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PubMedDate not supplied

Available bone is the foremost criterion in the insertion of endosteal implants.

The foremost criterion in the insertion of endosteal implants is bone availability. Implant dentists should consider first the amount of available bone of the edentulous ridge where the endosteal implant will be inserted. A common error and cause of many implant failures is the dentist's use of an implant modality which is not indicated for the density and morphology of the available bone in the edentulous ridge. Implant modality/system is not the primary criterion in the insertion of endosteal implants. Before the dentist inserts an endosteal implant, he should gauge or measure the amount of bone where the implant is intended to be placed. It should be measured in width, height, length, trajectory, and implant-crown ratio. After recording the measurements of the available bone, these should be placed in different categories to serve as guides in implant selection. If there is not enough bone for the endosteal implant, bone modification should be performed. This can be done either by osteoplasty or ridge augmentation with the use of bone grafting materials. Aside from the amount of available bone in the edentulous ridge, another very, very important thing that should be considered is the quality or its density. Any biocompatible implant demonstrates some osseointegrated surfaces depending upon the bone type into which it is placed and the loads placed upon it. Implant body must exhibit a macrogeometry suitable for acceptable levels of force transfer to the surrounding tissues as well as for implantation into a bony site of a particular anatomic size.

Adult↗

PubMed1998

Evaluation of in vivo models for studying calcification behavior of commercially available bovine pericardium.

BACKGROUND AND AIM OF THE STUDY: A common frame of reference is essential when attempting to determine if new treatments intended to reduce calcification of bioprostheses are superior to existing processes and products. The aim of this study was to examine calcification behavior for a commercially available pericardial bioprosthesis in subcutaneous and sheep valve models, and to evaluate the importance of appropriate control treatments in comparative studies with proposed new treatments. METHODS: Samples of bovine pericardium were placed subcutaneously under the dorsal skin of weanling rats and juvenile rabbits for 30-, 60- and 90-day intervals. Samples were either commercially available pericardial tissue or tissue processed with phosphate-buffered glutaraldehyde alone. Commercially available pericardial valves were also implanted in the mitral position in juvenile sheep, with elective sacrifice at 20 weeks. Retrieved samples underwent X-ray, histologic and elemental analysis. RESULTS: Commercial samples retrieved from the subcutaneous and sheep models showed similar, minimal calcification behavior on X-ray and histologic slides, whereas pericardium exposed to glutaraldehyde alone demonstrated rapid calcification. CONCLUSIONS: The 90-day subcutaneous rabbit model produced patterns of calcification similar to those in valves explanted from juvenile sheep after 20 weeks. A statistically significant decrease (p < 10(-8)) in calcification was demonstrated for clinical pericardium when compared with pericardium exposed to glutaraldehyde alone in the subcutaneous model. This suggests that subcutaneous models may be a cost-effective, time-efficient means of evaluating and comparing various tissue treatment methods. The rabbit methodology may provide a more accurate prediction of clinical performance, offering a greater degree of sensitivity. These studies also indicate that the commercially available process shows minimal calcification in the commonly used 30-day weanling rat subcutaneous model, contradicting other reported studies that may not accurately represent commercially available processes.

Animals↗

PubMed1998

Beclomethasone relative availability of oral versus inhaled beclomethasone dipropionate from an HFA-134A metered dose inhaler.

