Oblique Direction Research Articles

Improvement of image sticking on a polymer-sustained-alignment liquid crystal displays with photo-alignment layers

ABSTRACT New polymer-sustained-alignment liquid-crystal-displays (PSA-LCDs) with photo-alignment layers are proposed in this study. The fabrication process of the new PSA-LC cell is followings; a photo-alignment treatment is firstly conducted by exposing polarised UV from oblique direction to the photo-alignment layer. After construction of the LC cell having monomers in a LC layer, unpolarised UV is exposed for forming a polymer layer. During the exposure of the unpolarised UV, application of electric-field is not necessary because the pretilt angle is determined by the photo-alignment treatment. In order to avoid a shift of the pretilt angle during the unpolarised UV exposure, a relatively fast rate constant of polymerisation is important. Furthermore, residual-direct-current-voltage (V rDC), which is one of image sticking parameters, is also affected by the rate constant of the polymerisation, and the V rDC becomes small with increasing the rate constant. In contrast, the shift of the pretilt angle (Δtilt), which is another image sticking parameter, depends on molecular structures of the monomers, and the Δtilt becomes small for the monomers with linear structure between a core unit and polymerisable units. The results indicated that the monomer 2,7-dimethacryloyl-oxy-phenanthrene would be suitable for fabrication and small level of the image sticking of the PSA-LC cells with the photo-alignment layers.

Characteristics of Retained Foreign Bodies in the Tongue: A Retrospective Study of 35 Cases

There are only a few case reports of foreign bodies (FBs) in the tongue. Delayed diagnosis or misdiagnosis is commonly reported. The purpose of this study was to identify the demographic, clinical, and radiological features that might facilitate the diagnosis of retained FBs in the tongue. A retrospective case series was performed. Clinical and imaging data of patients with FBs in the tongue at Wuhan University Hospital of Stomatology were reviewed. The outcome variable was a preliminary, radiological, intraoperative, or pathological diagnosis. Covariates included age, sex, FB-related history, symptoms and signs, duration, and computed tomography (CT) imaging features. Descriptive statistics were computed for each study variable. Thirty-five patients were included. The sample's mean age was 54.5±11.2years, included 19 males (54.3%). Eighty percent of the patients reported FB-related history with a mean duration of 4weeks. More than 70% of the patients presented with tongue swelling. Approximately half of the 35 cases were preliminarily misdiagnosed, and 15 of them were initially suspected to be tumors. After CT examinations, 33 of the 35 cases were diagnosed as FB. Characteristic CT imaging feature of the FB was a radiopaque line. Most FBs were located at the anterior two-thirds and marginal area of the tongue and in an oblique direction. The depth of FB was 0.61±0.42cm. The superficial ends of most FBs were close to the surface of the dorsum and the tongue margin. The possibility of a retained FB should be included in the differential diagnosis of a nonhealing wound or tongue enlargement when a radiopaque line is present on CT images of patients presenting with or without FB-related history. It may be easier to detect a FB in the tongue when a CT imaging postprocessing protocol, including thin-slice reconstruction and multiplanar reformation visualization and careful interpretation, is used.

Fracture Resistance of Incisal Tooth Fragment reattached with different Materials and Preparation

The purpose of this study is to analyze the fracture resistance of reattached tooth according to the resin materials and tooth preparation type under physiological conditions. Uncomplicated crown fracture in the oblique direction was reproduced on the extracted 64 anterior teeth. Depending on the composite resin material, reattachment was performed using a flowable resin and a packable resin. Depending on retentive forms, reattachment was performed using simple reattachment, 1.0 mm × 1.0 mm labial chamfer bevel, 1.0 mm × 1.0 mm lingual chamfer bevel and 1.0 mm × 1.0 mm circumferential bevel. A load was applied to the palatal surface of the tooth using a universal testing machine at an angle of 125 degree, which is the interincisal angle of normal children. Under the masticatory pressure condition, fracture resistance of lingual chamfer groups was 28.28 ± 7.41 MPa and 27.54 ± 4.45 MPa, which was significantly higher than those of simple reattachment groups, 17.21 ± 5.87 MPa and 20.10 ± 6.00 MPa, in both flowable and packable resin groups. When considering the lingual force similar to masticatory pressure, the fragment retention was significantly improved when the lingual chamfer was formed compared to the simple reattachment. Clinicians may consider the design of the lingual chamfer in order to improve fracture resistance to masticatory pressure during fragment reattachment.

