approach, which is currently taught and practiced throughout many countries.