3M has formulated a new chlorofluorocarbon-free (CFC-free) beclomethasone dipropionate (BDP) metered-dose inhaler (MDI) with the use of the propellant HFA-134a (HFA). Lung deposition studies demonstrated that the HFA BDP MDI delivers to the lungs approximately 56% of the BDP dose (ex-adaptor), a substantially higher percentage than the 5-30% delivered by conventional CFC BDP MDIs. As new sensitive bioanalytical methods are becoming available to quantitate systemic levels of inhaled corticosteroids, pharmacokinetic evaluations are emerging as sensitive and reproducible methods that can be used as a complement to the data obtained from lung deposition studies to assess and compare the performance of MDIs. The present study was designed to determine the beclomethasone (BOH) availability of oral BDP relative to inhaled HFA BDP as a first step to alloy MDI product comparisons in the future. Forty mild asthmatic patients completed this open-label, randomized, single-dose, two-period crossover study. Each patient received an oral dose of BDP (0.2, 0.5, 1, 2 or 5 mg) in one period and an inhaled dose of BDP (0.2 or 0.8 mg) in the other period, with four patients allocated to each of ten different treatment sequences. The BOH availability of orally administered BDP was approximately 40% relative to inhaled HFA BDP. In addition, the fraction of an oral dose that reaches the systemic circulation was estimated from the 40% relative availability and previous lung deposition data to be 0.26. These estimated pharmacokinetic parameters will be used in the future to further characterize the pharmacokinetics of inhaled BDP and to compare the performance of different MDI products.

Administration, Inhalation↗

PubMed1988

Estimating reduced availability due to first pass elimination from relative total clearance and renal clearance.

A simple formula is presented for estimating the systemic availability of an orally administered drug from the relative total clearance (oral clearance) when renal clearance forms an important part of total clearance. Hepatic plasma flow is used in the equation and is represented by an average value taken from the literature. The formula is applied to data for cimetidine discussed in the literature. A further application is demonstrated for a drug under development for which an intravenous formulation was not available. It is possible to estimate the upper and lower limit of availability if some information on the amount of drug absorbed is available.

Administration, Oral↗

PubMed2003

Responses of soil nitrogen dynamics in a Mojave Desert ecosystem to manipulations in soil carbon and nitrogen availability.

We investigated the effects of changes in soil C and N availability on N mineralization, nitrification, denitrification, NH(3) volatilization, and soil respiration in the Mojave Desert. Results indicate a C limitation to microbial N cycling. Soils from underneath the canopies of Larrea tridentata (DC.) Cov., Pleuraphis rigida Thurber, and Lycium spp. exhibited higher rates of CO(2 ) flux, lower rates of NH(3) volatilization, and a decrease in inorganic N (NH(4)(+)-N and NO(3)(-)-N) with C addition. In addition to C limitation, soils from plant interspaces also exhibited a N limitation. Soils from all locations had net immobilization of N over the course of a 15-day laboratory incubation. However, soils from interspaces had lower rates of net nitrification and potential denitrification compared to soils from under plant canopies. The response to changes in C availability appears to be a short-term increase in microbial immobilization of inorganic N. Under controlled conditions, and over a longer time period, the effects of C and N availability appear to give way to larger differences due to spatial location. These findings have implications for ecosystems undergoing changes in soil C and N availability due to such processes as desertification, exotic species invasions, or elevated atmospheric CO(2) concentration.

Ammonia↗

PubMed2006

Copper availability and accumulation by Portulaca oleracea Linn. stem cutting.

The Cu accumulation capacity of stem cuttings of Portulaca oleracea was assessed in two different soils, alfisol and vertisol, which differ from each other mainly due to their clay content - several fold lower in the former than in the latter. The DTPA extractable concentration of Cu in soil and the level of its accumulation in stem cuttings were, therefore, greater in alfisol than in vertisol. In the mixed soils, the DTPA extractable as well as plant accumulated levels of Cu decreased with an increase in the proportion of vertisol. With an increase in the soil available and plant accumulated Cu, a decrease has been observed in the ability of stem cuttings to regenerate leaves and roots. As a consequence biomass reduction has been observed with an increase in the concentration of Cu in the soil and plant body. In view of comparatively low availability of Cu in vertisol, regeneration of stem cuttings occurred up to a concentration of 1600 microg of Cu/g of soil, whereas in alfisol it occurred only up to 200 microg of Cu/g of soil. The results of the present study showed that P. oleracea stem cutting is an accumulator of Cu and the availability of Cu in soils could be manipulated through addition of clay since the plant available concentration of Cu is less in the soil (vertisol) with high clay content.

