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PubMed1979

Distortions in indexing methods and investing media for soldering and remount procedures.

A three-dimensional distortion analysis was made of seven indexing-investment systems and six indexing-remount systems. Measurements were made to within +/- 0.005 mm with a Nikon Profile Projector and a linear variable differential transformer (LVDT); distortions (linear and rotational) were calculated by means of a PDP 11/40 computer system. Mean vector displacements, square root deltaX2 + deltaY2 + deltaZ2, were calculated, and a statistical evaluation of the data was completed. The results of the study indicate: 1. The zinc oxide-eugenol (ZOE) indexing-investment system produced a narrower range and a significantly smaller mean distortion than the other six indexing-investment systems. 2. The ZOE-stone remount technique showed significantly less distortion than the ZOE-low-fusing metal or the ZOE-acrylic resin techniques. 3. The polyether-stone remount technique demonstrated significantly less distortion than either the polyether-low-fusing metal or the polyether-acrylic resin system. 4. The polyether-stone remount system was not significantly different from the ZOE-low-fusing metal system. 5. The ZOE-stone remount technique demonstrated a smaller range of distortions, but those distortions were not significantly different from those of the polyether-stone remount technique.

Acrylic Resins↗

PubMed1985

Internal setting expansion of a dental casting investment measured with strain gauges.

A study was undertaken to investigate the feasibility of using strain gauges to evaluate the internal setting expansion of dental casting investments. A strain gauge was invested in the center of a casting ring to determine the linear setting expansion at the site of the wax pattern. The findings suggest that strain gauges can be used to measure setting expansion internally more accurately than volumetric or external surface measurement techniques. It was also found that winged strain gauges were more stable in the investment than wingless strain gauges.

Chemical Phenomena↗

PubMed1992

Use of plastic bar molded casting in the modification of variably expanding investment to compensate for casting shrinkage of nickel-chromium alloy.

Trial plastic bar molded castings were compared for accuracy with cast crowns by means of a nickel-chromium alloy, which was used to establish the liquid density of variably expanding investments. The plastic bars were invested to evaluate the change of expansion rate in a wide range of six liquid densities from 0% to 100%, and the distances between the sections were measured before and after casting. Wax crowns were cast to obtain a more detailed relation around 0% expansion at seven liquid densities, and the gaps between the base of the die and the margin of the crown were measured before and after casting. The expansion rates of both castings were calculated and thus were proportional to the liquid density; both regression curves indicated high correlation coefficients. As a result of the statistics of the Student's t-test, the difference between the two methods was not significant. The trial plastic bar was useful in establishing the variably expanding investment for precise casting of artificial crowns.

Chromium Alloys↗

PubMed1989

Effect of investment mass on distortion of MOD wax patterns.

Flaring of proximal walls of years, but not examined. In this experiment, the mass of investment peripheral to the wax patterns was varied by use of casting rings of the same lengths but of different diameters. Thirty castings were made individually, ten from each ring of 28 mm, 48 mm, and 60 mm diameter. The castings were cemented to their parent dies, sectioned mesiodistally, and the cement spaces at specific sites measured. Flaring angles were calculated for the proximal walls and were found to be inversely proportional to the diameters of the casting rings, and, thus, to the peripheral mass of investment. Further studies to detail the fluid mechanics of investments and to predict wax pattern behavior are warranted.

Dental Casting Investment↗

PubMed2006

Blood pressure control and cardiovascular outcomes in high-risk Hispanic patients--findings from the International Verapamil SR/Trandolapril Study (INVEST).

