Study on the potential inhibition of root dentine wear adjacent to fluoride-containing restorations

The purpose of this in vitro study was to determine whether the vicinity of root dentine that had been restored with fluoride-releasing materials was at reduced risk for erosive/abrasive wear compared to root dentine restored with a non-fluoride-containing material. According to a randomized complete block design, standardized cavities prepared on the surface of 150 bovine root dentine slabs were restored with glass-ionomer cement, resin-modified glass ionomer, polyacid-modified resin composite, fluoride-containing or conventional composite. Specimens were coated with two layers of an acid-resistant nail varnish exposing half of the dentine surface and half of the restoration. Subsequently, specimens were either eroded in an acidic drink or left uneroded, then exposed to artificial saliva and abraded in a toothbrushing machine. Wear depth in the vicinity of restorations was quantified by a stylus profilometer, based on the nonabraded areas surrounding the erosion/abrasion region. Two-way ANOVA did not demonstrate significant interaction between restoratives and eroded-uneroded dentine (p = 0.5549) nor significant difference among restorative materials (p = 0.8639). Tukey`s test ascertained that the wear depth was higher for eroded than for uneroded groups. Fluoride-releasing materials seemed to negligibly inhibit wear in the vicinity of restored root dentine subjected to erosive/abrasive challenges.

Biofunctionalization of titanium surfaces for dental implants: osteogenic, anti-microbial and tribocorrosion resistant surfaces

PhD thesis in Biomedical Engineering

Impact of filler size and distribution on roughness and wear of composite resin after simulated toothbrushing

Objectives: Nanofilled composite resins are claimed to provide superior mechanical properties compared with microhybrid resins. Thus, the aim of this study was to compare nanofilled with microhybrid composite resins. The null hypothesis was that the size and the distribution of fillers do not influence the mechanical properties of surface roughness and wear after simulated toothbrushing test. Material and methods: Ten rectangular specimens (15 mm x 5 mm x 4 mm) of Filtek Z250 (FZ2), Admira (A), TPH3 (T), Esthet-X (EX), Estelite Sigma (ES), Concept Advanced (C), Grandio (G) and Filtek Z350 (F) were prepared according to manufacturer's instructions. Half of each top surface was protected with nail polish as control surface (not brushed) while the other half was assessed with five random readings using a roughness tester (Ra). Following, the specimens were abraded by simulated toothbrushing with soft toothbrushes and slurry comprised of 2: 1 water and dentifrice (w/w). 100,000 strokes were performed and the brushed surfaces were re-analyzed. Nail polish layers were removed from the specimens so that the roughness (Ra) and the wear could be assessed with three random readings (mu m). Data were analyzed by ANOVA and Tukey's multiple-comparison test (alpha = 0.05). Results: Overall outcomes indicated that composite resins showed a significant increase in roughness after simulated toothbrushing, except for Grandio, which presented a smoother surface. Generally, wear of nanofilled resins was significantly lower compared with microhybrid resins. Conclusions: As restorative materials suffer alterations under mechanical challenges, such as toothbrushing, the use of nanofilled materials seem to be more resistant than microhybrid composite resins, being less prone to be rougher and worn.

Wear and corrosion resistance of pack chromised carbon steel

Pack chromising treatment is an environmentally friendly alternative to hard chromium to form wear and corrosion resistant surface layers. In this work, samples of AISI 1060 steel were pack chromised for 6 and 9 h at 1000 and 1050 degrees C using different activator concentrations. Wear tests were performed in dry conditions and corrosion tests in natural sea water for the pack chromised samples and hard chromium. Pack chromising yielded the formation of layers with high chromium concentrations, high hardness and wear resistance. Increasing activator concentration causes no significant change on the morphology and thickness of the layers. The layers produced at 1050 degrees C yielded only a (Cr,Fe)(2)N1-x phase, and those obtained at 1000 degrees C are composed of a carbide mixture with (Cr,Fe)(2)N1-x. The sample treated at 1050 degrees C for 9 h resulted in an optimum condition by means of better wear resistance and corrosion properties, which were close to that exhibited by the hard chrome, indicating that pack chromising is a promising alternative.