Biological Availability↗

PubMed2005

Metabolism of chlorpyrifos in relation to its effect on the availability of some plant nutrients in soil.

A laboratory experiment was conducted to study the persistence and metabolism of chlorpyrifos in Gangetic Alluvial soil of West Bengal and also to evaluate their effect on the availability of the major plant nutrients (N, P and K) in soil following the application of chlorpyrifos @ 1 kg (T1), 10 kg (T2) and 100 kg (T3) a.i.ha(-1). The dissipation followed first order kinetics and the calculated half-life (T1/2) values ranged from 20 to 37 days. The primary metabolite of chlorpyrifos, 3,5,6-trichloropyridinol (TCP) was detected from 3rd day after application and was at maximum on 30th day which decreased progressively to non-detectable level (NDL) on 120th day for all the treatment doses. The secondary metabolite 3,5,6-trichloro-2-methoxy pyridine (TMP) was detected on 30th, 15th and 7th day in T1, T2 and T3 doses respectively which decreased to NDL during 90-120th day. ANOVA study revealed significant decrease in the available N and P content in soil treated with chlorpyrifos in comparison to the control set. The inhibitory effect on available N was attributable to TMP and for P it was due to the presence of TCP and TMP rather than chlorpyrifos itself as revealed by the step wise multiple regression technique. In the later stage of incubation, however the average N and P status was recovered significantly at 120 days which might be due to the disappearance of the metabolites. The variation due to time of observations or treatment doses was minimum in case of available K in soil.

Biological Availability↗

PubMed1991

Extent of damage to amino acid availability of whey protein heated with sugar.

The effect of heat treatments, at various water activities (aW), on digestibility and on the availabilities of amino acids of whey protein samples in the presence of lactose was estimated by an in vitro digestion method with continuous dialysis. Four aW (0.3, 0.5, 0.7 and 0.97), three temperatures (75, 100 and 121 degrees C) and three heating periods (50, 500 and 5000 s) were selected. The initial lysine:lactose molar ratio was 1:1. Amino acid profiles showed that excessive heating of whey (121 degrees C, 5000 s) destroyed a significant proportion of cystine at all aW, lysine at aW 0.3, 0.5 and 0.7, and arginine at aW 0.5 and 0.7. At aW 0.3, 0.5 and 0.7, protein digestibility decreased (P less than 0.05) as the temperature increased from 75 to 121 degrees C for a heating period of 5000 s, and as the heating time was prolonged, from 500 to 5000 s at 121 degrees C. Excessive heating also decreased (P less than 0.05) the availabilities of all amino acids at aW 0.3, 0.5 and 0.7. The availabilities of lysine, proline, aspartic acid, glutamic acid, threonine, alanine, glycine and serine were particularly affected. Severe heating at aW 0.97 did not seem to favour the Maillard reaction, but the availabilities of cystine, tyrosine and arginine were decreased, probably as a result of structural modifications of the protein upon heating. Heating whey protein concentrates in the presence of lactose not only affected lysine, but also impaired enzymic liberation of other amino acids, according to the severity of heat treatments and aW.

Amino Acids↗

PubMed2004

Oxalate reduces calcium availability in the pads of the prickly pear cactus through formation of calcium oxalate crystals.

The pads (nopales) of the prickly pear cactus are considered to be a good source of minerals and other nutrients on the basis of compositional analysis. In this study, this analysis is taken a step further by assessing the availability of selected minerals in nopales using an in vitro digestion and dialysis method. The results obtained suggest that although nopales are enriched in a number of minerals, their tissue calcium is not freely available. Microscopic analysis, energy-dispersive X-ray microanalysis, and oxalate measurements suggest that this reduction in available calcium is a result of its sequestration in the form of calcium oxalate crystals. The issue of mineral availability in plant foods is important when the dependence of many populations around the world on plant foods as their main source of minerals and other nutrients is considered.

Biological Availability↗

PubMed2000

Investigation of an in vitro model for predicting the effect of food components on calcium availability from meals.

