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At least 145 records · Page 8Linked to original sources

PubMed2004

Comparison of various vacuum mixing systems and bone cements as regards reliability, porosity and bending strength.

BACKGROUND: There are several vacuum mixing systems on the market which are arbitrarily used with various bone cements in clinical work. Hardly any studies have been done on the performance and handling of these systems in combination with different cement brands. MATERIAL AND METHODS: We therefore tested 6 vacuum mixing systems (Palamix, Summit, Cemvac, Optivac, Vacumix, MixOR) in combination with 6 cement brands (Palacos R, Simplex P, CWM 1, CWM 2000, Palamed G, VersaBond) concerning their reliability, user-friendliness, porosity and bending strength. RESULTS: Our study indicated that each system has weak points. The preparation of the mixed cement for gun injection can present problems. If cement collection under vacuum fails, porosity is increased. Manual collection without a vacuum carries the risk of intermixing air. For comfortable and effective retrograde cement application, cement guns should have a stable connection with the cartridge and a high piston stroke. There are marked differences between the systems as regards overall porosity when all tested cements are considered (range 2-18%), and between the cements when all tested systems are considered (range 2-17%). All test samples exceeded the required bending strength of 50 MPa, according to ISO 5833. Palaces specimens showed excessive plastic deformation in the bending test. INTERPRETATION: There are better and worse mixing system/cement combinations for a given system and a given cement. Systems with cement collection under vacuum reduce porosity best.

Bone Cements↗

PubMed1991

Porosity of pit and fissure sealants.

The aim of this study was to investigate the bulk porosity of a range of pit and fissure sealants. The following materials were included in the study: Concise White Sealant and Delton (chemically cured); Delton (visible light-cured); Helioseal, Visioseal and Prolite (visible light-cured with delivery from the bottle via cannule); Delton, Luma Seal and Prisma Shield (visible light-cured with syringe-type direct delivery systems). Five cylindrical samples, 7 mm in diameter and 1 mm in thickness, were prepared from each sealant and the following parameters were analysed in a computer-controlled mercury porosimeter: (i) total cumulative pore volume; (ii) specific surface area of pores; (iii) percentage total porosity (iv) bulk density; and (v) pore radius distribution. According to the results, the chemically cured sealants exhibited total cumulative pore volume, specific surface area of pores and total porosity. Significant differences were detected within the group of visible light-cured materials. The visible light-cured sealants with syringe-type delivery exhibited the lowest porosity.

Analysis of Variance↗

PubMed2006

Marginal adaptation and micro-porosity of class II restorations of a high copper amalgam and a palladium-free gallium-based alloy.

The aim of the current investigation was to compare the marginal adaptation and internal porosity of a gallium (Ga)-based alloy (Galloy) with a high copper amalgam (Permite C DP) when used in moderately sized conventional class II cavities. Ten dentists placed two restorations of each material in standardized class II cavities in typodont teeth set in a phantom head. The proximal surfaces of the restored teeth were subsequently examined using an optical microscope and colour photographs were taken. The teeth were then serially sectioned before being re-examined microscopically and re-photographed. Three dentists rated the photographs of the restorations on two occasions, 2 weeks apart, for marginal adaptation and internal porosity using a six and five point scoring criteria, respectively. Inter- and intra-examiner agreements were assessed with weighted kappa statistics. The Ga-based alloy exhibited inferior marginal adaptation and a significantly higher level of porosity and internal defects compared with the dental amalgam. Marginal defects were mainly concentrated at the gingival third of the proximal boxes for both alloys. The poor marginal adaptation and extensive internal porosity detected for the Ga-based alloy was attributed to the difficulty in the alloy condensation related mainly to the 'stickiness' of the alloy to the condensers and to the rapid change in the plasticity of the alloy during condensation. This could possibly be a factor in the post-operative complications reported with the clinical use of this alloy.

Copper↗

PubMed2005

Regional variation of intracortical porosity in the midshaft of the human femur: age and sex differences.

This study investigated age and sex differences in patterns of porosity distribution in the midshaft of the human femur. Cross-sections were obtained from 168 individuals from a modern Australian population. The sample comprised 73 females and 95 males, aged between 20 and 97 years. Microradiographs were made of 100-microm sections and pore and bone areas were determined using image processing software. Initially the sample was divided by age: young (20-44 years), middle (45-64 years) and old (65+ years), but it was found that analysis on the basis of the ratio of medullary area to total subperiosteal area gave clearer results. The cortex was divided into three rings radially and into octants circumferentially and the porosity of each segment was calculated. Results showed that a pattern with raised porosity in the posterior and anterolateral regions, and with greater porosity in the inner parts of the cortex, becomes more pronounced with age. In males this pattern develops steadily; in females there are much greater differences between the middle and older groups than earlier in life. The patterns observed are consistent with progressive bone loss occurring along a neutral axis of the cortex where bending stress is lowest and the mechanical advantage of the bone is least.