Dynamic analysis using finite elements to calculate the critical wear section of the contact wire in suburban railway overhead conductor rails

The purpose of this study is to determine the critical wear levels of the contact wire of the catenary on metropolitan lines. The study has focussed on the zones of contact wire where localised wear is produced, normally associated with the appearance of electric arcs. To this end, a finite element model has been developed to study the dynamics of pantograph-catenary interaction. The model includes a zone of localised wear and a singularity in the contact wire in order to simulate the worst case scenario from the point of view of stresses. In order to consider the different stages in the wire wear process, different depths and widths of the localised wear zone were defined. The results of the dynamic simulations performed for each stage of wear let the area of the minimum resistant section of the contact wire be determined for which stresses are greater than the allowable stress. The maximum tensile stress reached in the contact wire shows a clear sensitivity to the size of the local wear zone, defined by its width and depth. In this way, if the wear measurements taken with an overhead line recording vehicle are analysed, it will be possible to calculate the potential breakage risk of the wire. A strong dependence of the tensile forces of the contact wire has also been observed. These results will allow priorities to be set for replacing the most critical sections of wire, thereby making maintenance much more efficient. The results obtained show that the wire replacement criteria currently borne in mind have turned out to be appropriate, although in some wear scenarios these criteria could be adjusted even more, and so prolong the life cycle of the contact wire.

Fracture toughness of a series of high chromium abrasion resistant alloys

The fracture properties of a series of alloys containing 15% chromium and 0.8 to 3.4% carbon are investigated using strain fracture toughness testing techniques. The object of the work is to apply a quantitative method of measuring toughness to abrasion resistant materials, which have previously been assessed on an empirical basis; and to examine the relationship between microstructure and K10 in an attempt to improve the toughness of inherently brittle materials. A review of the relevant literature includes discussion of the background to the alloy series under investigation, a survey of the development of fracture mechanics and the emergence of K10 as a toughness parameter. Metallurgical variables such as composition, heat treatment, grain size, and hot working are ???? to relate microstructure to toughness, and fractographic evidence is used to substantiate the findings. The results are applied to a model correlating ductile fracture with plastic strain instability, and the nucleation of voids. Strain induced martensite formation in austenitic structures is analysed in terms of the plastic energy dissipation mechanisms operating at the crack tip. Emphasis is placed on the lower carbon alloys in the series, and a composition put forward to optimise wear resistance and toughness. The properties of established competitive materials are compared to the proposed alloy on a toughness and cost basis.

Resistant Hypertension Revisited: Definition And True Prevalence.

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Adipokines: Novel Players In Resistant Hypertension.

Resistant hypertension (RH) is a multifactorial disease, frequently associated with obesity and characterized by blood pressure above goal (140/90 mm Hg) despite the concurrent use of ≥3 antihypertensive drugs of different classes. The mechanisms of obesity-related hypertension include, among others, aldosterone excess and inflammatory adipokines, which have demonstrated a significant role in the pathogenesis of metabolic syndrome and RH. This review aims to summarize recent studies on the role of the adipokines leptin, resistin, and adiponectin in the pathophysiology of RH and target-organ damage associated with this condition. The deregulation of adipokine levels has been associated with clinical characteristics frequently recognized in RH such as diabetes, hyperactivity of sympathetic and renin-angiotensin-aldosterone systems, and vascular and renal damage. Strategies to regulate adipokines may be promising for the management of RH and some clinical implications must be considered when managing controlled and uncontrolled patients with RH.

Tadalafil-induced Improvement In Left Ventricular Diastolic Function In Resistant Hypertension.