Oblique Alfvén waves in a stellar wind environment with dust particles charged by inelastic collisions and by photoionization

ABSTRACT The characteristics of Alfvén waves propagating in a direction oblique to the ambient magnetic field in a stellar wind environment are discussed. A kinetic formulation for a magnetized dusty plasma is adopted considering Maxwellian distributions of electrons and ions, and immobile dust particles electrically charged by absorption of plasma particles and by photoionization. The dispersion relation is numerically solved and the results are compared with situations previously studied where dust particles were not charged by photoionization, which is an important process in a stellar wind of a relatively hot star. We show that the presence of dust causes the shear Alfvén waves to present a region of wavenumber values with zero frequency and that the minimum wavelength for which the mode becomes dispersive again is roughly proportional to the radiation intensity to which the dust grains are exposed. The damping rates of both shear and compressional Alfvén waves are observed to decrease with increasing radiation flux, for the parameters considered. For the particular case where both modes present a region with null real frequency when the radiation flux is absent or weak, it is shown that when the radiation flux is sufficiently strong, the photoionization mechanism may cause this region to get smaller or even to vanish, for compressional Alfvén waves. In that case, the compressional Alfvén waves present non-zero frequency for all wavenumber values, while the shear Alfvén waves still present null frequency in a certain interval of wavenumber values, which gets smaller with the presence of radiation.

Low lying pubic tubercle: A predictor of development of inguinal hernia

All the inguinal hernias begin within a single weak area called myopectoneal orifice, the natural mechanisms in our body which support this area are oblique direction of the inguinal canal in abdominal wall, the tension mechanism of transversalis fascia and presence of aponeurotic extensions from the transverse abdominis aponeurotic arch in the posterior wall of the inguinal canal. As the distance from pubic tubercle to the horizontal line joining two anterior-superior iliac spine increases, the inguinal canal becomes less oblique that leads to increased risk of development of inguinal hernia. The present project was planned to study the role of low-lying pubic tubercle in development of inguinal hernia. The present case control study was conducted in our institute from June 2018 to April 2019 taking 100 cases and 100 control meeting inclusion criteria. In all patients, following parameters SS line, ST line, height, weight was recorded and evaluated. The mean value of ST line in our study group is7.3476±0.16354cm significantly greater (p=0.05) than the controls the mean value being 6.9242±0.12620cm. Group of people with low-lying pubic tubercle are at high risk of developing inguinal hernia.

Experimental study of rock ruptures shear strength anisotropy

Joints significantly reduce rock cohesion compared to unfractured rock, but the question is what effect the possible anisotropy of the shear strength of different types of rupture has on possible subsequent failure. Both natural samples of granodiorite with natural joints and fault surfaces and gypsum models have been tested on the Matest A129 Rock shear box apparatus. The shear strength of preexisting ruptures was measured under a fixed normal stress component. The anisotropy of the shear strength of the joints and fault surfaces reached more than 60 % of maximum strength, which is a very important value for solving structural loads. The shear strength was analyzed with polar plots. The pattern of the real joints typically showed a teardrop shape with one peak of strength in a certain direction and a minimum in the opposite direction. On the contrary, striated fault surfaces are characterized by two axial directions of minimal shear strength, i.e., longitudinal and transverse, and by two axial oblique directions with maximal shear strength, so the strength distribution in the polar graph has a four-cornered shape. The study showed that the anisotropy of the shear strength of various types of ruptures is their important feature.

Comparison of the strain developed around implants with angled abutments with two reinforced polymeric CAD-CAM superstructure materials: An in vitro comparative study

