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PubMed2005

Does the size of the vaginal probe affect measurement of pelvic floor muscle strength?

BACKGROUND: The most commonly used method to measure pelvic floor muscle (PFM) strength is vaginal squeeze pressure. There are, however, several apparatuses available for this purpose, and sizes of the probes differ significantly. The aim of the present investigation was to assess whether the size of two commonly used vaginal probes influences measurement of PFM strength. METHODS: Twenty female physical therapy students, mean age 25.1 years (range 21-38), participated in the study. All were able to contract the PFM, as assessed by means of vaginal palpation and observation of inward movement of the perineum. Two measuring devices with different lengths and diameters, the Peritron and the Camtech, were used in order to assess vaginal squeeze pressure. Each woman performed six contractions with each apparatus. RESULTS: Mean maximum squeeze pressure for the whole group with the Camtech was 19.7 cm H(2)O (95% CI: 16.5-22.9) and with the Peritron 36.5 cm H(2)O (95% CI: 31.7-41.3), P < 0.01. Nine women preferred the Camtech, four preferred the Peritron, and seven did not have any specific preferences. CONCLUSIONS: Measurements of vaginal squeeze pressure differ depending on the vaginal probe used. Results from published studies using various probes should, therefore, not be compared or combined in systematic reviews or meta-analysis.

Adult↗
PubMedDate not supplied

Rapid prototyping of tissue-engineering constructs, using photopolymerizable hydrogels and stereolithography.

One of the most important aspects of tissue engineering is the design of the scaffold providing the mechanical strength and access to nutrients for the new tissue. For customized tissue engineering, it is essential to be able to fabricate three-dimensional scaffolds of various geometric shapes, in order to repair defects caused by accidents, surgery, or birth. Rapid prototyping or solid free-form fabrication (SFF) techniques hold great promise for designing three-dimensional customized scaffolds, yet traditional cell-seeding techniques may not provide enough cell mass for larger constructs. This article presents a novel attempt to fabricate three-dimensional scaffolds, using hydrogels combined with cell encapsulation to fabricate high-density tissue constructs. A commercially available stereolithography technique was applied to fabricate scaffolds using poly(ethylene oxide) and poly(ethylene glycol)dimethacrylate photopolymerizable hydrogels. Mechanical characterization shows the constructs to be comparable with soft tissues in terms of elasticity. High cell viability was achieved and high-density constructs fabricated.

Animals↗
PubMed2005

Hydraulic strengthening affects the stiffness and strength of cortical bone.

A nonlinear, interstitial fluid flow constitutive model for cortical bone was developed to study the strain-rate dependency of cortical bone apparent modulus (Ea). Nine representative volume element (RVE) structural models of cortical bone spanning an effective pore volume fraction P range of 1-40% were examined. Dynamic loading conditions were used to study the fluid flow contribution or hydraulic strengthening (HS) effect on Ea for each RVE model. The model indicated that there is an upper and lower asymptotic bound of strain-rate (10(+/-3) sec(-1)) above or below which there are no further HS effects on Ea. At certain strain-rates (10(-1) to 10(0) sec(-1)) variations in cortical bone porosity had little or no influence on Ea. At lower and higher frequencies, the loss tangent, hence the magnitude of viscoelastic effects is greater. For strain-rates less than 10(-1) sec(-1), lower porosity RVE models were always stiffer than higher porosity RVE models. A generalized power law model is proposed to account for the fact that HS in cortical bone exhibits an upper and lower asymptotic bound and is bi-modal in terms of strain-rate.

Animals↗
PubMed2003

Electrical and dielectric properties of bovine trabecular bone--relationships with mechanical properties and mineral density.

