hardness
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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.
- MeSH
- složené pryskyřice * chemie MeSH
- testování materiálů * MeSH
- testy tvrdosti MeSH
- tvrdost * MeSH
- Publikační typ
- časopisecké články MeSH
Peroxidové bělicí přípravky mohou silným oxidačním účinkem působit na dříve zhotovené kompozitní výplně. Cílem práce bylo sledování vlivu bělicích systémů na dlouhodobou stabilitu okrajového uzávěru kompozitních výplní a na odolnost povrchu těchto materiálů. Studie byla provedena standardním testem mikroleakage na výplních V. třídy s okrajem ve sklovině a dentinu. Použity byly dvě skupiny vzorků (každá n=36) připravené s total-etch adhezivním systémem Gluma Comfort Bond a self-etching adhezivem iBond, vždy v kombinaci s mikrohybridním kompozitním materiálem Charisma. Peroxidový bělicí gel Opalescence PF 20 %, s obsahem 20% karbamid peroxidu určený pro domácí bělení, byl na zhotovené výplně (n=12) aplikován 25krát. Kontrolní skupiny po 12 vzorcích byly exponovány v destilované vodě po dobu 24 hodin a 2 měsíců. Změny povrchu kompozitního materiálu (n=5) byly charakterizovány měřením tvrdosti po 0, 2, 7, 14, a 25 aplikacích gelu a porovnávány s kontrolní skupinou (n=5) exponovanou po dobu 2 měsíců v destilované vodě. U vybraných vzorků byla hodnocena morfologie povrchu elektronovou mikroskopií. Po aplikaci peroxidového bělicího gelu nebyly prokázány významné změny okrajového uzávěru. U adheziva Gluma Comfort Bond v důsledku jeho dobrých adhezních schopností, u systému iBond proto, že vlivem jeho snížené adheze ke sklovině docházelo k porušení okrajového uzávěru již na počátku experimentu. Významné projevy degradace byly naopak pozorovány u kompozitního materiálu, kdy po aplikaci bělicího gelu byla nalezena výrazná povrchová porozita spojená s poklesem tvrdosti kompozitu.
Peroxide bleaching systems may affect resin composite restorations through their strong oxidative effect. The objective was to investigate the influence of bleaching systems on long-term stability of marginal integrity of composite restorations and composite surface resistance. Class V cavities were prepared at the enamel-dentine junction and filled using a total-etch adhesive system Gluma Comfort Bond (n=36) and self-etching adhesive iBond (n=36) in combination with the microhybrid resin composite material Charisma. The peroxide bleaching gel Opalescence PF 20% (20 wt. % carbamide peroxide) was applied 25 times on the restorations. The control groups were exposed to distilled water for 24 hours and two months before a microleakage test was performed. Composite hardness was characterized after 0, 2, 7, 14 and 25 applications of the gel and compared with the control group (each n=5) exposed to distilled water for two months. Surface morphology was evaluated using scanning electron microscopy. After the gel application no significant changes in marginal integrity were found for both groups of samples. With Gluma Comfort Bond due to its high bonding performance and with iBond due to its decreased performance on enamel causing marginal integrity failure at the beginning of the experiment. On the other hand, pronounced surface porosity and decreased hardness of the composite material indicated its significant degradation in the presence of the bleaching gel.
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.
- 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 MeSH
- velkoměsta 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.
- 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
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.
