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PubMed1978

Radiographic evaluation of porosities in removable partial denture castings.

Most of the removable partial denture castings examined showed radiographic evidence of internal porosity. In general the porosity ocurred in characteristic regions associated with abrupt changes in cross-sectional thickness. These were located either within the partial denture framework or at the casting-sprue junctions. The porosity is due to metal shrinkage caused by a premature solidification at some point, which in turn interferes with a controlled unidirectional soldification of the casting.

Dental Alloys↗
PubMed1996

Making the framework try-in, altered-cast impression, and occlusal registration in one appointment.

Making a bilateral distal extension removable partial denture usually requires multiple appointments for metal-framework try-in, altered cast impression, and occlusal registration. This article describes an altered cast impression procedure that uses the prefabricated impression trays and record base for obtaining the jaw relation record. This method allows the framework try-in, altered cast impression, and jaw relation record to be efficiently completed in a single appointment.

Dental Impression Technique↗
PubMed1996

A time-saving method for indirect fabrication of cast posts and cores.

Cast posts obtained from wax patterns often require tedious adjustments in the mouth to seat them passively in the prepared root canals. An indirect method that uses an elastic cast for the fabrication of resin patterns has been developed. A stone cast made from a second pour of the impression of the prepared canals is then used to adjust the patterns in the dental laboratory. Posts made with the use of this indirect method routinely seat in the root canals without adjustments at the chair. The procedure is especially useful for patients who require multiple posts in the same arch.

Acrylic Resins↗
PubMed1996

Marginal leakage of cast gold crowns luted with zinc phosphate cement: an in vivo study.

Marginal gaps of cast restorations are filled with luting agents that are soluble in intraoral fluids. This study investigated the marginal openings in eight extracted teeth with cast crowns that had been intraoral for 20 years or more. These teeth were extracted either because of periodontal disease or to facilitate insertion of a removable partial denture. Initially, the roots of the teeth were sealed with two coats of fingernail polish within 2 mm of the crown-tooth interface. Next, the teeth were immersed in a 0.05% aqueous solution of basic fuchsin die for 24 hours. Finally, each tooth was sectioned at four locations 1 mm apart. At each of these four sections, cement film thickness between tooth and casting, and microleakage were determined. The results of this study showed a mean cement film thickness of 74 microns on the mesial surface and 57 microns on the distal surface. Mean microleakage values were 432 microns on the mesial surface and 274 microns on the distal surface.

Adult↗
PubMed1997

The effect of environmental pressure changes during diving on the retentive strength of different luting agents for full cast crowns.

STATEMENT OF PROBLEM: The effect of pressure cycling on the bond strength of cement luting agents is largely unknown. PURPOSE: This study investigated the effect of pressure cycling on the retention of full cast crowns to extracted teeth. MATERIAL AND METHODS: Sixty extracted single-rooted premolar teeth had full cast crowns cemented, 20 with a zinc phosphate cement, 20 with a glass ionomer, and 20 with a resin cement. After 7 days of storage, each of the teeth in the experimental groups was pressure cycled 15 times from 0 to 3 atmospheres (304 KPa), after which the force required to dislodge the crowns was tested in an Instron testing machine. RESULTS: A significant difference was found (Students t test; p > 0.01) between the force required to remove the crowns in the zinc phosphate control (142.10 +/- 36.42 N) and experimental (15.93 +/- 11.13 N) groups and the glass ionomer cemented control (186.33 +/- 24.33 N) and experimental (91.50 +/- 33.07 N) groups; no difference was found between the resin cemented control (291.15 +/- 78.48 N) and experimental (281.32 +/- 85.43 N) groups. CONCLUSION: This study showed that the retention of full cast crowns to extracted teeth is reduced after pressure cycling if the crowns are cemented with either zinc phosphate cement or glass ionomer cement. Dentists should consider using a resin cement when cementing crowns and fixed partial dentures for patients, such as divers, who are likely to be exposed to pressure cycling.

Air Pressure↗
PubMed1997

Influence of tooth surface roughness and type of cement on retention of complete cast crowns.

STATEMENT OF PROBLEM: Bond strength of luting cements to dentin is a critical consideration for success of cast restorations. PURPOSE OF STUDY: This study determined the relationship between surface characteristics of teeth prepared for complete cast crowns and retention of respective cemented restorations. MATERIAL AND METHODS: Ninety artificial crowns were cast for standardized complete crown tooth preparations accomplished with the use of a milling machine on extracted human teeth. Diamond, tungsten carbide finishing, and cross-cut carbide burs of similar shape were used. The crowns in each group were randomly subdivided into three subgroups of 10 for the three luting cements selected for this study: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cement (Panavia-EX). Retention was evaluated by measuring the tensile load required to dislodge the artificial crowns from tooth preparations with an Instron testing machine. RESULTS: Analysis of forces with parametric analysis of variance and Tukey's Studentized Range (HSD) disclosed a statistically significant difference for both luting cement and finishing burs (p < 0.001). A statistically significant interaction effect (p < 0.001) was also found. The greatest retention value (372.9 N) was for tooth preparations refined with carbide burs and cemented with Panavia-EX cement. However, the least retention value (201.6 N) was for tooth preparations completed with finishing burs and luted with zinc phosphate cement. CONCLUSIONS: Significant differences were found among all three cements for finishing burs. However, there was a difference only between Panavia-EX cement and the other two cements for tungsten carbide burs. For diamond rotary instruments, zinc phosphate cement was significantly different from glass ionomer and Panavia-EX cements.

