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At least 217 records · Page 12Linked to original sources
PubMed2004

An ultrastructural study of cellular response to variation in porosity in phase-pure hydroxyapatite.

Hydroxyapatite has been shown to be biocompatible and bioactive. Incorporation of porosity has been shown to enhance osteointegration; however, difficulty in controlling the extent and type of porosity has limited investigation into determining the role of both macro- and microporosity. The current investigation reports on the synthesis of four types of phase-pure hydroxyapatite with varying levels of porosity (HA1-HA4), and with defined levels of macro- and microporosities. Transmission electron microscopy was used to evaluate qualitatively the effect of these two parameters on cell-material interactions following a 30-day incubation period. Biological mineralization was observed within vesicles and the needle-like minerals were confirmed as hydroxyapatite using X-ray microanalysis. This demonstrated the suitability of primary human osteoblast-like cells as a tool to assess the extent of mineralization. Furthermore, internalization of hydroxyapatite particles was observed. Our findings show that the variation in macro- and microporosity does not affect the extent of cell-material interaction, with collagen synthesis evident in all samples.

Cell Communication↗
PubMed2005

The effects of fluid penetration and interfacial porosity on the fixation of cemented femoral components.

We have investigated the role of the penetration of saline on the shear strength of the cement-stem interface for stems inserted at room temperature and those preheated to 37 degrees C using a variety of commercial bone cements. Immersion in saline for two weeks at 37 degrees C reduced interfacial strength by 56% to 88% after insertion at room temperature and by 28% to 49% after preheating of the stem. The reduction in porosity as a result of preheating ranged from 71% to 100%. Increased porosity correlated with a reduction in shear strength after immersion in saline (r = 0.839, p < 0.01) indicating that interfacial porosity may act as a fluid conduit.

Arthroplasty, Replacement, Hip↗
PubMed2006

Estimating the change of porosity in the saturated zone during air sparging.

Air sparging is a remedial method for groundwater. The remedial region is similar to the air flow region in the saturated zone. If soil particles are transported during air sparging, the porosity distributions in the saturated zone change, which may alter the flow path of the air. To understand better the particle movement, this study performed a sandbox test to estimate the soil porosity change during air sparging. A clear fracture was formed and the phenomenon of particle movement was observed when the air injection was started. The moved sand filled the porous around the fracture and the reparked sand filled the fracture, reducing the porosity around the fracture. The results obtained from the photographs of the sandbox, the current measurements and the direct sand sample measurements were close to each other and are credible. Therefore, air injection during air sparging causes sand particle movement of sand, altering the characteristic of the sand matrix and the air distribution.

Air↗
PubMed1994

Effect of bone mineral particles on the porosity of bone cement.

Bone particle-impregnated bone cement is investigated in vitro, which could be used to improve fixation between bone and cement interface by ingrowth of tissues that may replace bone particles. Inorganic bone particles (150-300 microns diameter) were mixed with regular bone cement powder by 0, 10, 20, and 30% by weight and implanted into the pre-drilled intramedullary canal (11cm long, 10mm diameter) of canine femur. A 4mm diameter, 10mm long stainless steel rod was implanted to simulate the prosthesis. The specimens were cut into 2mm thick discs transversely along the long axis of the bone and ground to examine with a confocal laser microscope. Diametral tensile strength tests were performed for the 0, 10, 20, and 30% bone particle impregnated bone cement discs without the intramedullary implant. Present results show that mixing bone particles with bone cement decreased the number of pores and porosity but increased the size of pores. The analysis of porosity distribution showed no significant difference between bone cement and bone particle-impregnated bone cement. Also, the strength of the bone particle-impregnated bone cement decreased linearly with increased amount of bone particles in spite of the decreased percent porosity. Using a bone particle-impregnated bone cement along with a pre-coated implant could be one of the solutions to the problems in the fixation of total joint arthroplasty.

Animals↗
PubMedDate not supplied

Accuracy and porosity of denture bases submitted to two polymerization cycles.

