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PubMedDate not supplied

[Influence of mercaptan impression storage conditions on linear dimensional changes in improved plaster-stone casts].

A study was conducted on the influence of storage conditions of mercaptan molds on the linear dimensional alterations occurring in improved plaster-stone casts. Two types of storage were used: A) in which the molds were left on the bench for 5 minutes at 25 degrees C and 55% relative humidity; and B) in which the molds were placed in an incubator at 37 degrees C and 100% relative humidity for 40 minutes. Casts were built using 5 different brands of improved plaster-stone, 5 casts per brand. Thus, considering the 2 types of storage, the 5 brands of plaster-stone and the 5 replications, a total of 50 improved plaster-stone casts were constructed. The linear dimensional alterations were measured with the aid of a linear measurement microscope, which measured the space between two hemisections of the standard fixed bridge, both when the fixed bridge was adapted to the master cast and to the plaster cast.

Calcium Sulfate↗
PubMed1989

Quantitative measurement from vascular casts.

A review of quantitative measurements show casting materials shrink from 0.2 - 20% and have viscosities ranging from 1.4 - 100,000 centipoise. Blood vessels have highly variable mechanical properties. Some microvessels are very stiff having little change in dimensions with pressure. Larger vessels generally change diameter significantly but show highly variable changes in length with pressure. Perfusion fixation does not fix the dimensions of blood vessels. Dog carotid arteries well fixed with glutaraldehyde at physiologic dimensions retain approximately 20% of their elastic recoil circumferentially and approximately 30% longitudinally. We recommend vascular casting as a method of accurately measuring the vasculature if care is taken to use low shrinkage casting resins and maintain physiologic transmural pressures for the duration of any casting procedure, even if prefixation is used. We measured a approximately 10% error in our method of measuring both the size and location of periorificial atherosclerotic lesions from aortic casts. Little is known about how vascular smooth muscle tone changes during casting.

Animals↗
PubMed1989

Microvascular casting of the lung: bronchial versus pulmonary artery filling.

To determine the importance of the pulmonary or bronchial arteries as the site of injection to cast the lung vasculature rats, we retrospectively compared a group of normal Sprague-Dawley rats that were cast through either the caudal vena cava and right ventricle leading to the pulmonary arteries or through the aorta and bronchial arteries. There was no difference in the appearance of the whole casts or cast-to-lung weight ratios between the two groups, although an incompletely cast lung that was injected through the aorta showed preferential filling of the pleural and peribronchial regions. Nuclear impressions, a sign of good filling, were more frequent and the grade of the images was higher in the group filled through the vena cava. The microvascular density index was not different between the two groups, and a multivariate analysis of variance showed the injection site was not important in determining vascular density. The pulmonary vessels fill nearly as well when injected from the bronchial circulation indicating that the bronchial circulation can immediately perfuse the lung if the pulmonary arteries are obstructed, and casting can be carried out from either side with nearly the same results.

Animals↗
PubMed1986

Anatomy and morphometry of myocardial capillaries studied with vascular corrosion casting and scanning electron microscopy: a method for rat heart.

The present paper describes a procedure for preparing vascular corrosion casts of rat myocardial microvasculature. Essential components of the procedure include: partial "self clearing" of the heart in vitro; cardiac arrest by infusion of KCl; retrograde aortic root infusion of Mercox-Sevriton casting resin; KOH digestion of ventricular tissue; and desiccation and mounting of casts for scanning electron microscopy. About 50% of rats yielded complete casts. Vasculature closely paralleled muscle fiber orientation. Capillary beds characteristically exhibited branching, many intercapillary cross bridges, and occasional coiling. Average capillary cast diameter (5.6 microns) and intercapillary distance (15 microns) are comparable to results from in vivo studies. From preliminary calculations, vascular volume represents about 10% of the ventricular walls. These data indicate that vascular corrosion casts may be useful in the analysis of pathologic states and in determining the role of potential therapeutic interventions.

