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At least 19 recordsLinked to original sources
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↗
PubMed1979

Surface smoothness and marginal fit with phosphate-bonded investments.

Two phosphate-bonded investments and one calcium sulfate investment were evaluated for the surface smoothness and marginal fit they impart to gold castings. A modified technique was also evaluated for each phosphate-bonded investment, where the silica sol was not diluted and the spatulation time was reduced. The results of this study lead to the following conclusions: 1. The marginal fits obtained with all four phosphate-bonded methods were comparable to each other and superior to that obtained with the calcium sulfate investment. 2. The presence of nodules on the surface of the castings was more prevalent with the phosphate-bonded investments. However, this effect was not statistically significant. 3. Clinical assessment of the roughness of the castings revealed that all the methods tested produced clinically acceptable castings. 4. Visual observation by five dentists revealed that both the recommended and modified techniques for one of the phosphate-bonded investments (Ceramigold) produced a smoother surface than any other investment tested. Rating of scanning electron microscope photographs (X600) revealed no difference in the surface roughness between any of the castings. Consequently, no definitive relation between investment type or technique and surface roughness was established. 5. No correlation was demonstrated between surface roughness, as evaluated by either clinical observation or scanning electron microscope photography, and marginal fit of the castings.

Dental Alloys↗
PubMedDate not supplied

The effect of five investing techniques on air bubble entrapment and casting nodules.

Five different investing techniques were used to invest lost-wax casting patterns. The use of an investing technique that subjects the invested casting ring to air pressure (40 lb per square inch) during setting was found to produce less air bubble/cast nodule incidence than did the other four techniques investigated. Not all cast nodules can be seen by the unaided eye; magnification is needed. More cast nodules than air bubbles were seen at the interface of pattern and investment, showing that there may be many air bubbles below the investment surface that are entered by the incoming alloy during casting. The effect of a surface-tension reducing (STR) agent on the air bubble incidence between pattern and investment depends on the investing technique used, although all techniques used showed a reduction in cast nodule incidence when an STR agent was used. Sprue direction was also found to influence the incidence of casting nodules.

Air↗
PubMed1990

[Effect of investment on adaptation of the PFM coping].

The purpose of this study is to investigate the influence of two investing methods, one time investment and two-time investment, to the adaptability of the PFM coping, using CW-PA base alloy and its phosphate investment. The result shows that the expansion of the investment is influenced by the investing methods (P less than 0.05). One-time investment has a larger expansion than two-time one for the cause of that it is without limit of the gypsum investment. It can compensate the Ni-Cr-Nb base alloy's contraction more fully, therefore a better fit of the PFM coping can be got.

Dental Alloys↗
PubMed1989

[The influence of mixing and heating on the compressive strength of investment materials].

In the present study, the compressive strength of four representative dental investment materials was compared. The whole investigation was divided in three experiments. In the first one the effect of different ways of mixing on the compressive strength of the investments was examined. In the second the compressive strength of investments mixed mechanically under vacuum was compared: a) two hours after mixing, b) at the highest heating temperature and c) at room temperature after the heating procedure. In the third experiment, a comparison was made between the compressive strength of investments at the highest heating temperature. The investments were mixed mechanically under vacuum but half of the specimens were placed in a pressure device during setting. From the results obtained the following conclusions were made: a) Mixing mechanically under vacuum increases the compressive strength of the investments, b) the compressive strength of phosphate-bonded investments increases at the highest temperature of the heating procedure and c) the use of a pressure device during the setting of the investments results also in an increased compressive strength.

Calcium Sulfate↗
PubMed1989

Development in vitro of investment-free marsupial embryos during cleavage and early blastocyst formation.

Twenty embryos at the cleavage-arrested four-cell stage of the brown antechinus, Antechinus stuartii, were used to develop a method to obtain investment-free embryos by incubation at 35 degrees C in 2.5% pancreatin, 0.05% trypsin, and 0.05% pronase. Control intact embryos and the investment-free embryos were incubated in Dulbecco's Modified Eagle's Medium with high glucose and 10% foetal calf serum in 5% CO2 in air at 35 degrees C for 48 h. Release of embryos from the investments (shell, mucoid, and zona pellucida) took 4-4 1/2 h in pancreatin, 6 h in trypsin, and 55 min to 1 1/4 h in pronase. Embryonic survival in vitro was best following pronase digestion. Pronase concentrations of 0.05%, 0.1%, 0.25%, 0.5%, and 1.0% were used to free one- to 16-cell stage embryos of brown antechinus and the stripe-faced dunnart, Sminthopsis macroura, from their investments. Postincubation survival and development of embryos in vitro was best using between 0.05% and 0.25% pronase. Blastomeres in both intact and investment-free embryos shared similar characteristics during cleavage and blastocyst formation. The combined effect of these characteristics was that in intact embryos, no morula was formed, and the blastocyst developed, when cell numbers were high enough (about 32 cells), as a unilaminar structure flattened against the zona pellucida and without an inner cell mass. In investment-free embryos, the blastomeres dispersed over the base of the culture vessel. The investments were necessary to confine the blastomeres, to provide a surface for blastomere flattening, and to allow normal cellular associations to develop.

Animals↗
PubMed1992

Relationships among marital investment, marital satisfaction, and marital commitment in domestically victimized and nonvictimized wives.