Statement of problemThe strain developed around implants with angled abutments should be considered when selecting a superstructure material. Studies that evaluated the strain developed around implants with angled abutments when using fiber-reinforced polymer as the implant superstructure material are lacking. PurposeThe purpose of this in vitro study was to assess the strain developed around implants with angled abutments (15 and 25 degrees) of biocompatible high-performance polymer (BioHPP) and reinforced nanohybrid polymer with a multilayered glass fiber (TRINIA) superstructure under axial and oblique loading. The strain developed around implants was evaluated by using strain gauges. Material and methodsThirty-two polyurethane test blocks were divided into 2 main groups (n=16) according to the degrees of buccal tilting of the implant platform (15 and 25 degrees). Each group was divided into 2 subgroups (n=8), and each subgroup received different superstructure materials (BioHPP or TRINIA). Two buccal and palatal strain gauges were installed on their corresponding prepared sites to measure the microstrains in the medium surrounding the implant. A universal testing machine was used to apply the static load from 0 to 100 N in the axial and 45-degree oblique direction, with the loading tip of the device on the loading point at the central fossa of the crown. For each tested implant, loads were applied, microstrains were recorded with the strain gauges, and the strain developed around the implant was statistically evaluated with 1-way ANOVA, followed by multiple pairwise comparisons by using the Bonferroni adjusted significance level (α=.05). ResultsFor superstructure materials, the microstrain values recorded around implants restored with TRINIA were significantly lower than those restored with BioHPP in all groups (P<.001). The 25-degree implant angulation recorded significantly higher microstrain than 15 degrees buccally and palatally when axial and oblique loads were applied (P<.05). The microstrain was significantly higher in the oblique load than in the axial load in both the BioHPP and TRINIA groups in 15- and 25-degree implant angulations on the buccal and palatal sides (P<.001). ConclusionsThe strain developed around dental implants was significantly affected by the superstructure material. The microstrain was considerably higher when the implant abutment angulation increased. When a 45-degree loading direction was used, this tendency became more pronounced.

Physical dosimetric reconstruction of a case of large area back skin injury due to overexposure in an interventional procedure

To estimate the physical dose of skin and key organs in a case of overexposure during a cardiac interventional procedure. MethodsThe female patient aged 50 suffered from overexposure during cardiac interventional therapy in a hospital, Xinxiang city, Henan province, China in January 2020. The mesh-type phantom for the patient was constructed based on the adult mesh-type reference computational phantoms (MRCPs) released by the International Commission on Radiological Protection Publication 145 (ICRP145) and phantom deformation technology. Models of exposure scenario were constructed and simulated with particle and heavy ion transport code system (PHITS) according to exposure conditions. ResultsThe maximum absorbed dose of key organs/tissues under irradiation in posteroanterior (PA) and 30° left anterior oblique directions(LOA) was 632.4 and 305.6 ​mGy, respectively. The left lung, heart, and left mammary gland received a larger dose under both irradiation conditions. The ratio of the absorbed dose with and without shielding was calculated, and the relative difference in most organs was <1% between two directions. The iso-dose curve of the back skin revealed the distribution of the absorbed dose (0.1 −5.2 ​Gy). The dose estimate of key tissues/organs was higher than the conventional level, especially the local skin, up to 5.2 ​Gy. ConclusionsThe interventional procedure in this case resulted in a higher dose. Monte Carlo codes combined with the MRCPs can be employed to estimate physical dose to individuals in concrete irradiation scenarios.

The metal post material influences the performance of artefact reduction algorithms in CBCT images.

This study aimed to assess the effect of the MAR tool on the expression of artefacts in different regions of a tooth restored with different types of metal posts. Alveolar sockets (anterior, and posterior region) of a mandible and an unirradicular tooth were used. Cone beam computed tomography scans of the tooth without a metal post, and with cobalt-chromium (Co-Cr), nickel-chromium (Ni-Cr), or silver-palladium (Ag-Pd) were individually obtained, with 2 MAR conditions: disabled, and enabled. In an axial reconstruction, lines of interest (LOIs) were set around the canal: 4 in oblique (mesiobuccal, distobuccal, mesiolingual, distolingual) directions, and 4 in orthogonal (mesial, distal, buccal, lingual) directions. Beam-hardening artefacts expression was determined by calculating the difference in the mean of gray values (DMGV) between the experimental and control groups for each LOI. There was no significant difference in the DMGV values between "without MAR" and "with MAR" for any LOI, in neither anterior nor posterior mandible (p>0.05), for the Ni-Cr and Co-Cr groups. For the Ag-Pd, significant differences in the DMGV values were observed between "without MAR" and "with MAR" for most LOIs (p<0.05), mainly in oblique directions in the anterior region, and mesio-distal direction in the posterior region. MAR acted mostly in hypodense artefacts (negative DMGV). The effectiveness of the MAR tool of the OP300 CBCT unit varied according to the post material tested. It was effective in reducing the expression of artefacts raised by the Ag-Pd post, mainly in the tooth regions affected by hypodense artefacts, regardless of the mandibular region.