Animals↗
PubMed1979

Large bronchial casts.

Unusually large bronchial casts developed in four patients. In two, the casts were associated with pneumonia. In one, a large RBC cast resulted from a complication of fiberoptic bronchoscopy. Bronchial casts developed in an additional patient as a manifestation of plastic bronchitis. Although unusual, bronchial cast formation may complicate a number of hypersecretory pulmonary diseases. Therapy ordinarily includes specific measures to treat the underlying disease state and maneuvers designed to remove or facilitate the expectoration of bronchial casts.

Adult↗
PubMed1993

Application of the model-positioning appliance for three-dimensional positioning of the maxilla in cast surgery.

During cast surgery the model-positioning appliance allows a controlled three-dimensional positioning of the maxillary incisors and of the entire maxilla in one- or two-jaw surgery. The model-positioning appliance is fastened, in place of the incisal pin or the incisal table, to the anterior end of the upper part of a semiadjustable articulator. Three reference points are marked with a pencil directly on three maxillary teeth. The reference plane during cast surgery is the hinge axis-infraorbital plane, which is represented by a parallel to the upper part of the articulator. All measurements during cast surgery are parallel or at a right angle to this reference plane. Three-dimensional adjustment of the maxillary cast is possible without measurements with a ruler and without the marking of reference points and drawing osteotomy lines on the base of the cast. Sawing cuts on the base of the cast corresponding to marked osteotomy lines is avoided. In this way errors are reduced and precision is increased. The advantage of model-positioning appliance is that the three reference points on the maxillary teeth can be adjusted simultaneously and that the relation of the whole maxillary dental arch to the mandibular dental arch can be controlled at the same time.

Dental Articulators↗
PubMed1996

Genetic differentiation and population structure of some occupational caste groups in Uttar Pradesh, India.

Phenotypes and gene frequencies of 24 genetic markers (9 blood groups, 11 red cell enzymes, and 4 serum proteins) were investigated in 5 occupational caste groups (Brahmin, Khatri, Vaish, Kayastha, and scheduled castes) and 1 religious group of Muslims in Uttar Pradesh, India. This is the first extensive genetic study in Uttar Pradesh that establishes the range of genetic variation in different endogamous groups. The extent of genetic variation among different occupational caste groups is low, and only two genetic systems (C3 and ACP) showed heterogeneity. The genetic affinity analysis showed an unexpected close affinity of scheduled castes with the Khatri. This observation warrants further analysis of these groups, but the present results may be a chance finding resulting from the nature of the samples, which represent individuals from vastly different regions of Uttar Pradesh. The affinity of the Muslim group with other caste groups suggests that the samples may include descendants of converts from the seventeenth century who are still at an early stage of differentiation. The FST estimate for the populations is 0.009, which is close to other estimates reported from north and northwest India. The overall mean FIS value is 0.066, and for each locus the FIS estimate is considerably higher than the FST estimate, suggesting that the infrastructure of the populations is influenced by nonrandom mating (inbreeding). There is no evidence of any disruptive selection, but the allele frequency of each caste group of Uttar Pradesh must be affected by its large population size, which, because of chance migration of individuals with different gene frequencies, would accentuate genetic differences.

Ethnicity↗
PubMed1997

Screening infants and young children for hearing loss: examination of the CAST procedure.

A computer-mediated visual reinforcement audiometry (VRA) screening procedure, the Classification of Audiograms by Sequential Testing (CAST), was used with 59 infants and young children who received both CAST screening and conventional audiologic assessment. Approximately one-third of the children had normal hearing, one-third had conductive hearing loss, and the remaining one-third had previously diagnosed sensorineural hearing loss. The sensitivity and specificity of CAST were calculated and the relationship between the predicted CAST pattern and the child's actual audiogram was examined. CAST outcome was also considered along with the results of tympanometry and pneumatic otoscopy to formulate proposed follow-up strategies. CAST appears to be a useful tool for the behavioral screening of infants and young children: one component of a screening program designed to maximize the efficient identification and follow-up of infants and children with hearing loss.

