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At least 685 records · Page 38Linked to original sources
PubMed1990

Casting pure titanium into commercial phosphate-bonded SiO2 investment molds.

Pure titanium was cast into five different phosphate-bonded SiO2 investment mold materials (at 350 degrees C) with an argon-arc melting and pressure casting machine. The mesh castability, the fit of the MOD inlay castings, and the Knoop hardness and the micro-structure in cross-sections of castings were examined. The setting and thermal expansion, the compressive strength, and the X-ray diffraction analysis of the investments were also measured. The castability, the fit, and the thickness of the reacted layer differed in degree among these investments, in spite of the same phosphate-bonded SiO2-type investment. A significant correlation was obtained between the thermal expansion (at 350 degrees C) and the casting accuracy.

Analysis of Variance↗
PubMed1985

Porosities in a dental silver-palladium casting alloy.

Twelve single crowns were cast in a silver-palladium alloy by six different casting techniques. Polished sections of the crowns were inspected and photographically recorded by light microscopy. The area of the inspected section of the casting and the number and area of pores were recorded on the photographs by means of a digitizing table connected to a microcomputer. A great number of defects were observed unevenly distributed in all castings. Only small variations were observed between the various casting techniques.

Crowns↗
PubMed2004

Thermal expansion typed investments for casting titanium.

New investments for titanium were developed by adding ZrC and ZrN as additives for thermal expansion to an MgO cement base investment with setting shrinkage and low thermal expansion. Setting, thermal and residual expansion, X-ray diffraction and compressive strength of these experimental investments, surface roughness of the cast plate and casting accuracy of titanium crowns were evaluated. Thermal expansion of investments increased with additive amounts, and residual expansion occurred even when cooling to room temperature after firing in an air atmosphere by the oxidation to ZrO2 of these additives. The casting accuracy of full-crowns cast into molds at room temperature correlated with the content of ZrC and ZrN. As the result the cast titanium crown could be obtained with low surface roughness and good adaptability.

Analysis of Variance↗
PubMed2004

Phosphate-bonded ZrSiO4 investments added with ZrC and ZrN for casting titanium.

In this study, new investments for titanium were developed by adding ZrC or ZrN as chemical additive for thermal expansion to a phosphate-bonded zircon (ZrSiO4) investment. The following effects were then examined: setting expansion, residual thermal expansion, and compressive strength of these experimental investments; surface roughness of cast plate; and casting accuracy of titanium crown. For residual thermal expansion, it occurred even while investments were cooled to room temperature after firing in air atmosphere. This was due to the additives' oxidation to ZrO2--suggesting that residual thermal expansion increased with increased amount of these additives. As for casting accuracy of full-crown cast into molds at room temperature, it correlated with the ZrN content. Hence by adding the right amount of ZrN, cast titanium crowns with low surface roughness and good adaptability could be obtained.

Analysis of Variance↗
PubMed2002

Dimensional accuracy of dental casts: influence of tray material, impression material, and time.

PURPOSE: This study evaluated the influence on dimensional accuracy of dental casts made with different types of trays and impression materials and poured at different and multiple times. MATERIALS AND METHODS: Two types of stock trays (plastic stock tray, perforated metal stock tray) and 4 types of custom tray materials (autopolymerizing acrylic resin, thermoplastic resin, and 2 types of light-polymerized acrylic resins) were used with 2 types of impression materials (addition polymerizing silicone and polyether), to make impressions of a metal master model. Each tray and impression material was used to make 5 impressions. Casts were made by multiple pourings at 30 minutes, 6 hours, 24 hours, and 30 days after impression making. Using a measuring microscope, 12 distances were calculated based on measurements of 8 reference points. The absolute value of the difference of each measurement was calculated, as was the corresponding measurement on the master model. A Bayesian model using a simple noninformative prior was used to analyze these data. RESULTS: Statistical differences within 6 microm were found only with thermoplastic resin tray material for addition silicone, and for thermoplastic resin tray material and 1 type of light-polymerized acrylic resin for polyether. Neither stock trays nor custom trays contributed to the differences in accuracy of the casts. All deviations in casts made with silicone impression material were within a clinically acceptable range. For the polyether, distortions occurred that were clinically unacceptable. Impressions made from polyether distorted over time. Silicone impression material has dimensional stability up to 30 days. CONCLUSION: Accurate casts can be made with either stock trays or custom trays. An impression made from polyether should be poured only once and within 24 hours after impression making, because of the distortion of the material over time. Silicone impression material has better dimensional stability than polyether. .