BACKGROUND: People of Hispanic origin are the fastest growing ethnic minority in the United States and often have hypertension and other comorbidities which increase the risk associated with coronary artery disease (CAD). METHODS AND RESULTS: An analysis of the 8045 Hispanic patients enrolled in INVEST was conducted, and comparisons were made to the 14,531 non-Hispanic patients. INVEST was a prospective, randomized, open, blinded end point study in CAD patients with hypertension. After 61,835 patient-years of follow-up, treatment with either a verapamil sustained release (SR) or atenolol antihypertensive strategy resulted in greater blood pressure control in Hispanic patients, and Hispanic patients were at significantly lower risk of experiencing a nonfatal myocardial infarction, nonfatal stroke, or death (hazard ratio [HR] 0.87, 95% CI 0.78-0.97). Hispanic ethnicity was associated with an increase (HR 1.19, 95% CI 1.04-1.36), and randomization to the verapamil SR strategy was associated with a decrease (HR 0.85, 95% CI 0.76-0.95), in the risk of new-onset diabetes. Use of trandolapril in the verapamil SR strategy was associated with reduced risk of new-onset diabetes, whereas increasing doses of atenolol and hydrochlorothiazide in the atenolol strategy were associated with increased risk of new-onset diabetes. CONCLUSIONS: The Hispanic cohort of INVEST had better blood pressure control and lower risk of adverse cardiovascular outcomes compared with the non-Hispanic cohort. A verapamil SR strategy is an alternative to an atenolol strategy for the treatment of Hispanic patients with hypertension and CAD and can reduce the risk of new-onset diabetes.

Aged↗

PubMed2004

Pure titanium casting into zirconia-modified magnesia-based investment molds.

OBJECTIVE: Molten titanium is highly reactive with common mold materials at elevated temperatures. The aim of this investigation was to improve the accuracy of pure titanium casting by adding unreactive zirconia into magnesia-based investment material. METHODS: An automatic thermal expansion laser-recording machine (TEM-1000/Pantos, Nippon Co.) was used to measure thermal expansion of investment materials. An automatic argon-casting machine (Castmatic-S, Iwatani Co.) was used to cast pure titanium samples. A stereomicroscope was used (Nikon SM-2T, Japan) to measure marginal discrepancy on a metal die. A Vickers microhardness indenter (MXT-50, Matsuzawa Seiki Co.) determined the Vickers hardness (VH) of the titanium samples. Interfacial reactivity of the titanium was evaluated with an X-ray diffractometer (Rigaku D/max VIII, Tokyo, Japan). A dental X-ray machine was used to examine internal porosity of the castings. Data was analysed with paired t-test (p < 0.05), ANOVA/Tukey's HSD test (p < 0.001) and Spearman's correlation test (p < 0.05). RESULTS: Addition of 5.0-6.0 mass% of zirconia to a magnesia-based investment material significantly increased its thermal expansion value (p < 0.05). ANOVA indicated significant marginal discrepancy differences within the zirconia-added group (p < 0.001). There was a significant correlation between thermal expansion at 750 degrees C and marginal discrepancy (p < 0.05). The addition of zirconia decreased interfacial reactivity and the VH of titanium. SIGNIFICANCE: Under appropriately adjusted conditions, the addition of zirconia to magnesia-based mold materials may be used to produce high quality pure titanium castings.

Analysis of Variance↗

PubMed2005

Expansion of high flow mixtures of gypsum-bonded investments in contact with absorbent liners.

OBJECTIVES: To evaluate the expansion of high flow mixtures of gypsum-bonded investments in contact with two dry absorbent liners since early setting. METHODS: Cristobalite-Dentsply and Cristobalite-Polidental gypsum-bonded investments were tested under 10 setting conditions (n=4): Normal and Hygroscopic (controls); four conditions of 'Dry-Lining' (set in contact with 3 different amounts of dry cellulose liner: 0.2, 0.4 or 0.8 g and with 0.1 g of a granulated Super Absorbent polymer liner) and four conditions of 'Dry-Lining with hygroscopic expansion' (initially setting in contact with dry absorbents, as 'Dry-Lining' conditions, followed by water immersion immediately after loss of gloss). The percent of expansion at 2h was analyzed. RESULTS: The 'Dry-Lining' condition, with 0.4 and 0.8 g of cellulose, for brand Dentsply (1.41+/-0.13 and 1.42+/-0.16) and Polidental (1.14+/-0.17 and 1.01+/-0.22) allowed a significant higher expansion than the controls Normal (Dentsply=0.30+/-0.04, Polidental=0.31+/-0.05) (P<0.05). The 'Dry-Lining with hygroscopic expansion' condition with 0.8 g of cellulose expanded significantly more (3.57+/-0.55) than the control Hygroscopic (2.63+/-0.31) in brand Dentsply (P<0.05). Super Absorbent did not produce different expansion (Dentsply=0.86+/-0.02, Polidental=0.79+/-0.18) than the controls Normal and Hygroscopic (Dentsply=2.93+/-0.17, Polidental=2.12+/-0.40). SIGNIFICANCE: The water removal with dry cellulose absorbent liner before loss of gloss increased the potential of setting expansion for Normal and Hygroscopic conditions. Thus, when using high fluid mixtures, which are more desirable for investment pouring, it will be possible to obtain enough setting expansion potential in order to adequately compensate for wax and alloy shrinkage in the casting process.

