OBJECTIVES: Comparisons of material hardness may be affected by the indentation size effect (ISE), which is characterized by increasing hardness values at decreasing loads. This study aimed to assess the influence of load, dwell time and measurement method on ISE in dental resin-based composites with different filler content. METHODS: Knoop (HK) and Vickers (HV) microindentation hardness of Filtek Ultimate Universal Restorative (FU) and Filtek Supreme Flowable Restorative (FF) was measured under different loads (0.098-2.96 N, i.e. 10-300 gf) and dwell times (5-30 s). Their effects on HK and HV were evaluated using repeated measures ANOVA, which was also used to compare the measurement methods. Coefficients of Meyer's equation, proportional specimen resistance (PSR) model and a modified PSR model were calculated using regression analyses. RESULTS: ISE was more pronounced for the highly-filled FU than for the less-filled FF, and HK was more susceptible to ISE than HV. The effect of dwell time was similar for both materials and measurement methods; hardness values decreased with dwell time, significantly between 5 s and 30 s. SIGNIFICANCE: The possible presence of ISE should be considered when determining measurement conditions for the microindentation hardness of dental resin-based composites. HV was found to be less sensitive to ISE and provided stable hardness values at lower loads than HK. Due to the high variability of composites, any hardness measurement should be preceded by mapping the effect of load to ensure that load-independent hardness is measured. If hardness values continue to decrease in the whole range of increasing loads, load-independent hardness can be calculated using the PSR model.

• Klíčová slova
• Dwell time, Load, Microhardness, Microindentation, PSR model, Resin composite,
• MeSH
• složené pryskyřice * chemie   MeSH
• testování materiálů * MeSH
• testy tvrdosti MeSH
• tvrdost * MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• složené pryskyřice * MeSH

This epidemiological study of ecological type deals with the analysis of relationship between drinking water hardness and health status of inhabitants of the Slovak Republic. This relationship was investigated in two groups of more than 50,000 inhabitants living in 53 different municipalities. The first group was supplied with drinking water with low hardness, and the second group was supplied with drinking water with increased hardness. The health status of the population of both groups was monitored by means of health indicators, which represented 15-year average values, for 1994-2008. We investigated four major causes of death, namely cardiovascular, oncological, gastrointestinal and respiratory tract mortality, and evaluated the average life expectancy. The health status of inhabitants supplied with drinking water with increased hardness was significantly better than the health status of people supplied with drinking water with low hardness. For example, the relative mortality for cardiovascular diseases, oncological diseases, digestive tract diseases and respiratory diseases was 56%, 62%, 128% and 121% higher in the population supplied with soft drinking water compared to the population supplied with hard water, respectively. In addition, life expectancy was more than 4.5 years higher in the population supplied with hard drinking water. Our observation confirms the findings of previous studies on relationship between the water hardness and human health.

• Klíčová slova
• Cardiovascular diseases, Drinking water, Gastrointestinal diseases, Hardness, Oncological diseases, Respiratory diseases,
• MeSH
• chemické látky znečišťující vodu analýza   MeSH
• lidé MeSH
• pitná voda analýza   MeSH
• tvrdost MeSH
• velkoměsta MeSH
• zásobování vodou normy   MeSH
• zdravotní stav * MeSH
• Check Tag
• lidé MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Slovenská republika epidemiologie   MeSH
• velkoměsta MeSH
• Názvy látek
• chemické látky znečišťující vodu MeSH
• pitná voda MeSH

OBJECTIVE: An inhomogeneous irradiance distribution from a light-curing unit (LCU) can locally cause inhomogeneous curing with locally inadequately cured and/or over-cured areas causing e.g. monomer elution or internal shrinkage stresses, and thus reduce the lifetime of dental resin based composite (RBC) restorations. The aim of the study is to determine both the irradiance distribution of two light curing units (LCUs) and its influence on the local mechanical properties of a RBC. METHODS: Specimens of Arabesk TOP OA2 were irradiated for 5, 20, and 80s using a Bluephase® 20i LCU in the Low mode (666mW/cm(2)), in the Turbo mode (2222mW/cm(2)) and a Celalux® 2 (1264mW/cm(2)). The degree of conversion (DC) was determined with an ATR-FTIR. The Knoop micro-hardness (average of five specimens) was measured on the specimen surface after 24h of dark and dry storage at room temperature. RESULTS: The irradiance distribution affected the hardness distribution across the surface of the specimens. The hardness distribution corresponded well to the inhomogeneous irradiance distributions of the LCU. The highest reaction rates occurred after approximately 2s light exposure. A DC of 40% was reached after 3.6 or 5.7s, depending on the LCU. The inhomogeneous hardness distribution was still evident after 80s of light exposure. SIGNIFICANCE: The irradiance distribution from a LCU is reflected in the hardness distribution across the surface. Irradiance level of the LCU and light exposure time do not affect the pattern of the hardness distribution--only the hardness level. In areas of low irradiation this may result in inadequate resin polymerization, poor physical properties, and hence premature failure of the restorations as they are usually much smaller than the investigated specimens. It has to be stressed that inhomogeneous does not necessarily mean poor if in all areas of the restoration enough light intensity is introduced to achieve a high degree of cure.