Acrylic Resins↗
PubMed1993

Titanium. A review of investments for high temperature casting.

Conventional silica (SiO2) based dental casting investments are used for the casting of pure titanium using casting machines specifically developed for this metal. Highly reactive molten titanium reduces SiO2 and titanium is in turn oxidised. For this reason possible alternatives to SiO2 have been studied in the past decade and MgO and Al2O3 are the most common in current commercial investments released for titanium casting. The surface of titanium castings presents a layered structure and its evaluation in relation to clinical performance requires further study. It is also urgently required to know setting and thermal behaviour of the newly developed investments for successful compensation of metal shrinkage.

Aluminum Oxide↗
PubMed1998

Perivascular structures in corrosion casts of the human central nervous system: a confocal laser and scanning electron microscope study.

Scanning electron microscopy (SEM) of microvascular corrosion casts revealed perivascular structures that resembled smooth muscle and pericyte cells. Although these structures have been studied in widely different experimental contexts, their origin, function, and distribution pattern in different tissues are not understood. Microvascular corrosion casts from 15 fresh human brains and 20 lumbar spinal cords were studied by SEM. In five cerebral hemispheres a fluorescent resin was injected in order to study the vascular bed by confocal laser scanning microscopy (CLSM). Microvascular casts showed two perivascular structures on their surfaces: plastic strips, which formed a muff around arteriolar vessels, and pericyte-like structures that were present around the capillary network. Their morphological characteristics and distribution were similar to those of smooth muscle cells and pericytes, respectively. The SEM study showed that these structures were not tightly joined to the cast surface, but were connected to the vascular cast by narrow plastic connections. The CLSM showed that the resin invaded the subendothelial space, thus giving rise to these structures. Perivascular structures associated with arteriolar and capillary vessels appear to represent smooth muscle cells and pericytes. They are formed by the passage of the resin to the subendothelial space, probably through weak endothelial cell junctions. The effusion of resin into the subendothelial space may represent evidence for the structural basis of myocyte and pericyte cell control. Chemical communication by substances released locally or transported to these cells through these junctions may regulate their functions, allowing them to regulate blood flow.

Adult↗
PubMed2001

Microvascular architecture of the rat choroid: corrosion cast study.

This study presents the details of the microvasculature of the rat choroid visualized by scanning electron microscopy of vascular corrosion casts. Wistar Kyoto rats were anesthetized with intraperitoneal sodium pentobarbital. The vascular system was perfused with heparinized saline, and Mercox resin was injected into the cannulated carotid arteries. After polymerization of the resin, the vascular casts were macerated with potassium hydroxide, washed with water, and freeze dried. The casts were examined with a Hitachi S-2360N scanning electron microscope (SEM). Corrosion casts of the entire choroidal vasculature revealed that the two long posterior ciliary arteries supplied the entire uveal vasculature. In the posterior choroid, these arteries formed five to seven branches on each side supplying the adjacent choriocapillaris. No interarterial or arteriovenous anastomoses were seen. The choriocapillaris appeared as a nonhomogeneous and nonlobular monolayer capillary network, consisting of dense honeycomb and irregular patterns. There are two distinct venous systems in the rat choroid. The venous blood from the central region, peripapillary choroid, and sometimes the optic nerve head drain into the posterior ciliary vein. The venous blood from the iris, ciliary body, anterior choroid, and half of the posterior choroid drain into the vortex veins. Corrosion casts and the SEM have shown details of the choroidal vascular architecture. These three-dimensional observations indicate that the rat choroidal vasculature has different features from those of humans and other primates. Despite these interspecies differences, the establishment of a thorough baseline concept of choroidal vasculature should permit additional studies of the choroidal pathology and enable the proper interpretation of results from rat experimental models for extrapolation to humans.