Analysis of Variance↗
PubMed1998

Effect of pH on element release from dental casting alloys.

STATEMENT OF PROBLEM: Dental casting alloys are subjected to transient acidity in the oral environment, yet most studies have not investigated the effects of these transient environments on elemental release from alloys. Elemental release is important because it plays a significant role in alloy biocompatibility. PURPOSE: It was hypothesized that acidic environments would increase elemental release from dental alloys during exposure and after the acidic environment was removed. This hypothesis was based on the known increase in release of nickel from nickel-based alloys in an acidic environment. MATERIAL AND METHODS: High-noble, noble, and base metal casting alloys were exposed for 30 minutes to solutions with pH ranging from 1 to 7. Elemental release of representative elements was measured by means of atomic absorption spectrometry during the exposure and in the week after the exposure. This release was compared with elemental release in the week before the exposure. RESULTS: High-noble and noble alloys were resistant to acidic environments. A pH of 4 did not increase elemental release during or after exposure. A pH 1 environment slightly elevated release of Ag, Cu, and Pd in some alloys. However, a Ni-based alloy released large amounts of Ni during the acidic exposure of pH 1 or 4, and more importantly, in the week after the exposure as well. Increased time of exposure to acid did not alter elemental release from noble or high-noble alloys, but markedly increased release from the Ni-based alloy. CONCLUSIONS: Transient exposure of casting alloys to an acidic oral environment is likely to significantly increase elemental release from Ni-based alloys, but not from high-noble or noble alloys.

Analysis of Variance↗
PubMed1994

Cast prosthesis removal using ultrasonics and a thermoplastic resin adhesive.

Nonsurgical endodontic procedures are routinely performed on teeth with existing cast restorations. The internal anatomy of the tooth and location of the root canals may be obscured by a crown or fixed partial denture. Tooth morphology and canal location may, therefore, be better visualized without the cast restoration in place. This article describes a conservative technique to remove an existing cast restoration to facilitate nonsurgical root canal treatment.

Crowns↗
PubMed2002

Biological interactions of dental cast alloys with oral tissues.

OBJECTIVE: All dental cast alloys release metal ions into the oral environment which have the potential to interact with the oral tissues. Amount and type of metal elements released are varying and not directly related to the composition of the alloy. The aim of the present literature survey was to describe the interactions of dental cast alloys with living tissues and to relate them to clinically adverse local reactions of the oral tissues. RESULTS: Interactions of dental cast alloys with the oral tissues take place by different mechanisms; e.g. bacterial adherence promotion, toxic and subtoxic effects and allergy. Whereas bacterial adhesion promotion may be counteracted by adequate oral hygiene measures, the other mechanisms may lead to clinically adverse local reactions due to the metal present. However, the number of cases, where such a relation can be safely diagnosed, is small. Safe ground is felt with proven allergies. The comparatively high allergy rate towards nickel should be the impetus to replace those alloys whenever there is a suitable alternative. Medical and dental impairments as well as general medication may lead to symptoms allegedly attributed to metal restorations. CONCLUSIONS AND SIGNIFICANCE: Patients relating oral symptoms to metal restorations should be subjected to a thorough dental and general medical examination in order to exclude non-material related diseases being the cause for their complaints/symptoms. These cases are a challenge for the collaboration between the medical and dental professions.

Animals↗
PubMed2002

Bioactivity of tape cast and sintered bioactive glass-ceramic in simulated body fluid.

A common ceramic processing technique, tape casting, was used to produce thin, flexible sheets of bioactive glass (Bioglass 45S5) particulate in an organic matrix. Tape casting offers the possibility of producing three-dimensional shapes, as the final material is built up layer by layer. Bioactive glass tapes were sintered together to form small discs for in vitro bioactivity testing in simulated body fluid (SBF). Four different sintering schedules were investigated: 800, 900, and 1000 degrees C for 3 h; and 1000 degrees C for 6 h. Each schedule produced a crystalline material of major phase Na2Ca2Si3O9. Tape cast and sintered bioactive glass-ceramic processed at 1000 degrees C formed crystalline hydroxyapatite layers after 20-24 h in SBF as indicated by Fourier transform infrared spectroscopy, Scanning electron microscopy, and EDS data. FTIR revealed that the greatest amount of hydroxyapatite formation after 2 h was observed for samples sintered at 900 degrees C. The differences in bioactive response were likely caused by the variation in the extent of sintering and, consequently, the amount of surface area available for reaction with SBF.