Adult↗

PubMed2006

Increase in pore area, and not pore density, is the main determinant in the development of porosity in human cortical bone.

This study investigated the relative contributions of pore size and pore density (number of pores per mm2) to porosity in the midshaft of the human femur. Cross-sections were obtained from 168 individuals from a modern Australian population (mostly Anglo-Celtic). The study group comprised 73 females and 95 males, aged from 20 to 97 years. Microradiographs were made of 100-microm sections and porosity, pore areas and pore densities determined using image processing software. The cortex was divided into three rings radially and into octants circumferentially, and the porosity, pore area and pore density of each segment were calculated. Results show that 81% of the variance in porosity can be explained by changes in mean pore area with only a further 12-16% explained by changes in pore density. These effects were found to be constant across all areas of the cortex and in both sexes. These results are significant in their consistency and ordered gradation and indicate a well-regulated and systematic process of bone removal with ageing. The results show a regular progression from less porous to more porous bone; this is a uniform process that occurs in all individuals, and factors such as sex and rate of ageing determine where on this continuum any individual is at a particular time.

Adult↗

PubMed2004

Effect of the fiber diameter and porosity of non-woven PET fabrics on the osteogenic differentiation of mesenchymal stem cells.

The proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) was investigated in three-dimensional non-woven fabrics prepared from polyethylene terephthalate (PET) fiber with different diameters. When seeded into the fabrics of cell scaffold, more MSC attached in the fabric of thicker PET fibers than that of thinner ones, irrespective of the fabric porosity. The morphology of cells attached became more spreaded with an increase in the fiber diameter of fabrics. The rate of MSC proliferation depended on the PET fiber diameter and porosity of fabrics: the bigger the fiber diameter of fabrics with higher porosity, the higher their proliferation rate. When the alkaline phosphatase (ALP) activity and osteocalcin content of MSC cultured in different types of fabrics was measured to evaluate the ostegenic differentiation, they became maximum for the non-woven fabrics with a fiber diameter of 9.0 microm, although the values of low-porous fabrics were significantly high compared with those of high porous fabrics. We concluded that the attachment, proliferation and bone differentiation of MSC was influenced by the fiber diameter and porosity of non-woven fabrics as the scaffold.

Alkaline Phosphatase↗

PubMed2000

Time-dependent decrease and seasonal variation of the porosity of recently erupted sound dental enamel in vivo.

Recently erupted teeth are more sensitive to dental caries than teeth that have remained free from caries lesions for a few years after eruption. It has been hypothesized that this may be ascribed to differences in enamel porosity. The objective of the present work was to assess the time-dependence of electrical conductance, as an indication of porosity, of occlusal enamel in recently erupted permanent molar teeth. Fifty children aged 5-15 years of age, receiving regular dental care at six-month intervals, participated in the study when their first molar teeth (in 5- to 6-year-olds) or their second molar teeth (in 11- to 15-year-olds) had not been exposed to the oral environment for more than six months. On the first semi-annual check-up after eruption of a first or second molar, baseline diagnostic measurements, i.e., visual inspection and electrical conductance measurements (ECMs), were made at three or four pre-defined sites in the fissures. Subsequently, data collection was repeated every six months for three years. Sites were excluded from ECMs when a caries lesion was observed at a site by visual inspection. After 36 months, there were 257 sites in teeth considered sound upon visual examination. The ECM values of these sound sites showed a clear decrease with time after the first examination. The conductance decreased on average from 0.13 (Momega)(-1) to 0.059 (Momega)(-1). Since the conductance is assumed to be proportional to the porosity of the enamel, the latter decreased by a factor of 2.2 over the 36-month period. The results furthermore indicated a higher conductance for maxillary than for mandibular enamel. Almost all sites in that sample appeared to be in teeth that were observed for the first time during the months September to December. Electrical conductance, and therefore enamel porosity, of the sites showed a periodic variation with season of observation: In the fall, the conductance was higher than in the spring. This implies that a dentist should be more prudent in the fall than in the spring when indicating restorative treatment of an incipient caries lesion.

Adolescent↗

PubMed1992

The dependence of shrinkage stress reduction on porosity concentration in thin resin layers.