Absorption↗

PubMed2006

The effect of mold temperature on castability of CP Ti and Ti-6Al-4V castings into phosphate bonded investment materials.

OBJECTIVE: The aim of this study was to evaluate the castability of CP titanium and Ti-6Al-4V alloy castings into Rematitan Plus investment at three different mold temperatures. METHODS: A nylon mesh pattern (20 mm with 64 squares and wire of 0.7 mm in diameter) was used for the castability testing. Initially, an image of the wax pattern was obtained by means of a digital camera and the total extension of filaments (mm) was then measured, using the Leica Qwin image analysis system. The mesh sprued was placed in the Rematitan Plus investment material and the castings were made in a Discovery Plasma machine at three different mold temperatures: 430 degrees C (control group), 480 degrees C or 530 degrees C. Ten castings were made for each temperature. The images of the castings were analyzed (Leica Qwin) and the castability index determined by the number of the completely cast segments as a percentage of the wax pattern. Data were analyzed by two-way ANOVA and Tukey's multiple comparison test (a = 0.05) using materials and temperatures as discriminating variables. RESULTS: The Ti-6Al-4V alloy (60.86%) presented a better castability index than CP Ti (48.44%) (p < 0.000001). For CP Ti, the temperature of 530 degrees C (23.96%) presented better castability than at other temperatures, 480 degrees C (14.66%) and 430 degrees C (12.54%), with no difference between them (p < 0.001). For Ti-6Al-4V alloy, there was a statistically significant difference among the three temperatures: 530 degrees C (28.36%) > 480 degrees C (19.66%) > 430 degrees C (15.97%) (p < 0.002). SIGNIFICANCE: Within the limitations of this study, the increase in the mold temperature of the Rematitan Plus investment resulted in a better castability index for both materials, and Ti-6Al-4V presented a better castability index than CP Ti.

Alloys↗

PubMed2006

Modeling the investment casting of a titanium crown.

OBJECTIVE: The objective of this study was to apply computational modeling tools to assist in the design of titanium dental castings. The tools developed should incorporate state-of-the-art micromodels to predict the depth to which the mechanical properties of the crown are affected by contamination from the mold. The model should also be validated by comparison of macro- and micro-defects found in a typical investment cast titanium tooth crown. METHODS: Crowns were hand-waxed and investment cast in commercial purity grade 1 (CP-1) titanium by a commercial dental laboratory. The castings were analyzed using X-ray microtomography (XMT). Following sectioning, analysis continued with optical and scanning electron microscopy, and microhardness testing. An in-house cellular-automata solidification and finite-difference diffusion program was coupled with a commercial casting program to model the investment casting process. A three-dimensional (3D) digital image generated by X-ray tomography was used to generate an accurate geometric representation of a molar crown casting. Previously reported work was significantly expanded upon by including transport of dissolved oxygen and impurity sources upon the arbitrarily shaped surface of the crown, and improved coupling of micro- and macro-scale simulations. RESULTS: Macroscale modeling was found to be sufficient to accurately predict the location of the large internal porosity. These are shrinkage pores located in the thick sections of the cusp. The model was used to determine the influence of sprue design on the size and location of these pores. Combining microscale with macroscale modeling allowed the microstructure and depth of contamination to be predicted qualitatively. This combined model predicted a surprising result--the dissolution of silicon from the mold into the molten titanium is sufficient to depress the freezing point of the liquid metal such that the crown solidifies the subsurface. Solidification then progresses inwards and back out to the surface through the silicon-enriched near-surface layer. The microstructure and compositional analysis of the near-surface region are consistent with this prediction. SIGNIFICANCE: A multiscale model was developed and validated, which can be used to design CP-Ti dental castings to minimize both macro- and micro-defects, including shrinkage porosity, grain size and the extent of surface contamination due to reaction with the mold material. The model predicted the surprising result that the extent of Si contamination from the mold was sufficient to suppress the liquidus temperature to the extent that the surface (to a depth of approximately 100 microm) of the casting solidifies after the bulk. This significantly increases the oxygen pickup, thereby increasing the depth of formation of alpha casing. The trend towards mold materials with reduced Si in order to produce easier-to-finish titanium castings is a correct approach.

