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PubMedDate not supplied

Porosity determination of ceramic materials by digital image analysis--a critical evaluation.

Measuring the porosity of materials by digital image analysis of micrographs is a well-established and convenient method for the testing of metallic samples. However, when applied to ceramic materials, this method has been shown to be much less reliable and poorly reproducible. The purpose of this present work is to clarify the reason for this deficiency, involving many porosity measurements, performed on plasma-sprayed zirconia, under systematically varied microscopic imaging conditions, and the porosities being calculated using various evaluation methods. Comparison between of the results has shown that the present state of the image analysis method is not satisfactory for absolute porosity measurements on ceramic materials. It can be useful as a convenient tool for comparative measurements, however, if the imaging conditions maintained in the microscope and the evaluation method are held to be exactly identical.

Journal Article↗

PubMed2000

Quantification of the Relationship between Porosity and Interparticle Forces for the Packing of Wet Uniform Spheres.

This paper presents an attempt to quantify the relationship between porosity and interparticle forces. In particular, it concerns the packing of wet mono-sized spheres where capillary force is dominant. The interrelationships between capillary force, porosity, and liquid content are first analyzed based on well-established theories and experimental observations. The resultant data are then used to correlate porosity with the force ratio defined as the average capillary force to the gravity of a particle. Application of this correlation is finally demonstrated by examples of porosity prediction. Copyright 2000 Academic Press.

Journal Article↗

PubMed1976

[The porosity of bone cement (author's transl)].

This paper describes a method of measuring the porosity, shape, distribution and formation of cavities in acrylic cement. We distinguish between big spherical cavities greater than 60 mu and small cavities less than 60 mu which form a variable "basic porosity" with a large number, but a minor volume of bubbles. The bubbles are formed in two different ways. The first is through introduction of air bubbles in the mixing phase by stirring the cement before the working time. These bubbles expand little by temperature rise. The second method of formation is through neoformation of bubbles by evaporation of the monomer at about 100 degrees C. This neoformation of porosity expands the cement. The rise of volume through the neoformation and expansion of bubbles is able to compensate the shrinking of cement due to the polymerization. This effect, however, cannot be currently controlled. Cement strength is influenced by the degree of porosity.

Air↗

PubMed1975

Permeability and porosity of dental casting investments.

Permeability of various gypsum- and phosphate-bonded investments was measured during conventional burn-out procedures. Porosity determinations were made on specimens cooled to room temperature after burn-out. As a group, the gypsum-bonded investments were found to be more permeable than the phosphate-bonded investments. Two phosphate-bonded investments were determined to be relatively impermeable to gas flow, while another exhibited permeability comparable to that of the gypsum-bonded investments. In spite of differences in permeability, the porosity of each type of investment was nearly constant. The porosity of the phosphate-bonded investment was approximately three-fourths that of the gypsum investments. These investments were modified by the addition of varying amounts of acrylic polymer for the purpose of altering permeability. The addition of acrylic polymer increased porosity and permeability of all of the materials included in this investigation. The acrylic additives, however, had no effect on the permeability of relatively impermeable investments unless used in high concentration. The results of this investigation would tend to substantiate the need for special spruing and venting procedures.

Acrylic Resins↗

PubMed1983

Porosity in boilable acrylic resin.

An acrylic resin developed to be processed by boiling for 20 minutes in water was compared to a conventional heat-processed acrylic resin for porosity when processed according to the manufacturer's directions. No porosity was found in the conventional resin in thicknesses up to 19.5 mm. The boilable resin developed porosity in thicknesses of 6 mm and greater. The porosity increased with increased thickness. The boilable resins should not be used for long-term prostheses or those requiring a thickness of acrylic resin that approaches 6 mm.

Acrylic Resins↗

PubMed1990

Comparison of the effects of three sprue designs on the internal porosity in crowns cast with a silver-free high-palladium alloy.

This study tested the effect of bsprue design on internal porosity of a silver-frees high-palladium alloy. The designs evaluated consisted of: (1) a cylindrical sprue, (2) a cylindrical sprue with a reservoir, and (3) cylindrical sprue with a constriction at the point of attachment with the pattern. Ten identical complete crowns were made with each sprue design. The cast crowns were embedded in epoxy resin, sectioned, and polished. A total of six sites for each sample were analyzing computer. The mean amount of internal porosity from all analyzed sites for each sprue design was calculated as a percent site porosity per total site and differences between the experimental sites and groups tested. The analysis of variance found no significant differences among the sprues and no significant interaction, but determined a significant difference (p less than 0.05) among the sites analyzed. Tukey's studentized range test showed that the sprue contained a significantly greater percentage of porosity than any of the other sites analyzed.