Aerodynamic shape optimization of large-span coal sheds for wind-induced effect mitigation using surrogate models

Large-span coal sheds commonly used in thermal power plants are particularly vulnerable to wind loads, and the aerodynamic performances are largely affected by their external shapes. The search for the best performing shape through an aerodynamic optimization is still of importance for the mitigation of the design wind loads and responses. This study investigated the possibility of using surrogate models combined with genetic algorithm to carry out the aerodynamic shape optimization of large-span roof structures. The approach is applied to tri-centered coal sheds with closed and open gables, respectively. The shape optimization is numerically performed to minimize the vertical displacement of the shed model while subjecting to one normal and two oblique wind directions, 0°, 30° and 45°. The aerodynamic forces acting on coal sheds immersed in turbulent flow are obtained by the CFD simulation with RSM turbulence model, and the results are validated with wind tunnel tests. Kriging model is used to establish a global mapping between design variables and objective function by conducting a set of CFD and structural static response analyses. Results show that the aerodynamic loads and the optimal geometry are sensitive to the selection of gable types and wind directions. The optimal design presents a reasonable performance improvement compared with the near-optimal and original designs. Several compromised designs are finally provided in order to seek a balance between the effects of wind directionality and construction cost.

Wind Turbulence over Misaligned Surface Waves and Air–Sea Momentum Flux. Part II: Waves in Oblique Wind

AbstractThe coupled dynamics of turbulent airflow and a spectrum of waves are known to modify air–sea momentum and scalar fluxes. Waves traveling at oblique angles to the wind are common in the open ocean, and their effects may be especially relevant when constraining fluxes in storm and tropical cyclone conditions. In this study, we employ large-eddy simulation for airflow over steep, strongly forced waves following and opposing oblique wind to elucidate its impacts on the wind speed magnitude and direction, drag coefficient, and wave growth/decay rate. We find that oblique wind maintains a signature of airflow separation while introducing a cross-wave component strongly modified by the waves. The directions of mean wind speed and mean wind shear vary significantly with height and are misaligned from the wind stress direction, particularly toward the surface. As the oblique angle increases, the wave form drag remains positive, but the wave impact on the equivalent surface roughness (drag coefficient) rapidly decreases and becomes negative at large angles. Our findings have significant implications for how the sea-state-dependent drag coefficient is parameterized in forecast models. Our results also suggest that wind speed and wind stress measurements performed on a wave-following platform can be strongly contaminated by the platform motion if the instrument is inside the wave boundary layer of dominant waves.Significance StatementSurface waves increase friction at the sea surface and modify how wind forces upper-ocean currents and turbulence. Therefore, it is important to include effects of different wave conditions in weather and climate forecasts. We aim to inform more accurate forecasts by investigating wind blowing over waves propagating in oblique directions using large-eddy simulation. We find that waves traveling at a 45° angle or larger to the wind grow as expected, but do not increase or even decrease the surface friction felt by the wind—a surprising result that has significant implications for how oblique wind-waves are represented as a source of surface friction in forecast models.

Optical Interactions in Subwavelength Metallic Materials Array

When light is incident on the interface of different media, refraction and reflection occur. Also, while light propagates through a medium, scattering by particles constituting the medium is a well-known basic property. Recently, the non-classical phenomenon is expected to be the core of many technologies such as resonantly transfer energy, nanosized quantum optical energy amplifiers, and nano-sensing technique. This technique uses a surface plasmon induced by the reconfiguration of the distribution of electrons in a metallic material by stimulation of an external field. This is because, in the nanoscale structure of the medium, the light intensity distribution in the medium is changed by the interaction of the fields in the medium including the surface plasmon. In this study, the light transmission characteristics of the metal material array medium with a size smaller than the skin-depth were investigated by 3D simulation of the FDTD method. The light intensity distribution and light transmittance of the light passing through the medium of the metal (Au) cylinder and sphere array structure were analyzed. The synergistic effect of light transmittance appeared as the light spread was reduced due to the interaction between metal materials. In addition, when light is incident on the interface in an oblique direction, the beam peak is split into several parts.