The availability of calcium from semi-synthetic meals and model food systems was studied by an in vitro method using equilibrium dialysis after simulating gastric digestion. Twelve different food components (phytate, oxalate, wheat fibre- and barley fibre-extract, D-sorbitol, xylitol, galactitol, casein, three different casein phosphopeptide preparations, and lactose) were added to the semi-synthetic meal and their effect on the relative index of availability of 45Ca was studied. Phytate, oxalate, wheat fibre-extract and barley fibre-extract, and, surprisingly, casein had a negative effect on availability of calcium. The most pronounced effect was observed for the addition of phytate. The other dietary factors had no effect on calcium availability. Therefore, this rapid and inexpensive in vitro model could be a useful screening method for factors affecting calcium absorption, especially inhibitory factors, in future human calcium bioavailability studies.

Biological Availability↗

PubMed1992

The effect of dairy products on iron availability.

Many researchers report substantial reductions in iron availability when dairy products are consumed with solutions of iron. Yet other studies indicate that dairy products have little effect on iron availability when added to complex meals. The conflicting data may be due to differences in the technique used to measure availability, species of animal used, form of iron in the diet, and meal composition. Human studies show superior bioavailability of iron in human milk when compared with cow's milk. Definitive causes for the differences between human and cow's milk have not been identified. Human milk contains lower amounts of casein, phosphate, and calcium, components thought to inhibit iron absorption. More work is needed to identify the factors that influence iron-dairy interactions. The nutritional benefits provided by dairy products outweigh the slight inhibitory effect they may have on iron availability.

Animals↗

PubMed2003

Plant availability of heavy metals and phosphorus in the agricultural reuse of biological sludges.

Concerns about the agricultural use of sludges are usually associated with heavy metals. In this study, plant-availabilities of heavy metals and phosphorus (P) in different P amendments were investigated. The dewatered sludge from Paşaköy Biological Nutrient (N, P) Removal (BNR) Plant in Istanbul, a chemical fertilizer (Triple Superphosphate), and a P-deficient, alkaline soil were used in pot experiments. Unstabilized sludge (S), lime-stabilized sludge (LS), and triple superphosphate (TSP) were applied to pots in a manner to supply 0, 100, 200, 300, 400 ppm P. Lollium Perenne was grown on these soils to compare P and heavy metal (Cu. Ni, Zn) availabilities in terms of plant uptake. The results of plant analyses showed that P-recycling through the agricultural use of biological nutrient removal (BNR) sludges was possible. Plant availability of heavy metals in sludge amended soil samples was comparable with those in control samples (soil only) and chemical fertilizer amended samples. Lime stabilization reduced the plant-availability of P and heavy metals. The choice of lime stabilization must depend on the specific soil to be amended.

Agriculture↗

PubMed2006

Availability, fermentability, and energy value of resistant maltodextrin: modeling of short-term indirect calorimetric measurements in healthy adults.

BACKGROUND: Determination of the metabolizable (ME) and net metabolizable (NME) energy of total carbohydrate requires estimation of its available (AC) and fermentable (FC) carbohydrate content. Modeling of indirect calorimetric observations (respiratory gas exchange) and breath hydrogen would appear to make it possible to estimate noninvasively these nutritional quantities and the approximate time-course of availability. OBJECTIVE: We assessed the time-course of metabolism and energy availability from resistant maltodextrin (RMD) by modeling of respiratory gases after a single oral dose. DESIGN: Seventeen healthy adults (13 M, 4 F; aged 25-46 y) were randomly assigned to treatments (water, maltodextrin, or RMD) in a multiple-crossover, single-blinded trial with > or = 7 d washout. We monitored 8-h nitrogen-corrected oxygen and carbon dioxide exchanges and breath hydrogen. All treatment groups took low-carbohydrate meals at 3 and 6 h. RESULTS: Indirect calorimetry alone provided only qualitative information about the nutritional values of carbohydrate. In contrast, modeling of gaseous exchanges along with the use of central assumptions showed that 17 +/- 2% of RMD was AC and 40 +/- 4% was FC. As compared with 17 kJ gross energy/g RMD, mean (+/- SE) energy values were 7.3 +/- 0.6 kJ ME/g and 6.3 +/- 0.5 kJ NME/g. The fiber fraction of RMD provided 5.2 +/- 0.7 kJ ME/g and 4.1 +/- 0.6 kJ NME/g. CONCLUSIONS: Modeling with the use of this noninvasive and widely available respiratory gas-monitoring technique yields nutritional values for carbohydrate that are supported by enzymatic, microbial, and animal studies and human fecal collection studies. Improvement in this approach is likely and testable across laboratories.