In this study was verified accuracy and porosity of denture bases submitted to double cycles of polymerization. Thirty-Six master casts were made in dental stone from the impression of the metal die. They were divided in three groups. Denture bases of conventional acrylic resin were made on the casts of the groups I (GI-control) and II (GII), polymerized in water bath during 9 hours at 73 degrees C, and specific resin for microwave polymerization were made on the casts of the group III (GIII) and cured at 500 W during 3 minutes. Accuracy was verified by the weight of a impression material put between the denture base and cast die under load of 2 Kg. Afterwards, all the denture bases were relined by addition method and those of the group I and II were relined with the same material and polymerization technic. The denture bases of the group II were filled with the same resin, however cured in microwave oven with 500 W during 3 minutes. Accuracy was reevaluated. The porosity was verified by the immersion of the specimens in a solution of permanent black ink and the pores were counted through a stereo light microscope under magnification of 6.3 x. The average and standard deviation obtained for accuracy before and after the relining were respectively: GI: 0.63 +/- 0.02 - 0.66 +/- 0.03; GII: 0.63 +/- 0.03 - 0.68 +/- 0.03: GIII: 0.58 +/- 0.02 - 0.80 +/- 0.05. There was a significant difference (p < 0.05 as tested by Tukey) only for the group III. The average and standard deviation for porosity before and after the relining were respectively: GI: 8.33 +/- 0.63 - 9.25 +/- 0.85; GII: 8.17 +/- 0.98 - 10.08 +/- 1.63: GIII: 5.41 +/- 0.78 - 6.58 +/- 1.02. There was a significant difference (p < 0.05) for the group III before relining. The conclusion is that after relining, the conventional resin cured by water bath or microwaves energy showed a better adaptation, and the highest number of pores.

Composite Resins↗
PubMed1998

Mechanical properties of buccal compact bone of the mandibular ramus in human adults and children: relationship of the elastic modulus to the direction of the osteon and the porosity ratio.

With recent advances in computers, the finite element method has been used for stress analysis of bone. In particular, the dynamic behavior of the jaw bone has been a subject of interest and analyzed by this method. However as the elastic modulus needed for this method, a uniform value is used without considering differences according to site or direction. Therefore, we measured the elastic modulus at various sites and in various directions of the mandible in adults and children. In addition, the association between the elastic modulus and histological structures was evaluated. Ten specimens of dried mandible from human adults and children were used. The elastic modulus was measured in two regions prepared by equally dividing the ramus of the mandible into lower and upper regions. Samples of 6 mm x 960 microns x 425 microns were collected from the buccal compact bone. The elastic modulus was measured using a three-point bending test. After measurement, the direction of the osteon was examined using SEM. The porosity ratio was also measured after CMR were taken. In both adults and children, anisotropy in the elastic modulus of each direction in the upper region was similar to the anisotropy in unidirectional fiber reinforced composite materials, but not in the lower region. The elastic modulus decreased slightly with an increase in the angle of the direction of osteons to the longitudinal axis of specimens. The direction of osteon may significantly influence anisotropy in the elastic modulus. The elastic modulus in adults was higher than in children in all directions. The porosity ratio in adults was smaller than that in children in all directions. The difference in the porosity ratio between adults and children may significantly influence the value of the elastic modulus.

Adult↗
PubMedDate not supplied

Diachronic patterns of dental hypoplasias and vault porosities during the predynastic in the Naqada region, Upper Egypt.

The diachronic pattern of the frequencies of linear enamel hypoplasias and porotic hyperostosis was studied in temporally separated samples of adult predynastic Egyptian remains from the Naqada region, Upper Egypt. The samples covered a period of increasing population density and social complexity as well as decreasing Nile flooding in Egypt. First and second molars were evaluated for hypoplasias in material from the Naqada I, II, and III periods; sample sizes were 13, 30, and 25, respectively, for the first molar, and 11, 28, and 24 for the second molar. Cranial vaults were examined for porotic hyperostosis using several approaches; sample sizes were 26, 66, and 51 for Naqada I, II and III, respectively. Linear regression showed a decreasing trend for several variables: for the individual frequency of first molar hypoplasias (rho = 0.025), the vault porosity score, which indicates the severity of the lesions (rho < 0.001), and the extent score, which indicates the number of superior vault bones having porosities (rho < 0.001). Logistic regression showed a temporal decline in the percentage of crania per sample having any vault porosities and only higher grade lesions (rho < 0.012 and rho < 0.003, respectively). Lesions of the second molar showed no directional trend. The results contrast with the common observation that these skeletal markers usually increase in contexts of increasing population density and social complexity.

