Extrinsic causes of erosion. Diet. Chemical factors

pH value, calcium, and phosphate and to a lesser extent fluoride content of a drink or foodstuff are important factors explaining erosive attack. They determine the degree of saturation with respect to tooth minerals, which is the driving force for dissolution. Solutions oversaturated with respect to dental hard tissue will not dissolve it. Addition of calcium (and phosphate) salts to erosive drinks showed protection of surface softening. Today, several Ca-enriched soft drinks are on the market or products with naturally high content in Ca and P are available (such as yoghurt), which do not soften the dental hard tissue. The greater the buffering capacity of the drink or food, the longer it will take for the saliva to neutralize the acid. The buffer capacity of a solution has a distinct effect on the erosive attack when the solution remains adjacent to the tooth surface and is not replaced by saliva. A higher buffer capacity of a drink or foodstuff will enhance the processes of dissolution because more ions from the tooth mineral are needed to render the acid inactive for further demineralization. Further, the amount of drink in the mouth in relation to the amount of saliva present will modify the process of dissolution. There is no clear-cut critical pH for erosion as there is for caries. Even at a low pH, it is possible that other factors are strong enough to prevent erosion.

Multicentre study on peri- and postoperative central venous oxygen saturation in high-risk surgical patients

Introduction Low central venous oxygen saturation (ScvO2) has been associated with increased risk of postoperative complications in high-risk surgery. Whether this association is centre-specific or more generalisable is not known. The aim of this study was to assess the association between peri- and postoperative ScvO2 and outcome in high-risk surgical patients in a multicentre setting. Methods Three large European university hospitals (two in Finland, one in Switzerland) participated. In 60 patients with intra-abdominal surgery lasting more than 90 minutes, the presence of at least two of Shoemaker's criteria, and ASA (American Society of Anesthesiologists) class greater than 2, ScvO2 was determined preoperatively and at two hour intervals during the operation until 12 hours postoperatively. Hospital length of stay (LOS) mortality, and predefined postoperative complications were recorded. Results The age of the patients was 72 ± 10 years (mean ± standard deviation), and simplified acute physiology score (SAPS II) was 32 ± 12. Hospital LOS was 10.5 (8 to 14) days, and 28-day hospital mortality was 10.0%. Preoperative ScvO2 decreased from 77% ± 10% to 70% ± 11% (p < 0.001) immediately after surgery and remained unchanged 12 hours later. A total of 67 postoperative complications were recorded in 32 patients. After multivariate analysis, mean ScvO2 value (odds ratio [OR] 1.23 [95% confidence interval (CI) 1.01 to 1.50], p = 0.037), hospital LOS (OR 0.75 [95% CI 0.59 to 0.94], p = 0.012), and SAPS II (OR 0.90 [95% CI 0.82 to 0.99], p = 0.029) were independently associated with postoperative complications. The optimal value of mean ScvO2 to discriminate between patients who did or did not develop complications was 73% (sensitivity 72%, specificity 61%). Conclusion Low ScvO2 perioperatively is related to increased risk of postoperative complications in high-risk surgery. This warrants trials with goal-directed therapy using ScvO2 as a target in high-risk surgery patients.

Incidence of low central venous oxygen saturation during unplanned admissions in a multidisciplinary intensive care unit: an observational study

INTRODUCTION: It has been shown that early central venous oxygen saturation (ScvO2)-guided optimization of hemodynamics can improve outcome in septic patients. The early ScvO2 profile of other patient groups is unknown. The aim of this study was to characterize unplanned admissions in a multidisciplinary intensive care unit (ICU) with respect to ScvO2 and outcome. METHODS: Ninety-eight consecutive unplanned admissions to a multidisciplinary ICU (median age 63 [range 19 to 83] years, median Simplified Acute Physiology Score [SAPS II] 43 [range 11 to 92]) with a clinical indication for a central venous catheter were included in the study. ScvO2 was assessed at ICU arrival and six hours later but was not used to guide treatment. Length of stay in ICU (LOSICU) and in hospital (LOShospital) and 28-day mortality were recorded. RESULTS: ScvO2 was 70% +/- 12% (mean +/- standard deviation) at admission and 71% +/- 10% six hours later (p = 0.484). Overall 28-day mortality was 18%, LOSICU was 3 (1 to 28) days, and LOShospital was 19 (1 to 28) days. Patients with an ScvO2 of less than 60% at admission had higher mortality than patients with an ScvO2 of more than 60% (29% versus 17%, p < 0.05). Changes in ScvO2 during the first six hours were not predictive of LOSICU, LOShospital, or mortality. CONCLUSION: Low ScvO2 in unplanned admissions and high SAPS II are associated with increased mortality. Standard ICU treatment increased ScvO2 in patients with a low admission ScvO2, but the increase was not associated with LOSICU or LOShospital.