The development of polymerization contraction stress was determined as a function of the surface area of porosity, so that the contribution of voids in resin composite to stress relief could be investigated. Experiments were carried out on 200-microns-thick layers of resin bonded from wall to wall in a restrained condition. The resin samples were divided into three groups: Group A was without porosity, group B contained a small number of pores, and group C contained a large number of pores in comparison with group B. For each group, porosity area, maximal stress, and stress development rate were determined. The mean maximal stress and stress development rate were inversely proportional to the mean porosity surface. These characteristics differed significantly (p less than 0.01) between group A and C. For determination of whether shrinkage stress reduction has to be ascribed to flow from the outer surfaces of the voids or to inhibition of the setting reaction by oxygen in the voids, resin containing only nitrogen bubbles was also tested. The results indicated that both aspects contributed substantially to shrinkage stress relief. Incorporation of pores by the stirring of a luting cement contributes to stress reduction and can therefore be considered as a contribution to the maintenance of marginal integrity.

Analysis of Variance↗

PubMed2003

Thermal porosity analysis of croscarmellose sodium and sodium starch glycolate by differential scanning calorimetry.

The aim of the study was to demonstrate the applicability of differential scanning calorimetry (DSC) on porosity analysis for cellulose and starch. Croscarmellose sodium (CCS) and sodium starch glycolate (SSG) were allowed to sorb moisture in 85%, 90%, 95%, and 100% relative humidity (RH) at 40 degrees C for 24 hours. The pretreated samples were then subjected to DSC running temperature ranging from 25 degrees C to -50 degrees C at a cooling rate of 10 degrees C/min. The cooling traces of water crystallization, if present, were transformed to porosity distribution via capillary condensation using Kelvin's equation. The porosity analysis of CCS and SSG was also done using nitrogen adsorption as a reference method. It was found that sorbed water could not be frozen (in cases of 85% and 90% RH) until the moisture content exceeded a cutoff value (in cases of 95% and 100% RH). The nonfreezable moisture content was referred to tightly bound, plasticizing water, whereas the frozen one may be attributed to loosely bound water condensation in pore structure of CCS and SSG surfaces. Not only capillary condensation but also the tightly bound, nonfreezable monolayer water lying along the inner pores of the surface contributed to porosity determination. Good agreement with less than 5% deviation of mean pore size was observed when the results were compared with nitrogen adsorption. The narrower pore size distributions, however, were obtained because of the limitations of the technique. It was concluded that pore analysis by DSC could be successful. Further research needs to be done to account for limitations and to extend the applicability of the technique.

Calorimetry, Differential Scanning↗

PubMed1999

An investigation into the erosion behaviour of a high drug-load (85%) particulate system designed for an extended-release matrix tablet. Analysis of erosion kinetics in conjunction with variations in lubrication, porosity and compaction rate.

The effects of the amounts of lubricants (magnesium stearate 0-5% and talc 0-3%) and changes in compaction rate and tablet porosity on the mechanism of drug release from high drug-load controlled-release theophylline tablets have been examined. Drug release was satisfactorily described by a surface-erosion model that takes into account the geometry of the tablet, differential radial and axial erosion rates, and the initial burst effect (r2 > 0.99 for all formulations). The axial and radial erosion rate constants were inversely proportional to the amount of magnesium stearate in the formulation (P < 0.0001). The most dramatic reductions in erosion rate occurred between 0 and 1% magnesium stearate content. For magnesium stearate concentrations > or =2.5% the ratio of radial to axial erosion rate constants was essentially constant at 3 (approx.); however, for formulations with magnesium stearate < or =1% the ratio tended toward unity. Reducing matrix porosity over the range 26 to 14% resulted in reduced erosion rates. However, a threshold of 17% (approx.) porosity was identified below which further reductions in porosity resulted in only incremental changes in release rates. The rate of erosion and drug release was insensitive to changes in machine speed over the range 20 to 100 rev min(-1). For highly loaded matrix tablets containing sparingly soluble drugs, such as theophylline, magnesium stearate at appropriate levels can modulate the erosion rate constants and act as an effective release-controlling excipient. Drug-release profiles are predictable and relatively robust in terms of changes in compaction rate and applied force routinely encountered in large-scale tablet manufacturing.

Chemistry, Pharmaceutical↗

PubMed2004

Continuous parathyroid hormone induces cortical porosity in the rat: effects on bone turnover and mechanical properties.