Analysis of Variance↗

PubMed1989

Porosity determination of cast investment by a wax-infiltration technique.

A reproducible method of determining the porosity (pore volume) of cast investment materials is described. This procedure, requiring no highly specialized equipment, involved the infiltration of a test sample with paraffin wax and the weighing of the wax-infiltrated sample in both air and water. Pore-volume wax is then extracted with chloroform and the sample reweighed. The difference in weight is used to calculate the porosity of the investment material. Pore-volume data thus obtained are comparable to those resulting from standard techniques and far more sophisticated (and expensive) instrumentation. The porosities of hand-mixed samples of gypsum-bonded, phosphate-bonded and silica-bonded investments were 53.9 per cent, 36.9 per cent and 31.4 per cent and those of the vacuum-mixed samples were 52.5 per cent, 31.3 per cent and 26.9 per cent, respectively. The results show that gypsum-bonded investments were more porous than phosphate-bonded investments while silica-bonded investments were the least porous. Hand-mixed samples appeared to have greater porosity than vacuum-mixed samples.

Calcium Sulfate↗

PubMed1985

The effects of eggshell porosity on blood-gas and acid-base status of domestic fowl embryos within eggs of the same weight.

Eggshell porosity affects the metabolism and growth of the developing embryo and is likely, therefore, to influence blood-gas and acid-base status. PO2 in the airspace and in blood from the allantoic vein, PCO2 in the airspace and in blood from the allantoic artery and allantoic vein, and pH of blood from the allantoic artery and vein are all affected by shell porosity. Low porosity eggshells result in an increased retention of carbon dioxide within the egg, in partial compensation for which an increase in the level of bicarbonate in the blood is predicted. It is concluded that some of the wide variation in blood physiology data between eggs at the same stage of incubation, which has been recorded in the scientific literature, is the result of variation in shell porosity between eggs.

Acid-Base Equilibrium↗

PubMed1987

The rhythmic relation between antler and bone porosity in Danish deer.

The interrelationship between porosity of antlers and metacarpal bones and annual physiologic osteopenia has been investigated in mature Danish male Roe deer (Capreolus capreolus). The study shows a highly significant inverse correlation between porosity in the antlers and porosity in the metacarpal bones, indicating a necessary calcium mobilization from the bones for the mineralization of the antlers. The investigation further suggests that the decreasing porosity of the antlers throughout the antler period, reaching very low values, may be the cause of antler shedding.

Animals↗

PubMed2000

Surface roughness, porosity and wettability of gentamicin-loaded bone cements and their antibiotic release.

In this study, the release of gentamicin as a function of time was measured for six different gentamicin-loaded bone cements and related with the surface roughness, porosity and wettability of the cements. Initial release rates varied little between the six bone cements (CMW1, CMW3, CMW Endurance, CMW 2000, Palacos, and Palamed) and ranged from 8.6 to 14.1 microg/cm2/h. The total amounts of gentamicin released after 1 week varied between 4.0 and 5.3% of the total amount of antibiotic incorporated for the CMW cements and was 8.4% for Palacos. Palamed released after 1 week significantly more of the gentamicin incorporated (17.0%). The wettability of all cements was similar (water contact angles between 70 and 80 degrees), but the surface roughness and the porosity of the cements varied markedly. Initial release rates increased with surface roughness, although the correlation coefficient was low (0.64), while total amounts released increased linearly (correlation coefficient 0.97) with the bulk porosity of the cements. Consequently, it can be concluded that the release kinetics of gentamicin from bone cements is controlled by a combination of surface roughness and porosity.

Bone Cements↗

PubMed2002

A synthetic aragonite-based bioceramic: influence of process parameters on porosity and compressive strength.

We investigate the influence of process parameters such as weight fraction and particle size of pore-former, and isostatic pressure, on porosity and compressive strength of non-sintered porous calcium carbonate biomaterials compacted at high pressure in uniaxial or isostatic mode. Experiment design and results analysis are performed according to a two-level 2k factorial design method (FDM). Results indicate that only the weight fraction of pore-former (wt fpf) influences significantly the porosity and the compressive strength. The porosity P, is described by a linear function of wt fpf, and the compressive strength sigma(comp), by an exponential one. For materials compacted under uniaxial pressing: P (vol%) = 33.7 + 85.4 (wt fpf) and sigma(comp) (MPa) = 28.8e(-9.2(wt fpf)) with 0.1 < or = wt fpf < or = 0.3. For materials compacted in isostatic mode: P (vol%) = 33.9 + 82.1 (wt fpf) and sigma(comp) (MPa) = 24.0e(-7.0(wt fpf)) with 0.15 < or = wt fpf < or = 0.35. The pore-former particle size has no significant influence on both properties. The increase in isostatic pressure provides slightly lower porosity and better compressive strength. For a fixed fraction of pore-former, isostatic pressing leads to a better compressive strength than uniaxial pressing. This study indicates that, for a constant amount of pore former, the size of macropores can be adjusted to reach optimal bone-ingrowth without change in compressive strength.