Animals↗
PubMed2001

Treatment of low-energy tibial shaft fractures: plaster cast compared with intramedullary nailing.

We analyzed data from 87 patients who had displaced closed or open grade I simple or spiral wedge tibial shaft fractures caused by low-energy impact. Fifty-four patients were treated with plaster cast and 33 with intramedullary locking nail (IMLN). Delayed union only occurred in 8 patients after plaster cast treatment. Forty-two patients in the IMLN group and one in the plaster cast group suffered from anterior knee pain. Final treatment outcome, healing time, hospitalization time and duration of sick leave were assessed on the basis of 25 matched pairs of patients. Mean healing time, hospitalization time and sick leave in the plaster cast and IMLN groups were 19 (SD 6.7) and 12 (SD 4.4) weeks (P<0.001); 8 (SD 4.8) and 7 (SD 2.7) days (P=0.686); and 195 (SD 81) and 106 (SD 31) days (P=0.001), respectively. No difference was found between plaster cast and IMLN groups when the outcome was evaluated using the criteria of Johner and Wruhs.

Adult↗
PubMed1985

Etched castings as an adjunct to mouth preparation for removable partial dentures.

Electrochemically etched nonprecious metal castings have been bonded to etched enamel for use in mouth preparation procedures for removable partial denture placement. The castings have been in service and subject to loading by the dentures for 26 to 42 months. To date, bond strengths have been sufficient to support function of both castings and removable partial dentures clinically. None of the castings has failed in its bond. Evidence that the technique may be a valuable adjunct is building in the field of prosthodontics. Use may be far reaching as dentists apply the concept to a wide variety of patient requirements in dental treatment. As more commercial dental laboratories acquire the capability to etch metals, cost should be minimized. Application is not time-consuming. Some steps are technique-sensitive, however, and short cuts are not well tolerated. This is especially true of cementation procedures where moisture or contamination of the field may lead to failure of the bond. It should be noted that each nonprecious metal is different from other metals in its composition, and therefore, results and techniques reported in this study can only be cited for the metal used. In addition, the acid used for etching one alloy may not be effective on another alloy. Finally, it is important that all castings be checked under a binocular microscope to ensure that proper etching did occur. Underetching and overetching both lead to a weakened bond and potential failure.

Acid Etching, Dental↗
PubMed1986

Evaluating six sprue designs used in making high-palladium alloy castings.

Six different sprue designs were studied to determine which, if any, could be used to produce more complete castings with a high-palladium alloy. A standardized mesh test pattern was used to ensure objective measurements and accurate evaluations of the spruing techniques. This study of problems usually encountered when casting high-palladium alloys found that: Differing sprue designs effect significant differences in obtaining complete castings (p less than .05) as indicated in the ANOVA. The connection between the casting and the sprue should be constricted to improve castability of high-palladium alloys. Although this spruing technique may be used in different sprue designs to improve the quality of castings, further research seems indicated.

Dental Alloys↗
PubMed1987

Cast aluminum denture base.

The laboratory procedures for a cast aluminum base denture have been presented. If an induction casting machine is not available, the "two-oven technique" works well, provided the casting arm is kept spinning manually for 4 minutes after casting. If laboratory procedures are executed precisely and with care, the aluminum base denture can be cast with good results.

Aluminum↗
PubMedDate not supplied

Preparation of void-free casts from vinyl polysiloxane impressions.

