Summary
In modern industrial production lines various process and material parameters determine the properties of the final product. Thus, a process optimization procedure has to take into account a ...large design space containing several parameters. As a consequence, the evaluation of the influence of single process parameters on the final product properties can be quite complicated. Usually a certain property of a product, for example the mechanical strength, has to satisfy a defined specification. In terms of quality control not only the performance of the material but also the reliability of the specified values has to be considered. The Weibull statistic gives an interesting approach to evaluate both, material's performance and reliability. Regarding the mechanical properties e.g. in terms of the stress at break σb the Weibull analysis leads to a characteristic failure constant σb,0 at which 63.2 % of the samples will break. Additionally, the Weibull modulus m can be regarded as a measure for the width of the distribution of the measuring results. High values of m represent a narrow distribution and thus a better reliability. Moreover, the Weibull modulus m is independent of the absolute value of the measuring data. Therefore, it is possible to compare samples produced under different conditions. The standard deviation and the interquartile range are often used to quantify the scatter of empirical data. It is shown within this work that the Weibull modulus m can be a more precise discriminator for the evaluation of the reliability because it is rather stable against outlaying values. As an example this study concentrates on the mechanical properties of melt spun fibres consisting of blends from polypropylenes with different molar masses produced under various process conditions. This work presents a novel chart which allows one to compare different samples on the basis of the Weibull statistics whereat the Weibull modulus m is plotted over σb,0. Defining a reference material, the m‐σb,0‐map can be split into quadrants, whereat each quadrant designates an improvement or worsening of material's performance and reliability with respect to the reference. An evaluation in terms of performance and reliability of great sets of data is easily applicable. It will be shown that the Weibull statistic can also be applied to Young's Modulus, the elongation at break and the tensile energy absorption.
Summary
Biaxial‐oriented polypropylene (BOPP) is one of the most used materials for industrial films and food packaging. In terms of environmental and economic issues, the reduction of the film ...thickness, increasing the homogeneity, enhancing the process efficiency and stability are in the focus of this work. A systematic investigation on the biaxial stretching process is presented in this study. Therefore, two commercial linear polypropylenes with different molar masses and a commercial long‐chain‐branched polypropylene were used to obtain binary and ternary blends to adjust the elongation behavior on the molecular level. The blending was carried out using a cast film process on a twin‐screw extruder. The cast films obtained, were investigated before and after biaxial stretching. The thickness distribution of the films, were used as a measure of the film homogeneity, before and after the film stretching process. It turns out that casting and biaxial stretching are competing steps with respect to the film homogeneity. The casting step is dominated by the extrusion behavior of the blends. With increasing amount of the long‐chain branched material extrusion flow instabilities appear leading to an irregular surface and to a poor film homogeneity. Contrarily, long‐chain branches promote a more homogeneous deformation during the biaxial stretching inducing strain hardening which leads to a self‐healing effect and thus to an improved film homogeneity. The homogeneity of the final stretched film depends on both, casting and stretching. Therefore, a desirable polymer blend recipe with a medium amount of long‐chain branches is revealed for the stretched film.
The synthesis of 2-(E)-O-(4-hydroxy-cinnamoyl)-ᴅ,ʟ-galactaric acid (1a) is described. Starting with free galactaric acid (2) and 4-acetoxy-cinnamoyl-chloride (3), these compounds were esterified ...under regioselective conditions to racemic 2-(E)-O-(4-acetoxy-cinnamoyl)-galactaric acid (4). After deprotection of the p-coumaroyl moiety 1a was obtained as a photo-unstable product. Optical resolution of racemate l a on bovine serum albumin covalently bound to silica resulted in the isolation of the pure optical isomers. The (+)-dextrorotatory synthetic enantiomer l a proved to be identical with the natural factor.
Gleditsia triacanthos L. (honey locust), a plant of the widespread family Leguminosae, shows strong nyctinastic behaviour. Guided by the bioassay, a number of turgor influencing substances - PLMF 1, ...PLMF 3, PLMF 4, PLMF 5 and PLMF 6 - could be isolated and characterized from aqueous extracts of this plant. Structure and biological relevance of this phenolic-acid-glycosidesulfates are confirmed by synthesis. The multitude and the graduated biological activity of that factors suggests a biological way of irritation, who is after all responsible for the nyctinasty of G. triacanthos.
The fracture resistance of ultrathin computer-aided design and computer-aided manufacturing (CAD/CAM) occlusal veneers with different preparation designs was investigated under cycling mechanical ...loading and via finite element analysis (FEA).
Eighty molars were prepared with a circular enamel ring until complete exposure of the occlusal dentin occurred. Forty were prepared via additional circular chamfer preparation. The teeth were restored with 0.5 mm-thick occlusal veneers. Each group received a CAD/CAM fabricated occlusal veneer with a low modulus of elasticity (composite, CeraSmart) and a high modulus of elasticity material (ceramic, Celtra Duo). The restorations were adhesively luted and underwent 2000 thermocycling cycles. The samples were loaded at 50 N under 1,000,000 cycles in a chewing simulator and were checked for failure after various cycles. A visible crack was defined as failure, and the Kaplan-Meier survival rate was used for data analysis.
One sample per group was digitized using microcomputed tomography, and FEA was performed using open-source software. The comparative stresses were analyzed for specimens with and without chamfer preparation.
The survival probabilities were 60% for occlusal ceramic veneers without preparation and 40% for veneers with chamfer preparation, with no statistically significant differences. Composite veneers achieved 95% survival probability regardless of the preparation method.
The main principal stress in ceramic restoration was visualized via FEA. In composite veneers, stress was also visible in the luting composite and dentin.
The preparation method had no influence on mechanical fatigue. Minimally invasive preparation can be recommended. The restoration material is crucial for survival.