Biocompatible Materials↗

PubMed2001

Effect of drying rate on porosity and tabletting behaviour of cellulose pellets.

The purpose of this study was to investigate the effect of drying rate during static drying on certain physical properties of pellets. Pellets were prepared from microcrystalline cellulose by granulation with different agglomeration liquids (various ethanol/water ratios) and thereafter dried without agitation at different drying rates. The dry pellets were characterised with respect to their shape, porosity, and compression shear strength and the tensile strength of tablets formed from pellets with low and high drying rates was determined. Drying of the pellets occurred at a falling rate and the reduction in liquid content with time obeyed a first order type of relationship. An increased drying rate did not affect the shape and surface texture of the dried pellets and did not cause them to fracture. However, the drying conditions did affect pellet porosity, with an increased drying rate resulting in more porous pellets. Through a relationship with pellet porosity, the drying rate also affected the deformability of the pellets (as assessed from Kawakita 1/b values) and their ability to form tablets. Owing to a strong effect of porosity on pellet compactability, marked changes in tablet tensile strength with variations in drying rate may be obtained.

Cellulose↗

PubMed1998

Fatigue of bone cement with simulated stem interface porosity.

Cracks in bone cement have been observed in carefully examined post-mortem preparations of cemented stems. These cracks were probably caused by fatigue, and frequently appeared to initiate at pores. Ubiquitous porosity, occurring preferentially at, or near, the stem, is most likely caused by polymerization shrinkage. Preparation of air-free cement has only a marginal influence on the interface porosity, but pre-heating the stem in order to reverse the direction of polymerization can reduce or eliminate it. To estimate the impact of interface porosity on the fatigue strength of bone cement, test plates for this study were cast in a steel mold without release foils, and with one side of the mold warmer. Sample plates so prepared from chilled, partial vacuum-mixed PALACOS, have one face essentially pore-free and the other porous, the extent and morphology of the porosity being very similar to that observed on the stem-cement interface. Four-point bending fatigue strength, determined after 60 d conditioning in Ringer's solution at 37 degrees C, was only 20 MPa (at 10(6) cycles, with the porous side under tension) compared to 30 MPa for conventionally prepared, pore-free material. This corresponds to a 10-100 fold reduction in cycles to failure in the range of stresses predicted to occur in vivo.

Journal Article↗

PubMedDate not supplied

The effects of acetabular cup temperature and duration of cement pressurization on cement porosity in a canine total hip replacement model.

OBJECTIVE: To determine the effect of acetabular cup temperature and duration of cement pressurization on porosity of the acetabular cement mantel. STUDY DESIGN: In vitro study. METHODS: Twenty-four polyurethane foam blocks prepared for acetabular prosthetic implantation were implanted with polyethylene acetabular cups using four combinations and variations of temperature and pressure: (1) high temperature/short-term pressurization; (2) high temperature/long-term pressurization; (3) low temperature/long-term pressurization; and (4) low temperature short-term pressurization. Five 1-mm-thick slices were taken from the center of each block using a tissue processing system. The slices were scanned into a personal computer using a photo slide scanner. Imaging software was used to determine cement surface area and size, number, and distribution of pores. The quality of the cement-implant interface was subjectively evaluated. Statistical analysis of relative cement porosity was performed by a Kruskal-Wallis analysis of variance comparing the four groups individually and combining the short-term pressurization groups versus the long-term pressurization groups. RESULTS: There were no significant differences in cement porosity between the four test groups (P =.11). There were no significant differences in porosity between the combined groups (P =.48). CONCLUSIONS: There is no benefit in prewarming acetabular cups before implantation. There are no deleterious effects of short-term pressurization of the cement during implantation.

Acetabulum↗

PubMed1996

Acetylsalicylic acid may protect the patient by increasing fibrin gel porosity. Is withdrawing of treatment harmful to the patient?