Adult↗
PubMed1992

A fractographic investigation of PMMA bone cement focusing on the relationship between porosity reduction and increased fatigue life.

Fracture surfaces of both monotonic and fatigue loaded bone cement samples were examined to investigate the fractographic characteristics of PMMA. Classic cleavage step river patterns were observed on all monotonically loaded samples, running downstream in the direction of crack propagation. All fatigue cracks initiated at internal pores and the direction of crack propagation of many cracks was discernible. Porosity, pore size, and pore size distribution were found to affect the crack initiation and fatigue behavior of bone cement. Statistical analysis revealed a strong negative correlation between two-dimensional porosity present on the fracture surfaces and the cycles to failure. The fractographic observations of these fatigue samples elucidate one reason why porosity reduction by centrifugation or vacuum mixing increases the fatigue life of PMMA bone cement.

Biocompatible Materials↗
PubMed2006

Buffer solution can control the porosity of DNA-chitosan complexes.

The current studies examine the pore properties and biological effects of DNA-chitosan complexes, which may be useful as scaffolds for tissue engineering. The porosity of the DNA-chitosan complexes was controlled by rinsing them with several different pH 7.2 buffer solutions, including phosphate-buffered saline (PBS), Tris-HCl, boric acid, and N-(2-hydroxyethyl)piperazine-N'-(2-ethanesufonic acid) (HEPES). Rinsing with PBS resulted in 84% porosity, whereas rinsing with Tris-HCl produced 94% porosity. It was further found that daunorubicin hydrochloride complex intercalated with and bound to the groove of the DNA-chitosan complexes, indicating that DNA in the complexes maintains its double-stranded helical structure. The DNA-chitosan complexes were not toxic to MG-63 osteoblast-like cells and caused only a mild tissue response when implanted subcutaneously in the backs of rats. These results suggest that buffer-rinsed DNA-chitosan complexes may be useful as a scaffold material in tissue engineering.

Buffers↗
PubMed1977

Determination of porosity and pore-size distribution of aspirin tablets relevant to drug stability.

Total porosity and pore-size distribution of aspirin tablets prepared from aspirin, starch USP, and precipitated colloidal silicon dioxide were determined using mercury porosimetry. The model represented a hydrolyzable drug substance in combination with simple excipients. The role of starch and silicon dioxide on the microstructure of the tablets was investigated, as was the chemical stability of various systems. In general, the porosity of tablets containing a constant quantity of starch increased linearly with silicon dioxide concentration. Examination of the pore-size distribution, however, revealed that a low concentrations silicon dioxide functioned primarily to reduce the size and volume of coarse pores representing the spaces between the agglomerates of starch and aspirin particles. This effect was optimum at 3%. A further increase in silicon dioxide concentration produced tablets with relatively larger pore sizes. Studies of changes in the porosity characteristics of tablets as influenced by water vapor over time showed distinct differences in this complex parameter. A unique trend in the change of the pore-size distribution was noted with tablets containing 3% silicon dioxide. These observations are discussed relative to the stability of aspirin tablets in which this concentration of silicon dioxide produced a maximum stabilizing effect.

Aspirin↗
PubMed1997

Experimental replacement of the thoracic inferior vena cava with a high-porosity expanded polytetrafluoroethylene graft wrapped in an omental pedicle flap.