A Three-dimensional Finite Element Analysis of Effect of Abutment Materials on Stress Distribution around Peri-Implant Bone in Immediate and Delayed Loading Conditions

Introduction: Osseointegration is important for successful dental implant treatments. Abutment materials affect the load transfer to the implant and surrounding bone thus determining the long term implant survival. Aim: Stress analysis around peri-implant hard tissue with different abutment materials and their comparative evaluation in immediate and delayed loading conditions using finite element analysis. Material and Methods: An in-vitro experimental study was carried out on a root form titanium grade IV Implant, assembled with an abutment Ø4.0-0.5GH and this test model was Threedimensional (3D) scanned, reconstructed on Computer-aided design software CREO. Six abutment groups: Group 1- Zirconia with DL (Delayed Loading), Group 2- Polyether Ether Ketone (PEEK) with DL, Group 3- Titanium grade Extra Low Interstitial (ELI) with DL, Group 4- Zirconia with IL (Immediate Loading), Group 5- PEEK with IL, Group 6- Titanium Grade ELI with IL, were loaded from vertical, horizontal and oblique direction. Von Mises and principal stress analysis was done on the implant and the peri-implant bone using the finite element method and the statistical analysis was done. Results: For delayed loading group, highest stresses were generated in group 1 (462.88 MPa), followed by group 3 (413.72 MPa) and least in group 2 (319.38 MPa). For immediate loading, highest to lowest stresses were in group 4 (694.32 MPa), Group 6 (620.58 MPa) and group 5 (479.07 MPa). The principal stress analysis showed significant difference between all groups in cancellous bone and cortical bone except between titanium and customised zirconia abutment in cortical bone in delayed loading (p=0.0846) and in immediate loading (p=0.1125). Conclusion: Change in abutment materials significantly affects the stress generated in and around the implant thus more studies must be carried out to reach a consensus on the most optimal material encouraging least dissipation in peri-implant hard tissues.

Three for the Road

Three for the Road Kwon Yeo-sun (bio) Translated by Ann Meejung Kim (bio) They had agreed to meet at the public parking lot at nine o'clock, but only at five minutes past did Kyu call Hun, saying they should push back the departure to ten minutes later. It was quite chilly, so Hun headed into the coffeehouse next to the parking lot. Sipping a hot cup of awful coffee, he stared absentmindedly at the parking lot embankment out of a large windowpane. The grey stones making up the embankment were remarkably identical, as if they had been rolled off a production line. But even aside from their size, something about the pattern on the surfaces struck him as weird and disproportionate. There were two lines running parallel to each other in an oblique vertical direction, with a small square placed on the left and an elongated oval on the right. Not just one but dozens of such ugly stones—each bearing a crude pattern worse than a child's doodle—made up the embankment, one stacked on top of another. The coffee tasted even worse as it cooled, and suddenly it occurred to Hun how peculiar Kyu's phrasing had been. Let's push back the departure to ten minutes from now. It was a simple one-way notice telling him that Kyu and Churan were going to be fifteen minutes late. But Kyu made it sound as if the married couple, the pubu, was somehow suggesting or reaching for a mutual agreement. That is, if Kyu and Churan could still be called a pubu at all. [End Page 299] Their car arrived at the parking lot entrance at eighteen minutes past nine. As usual, Churan was sitting behind the wheel and Kyu was in the passenger seat. As Hun opened the back door, Churan turned and said, Sorry we're late. Hun got into the backseat without saying anything. It's because Kyu had to go back in the house just as we were about to leave, Churan said. I forgot to turn off the coffeemaker, Kyu said. His hair in the back was squashed in clumps. Did you drink last night? Hun asked. No, I did not. He didn't, confirmed Churan, meeting Hun's eyes in the rearview mirror. It's because I didn't drink! And so I couldn't get to sleep! Kyu rubbed his eyes violently. Kyu explained he needed a strong cup of coffee to get going since he hadn't slept at all, and how he had meant to turn off the machine until Churan was suddenly everywhere searching for her shawl, which distracted him so much that he just forgot. Why do you always blame other people? Churan shot back. I'm not blaming other people. I'm just saying there's a reason, Kyu said. All right, let's just go. Churan started the car at Hun's urging. They skirted the city center and cruised along Kangbyŏnbuk-ro. The river—not yet frozen over—glistened by under the roadway. What should we do about breakfast, wondered Kyu, to which Churan replied that they shouldn't eat anything until they reached the restaurant. The restaurant? Hun asked. Kyu explained there was a restaurant in Wŏnju that was famous for samgyet'ang. The only fault of that place is that you won't be able to eat samgyet'ang anywhere else after dining there, he said. [End Page 300] A chicken is a chicken. How good could it be? Kyu turned around to face him. Just try to think of the taste of chicken. Don't imagine anything special. The taste of chicken? Exactly, the taste of chicken! It does exactly what chicken is supposed to do in soup! As Kyu turned back to face the front, his bloodshot eyes came into view. He's right about not having slept, Hun thought, leaning back into the seat and pulling a blanket from beside him over his knees. After passing the tollgate, the traffic was light, and they were able to drive comfortably at 120km per hour. As they were nearing Shin'gal Junction, Churan let out a...