Left ventricular hypertrophy and diastolic dysfunction (LVDD) remain highly frequent markers of cardiac damage and risk of progression to symptomatic heart failure, especially in resistant hypertension (RHTN). We have previously demonstrated that administration of sildenafil in hypertensive rats improves LVDD, restoring phosphodiesterase type 5 (PDE-5) inhibition in cardiac myocytes. We hypothesized that the long-acting PDE-5 inhibitor tadalafil may be clinically useful in improving LVDD in RHTN independently of blood pressure (BP) reduction. A single blinded, placebo-controlled, crossover study enrolled 19 patients with both RHTN and LVDD. Firstly, subjects received tadalafil (20 mg) for 14 days and after a 2-week washout period, they received placebo orally for 14 days. Patients were evaluated by office BP and ambulatory BP monitoring (ABPM), endothelial function (FMD), echocardiography, plasma brain natriuretic peptide (BNP-32), cyclic guanosine monophosphate (cGMP) and nitrite levels. No significant differences were detected in BP measurements. Remarkably, at least four echocardiographic parameters related with diastolic function improved accompanied by decrease in BNP-32 in tadalafil use. Although increasing cGMP, tadalafil did not change endothelial function or nitrites. There were no changes in those parameters after placebo. The current findings suggest that tadalafil improves LV relaxation through direct effects PDE-5-mediated in the cardiomyocytes with potential benefit as an adjunct to treat symptomatic subjects with LVDD such as RHTN patients.

Deregulation Of Adipokines Related To Target Organ Damage On Resistant Hypertension.

Resistant hypertension (RHTN) includes patients with controlled blood pressure (BP) (CRHTN) and uncontrolled BP (UCRHTN). In fact, RHTN patients are more likely to have target organ damage (TOD), and resistin, leptin and adiponectin may affect BP control in these subjects. We assessed the relationship between adipokines levels and arterial stiffness, left ventricular hypertrophy (LVH) and microalbuminuria (MA). This cross-sectional study included CRHTN (n=51) and UCRHTN (n=38) patients for evaluating body mass index, ambulatory blood pressure monitoring, plasma adiponectin, leptin and resistin concentrations, pulse wave velocity (PWV), MA and echocardiography. Leptin and resistin levels were higher in UCRHTN, whereas adiponectin levels were lower in this same subgroup. Similarly, arterial stiffness, LVH and MA were higher in UCRHTN subgroup. Adiponectin levels negatively correlated with PWV (r=-0.42, P<0.01), and MA (r=-0.48, P<0.01) only in UCRHTN. Leptin was positively correlated with PWV (r=0.37, P=0.02) in UCRHTN subgroup, whereas resistin was not correlated with TOD in both subgroups. Adiponectin is associated with arterial stiffness and renal injury in UCRHTN patients, whereas leptin is associated with arterial stiffness in the same subgroup. Taken together, our results showed that those adipokines may contribute to vascular and renal damage in UCRHTN patients.

Increased Arterial Stiffness In Resistant Hypertension Is Associated With Inflammatory Biomarkers.

Increased levels of inflammatory biomarkers such as interleukin-6 (IL-6), 10 (IL-10), 1β (IL-1β), tumor necrosis factor-α (TNF-α) high-sensitivity C-reactive protein (hs-CRP) are associated with arterial stiffness in hypertension. Indeed, resistant hypertension (RHTN) leads to unfavorable prognosis attributed to poor blood pressure (BP) control and target organ damage. This study evaluated the potential impact of inflammatory biomarkers on arterial stiffness in RHTN. In this cross-sectional study, 32 RHTN, 20 mild hypertensive (HTN) and 20 normotensive (NT) patients were subjected to office BP and arterial stiffness measurements assessed by pulse wave velocity (PWV). Inflammatory biomarkers were measured in plasma samples. PWV was increased in RHTN compared with HTN and NT (p < 0.05). TNF-α levels were significantly higher in RHTN and HTN than NT patients. No differences in IL-6 levels were observed. RHTN patients had a higher frequency of subjects with increased levels of IL-10 and IL-1β compared with HTN and NT patients. Finally, IL-1β was independently associated with PWV (p < 0.001; R(2) = 0.5; β = 0.077). RHTN subjects have higher levels of inflammatory cytokines (TNF-α, IL-1β and IL-10) as well as increased arterial stiffness, and detectable IL-1β levels are associated arterial stiffness. These findings suggest that inflammation plays a possible role in the pathophysiology of RHTN.