Interrelationships of trabecular bone electrical and dielectric properties with mechanical characteristics and density are poorly known. While electrical stimulation is used for healing fractures, better understanding of these relations has clinical importance. Furthermore, earlier studies have suggested that bone electrical and dielectric properties depend on the bone density and could, therefore, be used to predict bone strength. To clarify these issues, volumetric bone mineral density (BMDvol), electrical and dielectric as well as mechanical properties were determined from 40 cylindrical plugs of bovine trabecular bone. Phase angle, relative permittivity, loss factor and conductivity of wet bovine trabecular bone were correlated with Young's modulus, yield stress, ultimate strength, resilience and BMDvol. The reproducibility of in vitro electrical and dielectric measurements was excellent (standardized coefficient of variation less than 1%, for all parameters), especially at frequencies higher than 1 kHz. Correlations of electrical and dielectric parameters with the bone mechanical properties or density were frequency-dependent. The relative permittivity showed the strongest linear correlations with mechanical parameters (r > 0.547, p < 0.01, n = 40, at 50 kHz) and with BMDvol (r = 0.866, p < 0.01, n = 40, at 50 kHz). In general, linear correlations between relative permittivity and mechanical properties or BMDvol were highest at frequencies over 6 kHz. In addition, a significant site-dependent variation of electrical and dielectric characteristics, mechanical properties and BMDvol was revealed in bovine femur (p < 0.05, Kruskall-Wallis H-test). Based on the present results, we conclude that the measurement of electrical and dielectric properties provides quantitative information that is related to bone quantity and quality.

Animals↗
PubMed2005

Beneficial effect of copper supplementation on deposition of fluoride in bone in fluoride- and molybdenum-fed rabbits.

Fluorosis is a major public health problem in the world, including India. The present study was undertaken to investigate the role of molybdenum (Mo) in the deposition of fluoride (F) in bone and whether copper (Cu) supplementation has any alleviating role when F and Mo are ingested together. For this purpose, four groups of rabbits were used [control (C), fluoride (F), fluoride + molybdenum (F + Mo), and fluoride + molybdenum + copper (F + Mo + Cu)] to find out the effect of these treatments on various bone-related parameters like intact parathyroid hormone (iPTH), alkaline phosphatase and Cu in serum, hydroxyproline and calcium (Ca) in urine, and minerals (F, Cu, manganese, and zinc) in femur bone ash. Bone mineral content (BMC), bone mineral density (BMD) [by dual energy X-ray absorptiometry (DXA)], and strength of femur bones were also assessed. F content in the femur was significantly higher (P < 0.01) in all experimental groups compared to control group. Mo supplementation increased F deposition in femur bone in the F + Mo group, whereas supplementation of Cu reduced F deposition in the F + Mo + Cu group compared to the F + Mo and F groups. Levels of Cu in femurs of the F + Mo and F + Mo + Cu groups were significantly higher (P < 0.05, P < 0.01, respectively) than in the C group, although serum Cu was significantly lower in the F and F + Mo than the C and F + Mo + Cu groups. Magnesium levels in the F + Mo group were significantly higher (P < 0.05) than in the F and F + Mo + Cu groups. Cu supplementation in the F + Mo + Cu group increased deposition of zinc significantly (P < 0.05) compared to the F and F + Mo groups. Serum iPTH, alkaline phosphatase, and urinary hydroxyproline and Ca were significantly higher (P < 0.01) in the F and F + Mo than in the C and F + Mo + Cu groups. However, serum iPTH and urinary hydroxyproline were higher in the F + Mo group than the F group. Alkaline phosphatase was significantly higher in the F + Mo group than the F and F + Mo + Cu groups. Levels of serum Cu in the F and F + Mo groups were lower than in the C group, though serum Cu was significantly higher in the F + Mo + Cu than in all other groups. DXA analysis of femur bone indicated that BMD in the F + Mo group was significantly higher than in the F (P < 0.05), C (P < 0.01), and F + Mo + Cu (P < 0.05) groups. However, there was no significant difference in BMC among the groups. Bone strength was significantly higher (P < 0.05) in the F + Mo group than in the C group. Results of the present study show that ingestion of Mo with F does not create secondary Cu deficiency (due to increased excretion of Cu through urine). However, Cu concentration was decreased in serum in this group (F + Mo) compared to the C and F + Mo + Cu groups. Deposition of F in femur bone was more (22%) when it was given along with Mo compared to F alone, while F deposition in femur bone was less in the F + Mo + Cu group by 80% compared to the F group. Also, deposition of F in the F + Mo + Cu group was 120% less compared to the F + Mo group. The increase in F level due to Mo addition appears to be offset by supplementation with Cu. Supplementation with Cu showed a beneficial effect on bone resorption as well as bone formation.