Chemical Phenomena↗

PubMed2006

Deformation of phosphate-bonded investment materials at elevated temperatures.

OBJECTIVES: To determine deformation in phosphate-bonded investment (PBI) materials for "in-service conditions" and to investigate the influence of air bubble pores on deformation at 900 degrees C. METHODS: Surviving high and low strain-rate disc-rupture strength test samples were assessed for deformation. A dental centrifugal casting machine and a dental superplastic-forming machine were used to apply the loads. An indirect technique was used to measure the deformation of investment diaphragms with both a wide pore size distribution and with very low porosity for four investment materials. A total of 128 high strain-rate and 29 low strain-rate samples were investigated. A one-way analysis of variance was carried out. RESULTS: All but one of the high strain-rate test samples showed measurable deformation. All of the low strain-rate test samples containing pores showed measurable deformation. Six out of 14 samples, in which pores had been eliminated, showed no deformation. There was no statistically significant difference in deformation between samples with no pores and those with a large pore size distribution for either the high or low strain-rate tests (P>0.05). SIGNIFICANCE: PBI must survive all forming procedures without deformation if the resultant prosthesis is to fit. One hundred micrometres is generally recognized as the acceptable tolerance of fit for removable metal-based prostheses. The vast majority of deformations measured during this investigation were considerably greater than 100 microm.

Acrylates↗

PubMed2006

(31)P solid-state MAS-NMR spectroscopy of the compounds that form in phosphate-bonded dental casting investment materials during setting.

OBJECTIVES: To use (31)P solid-state MAS-NMR to determine which compounds form in phosphate-bonded dental casting investment material during setting, when the ambient temperature is altered. To determine whether they differ in material originating at the center of the mix from material that adheres to the mixing bowl wall. METHODS: (1)H high powered decoupled (HPDC) and (1)H cross polarized (CP) (31)P solid-state MAS-NMR spectroscopy were used at a resonance frequency of 121.4MHz to determine molecular structure. Four commercial products were examined. Manufacturer's instructions were followed and special liquid used without dilution. Ambient temperature was between 18 and 37 degrees C. RESULTS: Molecular structures change with ambient temperature and product. Amorphous Mg(3)(PO(4))(2) or struvite dominate with newberyite, cattiite, amorphous Mg(2)P(2)O(7) and amorphous MgHPO(4) present as minor phases. Exceptionally, amorphous MgHPO(4) dominates. Differences in structure were found in material taken from the center of the mix compared with that scraped from the bowl wall, but the incidence may be specific to the product/mixer combination and not a general effect. SIGNIFICANCE: The formation of compounds in phosphate-bonded investment can be affected by ambient temperature. This effect and the use of material adhering to the bowl wall (instead of that from the center of the mix) are possible causes for the unpredictability of setting expansion measurements between laboratories. There is variation between products. When phosphate-bonded investment is required for casting, a consistent ambient temperature must be used and it would be wise to mix sufficient material to avoid scraping the bowl.