Acoustic Impedance Tests↗
PubMed1997

A three-dimensional imaging system for archiving dental study casts: a preliminary report.

Dental study casts form an essential part of patient records for both diagnostic and medicolegal purposes. Storage of study casts poses major problems because of inconvenience and cost of mass storage. Various methods for recording and storage of study casts are discussed. A new biostereometric technique for digitally recording and storing dental casts, and using the recent advances in stereophotogrammetry, is presented. Archiving dental casts in a digital format would reduce problems of mass storage and provide new benefits such as duplication of casts and use in clinical and research studies.

Archives↗
PubMed1993

Mold filling and porosity in castings of titanium.

The present study focused on the effects of argon pressure, mold venting, and investment permeability on the mold filling of titanium and the soundness of titanium castings. Casting soundness was determined by density measurement and x-ray radiography. To achieve complete filling of molds made from a relatively impermeable investment, the molds were vented. Regardless of the presence or absence of vents, all of the molds made from a highly permeable refractory material filled completely. The soundness of castings made under an argon pressure of 50 torr was significantly greater than that of castings made under a pressure of 400 torr. The non-vented molds of the highly permeable refractory material yielded the soundest castings (mean density = 4.45 g/cm3).

Dental Casting Investment↗
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↗
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↗
PubMed1995

Porosity and accuracy of multiple-unit titanium castings.

The objective of this investigation was to determine whether titanium could be used to cast reproducible multiple-unit dental restorations. A metal analog was machined to simulate preparations for a three-unit fixed partial denture. Castings were made with four different sprue designs at three temperatures. Marginal accuracy and porosity were evaluated. A total of 70 titanium castings were made with an argon/electric arc/vacuum/pressure casting machine. Ten castings were made in the conventional manner by use of gold-palladium alloy as a control to compare the marginal gap. The results revealed that the porosity was less when a large individual sprue (6-gauge) was used. It was also noted that the lower pattern burnout temperatures of 910 degrees C and 920 degrees C exhibited significantly smaller marginal gaps than did the higher temperature of 930 degrees C.

Analysis of Variance↗
PubMed1999

Use of a flexible cast for fabrication of multiple post-coping overdenture restorations.

Direct intraoral fabrication of multiple post-coping restorations for an overdenture in the same arch can be a time-consuming chairside clinical procedure. In addition, accurate intraoral fabrication of resin patterns with intracrevicular margins is not always possible as a result of limited access. This article presents a direct-indirect method that uses an elastic cast for fabrication of multiple post-coping restorations with intracrevicular margins. Custom post patterns are fabricated directly in the root canal with autopolymerizing resin (Duralay). An impression is made of the remaining tooth structure, which also includes the post patterns, and a flexible cast is poured chairside. The cast is available within 6 to 8 minutes of impression making and can be trimmed similar to a stone die. The procedure also provides flexibility that allows separation of the cast from the impression without fracture of the custom post pattern or cast. The fabrication of the post-coping restoration can be completed in the laboratory, or if necessary, completed chairside and verified intraorally, before dismissing the patient.

Dental Abutments↗
PubMed2003

Corrosion behavior of cast titanium with reduced surface reaction layer made by a face-coating method.