Alkaline Phosphatase↗
PubMed2006

Utilization of municipal solid waste incineration (MSWI) fly ash in blended cement Part 2. Mechanical strength of mortars and environmental impact.

This second of two articles dealing with the utilization of MSWI fly ash in blended cement studies the effects of two variants of the stabilization process on the behavior of the treated fly ash (TFA) introduced into cement-based mortars. From a technological point of view, the modifications of the process are very efficient and eliminate the swelling produced by the introduction of MSWI fly ash in cement-based mortars. TFA has a significant activity in cement-based mortars and can also advantageously replace a part of the cement in cement-based material. From an environmental point of view, the results of traditional leaching tests on monolithic and crushed mortars highlight a poor stabilization of some harmful elements such as antimony and chromium. The use of a cement rich in ground granulated blast furnace slag (GGBFS) with a view to stabilizing the chromium is not efficient. Since neither adequate tests nor quality criteria exist to evaluate the pollutant potential of a waste with a view to reusing it, it is difficult to conclude on the environmental soundness of such a practice. Further experiments are necessary to investigate the environmental impact of TFA introduced in cement-based mortars depending on the reuse scenario.

Carbon↗
PubMed2003

Morphological determinants of femoral strength in growth hormone-deficient transgenic growth-retarded (Tgr) rats.

UNLABELLED: The extent to which childhood GHD affects adult fracture risk is unclear. We measured femoral strength in adult transgenic growth-retarded rats as a model of GHD. Long-term, moderate GHD was accompanied by endocrine and morphometric changes consistent with a significant reduction in femoral strength. INTRODUCTION: Childhood growth hormone deficiency (GHD) is associated with osteopenia, but little is known about its effects on subsequent adult bone strength and fracture risk. MATERIALS AND METHODS: We have therefore measured femoral strength (failure load measured by three-point bending) in a new model of moderate GHD, the transgenic growth-retarded (Tgr) rat at 15, 22-23, and 52 weeks of age, and have quantified potential morphological and endocrine determinants of bone strength. RESULTS: Skeletal growth retardation in Tgr rats was accompanied by a sustained reduction in the anterior-posterior diameter of the femoral cortex, whereas mid-diaphyseal cortical wall thicknesses were largely unaltered. Total femoral strength was significantly impaired in Tgr rats (p < 0.01), and this impairment was more pronounced in males than females. Compromised bone strength in Tgr rats could not be accounted for by the reduction in mechanical load (body weight) and was not caused by impairment of the material properties of the calcified tissue (ultimate tensile stress), despite marked reductions in femoral mineral density (areal bone mineral density; p < 0.001). Microcomputerized tomographical analysis revealed significant modification of the architecture of trabecular bone in Tgr rats, with reductions in the number and thickness of trabeculae (p < 0.05) and in the degree of anisotropy (p < 0.01). The marked reduction in plasma insulin-like growth factor-1 in Tgr rats was accompanied by the development of high circulating leptin levels (p < 0.01). CONCLUSION: These results show that the changes in endocrinology and bone morphology associated with long-term moderate GHD in Tgr rats are accompanied by changes consistent with a significant reduction in the threshold for femoral fracture.

Age Factors↗
PubMed2004

Design of biomimetic fibrillar interfaces: 2. Mechanics of enhanced adhesion.