Dental Casting Investment↗

PubMed2005

An overview to CERSSO's self evaluation of the cost-benefit on the investment in occupational safety and health in the textile factories: "a step by step methodology".

INTRODUCTION: The Pan American Health Organization (PAHO) and CERSSO collaborated to develop a new Tool Kit (TK), which became available in May 2002. PAHO already had a TK in place, and CERSSO requested that one be developed for their needs. CERSSO wanted to enable managers and line workers in garment factories to self-diagnose plant and workstation hazards and to estimate the costs and benefits of investing in occupational safety and health (OSH) as a way to improve productivity and competitiveness. METHODS: For consistency, the collaborating organizations agreed to construct the TK according to PAHO's methodology. The instrument was developed to be comprehensive enough that any user can collect the data easily. It integrates epidemiologic, risk assessment, clinic, engineering, and accountability issues, organized to include step-by-step training in: (a) performing risk assessments in the workplaces (risk factors); (b) making cause-effect relationships; (c) improving decision making on OSH interventions; (d) doing calculations of direct and indirect costs and savings; and (e) doing calculation of the overall cost-benefit of OSH interventions. RESULTS AND CONCLUSIONS: Since July 2002, about 2,400 employees and officials from 736 garment factories, Ministries of Labor, Health, Social Security Institutes, and Technical Training Institutions of Central America and the Dominican Republic have used this instrument. Systematically, they have calculated a positive relationship of the investment (3 to 33 times). Employers are now aware of the financial rewards of investing in OSH. The TK is available in Spanish, Korean, and English. In July 2003, a software program in Spanish and English was developed (180 persons have been trained in the region), which requires less time to execute with better reliability.

Central America↗

PubMed2004

Foreign direct investment and trade in health services: a review of the literature.

Globalization is a key challenge facing health policy-makers. A significant aspect of this is direct trade in health services, a result of the rise of transnational corporations, challenges in health care financing, porous borders and improved technology creating the scope for increased 'foreign direct investment' (FDI) in health care. This has gathered momentum with the General Agreement on Trade in Services (GATS), which aims to further liberalize trade in services, and within which FDI has been noted as perhaps the most critical area for trade negotiation. Given the rapid development of this area, there are little empirical data. This paper therefore seeks to provide the first comprehensive and systematic review of evidence concerning FDI and health services. This process included electronic bibliographic database searches, website searches and correspondence with experts in the area of trade in health services, from which 76 papers, books and reports were reviewed. Perhaps due to the rapid developments in this area, most of the literature is speculative, polarized between those arguing for the benefits of liberalization and those arguing against. However, there seem to be three issues which emerge as of most importance: (i) the extent to which a national health system is commercialized per se is of more significance than whether investment in it is foreign or domestic; (ii) the national regulatory environment and its 'strength' will significantly determine the economic and health impact of FDI, the effectiveness of safeguard measures, and the stability of GATS commitments; and (iii) any negotiations will depend upon parties having a common understanding of what is being negotiated, and the interpretation of key definitions is thus critical. Each of these issues is explored in some depth, with the overall conclusion that countries should take a step back and first think through the risks and benefits of commercialization of their health sector, rather than being sidetracked in to considering the level of foreign investment.

Commerce↗

PubMed1996

Effect of wet and dry cellulose ring liners on setting expansion and compressive strength of a gypsum-bonded investment.

Effective setting expansion of gypsum-bonded investments is influenced by many variables. The purpose of this study was to determine the effect of using either water-saturated or dry cellulose ring lining material on (1) the fit of castings on a steel die and (2) the compressive strengths of investment cores using either type of liner. The mean gingival space in the water-saturated liner group was 0.241 +/- 0.048 mm and was 0.071 +/- 0.029 mm in the dry liner group (p < 0.001). The compressive strengths of investment cores from the dry liner group were 36.5% greater than those of cores from the water-saturated liner group. The results demonstrated that the use of dry liners may improve the fit of castings to dies.