Surgical Pearl: Disposable Syringe as Modified Customized Comedone Extractor.

The conventional comedone extractors available are not able to evacuate contents properly, because of their vertical pressure. So, the comedone extractor which can exert pressure simultaneously in vertical and oblique direction for complete evacuation is the need of the hour.

Lower extremity muscle strength reference values for young Saudi male adults aged 21 to 23 years and their correlation with anthropometric parameters and balance

Normative reference values for muscle strength are needed for muscle strength assessment and estimation of prognosis in lower extremity related neuromuscular disorders, as muscle strength influenced by anthropometric parameters and muscle strength itself affects balance. Normative reference values for muscle strength in the Saudi Arabian population is lacking in the literature. Hence, the current study aimed to establish normative reference values for lower extremity muscle strength and to correlate these values with anthropometric parameters and balance. Lower extremity muscle strength and balance were assessed by baseline hand-held dynamometer and by forward, lateral, and oblique direction reach tests in 421 young male adults between 21 and 23 years of age. The mean and standard deviation of lower extremity strength ranged from 43.83 ± 16.92 lb to 62.07 ± 10.74 lb. Body weight, body mass index, and oblique and lateral reach distances were correlated with some knee and ankle muscle strength values. Body weight, body mass index, and balance showed significant effect on lower extremity muscle strength. Furthermore, decreased muscle strength may impair balance; the current clinical practice should evaluate body weight, body mass index, and muscle strength during the assessment process.

Removable Overdenture versus fixed Bridge fabricated on all-on-4 implants using CAD/CAM technology (Strain Gauge Analysis)

Assessing the effects on maxilla when using fixed vs. removable prosthesis on All-On-4® protocol. This in-vitro study was conducted to compare stresses induced on distal implants in All-On-4® concept, between digitally constructed removable overdenture and fixed bridge, using strain gauge analysis. Four dummy implants were placed in their designed locations according to the All-On-4® concept; in 3D printed completely edentulous maxillary acrylic cast. Multiunit abutments were secured to the implants. Two groups were defined: Group A: in which the framework was cemented to the four titanium copings over the implants (Fixed bridge). Group B: in which the same framework was picked up after relief was done and then seated on the ball attachments (Removable overdenture). Stresses were measured using strain gauges installed in their designed sites in the 3D printed cast. Loads of 100N were applied in a vertical and oblique direction on the right molar area. Paired t test was used to compare between two different load directions within the same group and unpaired t test was used to compare between different groups. P-value ? 0.05 was statistically significant. Group A with vertical loads (532±9.2) and oblique loads (464±40.3) showed significantly higher stresses on the supporting structures of the distal implants than group B with vertical loads (64 ±7.75) and oblique loads (41.5±2.42). Within group A, higher microstrains were recorded on the distal implants in the loaded side in case of applying vertical loads (532±9.2) than in case of oblique loads (464±40.3). Also, lower microstrains were recorded in the unloaded side in case of vertical loads (21.5±2.42) than in case of oblique loads (43±2.58). Within group B, higher microstrains were recorded in the loaded side in case of applying vertical loads (64±7.75), than in case of oblique loads (41.5±2.42). Also, lower microstrains were recorded in the unloaded side in case of vertical loads (10.5±1.58) than in case of obliq

Numerical investigation of oblique impact behavior of a helmeted headform on a windshield considering failure

