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PubMedDate not supplied

Voids and porosities in class I micropreparations filled with various resin composites.

In this in vitro study, voids inside a minimal occlusal restoration using different consistencies of resin composite and various application techniques were investigated. One hundred and fifty-two simulated, minimally invasive preparations, including a prepared fissure and an excavated carious dentin lesion, were ground in perspex blocks. After applying an acrylic primer (Artglass Connector, Kulzer), the preparations were restored with the adhesive PhotoBond (Kuraray) and one of three resin composites: a packable composite (Prodigy Condensable-Kerr), a syringable composite (Clearfil Photo Posterior, Kuraray) and a flowable composite (Revolution, Kerr). The restorations were inserted according to eight protocols (n = 19). In three groups, the composite was placed in bulk. In another three groups, a layer of flowable composite was placed first, then cured, followed by a second layer of one of the three composites. In two groups, the first layer of flowable composite was left uncured before a second layer of a packable or syringable composite was inserted. The perspex blocks were sectioned and inspected for the presence of voids. Statistical analysis was conducted using Fischer's exact tests at p < 0.05. The results showed that restoring minimal preparations in the absence of porosities and voids was very difficult to achieve. Placing a layer of flowable composite that was left uncured, directly followed by injecting a medium-viscous composite, was the technique that resulted in the most homogeneous restoration.

Composite Resins↗
PubMed2004

The influence of sintering temperature on the porosity and strength of porous hydroxyapatite ceramics.

The present paper reports on the influence of sintering temperature on the porosity and strength of porous hydroxyapatite (HA). HA powder was first prepared by the sol-gel precipitation method using calcium hydroxide and ortho-phosporic acid. The fine HA powder, measuring <50 microm was then mixed into a slurry with the addition of binder agent, being a mixture of sago and PVA. A small amount of sodium dodecyl sulphate was also used as a foaming agent. Porous HA samples were then prepared via slip casting technique. The surface morphology of the sintered samples was observed under scanning electron microscopy at 20 kV and the compositions were determined via SEM-EDX. A universal testing machine was used to determine the compaction strength of the sintered samples.

Ceramics↗
PubMedDate not supplied

Optimum surface properties of oxidized implants for reinforcement of osseointegration: surface chemistry, oxide thickness, porosity, roughness, and crystal structure.

PURPOSE: To investigate detailed surface characterization of oxidized implants in a newly invented electrolyte system and to determine optimal surface oxide properties to enhance the bone response in rabbits. MATERIALS AND METHODS: A total of 100 screw-type titanium implants were prepared and divided into 1 control group (machine-turned implants) and 4 test groups (magnesium ion-incorporated oxidized implants). Forty implants were used for surface analyses. A total of 60 implants, 12 implants from each group, were placed in the tibiae of 10 New Zealand white rabbits and measured with a removal torque test after a healing period of 6 weeks. RESULTS: For the test groups, the oxide thicknesses ranged from about 1,000 to 5,800 nm; for the control group, mean oxide thickness was about 17 nm. The surface morphology showed porous structures for test groups and nonporous barrier film for the control group. Pore diameter ranged from < or = 0.5 microm to < or = 3.0 microm. In regard to surface roughness, arithmetic average height deviation (Sa) values varied from 0.68 to 0.98 microm for test implants and 0.55 microm for control implants; developed surface ratio (Sdr) values ranged from 10.6% to 46% for the test groups and were about 10.6% for the control group. A mixture of anatase and rutile-type crystals were observed in the test groups; amorphous-type crystals were observed in the control group. After a healing period of 6 weeks, removal torque measurements in all 4 test groups demonstrated significantly greater implant integration as compared to machine-turned control implants (P < or = .033). DISCUSSION: Determinant oxide properties of oxidized implants are discussed in association with bone responses. Of all surface properties, RTVs were linearly increased as relative atomic concentrations of magnesium ion increase. CONCLUSIONS: Surface properties of the oxidized implants in the present study, especially surface chemistry, influenced bone responses. The surface chemistry of the optimal oxidized implant should be composed of approximately 9% magnesium at relative atomic concentration in titanium oxide matrix and have an oxide thickness of approximately 1,000 to 5,000 nm, a porosity of about 24%, and a surface roughness of about 0.8 microm in Sa and 27% to 46% in Sdr; its oxide crystal structure should be a mixture of anatase- and rutile-phase crystals.