Objectives
Sufficient depth of cure allows bulk-fill composites to be placed with a 4-mm thickness. This study investigated bulk versus incremental application methods by visualizing shrinkage ...vectors in flowable bulk-fill and conventional composites.
Materials and methods
Cylindrical cavities (diameter = 6 mm, depth = 4 mm) were prepared in 24 teeth and then etched and bonded with OptiBond FL (Kerr, Italy). The composites were mixed with 2 wt% radiolucent glass beads.
In one group, smart dentin replacement (SDR, Dentsply) was applied in bulk “SDR-bulk” (
n
= 8). In two groups, SDR and Tetric EvoFlow (Ivoclar Vivadent) were applied in two 2-mm-thick increments: “SDR-incremental” and “EvoFlow-incremental.” Each material application was scanned with a micro-CT before and after light-curing (40 s, 1100 mW/cm
2
), and the shrinkage vectors were computed via image segmentation. Thereafter, linear polymerization shrinkage, shrinkage stress and gelation time were measured (
n
= 10).
Results
The greatest shrinkage vectors were found in “SDR-bulk” and “SDR-increment2,” and the smallest were found in “SDR-increment1-covered” and “EvoFlow-increment1-covered.” Shrinkage away from and toward the cavity floor was greatest in “SDR-bulk” and “EvoFlow-increment2,” respectively. The mean values of the shrinkage vectors were significantly different between groups (one-way ANOVA, Tamhane’s T2 test,
p
< 0.05). The linear polymerization shrinkage and shrinkage stress were greatest in Tetric EvoFlow, and the gelation time was greatest in “SDR-bulk.”
Conclusions
The bulk application method had greater values of shrinkage vectors and a higher debonding tendency at the cavity floor.
Clinical relevance
Incremental application remains the gold standard of composite insertion.
Aim
The aim of the present randomized, controlled trial was to compare the impact of the regular use of a fluoride‐free microcrystalline hydroxyapatite (HAP) dentifrice and a 1400 ppm fluoride ...control dentifrice on caries progression in 150 highly caries‐active orthodontic patients.
Methods
The primary outcome was the occurrence of lesions with International Caries Detection and Assessment System (ICDAS) ≥code 1 on the vestibular surfaces of teeth 15‐25 within 168 days after fixation of orthodontic brackets. Secondary outcomes were lesion development ICDAS ≥code 2, the plaque index, and the gingival index.
Results
In total, 147 patients were included in the intent‐to‐treat (ITT) analysis; 133 finished the study per protocol (PP). An increase in enamel caries ICDAS ≥code 1 was observed in 56.8% (ITT) and 54.7% (PP) of the HAP group participants compared with 60.9% (ITT) and 61.6% (PP) of the fluoride control group. Non‐inferiority testing (ITT and PP) demonstrated the absence of a significant difference between the groups. No significant differences in secondary outcomes were observed between the groups.
Conclusion
In highly caries‐active patients, the impact of the regular use of a microcrystalline HAP dentifrice on caries progression is not significantly different from the use of a 1400 ppm fluoride toothpaste (ClinicalTrials.gov: NCT02705456).
•CFTR inhibition by toxic factors is common in everyday life and may exacerbate pancreatitis.•CF-associated decrease in intestinal luminal fluidity may be ameliorated by apical Na+/H+ exchange ...inhibition.•Loss of CFTR function may reduce renal HCO3−secretion, causing metabolic alkalosis and reducing ventilatory drive.
With increased longevity of patients suffering from cystic fibrosis, and widespread lung transplantation facilities, the sequelae of defective CFTR in other organs than the airways come to the fore. This minireview highlights recent scientific progress in the understanding of CFTR function in the pancreas, the intestine and the kidney, and explores potential therapeutic strategies to combat defective CFTR function in these organs.
Display omitted
•Initial proximal wall build-up in a class-II cavity yielded smaller shrinkage vectors.•Applying a thin flowable liner decreased the shrinkage vectors.•A thin flowable liner is recommended when ...building a proximal resin composite wall.
Upon initial proximal wall construction, the favorable C-factor of class-II cavities may become unfavorable. This study investigated the application method on bulk-fill resin composite polymerization shrinkage.
Occluso-proximal class-II cavities were prepared in 40 molars and bonded with a self-etch adhesive (Adhese Universal). The study groups varied according to the resin composite application: group-1: bulk application, Tetric EvoCeram Bulk Fill (TBF); group-2: proximal wall construction (TBF) and occlusal cavity filling (TBF); group-3: thin flowable liner layer, Tetric EvoFlow Bulk Fill (TEF) and bulk filling (TBF); group-4: flowable liner (TEF), proximal wall (TBF), occlusal cavity (TBF); and group-5: bulk application, SDR (3 mm) and capping layer (TBF, 1 mm). Each resin composite increment was scanned twice using micro-CT (uncured, cured 40 s) at a resolution of 16 µm. Shrinkage vectors and volumetric polymerization shrinkage were evaluated and statistically analyzed (one-way ANOVA). SEM images were used to investigate the tooth-restoration interface.
Shrinkage vectors differed significantly among the groups and were greatest in gp5-fl/SDR (47.6 µm), followed by gp1-TBF (23.8 µm) and least in gp5-fl/SDR+TBF (11.1 µm). Volumetric shrinkage varied significantly with the use of SDR (gp5-fl/SDR: 2.6%) and TEF (gp4-fl/TEF: 2.5%) to TBF (gp4-fl/TEF+wl/TBF: 0.6%) in the incremental application.
Building a proximal resin composite wall yielded smaller shrinkage vectors than the bulk application. Applying a thin flowable liner decreased the shrinkage vectors, even more when building a proximal wall. A thin flowable liner is recommended when building a proximal resin composite wall.
PDF