• Klíčová slova
• Degree of conversion, Dental resin, FTIR, Hardness mapping, Irradiance distribution, Knoop micro-hardness, Light curing units,
• MeSH
• časové faktory MeSH
• povrchové vlastnosti MeSH
• radiační rozptyl * MeSH
• spektroskopie infračervená s Fourierovou transformací MeSH
• stomatologické polymerizační lampy * MeSH
• světlo * MeSH
• syntetické pryskyřice chemie   MeSH
• testování materiálů MeSH
• tvrdost MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• syntetické pryskyřice MeSH

In this paper, an iron-aluminide intermetallic compound with cerium addition was subjected to Vickers microhardness testing. A full range of Vickers microhardness loadings was applied: 10, 25, 50, 100, 200, 300, 500, and 1000 g. Tests were conducted in two areas: 0.5 mm under the surface of the rolled specimen and in the center. The aim was to find the optimal loading range that gives the true material microhardness, also deemed load-independent hardness, HLIH. The results suggest that in the surface area, the reverse indentation size effect (RISE) occurred, similar to ceramics and brittle materials, while in the center, indentation size effect (ISE) behavior was obtained, more similar to metals. This clearly indicated an optimal microhardness of over 500 g in the surface region and over 100 g in the central region of the specimen. Load dependencies were quantitatively described by Meyer's law, proportional specimen resistance (PSR), and the modified PSR model. The modified PSR model proved to be the most adequate.

• Klíčová slova
• intermetallic compounds, load-independent hardness, microhardness,
• Publikační typ
• časopisecké články MeSH

Commercially pure titanium grade II was kinetically nitrided by implanting nitrogen ions with a fluence in the range of (1-9)·1017 cm-2 and ion energy of 90 keV. Post-implantation annealing in the temperature stability range of TiN (up to 600 °C) shows hardness degradation for titanium implanted with high fluences above 6·1017 cm-2, leading to nitrogen oversaturation. Temperature-induced redistribution of interstitially located nitrogen in the oversaturated lattice has been found to be the predominant hardness degradation mechanism. The impact of the annealing temperature on a change in surface hardness related to the applied fluence of implanted nitrogen has been demonstrated.

• Klíčová slova
• hardness, nitrogen ion implantation, titanium,
• Publikační typ
• časopisecké články MeSH

Silicon carbide (SiC) is one of the hardest known materials. Its exceptional mechanical properties combined with its high thermal conductivity make it a very attractive material for a variety of technological applications. Recently, it is discovered that two-layer epitaxial graphene films on SiC can undergo a pressure activated phase transition into a sp3 diamene structure at room temperature. Here, it is shown that epitaxial graphene films grown on SiC can increase the hardness of SiC up to 100% at low loads (up to 900 µN), and up to 30% at high loads (10 mN). By using a Berkovich diamond indenter and nanoindentation experiments, it is demonstrated that the 30% increase in hardness is present even for indentations depths of 175 nm, almost three hundred times larger than the graphene film thickness. The experiments also show that the yield point of SiC increases up to 77% when the SiC surface is coated with epitaxial graphene. These improved mechanical properties are explained with the formation of diamene under the indenter's pressure.

• Klíčová slova
• SiC, Young's modulus, diamene, epitaxial graphene, hardness,
• Publikační typ
• časopisecké články MeSH

The AlSi10Mg alloy is characterized by a high strength-to-weight ratio, good formability, and satisfying corrosion resistance; thus, it is very often used in automotive and aerospace applications. However, the main limitation of using this alloy is its low yield strength and ductility. The equal-channel angular pressing is a processing tool that allows one to obtain ultrafine-grained or nanomaterials, with exceptional mechanical and physical properties. The purpose of the paper was to analyze the influence of the ECAP process on the structure and hardness of the AlSi10Mg alloy, obtained by the selective laser melting process. Four types of samples were examined: as-fabricated, heat-treated, and subjected to one and two ECAP passes. The microstructure analysis was performed using light and electron microscope systems (scanning electron microscope and transmission electron microscope). To evaluate the effect of ECAP on the mechanical properties, hardness measurements were performed. We found that the samples that underwent the ECAP process were characterized by a higher hardness than the heat-treated sample. It was also found that the ECAP processing promoted the formation of structures with semicircular patterns and multiple melt pool boundaries with a mean grain size of 0.24 μm.