PURPOSE: To investigate two techniques to produce void-free casts from vinyl polysiloxane impressions. MATERIALS AND METHODS: Thirty casts prepared using a conventional technique were compared with 30 casts prepared using a technique involving syringing of stone in terms of numbers of surface voids. RESULTS: Significantly fewer surface voids were observed in the casts prepared using syringing technique. CONCLUSION: The syringing technique investigated is considered to have advantages over the conventional technique for the production of casts from vinyl polysiloxane impressions.

Air↗
PubMed2005

An experimental study of pressure-volume dynamics of casting materials.

Casting materials are commonly used in a trauma and post-operative setting in orthopaedic practice. Swelling after trauma or surgery is universal, hence, the importance of understanding the pressure-volume dynamics of various materials commonly used for casting. This study attempts to define the pressure response of casts made from three commonly used materials to increasing volume, using a cylindrical model cast. Plaster of Paris (PoP), rigid fibreglass and semi-rigid non-fibreglass (Softcast) were chosen for comparison. Softcast had the best compliance and rate dependency characteristics, accommodating significantly more volume of fluid compared to plaster of Paris or Rigid fibreglass material. The latter two had similar compliance. All three materials demonstrated stress-relaxation which is of advantage in reducing peak pressures for a given volume change. This study shows that the casting materials behave in a viscoelastic manner, which allows them to accommodate more volume change than would otherwise be possible. The use of semi-rigid material may be safer than other materials as far as response to swelling (volume expansion) is concerned.

Calcium Sulfate↗
PubMed2004

A method for selectively limiting lumen diameter in corrosion casting.

Corrosion casting is a technique frequently used to evaluate the form and spatial relationship of three dimensional biological structures, such as vascular networks, in vitro [Scann. Microsc. 5 (1991) 1097; Schraufnagel, D.E. The lung microstructure. In: Motta, P.M., Murakami, T. Fujita, H. eds. Scanning Electron Microscopy of Vascular Casts: Methods and Applications. Boston: Kluwer Academic Publishers; 1992:123-137]. However, because corrosion casts tend to reproduce the complexity of surrounding vascular structures as well as the structures of interest, the use of this technique in highly complex vascular systems may obscure important changes such as A-V shunts because they may get lost among the myriad of capillaries. We developed a novel modification for creating vascular corrosion casts by utilizing polystyrene microspheres to selectively embolize normal capillary networks and thereby reduce the overall complexity of the cast. his technique may aid investigators in the evaluation of a variety of vascular beds and is useful in demonstrating non-capillary arteriovenous communications.

Animals↗
PubMed2004

Comparison of cast Ti-Ni alloy clasp retention with conventional removable partial denture clasps.