Animals↗
PubMedDate not supplied

[Aortobifemoral prostheses with "0" porosity. Results after 2 years' experience].

During the last years diverse types of Dacron prosthesis without porosity (because to be impregnated by different materials) have appeared. In the presented study, outcomes from three different types of prosthesis (differentiated by the impregnated material) were evaluated and a comparison with classical prosthesis was made.

Aorta, Abdominal↗
PubMed1993

High porosity PTFE improves endothelialization of arterial grafts without increasing early thrombogenicity.

OBJECTIVE: High porosity (HP) (90 micron internodal distance) PTFE grafts were implanted into the carotid and femoral arteries of dogs to investigate early thrombogenicity, patency, and endothelialization. EXPERIMENTAL DESIGN: Standard PTFE (STD) grafts (30 micron internodal distance) were used as controls. 12 HP and 12 STD grafts were implanted into 6 dogs. Indium-111 labeled platelets were infused intravenously after graft implantation. A graft platelet accumulation index (GPAI) was calculated as the ratio of radioactive emission from the PTFE grafts excised at 48 hours to the emission from a native arterial segment. Another 12 HP and 12 STD grafts were implanted into femoral and carotid arteries to assess patency and endothelialization at 4 and 18 weeks. RESULTS: There was no significant difference in the GPAI of the HP and STD grafts at either the carotid (HP = 31.5 +/- 9.7, STD = 30.6 +/- 11.8; p > 0.05) or femoral (HP = 34.0 +/- 5.0, STD = 31.5 +/- 7.9; p > 0.05) positions. Combined data (carotid and femoral HP vs. carotid and femoral STD) also did not demonstrate a difference in GPAI (HP = 32.8 +/- 7.5, STD = 31.1 +/- 9.6; p > 0.05). Patency rates were the same at 4 weeks (75%), but greater in the HP grafts at 18 weeks (HP = 75%, STD = 37%; p > 0.05). No difference was noted in the percentage of graft endothelialization at 4 weeks (HP = 5.2 +/- 5.8, STD = 5.0 +/- 4.0; p > 0.05), however, at 18 weeks the HP graft had significantly more endothelial coverage compared to STD grafts (HP = 75.2 +/- 13.9, STD = 22.6 +/- 9.5; p < 0.01). CONCLUSIONS: Given that HP PTFE is no more thrombogenic than STD PTFE, and that it provides superior endothelialization, HP grafts should continue to be developed and studied for potential clinical use.

Animals↗
PubMed2000

Effect of porosity and surface hydrophilicity on migration of epithelial tissue over synthetic polymer.

The relative effects of porosity and surface chemistry on the migration of epithelial tissue over the surface of a polymer were determined in vitro. These studies compared nonporous polymers with those having 0.1-microm diameter track-etched pores and were conducted on polycarbonate and polyester. Epithelial tissue migration over the polymer surface was stimulated by the presence of these pores. The surface chemistries of the polymers were modified by deposition of various polymer films using radio frequency gas deposition, giving a range of surfaces that varied in air:water sessile contact angle (SCA) of between 26 and 100 degrees. Tissue migration on the nonporous surfaces was affected by the surface chemistry, being generally linear as a function of the SCA and higher on hydrophilic than on hydrophobic surfaces but reduced if the hydrophilic surface had a mobile chemistry. The effects of the 0.1-microm diameter pores and the surface hydrophilicity were additive with the maximal level of epithelial tissue migration occurring on a porous, hydrophilic polymer surface.

Animals↗
PubMed2000

Separation of different physical forms of plasmid DNA using a combination of low electric field strength and flow in porous media: effect of different field gradients and porosity of the media.