A helmet, usually comprised of a composite shell, a foam liner and a chin strap, plays an important role for human head protection. Windshield glazing is a sandwiched structure which generally consists of two soda-lime glass layers bonded by a polyvinyl butyral (PVB) interlayer. In a motorcycle-vehicle accident, the rider’s head wearing a helmet (i.e. so-called helmeted head) frequently collides onto the windshield laminated glass of a vehicle along an oblique direction. Such an oblique collision commonly results in head injury, helmet failure and windshield fracture. To model the oblique collision, the validated windshield model with the intrinsic cohesive zone model is adopted for the glass fracture and glass-PVB debonding, while an existing helmet model is employed with a continuum damage method and a crushable foam model for simulating the failure of the composite shell and the foam liner. Then, different impact velocities, foam liners with different densities, impact angles and headform postures are considered to thoroughly investigate their effects on the headform response and energy absorption performance of the helmet during the oblique collision. The simulation results show that a larger density or stiffer foam liner absorbs less energy and causes a larger maximum acceleration; and a composite liner has a better comprehensive performance than a single uniform liner, while the helmet posture has small effects on headform response and energy absorption.

Astigmatic Vectorial Analysis in Pediatric Keratoconus After Unilateral Cross-Linking Treatment.

The aims of this study were to evaluate the treatment response of pediatric keratoconus (KC) patients to unilateral corneal collagen cross-linking (CXL) in treated eyes, disease progression in untreated eyes, and define the predictive value of astigmatic parameters by astigmatic vectorial analysis. Pediatric patients with KC with CXL-treated progressive eye and untreated fellow eye were included. Patients with other ocular conditions and a history of previous ocular surgery were excluded. Astigmatic changes in anterior and posterior corneal surfaces were evaluated with vectorial analysis. The receiver operating characteristic curves were analyzed to detect the best parameter that discriminates treated and untreated groups. Thirty-two eyes of 16 patients with at least 2-year follow-up were analyzed. The maximum keratometry (K) in CXL-treated eyes remained stable (from 53.51 ± 2.86-53.41 ± 2.84 diopter (D), P = 0.84) while the steepest K increased in untreated eyes (from 47.82 ± 1.71-49.59 ± 3.32 D, P = 0.03). The oblique components of corneal astigmatism in CXL-treated eyes were higher than those of fellow eyes (all P < 0.05), which significantly decreased in the anterior 3-mm zone after treatment (P = 0.048). The mean differential astigmatism magnitudes were significantly higher in treated eyes (all P < 0.05). The refractive centroid remained unchanged in treated eyes (P = 0.553) and shifted in the oblique direction in untreated eyes (P = 0.04). The oblique differential astigmatism in the anterior 7-mm zone showed the highest area under the curve value in predicting treatment efficacy (0.813, 95% confidence interval: 0.646-0.981, P < 0.001). Astigmatic vectorial analysis is an objective tool for longitudinal assessment of clinical outcomes in KC. Changes in the oblique components of corneal astigmatism might predict progression and treatment efficacy.

Comparison of stresses in monoblock tilted implants and conventional angled multiunit abutment-implant connection systems in the all-on-four procedure

BackgroundThe All-on-four dental implant method is an implantology method designed to provide a comfortable prosthetic treatment option by avoiding advanced surgical procedures. This research aims to compare and evaluate the stress and tension values in conventional angled multiunit abutment-implant connection systems and monoblock dental implants used in the all-on-four procedure with finite element analysis.MethodsTwo master models were created by placing four implants connected to multiunit abutments (group A) in the interforaminal region of a completely edentulous mandible and four monoblock implants (group B) in the same region of another completely edentulous mandible. Group A implants were classified according to their diameter as follows: 3.5 mm (M1A), 4.0 mm (M2A), and 4.5 mm (M3A). Similarly, group B implants were classified as M1B, M2B, and M3B. In the six models rehabilitated with acrylic fixed prostheses, a 100 N force was applied to the anterior implant region, and a 250 N force was applied to the posterior cantilever in both axial and 30° oblique directions. Von Mises stresses were analyzed in the bone and implant regions of all models.ResultsM1A and M1B, M2A and M2B, and M3A and M3B were compared with each other under axial and oblique forces. The maximum Von Mises stresses in the bone around implants and the prosthesis screws, and the maximum and minimum principal stresses in the cortical and trabecular bone in group A models were significantly higher than those in group B models.ConclusionsIn monoblock implant systems under axial and oblique forces, higher stress is accumulated in the bone, prosthesis screw and implant compared to multiunit abutment-implant connection systems.