UNLABELLED: We examined the time course effects of continuous PTH on cortical bone and mechanical properties. PTH increased cortical bone turnover and induced intracortical porosity with no deleterious effect on bone strength. Withdrawal of PTH increased maximum torque to failure and stiffness with no change in energy absorbed. INTRODUCTION: The skeletal response of cortical bone to parathyroid hormone (PTH) is complex and species dependent. Intermittent administration of PTH to rats increases periosteal and endocortical bone formation but has no known effects on intracortical bone turnover. The effects of continuous PTH on cortical bone are not clearly established. MATERIALS AND METHODS: Eighty-four 6-month-old female Sprague-Dawley rats were divided into three control, six PTH, and two PTH withdrawal (WD) groups. They were subcutaneously implanted with osmotic pumps loaded with vehicle or 40 microg/kg BW/day human PTH(1-34) for 1, 3, 5, 7, 14, and 28 days. After 7 days, PTH was withdrawn from two groups of animals for 7 (7d-PTH/7d-WD) and 21 days (7d-PTH/21d-WD). Histomorphometry was performed on periosteal and endocortical surfaces of the tibial diaphysis in all groups. microCT of tibias and mechanical testing by torsion of femora were performed on 28d-PTH and 7d-PTH/21d-WD animals. RESULTS AND CONCLUSIONS: Continuous PTH increased periosteal and endocortical bone formation, endocortical osteoclast perimeter, and cortical porosity in a time-dependent manner, but did not change the mechanical properties of the femur, possibly because of addition of new bone onto periosteal and endocortical surfaces. Additionally, withdrawal of PTH restored normal cortical porosity and increased maximum torque to failure and stiffness. We conclude that continuous administration of PTH increased cortical porosity in rats without having a detrimental effect on bone mechanical properties.

Animals↗

PubMed2005

PBS buffer solutions with different pH values can change porosity of DNA-chitosan complexes.

We examined the effect of phosphate-buffered saline (PBS) solution with different pH values on the formation of porosity in the DNA/chitosan complexes, and evaluated the intercalation behavior of the complexes. Four different PBS solutions with pH = 6.0, 7.0, 7.4, and 7.8 were used for rinsing water-insoluble DNA-chitosan complexes. All complexes showed high porosities ranging from 83 to 95%. Rinsing with PBS at pH 7.0, 7.4, and 7.8 reduced the porosity of the DNA-chitosan complexes. Re-rinsing with PBS at pH 7.4 reduced the porosity of the DNA-chitosan complex rinsed with PBS at pH 6.0. The appearances for porous formation were influenced by the differences in pH of PBS. Daunorubicin hydrochloride intercalated and bound in the grooves of DNA within all of the DNA-chitosan complexes, indicating that DNA in the complexes maintained its double-stranded helical structure. These results suggested that PBS-rinsed DNA-chitosan complex is promising as a scaffold material in tissue engineering.

Biopolymers↗

PubMed2001

Porosity of resin cements and resin-modified glass-ionomers.

PURPOSE: To quantify the internal free surface in various resin cements and glass-ionomer-based materials. MATERIALS AND METHODS: Materials tested were Nexus fluid (NXF) and viscous (NXV), Vitremer (VTM), Fuji II LC (FII), Vitremer Luting Cement (VLC), Dyract (DYR) and Compoglass (COM). Samples (n=5) were made of each material between two microscopic glass slides under same weight. With a transmitted light microscopy, four zones of each sample were evaluated, finding the number of porosities per mm2 (NP), the average radius of porosities (RP), the ratio of total area of surface porosities (micron2) to area (mm2) of specimen surface (TA) and the ratio of total volume of porosities (micron2) to area (mm2) of material surface (VP). RESULTS: Median test was used. NP: NXV, NXF and DYR had smaller NP than VTM and FII and (likely) than VLC (P> 0.0000001). RP was smaller for DYR than for VLC and (likely) than for NXV (P= 0.00019). TA: NXV, NXF and DYR had smaller TA than VTM, FII and VLC (P< 0.0000001). VP: NXV and DYR had smaller VP than FII and (likely) than VTM and VLC (P< 0.0000001).

Chi-Square Distribution↗

PubMed2003

[Influence of external electric current on the spatial distributions of porosity and fractional dimension of biofilms].

The spatial distributions of porosity and fractional dimension of autotrophic and heterotrophic/autotrophic biofilms applied by direct current in the range of 0-25 A/m2 were investigated by using the micro-slicing technique and image analysis. The results showed that the porosities of the autotrophic and heterotrophic/autotrophic biofilms respectively decreased from ca. 92% and 96% in the top layer to ca. 54% in the bottom layer while the fractional dimensions increased from 1.1 and 1.05 in the top layer to 1.4 in the bottom layer in the absence of current. The increase in the current density decreased the porosities and increased the fractional dimensions in the top layers. In the deeper layers, the current had insignificant influence on the porosity and fractional dimension.