The retention of different physical forms of DNA by an electric field in a chromatography system was studied. We were able to effectively separate the supercoiled and the open circular forms of plasmid DNA using this type of electrochromatography system. Chromatography columns were packed with porous beads, and an axial electric field was applied so that convective buffer flow opposed the direction of electrophoresis of the DNA. A model system composed of approximately equal amounts of the super-coiled and open circular forms of the plasmid pBR 322 (4322 base pairs) was used to test the separation. Chromatography beads (agarose-based) with different porosities were used to determine the effect of the stationary phase on the separation. The porous media did not have a major effect on the separation, but the best separations were obtained using porous chromatography media made with the highest agarose concentration (10% agarose). Selective elution of plasmid DNA with different forms was obtained by either increasing the flow rates or decreasing the electric field strength (by steps or a gradient). In all the separations, the more compact supercoiled form of the plasmid was retained less strongly than either the open circular form (nicked) or the linear form. High molecular weight host genomic DNA was more strongly retained than the plasmid DNA. Increasing the ionic strength of the buffer improved resolution and capacity. The capacity of the separation was determined by injecting increasing amounts of plasmid DNA. Satisfactory separation was obtained at sample loading of up to 360 microg of total DNA on a column with dimensions of 2.5 by 11 cm (bed volume of 54 mL). The retention of DNA depends upon a counter-current flow of electrophoresis and convective flow and could be regarded as a type of field flow fractionation. The retention of the DNA by the electric field and flow is discussed in relation to the diffusion coefficients of the DNA.

Buffers↗
PubMed1984

Microdissection by ultrasonication: porosity of the intestinal epithelial basal lamina.

The porosity of the epithelial basal lamina of normal rat intestine was studied by SEM. Epithelial removal was accomplished by prolonged fixation of tissue samples in OsO4 or immersion in aqueous H3BO3, followed by dehydration in acetone and microdissection by ultrasonic vibration. The underlying basal lamina of intestinal epithelium reveals numerous pores of variable size. These pores are more numerous in small than in large intestine and penetrate the entire thickness of the basal lamina. Within the basal lamina overlying lymph nodules, they are numerically increased. Their occurrence is evident in fixed and unfixed, sonicated and unsonicated tissue samples. Microprojections of epithelial cytoplasm are often observed within these pores. The results of this study suggest that migrating cells or epithelial-cell processes induce pore formation in epithelial basal laminae and that these pores may be eventually repaired.

Animals↗
PubMed2005

Mechanism of hierarchical porosity development in MFI zeolites by desilication: the role of aluminium as a pore-directing agent.

The role of the concentration and the nature of aluminium in the creation of hierarchical porosity in both commercial and synthesized MFI zeolites have been investigated through controlled mesoporosity development by desilication in alkaline medium. Framework aluminium controls the process of framework silicon extraction and makes desilication selective towards intracrystalline mesopore formation. An optimal molar Si/Al ratio in the range 25-50 has been identified; this leads to an optimal mesoporosity centred around 10 nm and mesopore surface areas of up to 235 m(2) g(-1) while preserving the intrinsic crystalline and acidic properties. At lower framework Si/Al ratios the relatively high Al content inhibits Si extraction and hardly any mesopores are created, while in highly siliceous ZSM-5 unselective extraction of framework Si induces formation of large pores. The existence of framework Al sites in different T positions that are more or less susceptible to the alkaline treatment, and the occurrence of re-alumination, are tentative explanations for the remarkable behaviour of Al in the desilication process. The presence of substantial extra framework Al, obtained by steam treatment, inhibits Si extraction and related mesopore formation; this is attributed to re-alumination of the extraframework Al species during the alkaline treatment. Removal of extraframework Al species by mild oxalic acid treatment restores susceptibility to desilication, which is accompanied by formation of larger mesopores due to the enhanced Si/Al ratio in the acid-treated zeolite.

Journal Article↗
PubMed2002

The relationship between stress, porosity, and nonlinear damage accumulation in acrylic bone cement.