STATEMENT OF PROBLEM: The elastic property of Ti-Ni alloy may be a desirable property for cast removable partial dentures. However, little is known about the retentive properties of cast Ti-Ni alloy clasps. PURPOSE: This in vitro study investigated the retentive force of various types of clasps during repeated cycles of placement and removal to determine whether Ti-Ni alloy clasps maintain their initial retentive force under varied conditions, including different retentive undercut depths and clasp size (thickness and width). MATERIAL AND METHODS: The test models were developed using a mandibular dentiform with a horizontal plane of occlusion. Two complete metal abutment crowns were made for the left second molar, differing only in retentive undercut depths. A total of 98 clasps (n=7) were fabricated, including 14 wrought wire clasps and 28 clasps from each of the following alloys: Co-Cr alloy (Biosil), Type IV gold alloy (Cast-4), and Ti-Ni alloy (TN-10). Clasps were made to engage one of 2 retentive undercut depths (0.25 mm or 0.75 mm) and were made in 2 sizes (0.8 mm or 1.4 mm). Each clasp was radiographically examined for casting defects and porosity. The force (N) required to remove the clasps was measured using a universal testing machine with a crosshead speed of 10 mm/min. After measuring the retentive force, a masticatory simulator was used to cycle the clasps on and off the metal crown 500 times, simulating the insertion and removal of a removable partial denture clasp. The cycling sequence was repeated 10 times, and retention force was measured after each sequence. The internal surface of the clasp arms was examined for evidence of metal fatigue using scanning electron microscopy. Data were subjected to 2-way and 4-way analysis of variance, followed by Scheffe's multiple comparison test (alpha=.05). RESULTS: Co-Cr alloy and gold alloy clasps in the 0.25-mm retentive undercut groups experienced a gradual decrease in retentive force measurements (P<.001). In contrast, the Ti-Ni alloy clasps maintained a retentive force of approximately 1.8 N and 2.6 N for the 0.8 mm and 1.4 mm clasp groups, respectively. Although Ti-Ni alloy clasps' retentive force was reduced slightly after the first cycling sequence, it was negligible compared with other clasps tested. The wrought wire clasps also retained their retentive force until the final cycling sequence. A similar trend was found in the clasp groups engaging 0.75-mm retentive undercuts. CONCLUSION: Although the end-point retention for all the clasps was similar, there was less change in the retentive force of the cast Ti-Ni alloy clasps after repeated cycling sequences of simulated placement and removal.

Analysis of Variance↗
PubMed2003

The anatomy of buccinator--insights from functional casts of the oral vestibule.

OBJECTIVE: When a dental elastomer is placed in the oral vestibule and the facial muscles contracted while it sets, the functional cast produced frequently shows a deep anteroposterior groove, and marked posterosuperior and smaller anteroinferior bulges. This study investigates whether these features have a structural or a physiological basis. DESIGN: Casts of the right side of the oral vestibule of dissecting room cadavers and living volunteers were made using a polyvinylsiloxane dental elastomer. The volunteers each produced two functional casts in each of the following situations: while the teeth were clenched but the facial muscles inactive, while grimacing, and while swallowing. RESULTS: Grooves and bulges were largely absent in casts from the dissecting room cadavers and of living volunteers with the teeth clenched but the facial muscles inactive. They were present when the elastomer set while the subjects grimaced but most marked when they had been swallowing their saliva. The depth of the grooves varied between individuals and generally was greatest alongside the second molar teeth. We found that the posterosuperior bulge did not coincide with the position of the parotid duct. CONCLUSIONS: The anteroposterior groove represents a well developed horizontal part of buccinator. The regions of the casts bulging superior and inferior to the groove probably represent weaker regions of buccinator towards its maxillary and mandibular attachments. The bulge superior to the groove was not explained by a weakness in buccinator where it is pierced by the parotid duct.

Adult↗
PubMed1997

Total contact casts: pressure reduction at ulcer sites and the effect on the contralateral foot.

OBJECTIVE: To compare the effectiveness of total contact casts with a cast boot (TCCB), total contact casts with a cast heel (TCCH), and therapeutic XtraDepth shoes (XDS) to reduce ulcer site pressures and to determine if total contact casts increase contralateral pressures. DESIGN: Repeat measure design with 40 replications nested within each treatment for each patient. METHODS: Peak contralateral foot pressures and ulcer site pressures under the 1st metatarsal (1MET; n = 10), 2nd to 5th metatarsals (2-5MET; n = 10), and great toe (GT; n = 5) were compared using the Novel-Pedar system and three treatments: TCCB, TCCH, and XDS. Baseline pressures were established using canvas oxfords. RESULTS: There was no difference in pressure reduction with TCCH vs. TCCB for 1MET or GT ulcers, but TCCH reduced pressure better for 2-5MET ulcers (p < .001). Contralateral pressures were not elevated in either TCC group. CONCLUSIONS: TCCH were superior to TCCB in reducing 2-5MET ulcer pressures and equivalent to TCCB for 1MET and GT ulcers. Contralateral pressures are not increased by TCC use.

Adult↗