Prevalence Of Treponema Spp. In Endodontic Retreatment-resistant Periapical Lesions.

This study investigated the presence of the Treponema species in longstanding endodontic retreatment-resistant lesions of teeth with apical periodontitis, the association of this species with clinical/radiographic features, and the association among the different target species. Microbial samples of apical lesions were collected from twenty-five adult patients referred to endodontic surgery after unsuccessful root canal retreatment. Nested-PCR and conventional PCR were used for Treponema detection. Twenty-three periradicular tissue samples showed detectable levels of bacterial DNA. Treponema species were detected in 28% (7/25) of the cases. The most frequently detected species were T. socranskii (6/25), followed by T. maltophilum (3/25), T. amylovorum (3/25), T. lecithinolyticum (3/25), T. denticola (3/25), T. pectinovorum (2/25) and T. medium (2/25). T. vicentii was not detected in any sample. Positive statistical association was found between T. socranskii and T. denticola, and between T. maltophilum and T. lecithinolyticum . No association was detected between the presence of any target microorganism and the clinical or radiographic features. Treponema spp. are present, in a low percentage, in longstanding apical lesions from teeth with endodontic retreatment failure.

Predictors Of Silent Myocardial Ischemia In Resistant Hypertensive Patients.

Hypertension is the most prevalent and significant modifiable risk factor for coronary heart disease. A portion of patients with uncontrolled hypertension are considered to have resistant hypertension (RHTN). Myocardial ischemia incidence increases along with blood pressure (BP) levels. However, the prevalence of myocardial ischemia in patients with RHTN, as well as the factors associated with it, is unknown. We enrolled 129 patients with true RHTN regularly followed in our specialty hypertension clinic and evaluated then by resting and dipyridamole pharmacological stress myocardial perfusion scintigraphy. Patients were then divided into 2 groups: those with (I-RHTN; n = 36) and those without (NI-RHTN; n = 93) myocardial ischemia. Echocardiography, 24-hour ambulatory BP monitoring (ABPM), and flow mediated dilation (FMD) were also evaluated. Thirty six (28%) patients had myocardial ischemia. There was no difference between groups regarding age, sex, biochemical parameters, office, and 24-hour ABPM levels. Patients in the I-RHTN group were more likely diabetic (31% vs. 11%; P < 0.05) and obese (75% vs. 40%; P < 0.001). Adjusting for age and body mass index, multiple logistic regression showed that diabetes (odds ratio (OR) = 6.5; 95% confidence interval (CI) = 1.06-40.14; P = 0.04), FMD (OR = 0.18; 95% CI = 0.07-0.41; P < 0.001), heart rate (OR = 1.23; 95% CI = 1.11-1.36; P < 0.001), left ventricular mass index (OR = 1.02; 95% CI = 1.01-1.04; P = 0.04), and microalbuminuria (OR = 1.02; 95% CI = 1.01-1.04; P = 0.002) were independent predictors of ischemia. In conclusion, there is a high prevalence of myocardial ischemia in patients with RHTN. Increased microalbuminuria, heart rate, endothelial dysfunction, and left ventricular mass can be useful to guide the investigation for myocardial ischemia in these high risk patients.

Jnk And Ikkβ Phosphorylation Is Reduced By Glucocorticoids In Adipose Tissue From Insulin-resistant Rats.