The effect of acetylsalicylic acid in preventing cardiovascular complications is ascribed to acetylation of the enzyme cyclo-oxygenase thereby inhibiting prostaglandin synthesis. Acetylsalicylic acid, however, also acetylates fibrinogen. In the present pilot study, we investigated the permeability, i.e. porosity, of the fibrin gel in male patients with stable angina pectoris treated with this drug before and at 1 and 2 weeks after withdrawal. Ten patients were treated with 75 mg and eight with 160 mg. The results were compared to those in seven untreated healthy controls. Bleeding times were longer during treatment and were reduced after withdrawal indicating patient compliance. Fibrin gels were more porous during treatment although there were large inter-individual variations in porosity. One week after withdrawal, the porosity was reduced by 30 41%, i.e. the network became tighter (75 mg group P = 0.001; 160 mg group P = 0.002). The tightness was more pronounced after withdrawal than in the untreated controls. In conclusion, the protective effect of acetylsalicylic acid may be ascribed to its effect not only on platelets but also on fibrinogen. The withdrawal of acetylsalicylic acid may clause a markedly reduced fibrin gel porosity that we assume is disadvantageous in patients with cardiovascular disease.

Adult↗

PubMedDate not supplied

Effect of estrogen use on tooth retention, oral bone height, and oral bone porosity in Japanese postmenopausal women.

OBJECTIVE: Recent studies in the United States support the protective effect of estrogen use on tooth retention; however, little is known as to how estrogen promotes tooth retention. The aims of this study were to investigate the effects of estrogen use on tooth retention, oral bone height, and oral bone porosity in Japanese postmenopausal women and to clarify how estrogen promotes tooth retention. DESIGN: Relationships among the number of teeth remaining (total, anterior, and posterior teeth), oral bone height, oral bone porosity, bone mineral density of the lumbar spine and the femoral neck, estrogen use status, and the duration of estrogen use were evaluated in 330 Japanese postmenopausal women (mean age +/- SD, 56.8 +/- 7.6 y). RESULTS: Analysis of covariance adjusted for confounding variables revealed that estrogen users (66 women) tended to have more posterior teeth than did nonusers (264 women) (P = 0.065), although there were no significant differences in number of total (P = 0.196) and anterior (P = 0.751) teeth remaining, oral bone height (P = 0.970), oral bone porosity (P = 0.745), and bone mineral density of the lumbar spine (P = 0.459) and the femoral neck (P = 0.749) between estrogen users and nonusers. Multiple regression analysis showed that the duration of estrogen use was significantly associated with number of total (P = 0.019) and posterior (P = 0.007) teeth remaining, independent of age and oral bone height. CONCLUSION: Our results suggest that estrogen may promote tooth retention by strengthening the periodontal attachment surrounding the teeth, but not increasing oral bone height and not decreasing oral bone porosity.

Absorptiometry, Photon↗

PubMed2003

Measuring the porosity and the tortuosity of porous materials via reflected waves at oblique incidence.

An ultrasonic reflectivity method is proposed for measuring porosity and tortuosity of porous materials having a rigid frame. Porosity is the relative fraction by volume of the air contained within a material. Tortuosity is a geometrical parameter which intervenes in the description of the inertial effects between the fluid filled the porous material and its structure at high frequency range. It is generally easy to evaluate the tortuosity from transmitted waves, this is not the case for porosity because of its weak sensitivity in transmitted mode. The proposed method is based on measurement of reflected wave by the first interface of a slab of rigid porous material. This method is obtained from a temporal model of the direct and inverse scattering problems for the propagation of transient ultrasonic waves in a homogeneous isotropic slab of porous material having a rigid frame [Z. E. A. Fellah, M. Fellah, W. Lauriks, and C. Depollier, J. Acoust. Soc. Am. 113, 61 (2003)]. Reflection and transmission scattering operators for a slab of porous material are derived from the responses of the medium to an incident acoustic pulse at oblique incidence. The porosity and tortuosity are determined simultaneously from the measurements of reflected waves at two oblique incidence angles. Experimental and numerical validation results of this method are presented.

Journal Article↗

PubMed1980

Influence of porosity on the viability of the neointima. A histological investigation on implanted synthetic vascular prostheses.

The influence of porosity on the viability of the neointima was evaluated in two types of Dacron vascular prostheses with quite different porosities. It could be concluded that the observed parietal thrombus formation in functioning prostheses, and the dislodgement of the neointima in several of these, might well be attributed to the low porosity of the investigated prostheses, as compared to the recommended value. At the same time it is remarkable that no pronounced difference in the histological picture was observed in the two types of prostheses, despite large differences in their mutual porosities.

Animals↗