Adult↗

PubMed1981

Biological rat assay for total fluoride availability in foods.

A fluoride (F) bioassay procedure based on the method of standard additions and using weanling rats was designed and tested. Rats were distributed between a control (C) group fed MIT 200 diet (F conc. less than 0.5 ppm) and an experimental (E) group fed this diet plus 1% dehydrated instant tea used as a model test food. Both groups were further divided into subgroups fed the C or E diets, but supplemented with 0.5, 10, 20 or 40 ppm F as NaF, and offered deionized water for a period of 10 days. Rats were then killed and femur (fm) and tibia (tb) dissected. Bone samples were treated in a closed system with HCl (6 N) and later with sodium citrate (30%) to determine F concentration using a specific ion electrode. F values (y) for fm and tb were plotted against F amounts added to the diets (xt). Weighted regression equations describing the linear relationship between the two variables were used to calculate the available F content of dehydrated tea which was 830 +/- 43 ppm F (using fm data) and 836 +/- 67 ppm (using tb data). Chemical assay of the dehydrated tea used as a test food gave a F concentration of 887 +/- 16 or 93.5 +/- 5.1% availability. This rat bioassay to determine total available fluoride in a dried food can be combined with a chemical assay to obtain a measure of percent availability of F.

Animals↗

PubMed1997

Evaluation of the potential for olestra to affect the availability of dietary phytochemicals.

It has been hypothesized that phytochemicals found in fruits and vegetables are responsible for the inverse association observed between diets high in fruits and vegetables and risk of certain chronic diseases and cancer. This paper assesses the potential for olestra to affect the absorption of dietary phytochemicals and estimates the effect of olestra on the availability of carotenoids when olestra-containing snacks and foods containing carotenoids are eaten in free-living diets. Experimental data compiled on the effects of olestra on the availability of 29 compounds, mainly nutrients and oral medications, showed that olestra affects the availability of only molecules having octanol-water partition coefficients greater than approximately 7.5. Partition coefficients compiled for 382 dietary phytochemicals showed that only two classes of phytochemicals, phytosterols and carotenoids, contain molecules with octanol-water partition coefficients in the range in which olestra could potentially affect bioavailability. The potential effect on the bioavailability of phytosterols would be <10% and would not be expected to be of concern inasmuch as the hypothesized benefit of consuming pharmacological amounts of phytosterols is to reduce cholesterol availability, a function also of olestra. A 5.9% reduction in the average effective beta-carotene intake was calculated for individuals eating olestra-containing snack foods in free-living diets. The calculation was made by assuming that carotenoid bioavailability would be reduced to the extent measured in human clinical studies each time olestra-containing snacks and carotenoid-containing foods are eaten together and that all snacks eaten are made with olestra. Among individuals with low carotenoid intakes (the lowest 10%) the calculated reduction was 6.0%; for heavy snack eaters (the top 10%) it was 9.5%. These effects on carotenoid bioavailability are similar to those that can occur with other dietary factors.

Adolescent↗

PubMed1997

A new method for determining the availability of choline in soybean meal.