This study characterized the corrosion behavior of cast CP titanium made with a face-coating method. Wax patterns were coated with oxide slurry of Y(2)O(3) or ZrO(2) before investing with a MgO-based investment. Three surface preparations were tested: ground, sandblasted, and as-cast. Uncoated castings served as controls. Sixteen-hour open circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed in an aerated modified Tani-Zucchi synthetic saliva at 37 degrees C. Anodic polarization was conducted in the same deaerated medium. Polarization resistance (R(p)) and Tafel slopes were determined. Corrosion current density was calculated for each specimen. Results (n=4) were subjected to nonparametric statistical analysis (alpha=0.05). Cross sections of cast specimens were examined by optical microscopy. Energy dispersive spectroscopy (EDS) spot analysis was performed at various depths below the surface. The OCP stabilized within several hours for all the specimens. Apparent differences in anodic polarization behavior were observed among the different surfaces. A distinctive wide passive region followed by breakdown was seen on specimens with ground and sandblasted surfaces. There were no significant differences in the corrosion resistance among the control and the two face-coating groups for each group. The Mann-Whitney test showed significantly lower OCP and higher R(p) values for ground surfaces. The surface condition significantly affected the corrosion behavior more than the face coating methods. In most cases, specimens with as-cast surfaces exhibited the least corrosion resistance during the potentiodynamic anodic polarization.

Coated Materials, Biocompatible↗
PubMed1999

Numerical simulation of porosity-free titanium dental castings.

The objective of this research was to analyse, predict and control the porosity in titanium dental castings by the use of numerical simulation. A commercial software package (MAGMASOFT) was used. In the first part of the study, a model casting (two simplified tooth crowns connected by a connector bar) was simulated to analyse shrinkage porosity. Secondly, gas pores were numerically examined by means of a ball specimen with a "snake" sprue. The numerical simulation results were compared with the experimental casting results, which were made on a centrifugal casting machine. The predicted shrinkage levels coincided well with the experimentally determined levels. Based on the above numerical analyses, an optimised running and gating system design for the crown model was proposed. The numerical filling and solidification results of the ball specimen showed that this simulation model could be helpful for the explanation of the experimentally indicated gas pores. It was concluded that shrinkage porosity in titanium dental casting was predictable, and it could be minimised by improving the running and gating system design. Entrapped gas pores can be explained from the simulation results of the mould filling and solidification.

Chemical Phenomena↗
PubMed1998

The effect of sprue design on the marginal accuracy of titanium castings.

The purpose of this study was to measure the effects of sprue number and position on cast titanium crown margins. Twenty-four complete veneer crown wax patterns were fabricated on a stainless steel die with a 30 degrees bevel finish line. Twelve wax patterns were sprued with one 8-gauge wax sprue and the remaining 12-gauge double sprued. All patterns were invested with a phosphate bonded investment. Castings were made with a titanium casting machine following the manufacturer's instructions and using commercially pure titanium (> 99.5%) ingots. The castings were than carefully cleansed and the margins were examined with indirect impression technique. Data were analysed with an ANOVA and the Student's t-test with confidence level at 95%. The results revealed that the marginal discrepancy for the double sprueing group (32.1 +/- 12.8 microm) has significantly less discrepancy (P < 0.001) than the single sprueing group (49.8 +/- 16.4 microm). There was no statistically significant differences in marginal discrepancy between locations within the sprueing techniques (P > 0.05). An improvement in the degree of casting accuracy of titanium crown was indicated by the double sprue design used in this investigation.

Analysis of Variance↗
PubMed1994

The effect of investment type on the fit of cast titanium crowns.

In order to determine the best laboratory procedure for titanium crown casting, a set of thermal expansion measurements and casting experiments were carried out using a casting machine (argon arc, pressure difference type) and three different investments, two conventional SiO2 based investments and a new Al2O3/MgO based investment. The thermal expansion measurements involved a cycle of heating and cooling. The relatively low mould temperatures recommended (200 degrees C) or chosen (350 degrees C) for the conventional investments provided zero or negative mould expansion for the compensation of metal shrinkage. Crowns made from these investments exhibited heavy reaction with the mould, and the common cleaning method of sand blasting appeared to be essential. This cleaning process, however, was not adequate for the assessment of casting accuracy as the short sand blasting time (15 s) rapidly altered the fit of the crowns. The metal reacted little with the new investment and the best compensation (0.15 mm discrepancy) for the metal shrinkage, as assessed 'as cast', was achieved when the investment was heated to 950 degrees C and then cooled to the recommended mould temperature (600 degrees C).

Chemical Phenomena↗