Light curing through glass ceramics with a second- and a third-generation LED curing unit: effect of curing mode on the degree of conversion of dual-curing resin cements

Objectives The aim of this study was to measure the degree of conversion (DC) of five dual-curing resin cements after different curing modes with a second- and a third-generation light-emitting diode (LED) curing unit. Additionally, irradiance of both light curing units was measured at increasing distances and through discs of two glass ceramics for computer-aided design/manufacturing (CAD/CAM). Materials and methods Irradiance and spectra of the Elipar FreeLight 2 (Standard Mode (SM)) and of the VALO light curing unit (High Power Mode (HPM) and Xtra Power Mode (XPM)) were measured with a MARC radiometer. Irradiance was measured at increasing distances (control) and through discs (1.5 to 6 mm thickness) of IPS Empress CAD and IPS e.max CAD. DC of Panavia F2.0, RelyX Unicem 2 Automix, SpeedCEM, BisCem, and BeautiCem SA was measured with an attenuated total reflectance–Fourier transform infrared spectrometer when self-cured (negative control) or light cured in SM for 40 s, HPM for 32 s, or XPM for 18 s. Light curing was performed directly (positive control) or through discs of either 1.5- or 3-mm thickness of IPS Empress CAD or IPS e.max CAD. DC was analysed with Kruskal–Wallis tests followed by pairwise Wilcoxon rank sum tests (α = 0.05). Results Maximum irradiances were 1,545 mW/cm2 (SM), 2,179 mW/cm2 (HPM), and 4,156 mW/cm2 (XPM), and all irradiances decreased by >80 % through discs of 1.5 mm, ≥95 % through 3 mm, and up to >99 % through 6 mm. Generally, self-curing resulted in the lowest DC. For some cements, direct light curing did not result in higher DC compared to when light cured through ceramic discs. For other cements, light curing through ceramic discs of 3 mm generally reduced DC. Conclusions Light curing was favourable for dual-curing cements. Some cements were more susceptible to variations in curing mode than others. Clinical relevance When light curing a given cement, the higher irradiances of the third-generation LED curing unit resulted in similar DC compared to the second-generation one, though at shorter light curing times.

Combined effect of heterogeneity, anisotropy and saturation on steady state flow and transport: Structure recognition and numerical simulation

1 Natural soil profiles may be interpreted as an arrangement of parts which are characterized by properties like hydraulic conductivity and water retention function. These parts form a complicated structure. Characterizing the soil structure is fundamental in subsurface hydrology because it has a crucial influence on flow and transport and defines the patterns of many ecological processes. We applied an image analysis method for recognition and classification of visual soil attributes in order to model flow and transport through a man-made soil profile. Modeled and measured saturation-dependent effective parameters were compared. We found that characterizing and describing conductivity patterns in soils with sharp conductivity contrasts is feasible. Differently, solving flow and transport on the basis of these conductivity maps is difficult and, in general, requires special care for representation of small-scale processes.

Combined effects of heterogeneity, anisotropy, and saturation on steady state flow and transport: A laboratory sand tank experiment

Field soils show rather different spreading behavior at different water saturations, frequently caused by layering of the soil material. We performed tracer experiments in a laboratory sand tank. Such experiments complement and help comprehension of field investigations. We estimated, by image analysis, the first two moments of small plumes traveling through a two-dimensional, heterogeneous medium with strongly anisotropic correlation structure. Three steady state regimes were analyzed. Two main conclusions were drawn. First, low saturation led to very large heterogeneity and to strong preferential flow. Thus the description of the flow paths and the prediction of the solute arrival times require, in this case, more accurate knowledge about the topological structure. Second, saturation-dependent macroscopic anisotropy is an essential element of transport in unsaturated media. For this reason, small structural soil features should be properly upscaled to give appropriate effective soil parameters to be input in transport models.

Third degree atrioventricular block and accelerated idioventricular rhythm associated with a heart base chemodectoma in a syncopal Rottweiler.

A 7-year-old male intact Rottweiler was presented with a 1-week history of lethargy, anorexia, vomiting and multiple syncopal events. The results of the clinical examination and electrocardiography were consistent with a third degree atrioventricular block and an intermittent accelerated idioventricular rhythm. Haematology, serum biochemistry, serology for Borrelia burgdorferi, blood culture, total T4, thoracic radiography and echocardiography did not reveal the cause of the arrhythmia. Response to medical treatment with isoproterenol was poor. Pacemaker placement was declined by the owners and the dog was euthanized at their request. Histopathological examination of the heart revealed a chemodectoma at the base of the heart. There was no neoplastic infiltration of the conduction tissue. Potential mechanisms explaining the association of the arrhythmias and the tumour, such as vagal stimulation and neuroendocrine factors are discussed.

Understanding the chemistry of dental erosion.

Dental erosion is caused by repeated short episodes of exposure to acids. Dental minerals are calcium-deficient, carbonated hydroxyapatites containing impurity ions such as Na(+), Mg(2+) and Cl(-). The rate of dissolution, which is crucial to the progression of erosion, is influenced by solubility and also by other factors. After outlining principles of solubility and acid dissolution, this chapter describes the factors related to the dental tissues on the one hand and to the erosive solution on the other. The impurities in the dental mineral introduce crystal strain and increase solubility, so dentine mineral is more soluble than enamel mineral and both are more soluble than hydroxyapatite. The considerable differences in structure and porosity between dentine and enamel influence interactions of the tissues with acid solutions, so the relative rates of dissolution do not necessarily reflect the respective solubilities. The rate of dissolution is further influenced strongly by physical factors (temperature, flow rate) and chemical factors (degree of saturation, presence of inhibitors, buffering, pH, fluoride). Temperature and flow rate, as determined by the method of consumption of a product, strongly influence erosion in vivo. The net effect of the solution factors determines the overall erosive potential of different products. Prospects for remineralization of erosive lesions are evaluated.