Calcium Sulfate↗

PubMed1999

Nonuniform vertical and horizontal setting expansion of a phosphate-bonded investment.

PURPOSE: This study developed a new device for measuring the internal setting expansion of phosphate-bonded investment and assessed the effect that different pattern materials may have on the internal setting expansion. MATERIAL AND METHODS: The measuring device consisted of 2 horizontal plungers, a vertical needle, 2 digital dial gauges, and a protection tube with a disk. Outward displacement of the 2 horizontal plungers by investment setting expansion was transmitted to a digital dial gauge through the vertical needle. Upward displacement of a protection tube was measured by another digital dial gauge. Three pattern materials, including soft and hard inlay waxes and an autopolymerizing resin, were used. Data were analyzed with ANOVA and Scheffe's F test for all post hoc pairwise comparisons (95% confidence level). RESULTS: For all pattern materials, vertical setting expansion (range of means, 2.26% to 2.73%) was significantly higher than the horizontal setting expansion (range of means, 0.09% to 1.50%) (P <.05). In addition, for the hard inlay wax pattern, the horizontal setting expansion for the cervical aspect (means, 1.39%) was significantly higher than that of the occlusal aspect (means, 0.54%) (P <.05). CONCLUSION: In this study, the new measuring device was a convenient and reliable method for quantitative assessment of internal setting expansion. Regardless of the type of pattern material, a phosphate-bonded investment caused nonuniform setting expansion, especially in a horizontal direction, which lead to the distortion of the pattern.

Analysis of Variance↗

PubMed1999

Titanium full crown casting: thermal expansion of investments and crown accuracy.

OBJECTIVES: The aim of the present study was to establish a statistical model between thermal expansion values of investments and dimensional accuracy of cast titanium full crowns. METHODS: Thermal expansion (TE) measurements were made on cylindrical specimens (5O x 20 mm) dried to constant mass and full crown wax patterns were prepared from metal dies having the same design. Castings were made using a one-chamber high-pressure casting machine. Dimensional accuracy of the cast crowns was expressed by the discrepancy (micron) between the wax pattern and a casting prepared from the same die. A simple least squares linear regression analysis was made on data accumulated over the last five years. RESULTS: A high correlation coefficient (R = 0.87) was found between dimensional accuracy (Y) and thermal expansion value (X), and the accuracy was predicted by a formula Y = 1040.50X - 1004.45 microns. For zero discrepancy, a thermal expansion of 0.97% was required. SIGNIFICANCE: The dimensional accuracy expressed as the discrepancy between wax pattern and casting is easy to understand and less confusing than the traditional percentage value. The crown accuracy was highly predictable (R = 0.87) from the thermal expansion value of investments determined under controlled laboratory measuring conditions. New investments being released for titanium casting can be under constant modification. For this, regular monitoring of their TE behaviour is essential and use of the same batch is preferable for expansion measurement and crown accuracy assessment.

Analysis of Variance↗

PubMed2002

Employer investments in employee health implications for the family as health producer.

The model presented in this paper further extends the demand-for-health model in which the family is the producer of health investments, to consider the case in which an employer has incentives for investing in the health of a family member. The household and the employer are assumed to interact strategically in the production of health. The general insight provided is that the conditions which determine the nature of the relationship between the employer and the employee, for instance market conditions, production technologies, taxes, and government regulation, will also affect the allocation of health investments and health capital within the family.

Efficiency, Organizational↗

PubMed2002

Parental investment: how an equity motive can produce inequality.

The equity heuristic is a decision rule specifying that parents should attempt to subdivide resources more or less equally among their children. This investment rule coincides with the prescription from optimality models in economics and biology in cases in which expected future return for each offspring is equal. In this article, the authors present a counterintuitive implication of the equity heuristic: Whereas an equity motive produces a fair distribution at any given point in time, it yields a cumulative distribution of investments that is unequal. The authors test this analytical observation against evidence reported in studies exploring parental investment and show how the equity heuristic can provide an explanation of why the literature reports a diversity of birth order effects with respect to parental resource allocation.

Birth Order↗