Biofilms↗

PubMed1992

Experimental comparison of albumin-sealed and gelatin-sealed knitted Dacron conduits. Porosity control, handling, sealant resorption, and healing.

Two high-porosity knitted Dacron vascular grafts sealed with aldehyde cross-linked gelatin or albumin were compared with respect to the following characteristics. Porosity control by the absorbable sealant was assessed with a water porosity meter at 120 mm Hg pressure. Ease of suturing was determined by an objective needle penetration test. Sealant resorption was assessed histologically in a subcutaneous immature rat model as well as in circulatory implants. Gross and microscopic healing characteristics were compared in circulatory implants in the thoracic aorta of sheep with use of a composite conduit in every animal, which allowed direct comparison of the two graft materials and minimized differences in healing between individual animals. Both grafts demonstrated excellent porosity control and better handling characteristics than woven Dacron. Sealant resorption was generally rapid, although residual albumin sealant was often seen adjacent to anastomoses. Residual sealant appeared to result in focally poor healing with focal loss of adhesion of surrounding tissue to graft. We conclude that details of sealant preparation and application can importantly influence the performance of presealed knitted Dacron grafts and should be carefully evaluated in the laboratory before clinical implantation is begun.

Albumins↗

PubMed2005

[Preparation of porous silica microspheres with high porosity using base-dissolving method].

A novel method was proposed and studied for the preparation of porous silica with high porosity using base-dissolving technology. The relationships between the removal of silica and the base concentration, the reaction temperature as well as the reaction time were evaluated. The amount of silica removed from silica spheres was increased and silica-dissolving rate was also accelerated along with the increase of NaOH concentration. This was due to the damage of some inner walls of the porous silica and the dissolution of small fragments into the base solution. The amount of silica removed was in direct proportion to the reaction temperature and reaction time. Moreover, the specific pore volumes were linearly increased along with the increase of the amount of silica removed. The treated silica particles remained as homogeneous spheres and the changes of the particle diameter were not observed. Under the optimized conditions with the NaOH solution of 1.25 mol/L, the reaction temperature of 25 degrees C and the reaction time of 3.0 h, the original silica spheres with the diameter of 4 - 5 microm, the pore size of 8 nm and the specific pore volume (V(p)) of 1.4 cm3/g were modified to the high-porosity silica with the diameter of 4 - 5 microm, the pore size of 14 nm and the V(p) of 3.2 cm3/g. The porosity of the silica microspheres was changed from 75% to 88%. This high-porosity silica was suitable for the preparation of high performance gel filtration packings.

Chromatography↗

PubMedDate not supplied

Dual-porosity expanded polytetrafluoroethylene soft tissue implant: a new implant for facial soft tissue augmentation.

OBJECTIVE: To illustrate problems observed with low-porosity expanded polytetrafluoroethylene soft tissue implants and to describe a new dual-porosity implant, the technique for insertion, and this author's preliminary experience. METHOD: A review of 175 pieces of SoftForm (Collagen Corporation, Palo Alto, Calif) placed in 69 patients over 3 years was performed. Between October 1, 1997, and September 30, 2000, 106 Advanta implants (Atrium Medical Corporation, Hudson, NH) in 42 patients have been carried out. A new instrument for implant insertion and the procedure used is described herein. RESULTS: The low-porosity expanded polytetrafluoroethylene implants demonstrated a significant amount of problems with shrinkage and migration. CONCLUSIONS: Preliminarily, the dual-porosity implants would appear to offer a lower incidence of these complications. They are subjectively softer to feel once in place. Insertion is quick and easy using the method described herein.

Face↗

PubMed1987

Textile arterial prostheses: is water permeability equivalent to porosity?

Porosity and water permeability are two distinct terms that describe different characteristics of vascular prostheses. The porosity is a measure of the void fraction within the prosthesis wall and is believed to give a rough prediction of the capacity of the graft to anchor newly formed surrounding tissue after implantation, whereas the water permeability indicates the rate at which water can flow through the prosthesis wall and, when measured under physiological pressure conditions, provides the surgeon with information about the need for preclotting prior to implantation. The literature has not always clearly distinguished between these two terms, and some authors in fact have suggested that they both refer to the same property of a prosthesis. In an attempt to clarify the issue, porosity and water permeability measurements were made on 34 commercial vascular prostheses having different textile constructions. Linear regression analysis demonstrated that these two characteristics are only weakly related (r = 0.59). It is therefore recommended that the current draft standards for such devices reference both properties: porosity and water permeability.

Blood Vessel Prosthesis↗