This study addresses the strength and toughness of generic fibrillar structures. We show that the stress sigmac required to pull a fibril out of adhesive contact with a substrate has the form sigma(c) = sigma(0)Phi(chi). In this equation, sigma(0) is the interfacial strength, Phi(chi) is a dimensionless function satisfying 0 > 1, but is flaw insensitive for chi < 1. The important parameter chi also controls the stability of a homogeneously deformed non-fibrillar (flat) interface. Using these results, we show that the work to fail a unit area of fibrillar surface can be much higher than the intrinsic work of adhesion for a flat interface of the same material. In addition, we show that cross-sectional fibril dimensions control the pull-off force, which increases with decreasing fibril radius. Finally, an increase in fibril length is shown to increase the work necessary to separate a fibrillar interface. Besides our calculations involving a single fibril, we study the concept of equal load sharing (ELS) for a perfect interface containing many fibrils. We obtain the practical work of adhesion for an idealized fibrillated interface under equal load sharing. We then analyse the peeling of a fibrillar surface from a rigid substrate and establish a criterion for ELS.

Adhesiveness↗
PubMed2001

Effects of nicotine on bone mass, turnover, and strength in adult female rats.

This study investigated the effects of nicotine, the chemical responsible for tobacco addiction, on bone and on serum mineral and calcitropic hormone levels in adult, female rats to help resolve a current controversy regarding the impact of nicotine on bone health. Seven-month-old rats received either saline (n = 12), low-dose nicotine (4.5 mg/kg/day, n = 2), or high-dose nicotine (6.0 mg/kg/day, n = 12) administered subcutaneously via osmotic minipumps for 3 months. Blood, femora, tibiae, and lumbar vertebrae (3-5) were collected at necropsy for determination of serum mineral and hormonal concentrations, bone density (femora and vertebrae), bone turnover (tibiae), and bone strength (femora). The presence of nicotine in serum (111 +/- 7 and 137 +/- 10 ng/ml for the low- and high-dose nicotine groups, respectively) confirmed successful delivery of the drug via osmotic minipumps. Nicotine-induced treatment differences were not detected in serum calcium, 25-hydroxyvitamin D, and 1,25-dihydroxyvitamin D. However, serum phosphorus and parathyroid hormone (PTH) were higher in rats treated with high-dose nicotine, and serum calcitonin was lower in rats treated with both high- and low-dose nicotine than in control rats. Nicotine treatment had no effect on tibial cancellous or cortical bone turnover or femoral bone mineral content (BMC) and density (BMD). Femoral ultimate load and vertebral BMC were lower in rats treated with high-dose nicotine than in control rats. We conclude that nicotine at serum concentrations 2.5-fold greater than the average in smokers has limited detrimental effects on bone in normal, healthy female rats.

Absorptiometry, Photon↗
PubMed1999

Three-body wear of a hand-consolidated silver alternative to amalgam.

Recent studies have investigated a mercury-free silver alternative to amalgam, but the silver powders required a relatively high compaction pressure to consolidate. The aim of the present study was to consolidate a precipitated silver powder into a cohesive solid using an air-driven pneumatic condenser fitted with an amalgam plugger at a clinically realistic load, and to study the mechanisms and rates of three-body wear of the consolidated silver in comparison with that of an amalgam. The silver powder was annealed, rinsed with a dilute acid, and consolidated either in a prepared tooth cavity or in a specimen mold at a load of 15 N. A four-station wear machine was used where each specimen was immersed in a slurry containing polymethyl methacrylate beads, then a steel pin was loaded and rotated against the specimen at a maximum load of 76 N. The flexural strength in MPa (mean +/- SD; n = 10) was 86 +/- 20 for amalgam, 181 +/- 45 for silver with a polished surface, and 202 +/- 21 for silver with a burnished surface. After 4 x 10(5) wear cycles, the wear scar depth in microm was 134 +/- 54 for amalgam, 143 +/- 8 for polished silver, and 131 +/- 9 for burnished silver, which were not significantly different (Tukey's multiple comparison test; family confidence coefficient = 0.95). SEM examination revealed cracks and fracture pits in the worn surface of amalgam, in contrast to a smooth surface in silver. Wear and material removal in amalgam occurred by microfracture and dislodgement of cracked segments, while wear in the silver occurred by ductile deformation and flow of materials. To conclude, the consolidated silver possesses a three-body wear resistance similar to that of amalgam, and a higher resistance to wear-induced damage and cracking than amalgam. The mechanism of wear in amalgam is microfracture and material dislodgement, while that in consolidated silver is ductile deformation and flow of material.