Studies were conducted to evaluate the availability of choline in soybean meal, using a new approach: The basal diet contained soybean meal with a lowered choline content (partially extracted with methanol). Choline was added to the basal diet 1) by substituting intact soybean meal for the methanol washed soybean meal; or 2) from crystalline choline Cl. Four experiments were conducted with day-old male broilers housed in battery brooders and fed the experimental diets from 4 to 18 d posthatching. The basal diet contained corn, soybean meal, and isolated soy protein in Experiments 1 to 3, and also glucose in Experiment 4. In Experiment 1, chicks fed the basal diet (1,140 mg/kg choline, 0.61% sulfur amino acids) had a growth response to 1,000 mg/kg choline or 0.10% methionine (P < 0.05), but not to 0.10% cysteine (P > 0.05) supplementation. Supplementation of choline (0, 50, 100, 200, 400, 800, and 1,200 mg/kg) to the basal diet (1,230 mg/kg choline) in Experiment 2 resulted in a linear increase in growth up to 122 +/- 22 mg/kg supplemental choline (1,352 +/- 22 mg/kg total choline), reaching a plateau after that. In the slope ratio assays to determine choline availability, the basal diets in Experiments 3 (1,098 mg/kg choline) and 4 (920 mg/kg choline) were supplemented with either 50 or 100 mg/ kg choline (from choline Cl) or had approximately 50 or 100 mg/kg choline added with intact soybean meal (at the expense of washed soybean meal). There were significant linear responses of weight gain vs choline intake from either source (P < 0.001). The availability of choline in soybean meal was calculated to be 97 and 105% in Experiments 3 and 4, respectively. These results indicate that choline availability in soybean meal is close to 100%.

Animals↗

PubMed1998

Relative biologic availability and pharmacokinetics of albuterol preparations in healthy Chinese.

The authors' goal was to study the biologic availability and pharmacokinetics of two different formulations of controlled-release (CR) tablets of albuterol. A two-way, cross-over biologic availability study was performed with 20 healthy male volunteers to evaluate the relative biologic availability of two CR tablets of albuterol versus two different formulations of immediate-release (IR) albuterol tablets. Albuterol concentrations in plasma were measured using an HPLC procedure. Each patient subject received a 4.8-mg CR tablet every 12 hours for 6 days and a 4.8-mg IR tablet every 8 hours for 6 days. Tests of single doses and steady state were assayed for CR and IR albuterol tablets. The mean Cmax and tmax for two CR tablets given after a single dose were 7.3+/-1.5, 7.9+/-1.4 microg x L(-1) and 4.6+/-0.8, 4.8+/-0.5 hours, respectively. The Cmax and tmax for two IR tablets given after a single dose were 12.5-/+1.3, 15.3 +/-2.3 microg x L(-1) and 1.3+/-0.4, 1.6+/-0.4 hours, respectively. The relative biologic availability of two CR albuterol tablets were 106.0+/-6.2% and 109.8+/-9.0%, respectively. Administration of CR albuterol twice a day provides an alternative to administration of IR albuterol three or four times a day.

Adult↗

PubMed1999

Grapefruit juice decreases the systemic availability of itraconazole capsules in healthy volunteers.

The systemic availability of itraconazole capsules may be reduced secondary to elevated gastric pH and possibly by presystemic intestinal metabolism via CYP3A4. Grapefruit juice is acidic and an inhibitor of intestinal CYP3A4. To determine the effect of grapefruit juice on the systemic availability of itraconazole capsules, serum itraconazole and hydroxy-itraconazole concentrations were determined in eleven healthy volunteers studied in a randomized, two-way crossover design. Concurrent grapefruit juice resulted in a 43% decrease in the mean itraconazole AUC0-48 (2507 ng x hr/mL versus 1434 ng x hr/mL, p = 0.046) and a 47% decrease in the mean hydroxy-itraconazole AUC0-72 (7264 ng x hr/mL versus 3880 ng x hr/mL, p = 0.025). Grapefruit juice also significantly increased the mean itraconazole Tmax (5.5 versus 4 hours). We conclude that concomitant grapefruit juice does not enhance the systemic availability of itraconazole capsules, but rather appears to impair itraconazole absorption. Therefore, concomitant grapefruit juice will not likely be useful in improving the oral availability of itraconazole capsules.

Adult↗