The present investigation examined the association between marital investment, marital satisfaction, and commitment to marriage among physically abused women. We applied an investment model and a social learning model to understanding victimized wives' satisfaction and commitment to stay married. Thirty wives who reported physical abuse and 58 nonabused wives completed measures of marital stability, investment in marital problem solving, and dyadic adjustment. Investment in marital problem solving was assessed by having subjects indicate how much energy that they have put into solving 34 common marital problems and whether their efforts were successful or not successful. Consistent with a social learning model but counter to an investment perspective, correlational and multiple regression analyses for each group revealed that failed investment was significantly related to lower, not greater, commitment. Group differences also emerged. Whereas nonabused wives' commitment was related to their dyadic adjustment abused wives' commitment was related to their level of failed investment. Results are consistent with the notion that women may remain in abusive relationships because of psychological entrapment.

Adult↗
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↗
PubMed1986

Particle and pore size distributions of investments.

The particle-size distributions of investment powders and the pore-size distributions of set-fired investments were investigated by electrozone size analysis, and by mercury intrusion scanning porosimetry, respectively, for a number of different investments, representing all three types available, namely: the gypsum-, phosphate- and silicate-bonded. The pore volume (V), the pore surface area (S), and their first derivatives with respect to radius, r, dV/dr and dS/dr, were obtained with pressures up to 414 MPa corresponding to spherical pores of 0.0018 micron radius if the Washburn equation is to apply. Results distinguished pores with a range of different sizes. Besides the porosity due to the matrix binder, porosity was also attributable to the refractory components. This latter type of porosity occurred with pore radii below about 0.03 micron, whereas matrix porosity occurred above this pore size. Matrix porosity for the phosphate materials was smallest at about 0.03 to 0.5 micron in radius, followed by the gypsum materials at about 0.3 to 0.6 micron, and by the silicate materials at about 1 to 10 micron. The particle-size distribution of the investment powders may affect both types of porosities, whereas the setting chemistries of the particular investment types may affect matrix porosity, by the generation of gaseous by-products. No major distinctions in pore size and distributions occurred between air-set and hygroscopic-set materials. This study emphasizes that at present, knowledge of the total pore volume only is inadequate for characterizing porosity distribution and hence investment permeability.

Calcium Sulfate↗
PubMedDate not supplied

[High temperature investments. 1. Evaluation of some physical properties].

An evaluation of linear dimensional alterations of normal and hygroscopic setting of 3 phosphate-bonded investments and gypsum-bonded investments was made. The phosphate-bonded investments were processed with 100, 75, 50 and 25% special liquid. We investigated the maximum temperatures tolerated by the investments, in relation to the normal setting reactions. To evaluate expansion of normal and hygroscopic setting an electronic palpater was used, with the investments confined. The temperatures of the thermal reactions were detected by a digital thermometer. We confirmed that the CERAMIGOLD and HI-TEMP investments, processed with 75% special liquid, presented a greater linear expansion than the normal settings. The HI-HEAT presented less expansion than the normal setting and greater linear expansion than the hygroscopic setting. The MULTI-VEST tolerated the highest temperature during the evaluation.

Calcium Sulfate↗
PubMed1978

[Dilatometry of gypsum bonded investment (author's transl)].

Although many investigations on the thermal expansion of dental investments have already been done, the conditions upon which thermal expansion was measured were not always definitely shown and the phenomena on thermal behavior of dental investments were not reasonably interpreted. In this investigation the effects of W/P ratio of samples, heating rate and furnace atmosphere were studied by "Push Rod" Dilatometer in order to attempt to standardise dilatometry of dental investments. All experiments were designed with two-way layout techniques. The main results were as follows, 1) W/P ratio, heating rate and furnace atmosphere have significant effects on the thermal expansion curves of the gypsum bonded investments. 2) One steep expansion and three stages of shrinkage in heating process of these investments from room temperature to about 900 degrees C were observed. 3) The quantity of the steep expansion, first and second stages of shrinkage and the expansion at 650 degrees C were affected by W/P ratio. 4) The temperature at which the steep expansion or shrinkage occurred were affected by heating rate. 5) Furnace atmosphere affected on both quantity of the steep expansion or shrinkage and their temperature. It also affected on the expansion at 650 degrees C. Then, these factors should be considered in dilatometry of gypsum bonded investments and in dental practice.

Calcium↗
PubMed1992

Development of a new investment for high-frequency induction soldering.

This study developed a new investment for induction soldering using high frequency induction heating. Ninety-five mass% magnesia clinker and 5 mass% dental stone were selected for the main constituents. The magnesia investment itself was scarcely affected by induction heating, so the addition of metal powders such as Fe, Ni, Co were investigated. Among these three powders, the addition of 10 mass% cobalt powder was most effective. This investment needed only 40 seconds of high frequency induction heating to go from room temperature to 900 degrees C without preheating. Thermal expansion of this investment in a vacuum atmosphere was 1.25% at 1000 degrees C. Dimensional changes during induction soldering were measured using German-silver and silver solder. When the new magnesia investment containing 10 mass% Co powder was used, the dimensional change was -0.2%. This contraction was less than when a magnesia investment without metal additives was used.

Cobalt↗