Compressive Strength↗
PubMed2003

Material properties of subchondral bone from patients with osteoporosis or osteoarthritis by microindentation testing and electron probe microanalysis.

Cancellous bone from patients with osteoarthritis (OA) has a reduced material density and appears to be undermineralized. It is hypothesized that this will result in a reduction in the mechanical stiffness and strength of the bone matrix. In this study, bone was obtained from superior and inferior sites, subjected to relatively high and low loads, respectively, from human femoral heads retrieved after surgery for osteoporotic hip fracture (OP), or for hip arthroplasty due to OA. Microindentation testing was used to measure the hardness of cancellous bone at various depths from the subchondral bone plate. The elemental composition from immediately adjacent microscopic sites was determined using electron probe microanalysis (EPMA). Overall, OA bone was found to have hardness values that were 7% lower than those from OP bone. Bone from the inferior site was harder than that from the superior in both diseases except in female OP patients. There was no variation with depth below the subchondral plate and no difference between sexes. No difference was found in the composition of the bone from the different disease groups and no correlation was found between hardness and any of the composition measurements. Though only an indirect measurement of stiffness, the reduction in hardness values supports the hypothesis that OA bone has a reduced elastic modulus.

Aged↗
PubMed1998

Cyclic contact fatigue of a silver alternative to amalgam.

OBJECTIVE: To purpose of this study was to compare the cyclic contact fatigue resistance of a novel mercury-free silver direct filling material to that of a dental amalgam (Dispersalloy). METHODS: The silver specimens were made by pressing a precipitated powder at room temperature with a pressure of 150 MPa, which can be achieved in clinical hand-consolidation. To simulate clinical contact of restorations against enamel cusps, a cyclic contact fatigue methodology was employed. A spherical indenter was used to repeatedly indent the specimen, while the accumulation of deformation and damage was examined as a function of the number of cycles up to 5 x 10(5). Student's t test, analysis of variance (ANOVA) and Duncan's multiple range test were used to compare the specimen groups for significant differences in flexural strength, indentation impression diameter, and hardness. A type I error of alpha = 0.05 was considered as significant. Subsurface damage was examined by using a bonded-interface technique. RESULTS: As a result of cyclic indentation, microcracks were produced in the amalgam, but no cracks were found in the silver filling material. At fewer numbers of cycles, indentation produced larger impressions in silver (e.g., diameter = [450 +/- 31] microns at 10(2) cycles) than in amalgam ([145 +/- 20] microns) due to a lower hardness of the former. However, with increasing number of cycles, damage accumulated more rapidly in the amalgam, while the silver beneficially work-hardened in repeated indentations. At 5 x 10(5) cycles, the difference in impression diameter between silver and amalgam ([582 +/- 20] microns vs. [568 +/- 42] microns) become insignificant (p > 0.1, Student's t test). SIGNIFICANCE: The mercury-free silver direct filling material is more resistant to microcracking and to cyclic contact fatigue than amalgam, and the indentation impression sizes in the consolidated silver and dental amalgam are not statistically different at large numbers of cycles.

Analysis of Variance↗
PubMed2002

A comparative analysis based on different strength criteria for evaluation of risk factor for dental implants.

A numerical analysis is developed to study the interaction phenomena between endousseus titanium dental implants and surrounding jawbone tissue. The interest is focused on the most appropriate evaluation of the stress state arising in the tissue because of the implant under physiological loading. The problem is considered with regard to linear elastic response of the one and to short time effect. Different configurations of bone-implant system are described, using axial-symmetrical and three-dimensional models, by means of finite and geometric element method. The investigation attains to the stress states induced in bone that lead to a limit condition near the effective failure surface. The parameter commonly adopted in literature, such as the Von Mises stress, represents an excessive simplification of problem formulation, leading to an incorrect evaluation of the real failure risk for the implant, due to the assumption of the isotropic and deviatoric nature of the adopted stress measure. More suitable criterion can be assumed, such as the Tsai-Wu criterion, to take into account the anisotropy that characterises the response of bone, as well as the influence of a hydrostatic stress state. The analysis developed offers a comparison of results by using different criteria, leading to an evaluation of reliability of the procedure to be followed and addressing also to an evaluation of a risk factor for the implant investigated.