• Klíčová slova
• EBSD, ECAP, grain refinement, hardness, microstructure, selective laser melting,
• Publikační typ
• časopisecké články MeSH

The relationship between the tensile bond strength (TBS) and three dentin characteristics: remaining dentin thickness (RDT), Ca-concentration, and hardness, were investigated. Sixty-two extracted bovine incisors, divided into four groups, were prepared using 600-grit SiC paper to create flat dentinal surfaces. The materials tested in this study consisted of three commercially available and one experimental dentin bonding systems. The TBS and modes of failure were determined after storage for 24 h in 37 degrees C water. Then RDT, Ca-concentration, and hardness were measured. Data were statistically compared with TBS of each group. The mean bond strength of the commercial materials ranged from 2.5 +/- 0.9 MPa to 7.7 +/- 2.8 MPa. Correlations with Ca-concentration and RDT varied, depending on the product. The bond strength of the experimental material was 9.2 +/- 4.4 MPa and significantly correlated with RDT and hardness. With two of the dentin bonding agents, specimens showed a high number of cohesive fractures in dentin, 40% to 82%. It was concluded that the variability of TBS was influenced by dentinal characteristics in three of the four materials tested.

• MeSH
• adhezivita MeSH
• dentin anatomie a histologie   chemie   MeSH
• dentinová adheziva chemie   MeSH
• pevnost v tahu MeSH
• pryskyřičné cementy * MeSH
• skot MeSH
• složené pryskyřice chemie   MeSH
• testování materiálů MeSH
• tvrdost MeSH
• vápník analýza   MeSH
• vazba zubní * MeSH
• zvířata MeSH
• Check Tag
• skot MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• Clearfil Bonding Agent MeSH Prohlížeč
• Clearfil Photo Bond MeSH Prohlížeč
• dentinová adheziva MeSH
• pryskyřičné cementy * MeSH
• scotchbond 2 MeSH Prohlížeč
• složené pryskyřice MeSH
• vápník MeSH

The ability of cryogenic treatment to improve tool steel performance is well established; however, the selection of optimal heat treatment is pivotal for cost reduction and extended tool life. This investigation delves into the influence of distinct cryogenic and tempering treatments on the hardness, fracture toughness, and tribological properties of Vanadis 6 tool steel. Emphasis was given to comprehending wear mechanisms, wear mode identification, volume loss estimation, and detailed characterization of worn surfaces through scanning electron microscopy coupled with energy dispersive spectroscopy and confocal microscopy. The findings reveal an 8-9% increase and a 3% decrease in hardness with cryogenic treatment compared to conventional treatment when tempered at 170 °C and 530 °C, respectively. Cryotreated specimens exhibit an average of 15% improved fracture toughness after tempering at 530 °C compared to conventional treatment. Notably, cryogenic treatment at -140 °C emerges as the optimum temperature for enhanced wear performance in both low- and high-temperature tempering scenarios. The identified wear mechanisms range from tribo-oxidative at lower contacting conditions to severe delaminative wear at intense contacting conditions. These results align with microstructural features, emphasizing the optimal combination of reduced retained austenite and the highest carbide population density observed in -140 °C cryogenically treated steel.

• Klíčová slova
• cold-work tool steel, cryogenic treatment, fracture toughness, hardness, tribological properties, wear mechanisms,
• Publikační typ
• časopisecké články MeSH

Very low or very high concentrations of calcium (Ca) and magnesium (Mg) or total hardness in drinking water have been empirically recognized as the cause of the problems with corrosion, scaling, or taste of water. A large body of scientific evidence over the last 60 years has also attributed health problems to both extremes of these minerals in water. For example, drinking water low in Mg significantly increases the likelihood of cardiovascular mortality. This knowledge is not properly considered in the drinking water quality regulations, especially as more and more water is now produced by desalination disturbing its natural mineral composition. Although the current EU Drinking Water Directive does not include limits for hardness, Ca or Mg, most member states regulate these parameters either through law (12 countries) or technical guidance (7 countries), and several countries have issued educational information for the public. However, the regulations in most countries are not based on current research and not comparable because some provide a recommended range while others provide mandatory minimum or maximum limit values. This summary of the situation in 28 European Union countries is intended to provide information that can contribute to the implementation of the revised EU Directive.

• Klíčová slova
• Calcium, Drinking water, Magnesium, Regulation, Water hardness,
• MeSH
• Evropská unie * MeSH
• hořčík analýza   MeSH
• lidé MeSH
• pitná voda chemie   MeSH
• vápník analýza   MeSH
• zásobování vodou MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• hořčík MeSH
• pitná voda MeSH
• vápník MeSH