Peripheral insulin resistance (IR) is one of the main side effects caused by glucocorticoid (GC)-based therapies, and the molecular mechanisms of GC-induced IR are not yet fully elucidated. Thus, we aimed to investigate the effects of dexamethasone treatment on the main components of insulin and inflammatory signaling in the adipose tissue of rats. Male Wistar rats received daily injections of dexamethasone (1mg/kg body weight (b.w.), intraperitoneally (i.p.)) for 5 days (DEX), whereas control rats received saline (CTL). The metabolic status was investigated, and the epididymal fat fragments were collected for lipolysis and western blot analyses. The DEX rats became hyperglycemic, hyperinsulinemic, insulin resistant and glucose intolerant, compared with the CTL rats (P<0.05). The basal glycerol release in the fat fragments was 1.5-fold higher in the DEX rats (P<0.05). The phosphorylation of protein kinase B (PKB) at ser(473) decreased by 44%, whereas, the phosphorylation of insulin receptor substrate (IRS)-1 at ser(307) increased by 93% in the adipose tissue of the DEX rats after an oral bolus of glucose (P<0.05). The basal phosphorylation of c-jun-N-terminal kinase (JNK) and inhibitor of nuclear factor kappa-B (IKKβ) proteins was reduced by 46% and 58%, respectively, in the adipose tissue of the DEX rats (P<0.05). This was paralleled with a significant reduction (47%) in the glucocorticoid receptor (GR) protein content in the adipose tissue of the DEX rats (P<0.05). The insulin-resistant status of rats induced by dexamethasone administration have PKB and IRS-1 activity attenuated in epididymal fat without increases in the phosphorylation of the proinflammatory signals JNK and IKKβ.

Effects Of Pde Type 5 Inhibitors On Left Ventricular Diastolic Dysfunction In Resistant Hypertension.

Resistant hypertension (RHTN) is a multifactorial disease characterized by blood pressure (BP) levels above goal (140/90 mmHg) in spite of the concurrent use of three or more antihypertensive drugs of different classes. Moreover, it is well known that RHTN subjects have high prevalence of left ventricular diastolic dysfunction (LVDD), which leads to increased risk of heart failure progression. This review gathers data from studies evaluating the effects of phosphodiesterase-5 (PDE-5) inhibitors (administration of acute sildenafil and short-term tadalafil) on diastolic function, biochemical and hemodynamic parameters in patients with RHTN. Acute study with sildenafil treatment found that inhibition of PDE-5 improved hemodynamic parameters and diastolic relaxation. In addition, short-term study with the use of tadalafil demonstrated improvement of LVDD, cGMP and BNP-32 levels, regardless of BP reduction. No endothelial function changes were observed in the studies. The findings of acute and short-term studies revealed potential therapeutic effects of IPDE-5 drugs on LVDD in RHTN patients.A Hipertensão arterial resistente (HAR) é uma doença multifatorial caracterizada por níveis pressóricos acima das metas (140/90 mmHg), a despeito de tratamento farmacológico otimizado de 3 ou mais fármacos anti-hipertensivos de diferentes classes. Pacientes diagnosticados como hipertensos resistentes apresentam alta prevalência de disfunção diastólica do ventrículo esquerdo (DDVE) que proporciona risco aumentado para insuficiência cardíaca. Esta revisão reúne dados de estudos prévios avaliando os efeitos dos inibidores de fosfodiesterase-5 (PDE-5) (administração aguda de sildenafil e de curto prazo de tadalafil) na função diastólica e nos parâmetros bioquímicos e hemodinâmicos em pacientes com HAR. O estudo agudo com sildenafil demonstrou que a inibição da PDE-5 melhorou os parâmetros hemodinâmicos e de relaxamento diastólico. Além disso, o estudo curto prazo com o uso de tadalafil revelou melhora da DDVE e dos níveis de GMPc e BNP-32, independente de redução de pressão arterial. A função endotelial não apresentou alteração com ambos os tratamentos. Os resultados dos estudos agudo e de curto prazo sugerem efeitos terapêuticos potenciais dos fármacos inibidores da PDE-5 na disfunção diastólica em pacientes com HAR.