We examined the patency and healing of a high-porosity expanded polytetrafluoroethylene (ePTFE) graft implanted as an interposition graft in the thoracic inferior vena cava (IVC) and wrapped in an omental pedicle flap. High-porosity ePTFE grafts of 60 microns fibril length, with an internal diameter of 10 mm and a length of 4 cm, were implanted in 12 mongrel dogs. In 6 dogs, the grafts were wrapped in omental pedicle flap, and in the remaining 6 the grafts were unwrapped. The animals were killed 4 weeks after the replacement and the grafts were removed for examination. Patency of the graft in both groups was 100%; however, the thrombus-free area in the omentum-wrapped group was significantly larger (P < 0.05) than that in the unwrapped group. Light microscopy revealed the marked infiltration of cells and capillaries within the graft interstices in the omentum-wrapped group. These findings suggest that encapsulation of the high-porosity ePTFE graft is promoted by an omental pedicle flap.

Anastomosis, Surgical↗
PubMed2003

Bone strength during growth: influence of growth rate on cortical porosity and mineralization.

Although it is well accepted that bone architecture adapts to withstand the loads placed on it, the manner in which this occurs in the immature growing skeleton is not fully understood. To investigate the possible mechanisms, we have compared morphometric differences between tibiae from chickens with fast and those with slow growth potential and also distinguished between the effects of genetic potential and growth rate on their impact on bone quality. Two different fast-growing (ad lib modern) strains, one additionally feed-restricted and one slow-growing (control) strain of chicken, were compared at 15 and 42 days of age. The ad lib modern strains had similar final body weights and were approximately twice the weight of the control and restricted-fed birds. Tibiae from the control and restricted birds had a higher ash content and lower porosity than the ad lib modern strain at 42 days. The porosity was a result of rapid primary osteon formation at the periosteal surface and incomplete infilling of the resultant canal by osteoblasts. When adjusted to average body weight of contemporaries, bones from the control strain and the restricted-fed modern birds were stiffer and at least as strong as those from the fast growing ad lib-fed birds. In conclusion, rapid bone deposition at the periosteal surface was associated with decreased mineralization, increased cortical porosity, and altered biomechanical properties. Our results also indicate that growth rate, and not genetic potential, of the fast growing birds was responsible for the rapid periosteal bone deposition.

Acid Phosphatase↗
PubMed2000

Enhanced graft healing of high-porosity expanded polytetrafluoroethylene grafts by covalent bonding of fibronectin.

The effect of covalent bonding of fibronectin on the patency and graft healing of high-porosity expanded polytetrafluoroethylene (ePTFE) grafts was evaluated. Bilateral carotid grafting was performed in ten mongrel dogs using high-porosity (60 microm) ePTFE grafts, 4 cm in length and 4 mm in internal diameter, that either had been pretreated by the covalent bonding of fibronectin (fibronectin grafts) or were untreated (control grafts). The grafts were harvested 4 to 6 weeks after surgery and subjected to macroscopic and light-microscopic observations. There was no significant difference in patency between the fibronectin grafts and the control grafts with rates of 80% and 70%, respectively. The thrombus-free area score was significantly greater in the fibronectin grafts than in the control grafts, at 86.9% vs 34.0%. Furthermore, the pseudointima was better replaced by fibrous tissue in the fibronectin grafts than in the control grafts, being lined with a layer of endothelial-like cells. More transmural tissue ingrowth was evident in the fibronectin grafts than in the control grafts. The covalent bonding of fibronectin improves graft healing by stimulating transmural tissue ingrowth in high-porosity ePTFE grafts.

Animals↗
PubMed1986

Porosity-geometry interaction in the conservation of bone strength.

Automated image analysis of a small sample of femoral cross-section radiographs has revealed a consistent difference in bone porosity relative to geometry. Two sub-periosteal fields were assessed microscopically, with field location determined with reference to the principal moment axes (Imax, Imin). The data indicate that: (1) porosity is greatest in the direction of maximum geometric resistance to bending, along the Imin axis; and (2) porosity differences between the Imax and Imin fields decrease as the bone becomes more circular in cross-sectional shape.

Adult↗
PubMed1989

The relative effects of collagen fiber orientation, porosity, density, and mineralization on bone strength.