The long-term survival of cemented hip replacements depends on the ability of the cemented fixation to resist fatigue damage. Damage has been assumed to accumulate linearly (Miner's law) even though it is unlikely to be the case in such a porous brittle material. This study addresses the nonlinear stress-dependent nature of fatigue damage accumulation in acrylic bone cement. Specimens were subjected to a zero-to-tension fatigue load in water at 37 degrees C. A total of 15 specimens were tested, i.e., five specimens at each of three stress levels. The specimens were cyclically loaded to a certain fraction of their fatigue lives and the amount of microcracking present at that time was quantified by counting each crack and measuring its length. This procedure was repeated until the specimen failed. A total of 801 cracks formed in the 15 specimens. All cracks were found to initiate at pores. Crack propagation directions were distributed normally about the direction perpendicular to the applied load at the lower stress levels, but at higher stress, the distribution tended to be broader. At higher stresses, more cracks were produced per pore. The damage accumulation process in acrylic bone cement was found to be nonlinear with the degree of nonlinearity increasing with stress. Furthermore, great variability was found which was attributed to the differences in porosity between specimens. A power law equation is given which describes the predicted relationship between damage accumulation and number of loading cycles as a function of the stress level.

Bone Cements↗
PubMed1977

Porosity in the base metal removable partial denture casting alloys relative to observable metallographic features.

A series of tensile test pieces of the dimensions stated in the American Dental Association Specification No. 14 were produce using both nickel-base and cobalt-base removable partial denture casting alloys. Normal dental casting techniques were employed. Appropriate sections from each specimen were sectioned to half of their original thicknesses, embedded in heat-and pressure-cured conducting mounts, and polished for metallurgical examination. A double electrolytic etching technique was used, employing serially two solutions, in order to maximize the amount of metallographic detail visible. The method proved particularly valuable in the case of the nickel-base alloy as it indicated the presence of considerable interdendritic segregation. The incidence of porosity was evaluated throughout all sections of the specimens and, although found to be especially prevalent in those regions where gross shrinkage effects might be expected to occur, it was also shown to have a diffuse intergranular and interdendritic distribution.

Chromium Alloys↗
PubMed2006

Substrate porosity enhances chondrocyte attachment, spreading, and cartilage tissue formation in vitro.

Tissue engineering is being explored as a new approach to treat damaged cartilage. As the biomaterial used may influence tissue formation, the effects of substrate geometry on chondrocyte behavior in vitro were examined. Articular chondrocytes were isolated and cultured on the surface of smooth, rough, porous-coated, and fully porous Ti-6Al-4V substrates. The percentage of chondrocytes that attached to each substrate at 24 h was determined. After 24 and 72 h, chondrocytes were visualized by scanning electron microscopy and cell areas were measured. Collagen and proteoglycan accumulation within the first 24 h was determined by incorporation with [3H]-proline and [35S]-SO4, respectively. Chondrocyte attachment as well as matrix accumulation was enhanced as substrate surface area increased. Cell areas on the fully porous substrate were over four times greater than on any other substrate by 72 h in culture. After 8 weeks in culture, a continuous layer of cartilaginous tissue formed only on the surface of the fully porous substrate. This suggests that fully porous Ti-6Al-4V substrates provide the conditions that favor cartilage tissue formation by influencing cell attachment and extent of cell spreading. Understanding how substrate porosity influences chondrocyte behavior may help identify methods to further enhance cartilage tissue formation in vitro.

Alloys↗
PubMed1999

Effect of pH in an Aqueous Medium on the Surface Area, Pore Size Distribution, Density, and Porosity of Montmorillonite.

Surface area, pore volume distribution, and porosity of montmorillonite are determined after being exposed to aqueous solutions with various pH values. For measurement, after each pH treatment the clay samples were freeze-dried in order to keep the structure of the clay same as that in the aqueous solution. Surface area and pore size distribution measurements were performed on an unmodified and four pH (2.5, 4.0, 5.5, 9.0)-adjusted clay samples using N(2) and CO(2) as adsorbates. The surface area measurements at lower pH are lower than those measured at higher pH due to the replacement of Na(+) ions from interlayers at lower pH which may be followed by the reduction of repulsive forces. As the pH of the montmorillonite increases to 9.0, the surface area increases almost seven times compared to that at pH 2.5. Pore size distribution was determined by CO(2) adsorption at 273 K for micropores (<20 Å), by N(2) adsorption at 77 K for mesopores (between 20 and 500 Å), and by using both Hg intrusion and N(2) adsorption for macropores (>500 Å). Since N(2) molecules undergo a molecular sieving at 77 K, CO(2) gas at 273 K was used to measure the micropore surface area and gave higher surface area measurements than those measured by N(2). Surface area values measured by CO(2) adsorption ranged between 30 and 200 m(2)/g for montmorillonite while those measured by N(2) adsorption were 13.7-70 m(2)/g in the pH range studied. Copyright 1999 Academic Press.