Anisotropy↗
PubMed2005

Influence of the method of blending an antibiotic powder with an acrylic bone cement powder on physical, mechanical, and thermal properties of the cured cement.

Two variants of antibiotic powder-loaded acrylic bone cements (APLBCs) are widely used in primary total joint replacements. In the United States, the antibiotic is manually blended with the powder of the cement at the start of the procedure, while, in Europe, pre-packaged commercially-available APLBCs (in which the blending is carried out using an industrial mixer) are used. Our objective was to investigate the influence of the method of blending gentamicin sulphate with the powder of the Cemex XL formulation on a wide collection of properties of the cured cement. The blending methods used were manual mixing (the MANUAL Set), use of a small-scale, easy-to-use, commercially-available mechanical powder mixer, OmoMix 1 (the MECHANICAL Set), and use of a large-scale industrial mixer (Cemex Genta) [the INDUSTRIAL Set]. In the MECHANICAL and MANUAL Sets, the blending time was 3 min. In preparing the test specimens for each set, the blended powder used contained 4.22 wt% of the gentamicin powder. The properties determined were the strength, modulus, and work-to-fracture (all obtained under four-point bending), plane-strain fracture toughness, Weibull mean fatigue life (fatigue conditions: +/-15 MPa; 2 Hz), activation energy and frequency factor for the cement polymerization process (both determined using differential scanning calorimetry, at heating rates of 5, 10, 15, and 20 Kmin(-1)), the diffusion coefficient for the absorption of phosphate buffered saline, PBS, at 37 degrees C, and the rate of elution of the gentamicin into PBS, at 37 degrees C (E). Also determined were the particle size, particle size distribution, and morphology of the blended powders and of the gentamicin. For each of the cured cement properties (except for E), there is no statistically significant difference between the means for the 3 cements, a finding that parallels the observation that there are no significant differences in either the mean particle size or the morphology of the blended cement powders. Notwithstanding these results, it is suggested that when the powder mixture is blended in the operating room, using the OmoMix 1 is more likely to produce a more consistent and reproducible mixture than when manual mixing is used.

Absorption↗
PubMed1999

Biomechanical testing of resorbable screws used for mandibular sagittal split osteotomies.

PURPOSE: The object of the study was to determine the suitability of specific resorbable screws for fixation of mandibular sagittal split osteotomies by in vitro biomechanical strength testing. MATERIALS AND METHODS: Resorbable screws (2.5 mm diameter) composed of a polylactic acidpolyglycolic acid copolymer were placed in an inverted L-pattern in overlapping urethane blocks representative of sagittal split mandibular surgery. In an in vitro model at room temperature, the test specimens were statically loaded until tensile failure occurred. On a different set of test specimens, dynamic testing was done in an in vitro water bath at body temperature through cyclic loads representative of mastication until failure. RESULTS: In static testing, three 2.5-mm resorbable screws sustained an average peak load of 131 Kiloponds (Kp) (standard deviation, 5.2 Kp) with 5.5% strain at yield. In dynamic testing, the resorbable screws tolerated a 45.3-Kp load for an average of 340,675 cycles (22,783 standard deviation). Several of these test specimens did not ultimately fail and were further evaluated by static testing with an average load of 77.4 Kp until fixation failure occurred. CONCLUSIONS: These laboratory results indicate a relatively high resistance to biomechanical loads representative of mastication and suggest that 2.5-mm resorbable screws of this particular polylactic acid-polyglycolic acid copolymer may be effective in fixation of the postoperative unrestrained sagittal split mandibular osteotomy.