This investigation determined the relative importance of collagen fiber orientation, porosity, density, and mineralization in determining the tensile strength of bovine cortical bone. Thirty-nine specimens were tested for failure stress and the values of eight histologic and compositional parameters: collagen fiber orientation, wet and dry apparent density, percent mineralization of the bone matrix, and several components of porosity (Haversian canals, Volkmann's canals, and plexiform vascular spaces). Linear regression analysis showed that collagen fiber orientation was consistently the single best predictor of strength. Mineralization of the bone matrix was generally a poor predictor of strength. Density and porosity ranked between these variables in importance. Multiple regression equations containing all significantly correlated variables achieved correlation coefficients of 0.607 for plexiform bone and 0.881 for osteonal bone. Also, separate analysis of plexiform and osteonal specimens showed that the latter group was weaker even though it was less porous, apparently because it had collagen fibers which were less longitudinally oriented. This study suggests it is feasible to develop better empirical formulae for the prediction of cortical bone strength than are currently available if a variety of variables is introduced. Additional data are needed to confirm these results.

Animals↗
PubMed1985

Porosity reduction and its associated effect on the diametral tensile strength of activated acrylic resins.

Each acrylic resin tested is basic to the armamentarium of the clinical dentist. From this study it is apparent that there exist several possible mechanisms that will aid in the reduction of porosity and subsequently enhance the tensile strength properties of chemically activated acrylic resins. With the manufacturer's recommended powder to liquid ratio mixtures, indications are that only small increases in curing pressure (approximately 0.68 MPa) are required to substantially enhance strength levels of the test materials. Therefore, when cured under conditions that avoid residual stress buildup, the small increases in pressure attainable by modified pressurization devices may indeed be of benefit in reducing porosity and enhancing the tensile strength of the acrylic resins. Similar increases in strength appear possible with various combinations of powder particle sizes and powder/liquid ratios used in an effort to reduce the monomer concentration in clinically desirable acrylic mixtures. It is important to realize that alteration of powder/liquid ratio and powder particle size mixtures offers a method of reducing porosity without the addition of external pressure. However, at this time it is not recommended that these sophisticated alterations of the basic resin components be performed by the clinician.

Acrylic Resins↗
PubMed1988

The effect of vacuum-mixed autopolymerizing acrylic resins on porosity and transverse strength.

Three brands of autopolymerizing acrylic resin were mixed and polymerized three different ways and tested for transverse strength and porosity. The procedures tested were bench-curing at ambient temperatures, vacuuming the mix before bench-curing, and curing in a pressure device. The data indicate that both vacuuming the mix and pressure-curing are successful in reducing porosity and increasing transverse strength. These improved properties would be valuable in the fabrication of provisional restorations and occlusal splints. The following conclusions can be drawn: 1. Use of a pressure device decreases porosity and increases the transverse strength in samples of autopolymerizing acrylic resin. 2. Use of a vacuum device on the mixed acrylic resin works as well as pressure polymerizing. 3. Use of either technique is indicated to improve the quality and longevity of autopolymerizing acrylic resin restorations, orthodontic appliances, and occlusal splints.

Chemical Phenomena↗
PubMed1989

The effect of sprue attachment design on castability and porosity.

Sprue attachment design is an important and controversial variable that can affect casting characteristics of castability and porosity. Four sprue attachment designs--straight, flared, abrupt constriction, and gradual constriction--were investigated. Standardized wax copings simulating complete veneer metal ceramic crowns with knife-edge margins were sculpted on refractory investment dies, sprued, invested, and cast with Olympia alloy. The specimens were embedded, sectioned, and polished. Castability was analyzed by measuring the width of the cast meniscus of the margins. The margin widths of the flared and the straight sprue attachment groups were significantly less than the abrupt or gradual constriction attachment group (p less than 0.05). Photomicrographs revealed discernible differences in the relative quantity and location of porosity in the sprue-coping junctions. The straight and flared sprue attachment groups were less porous than the abrupt or gradual constriction groups (p less than 0.01). Flared and straight sprue attachments optimized castability and minimized porosity.

Chemical Phenomena↗