Journal Article↗
PubMed1987

Histology and ultrastructure of the glands associated with the porose areas on the gnathosoma of Rhipicephalus evertsi evertsi before and during oviposition.

Histological and electronmicroscopical studies have shown that the subcuticular tissue associated with the porose areas of female Rhipicephalus evertsi evertsi consists of paired multicellular, alveolar and lobularly arranged glands. At least two types of cells are clearly distinguishable, according with their location. Proximally, in direct association with the pores, cells with small and long nuclei are present. These cells are aligned along large, elongated lumina containing numerous microvilli and extend deep into the cuticular pores. They are separated from the extraintegumental space by cuticular valves. The distal gland sections are characterized by cells with large nuclei which are mostly arranged in the form of rosettes. These cells, which function as secretory cells, contain many mitochondria, smooth and rough endoplasmic reticulum and membrane-lined vesicles. The glands are always present in female ticks and their dorso-ventral extension increases continuously with feeding, reaching a maximum depth during oviposition.

Animals↗
PubMed2001

High-resolution scanning electron microscopic evaluation of cell-membrane porosity by ultrasound.

The effect of low-intensity ultrasound on HL-60 cells (human promyelocytic leukemia cells) in the presence of the photo sensitizing drug merocyanine 540 (MC 540) was evaluated morphologically, using a high-resolution scanning electron microscope and a transmission electron microscope. Exposure of HL-60 cells to ultrasound without MC 540 resulted in a decrease of finger-like processes in the cells. The cells showed many undulating ruffles on the surface. Distinct pits or holes in the membrane were not observed in these cells. The surface of HL-60 cells treated only with MC 540 was relatively smooth compared with that of control cells. HL-60 cells exposed to ultrasound in the presence of MC 540 showed apparent surface deformation. Numerous crater-like depressions of heterogeneous dimensions were observed in many cells. In addition, various-sized pores were noted in the cell membranes of more damaged cells. These results indicate that cell degeneration was induced by a rapid change in cell membrane porosity during sonication in the presence of MC540.

Apoptosis↗
PubMed1987

Early endothelial coverage of synthetic arterial grafts: porosity revisited.

Synthetic arterial grafts fail because of thrombosis. Rapid endothelial coverage would be expected to generate a minimally thrombogenic surface and reduce the rate of failure. We investigated the possibility that such a lining could be established by transmural capillary ingrowth in polytetrafluoroethylene (30 or 60 micron internodal distance) and Dacron baboon aortoiliac grafts of 4 mm in diameter and 5 to 7 cm in length. All grafts demonstrated endothelial ingrowth from the cut edges of adjacent artery. The central portions of the 30 micron polytetrafluoroethylene grafts were still not healed at 3 months. Two of six Dacron grafts were healed 1 month postoperatively and all were healed at 3 months, whereas all 60 micron polytetrafluoroethylene grafts were healed 2 weeks postoperatively. At early follow-up, islands of endothelium were seen in the middle of the 60 micron polytetrafluoroethylene and Dacron grafts. These observations support the concept that transmural migration of capillaries can provide multiple sources of endothelium and early endothelial coverage of porous synthetic arterial grafts. This response is affected by the porosity and possibly the thrombogenicity of the graft material.

Animals↗
PubMed1988

ATP hydrolysis induces variable porosity to mannitol in the mitochondrial inner membrane.

Osmotic titration of ATPase activity in rat liver mitochondria was consistent with enhanced porosity of the mitochondrial inner membrane to mannitol due to ATP hydrolysis even when endogenous respiration was inhibited by rotenone. The occluded ATPase activity, which exhibits osmotic activation with an optimum near isotonicity, depends both on the ATPase activity per se and on the activity of the ADP/ATP carrier. Purified ADP/ATP carrier incorporated into small, unilamellar liposomes was critically shown to exhibit dependence of its activity on the osmotic pressure differences across the membrane, with maximal activity corresponding to isotonicity, regardless of the actual internal tonicity.

Adenosine Triphosphate↗