Absorbable Implants↗
PubMed2005

Microencapsulation of living cells in semi-permeable membranes with covalently cross-linked layers.

Microencapsulation in semi-permeable membranes protects transplanted cells against immune destruction. Microcapsule strength is critical. We describe a method to microencapsulate living cells in alginate-poly-L-lysine (PLL)-alginate membranes with covalent links between adjacent layers of microcapsule membranes, while preserving the desired membrane molecular weight cut-off (MWCO) and microencapsulated cell viability. A heterobifunctional photoactivatable cross-linker, N-5-azido-2-nitrobenzoyloxysuccinimide (ANB-NOS) was used. The N-hydroxysuccinimide ester group of ANB-NOS was covalently linked to PLL. Islets of Langerhans were immobilized in alginate beads, incubated in PLL-ANB-NOS and again in alginate. Upon illumination with UVA, covalent links were created between the phenyl azide residue of ANB-NOS and alginate from both the core bead and the outer coating. Covalently linked microcapsules remained intact after 3 years in a strong alkaline buffer (pH 12), whereas standard microcapsules disappeared within 45 s in the same solution. A standardized mechanical stress broke 22-fold more standard than covalently linked microcapsules. The MWCO and microencapsulated cell viability were similar with standard and covalently linked microcapsules. These microcapsules, extremely resistant to chemical and mechanical stresses, will be useful in numerous applications.

Alginates↗
PubMed2000

Plasticisation of amylodextrin by moisture: consequences for drug release from tablets.

Moisture influences the consolidation behaviour of amylodextrin powders and the porosity and mechanical strength of compacts thereof. The aim of this study is to relate moisture content and compact properties to drug release characteristics of amylodextrin tablets. Therefore, amylodextrin tablets containing theophylline monohydrate were prepared and their release characteristics were studied as a function of moisture content and initial porosity. Drug release from amylodextrin tablets occurs through a leaching mechanism in which cracks are progressively formed in the hydrated part of the matrix leading to almost constant release rates. Small variations in moisture content resulted in large changes of the release rate. A unique relationship between porosity and release rate, which was independent on moisture content and compaction pressure, was observed. Above a critical porosity of 0.075 crack formation was followed by disintegration and fast release. Below this critical porosity, tablets stayed intact despite of the formation of cracks, and sustained release was observed. It is concluded that control over moisture content is essential for the production of amylodextrin tablets with reproducible release characteristics. Using amylodextrin containing 10-17%, moisture, tablets with a constant release behaviour can be obtained if sufficient compaction pressure ( > 300 MPa) is applied. Lubrication of amylodextrin powders reduces the effect of porosity significantly and improves the robustness of amylodextrin tablets as a release controlling excipient in tablets largely.

Bronchodilator Agents↗
PubMed2004

Shear bond strength after dentin bleaching with 10% carbamide peroxide agents.

This in vitro study evaluated the shear bond strength (SBS) of dentin treated with two 10% carbamide peroxide bleaching agents 15 days after bleaching and storage in artificial saliva. Dentin fragments were randomly divided into 3 groups (n = 20) for the treatment with the two different bleaching agents (Rembrandt 10% or Opalescence 10%) or with a placebo agent, applied to the tooth surface for 8 hours a day. During the remaining time, the specimens were stored in artificial saliva. After 42 days, the fragments were stored in artificial saliva for 14 days. Another group (n = 20) was exposed to distilled and deionized water for 56 days. An adhesive system and microhybrid composite resin were used to prepare specimens for the SBS test. SBS tests were performed and the fractured surfaces were visually examined using a stereoscope at 30 x magnification. The analysis of variance (ANOVA) and SIDAK tests showed higher SBS values for dentin treated with Opalescence 10% than for dentin treated with Rembrandt 10% or placebo. Groups treated with Rembrandt 10%, Opalescence 10% or placebo did not differ from the group treated with distilled and deionized water. Ten percent carbamide peroxide agents or a placebo agent caused no differences in SBS of dentin after 15 days of storage in artificial saliva.

Analysis of Variance↗