Biocompatible Materials↗
PubMed2003

Wear properties of Ti and Ti-6Al-7Nb castings for dental prostheses.

Titanium has been increasingly applied to dental prostheses because of its biocompatibility. However, application remains limited, due to the low strength and poor wear resistance of unalloyed titanium. The purpose of this study is to evaluate the wear resistance of high-strength Ti-6Al-7Nb alloy castings for dental application. Test specimens were cast from commercially pure titanium (CP-Ti grades 2 and 3) and Ti-6Al-7Nb alloy ingots, and subjected to a wear test simulating the occlusal loading pattern. Wear resistance was evaluated by the weight loss during the test. Ti-6Al-7Nb alloy was found to exhibit lower weight loss than CP-Ti. Moreover, scanning electron microscopic (SEM) observation after the test revealed that the worn surface of Ti-6Al-7Nb alloy is much smoother than that of CP-Ti. These results indicate that Ti-6Al-7Nb alloy castings can be used to produce dental prostheses of improved wear resistance and mechanical strength.

Biomechanical Phenomena↗
PubMed2002

Automated image analysis and in situ hybridization as tools to study bacterial populations in food resources, gut and cast of Lumbricus terrestris L.

An image analysis procedure was developed for bacterial cells after staining with the DNA-intercalating dye 4'-6-diamidino-2-phenylindole (DAPI), and after in situ hybridization with Cy3-labeled, rRNA-targeted oligonucleotide probes. DAPI- and Cy3-images were captured separately from the same scenery with a cooled digital video camera with three CCD chips for the basic colors red (R), green (G) and blue (B). Using the appropriate filter sets, images of DAPI-stained cells were captured with the red channel shut down, while Cy3-stained cells were captured with the green and blue channels shut down. DAPI images and Cy3 images were subsequently merged to produce virtual color (RGB)-images. Processing of all color channels allowed to specifically enumerate DAPI-stained and hybridized bacteria, to measure their cell sizes, to subsequently calculate their biovolumes and to estimate their biomass. Using this procedure, significant differences were detected in bacterial populations in food resources, digestive tract and cast of the earthworm L. terrestris L. In leaves, bacteria were on average ten times more abundant and two times larger than in soil. In the digestive tract of L. terrestris, however, numbers and volumes of bacteria were comparable to those in soil indicating the disruption of cells originating from leaves before arriving in the foregut. Passage through the digestive tract of L. terrestris significantly reduced bacterial populations belonging to the alpha-, beta- and gamma-subdivisions of Proteobacteria. While these populations did not recover during incubation of cast, populations of the delta-subdivision of Proteobacteria and the Cytophaga-Flavobacterium cluster of the CFB phylum increased in cast. These results suggest a large impact of passage through the digestive tract of L. terrestris on bacterial community structure and demonstrate the usefulness of our image analysis procedure for the determination of cell sizes and biovolumes and thus biomass of specific bacterial populations in different terrestrial habitats.

Animals↗
PubMed1984

The clinical significance of candidal casts.

Examination of the urinary sediment for fungal casts is a new and simple approach for assessing renal involvement in fungal infections. Identification of candidal casts was used to diagnose renal fungal involvement in five immunocompromised patients. In three cases, the examination of the urinary sediment permitted the diagnosis of early and presumably noninvasive renal candidal infections that cleared easily with relatively low doses of antifungal therapy. In two other cases, the recognition of candidal casts confirmed renal involvement in patients with disseminated disease.

Adult↗
PubMed1999

3-dimensional analysis of cleft palate casts.

It is the aim of presurgical infant orthopedics (PSIO) to reduce the width of the cleft and to achieve optimal alignment of the cleft palate segments within the first few months of infancy prior to any surgical cleft closure. The question about the amount that PSIO can stimulate and steer the growth of the maxilla using a Hotz and Gnoinski passive appliance has not yet been satisfactorily answered. In this study, a 3-dimensional digital computer-aided procedure was developed to analyze metrically and to visualize the growth of the edentulous maxilla of cleft lip and palate in infants. In a pilot study, a series of digital scans of consecutive plaster casts was carried out. 5 infants with complete unilateral cleft lip and palate (UCLP), who had been treated with passive appliances were evaluated. Impressions were taken at the age of one week and after 3, 6 and 12 months. Following digitizing, the casts were computer-reconstructed and segmented perpendicular to the alveolar crest, the reference points being C1, C1', C2, C2' and I. The volume of the resulting segments was ascertained. Computer superimposition of reconstructed consecutive casts was employed to facilitate a visualization of the extent and direction of morphological changes. Our first results have shown that with our method it is possible to quantify the growth rate of defined segments of the maxilla. The 3-dimensional analysis presented here will be the basis for further studies to objectify PSIO.

Cleft Palate↗
PubMed1996

Cough productive of casts.

Plastic bronchitis is a rare disorder characterized by the formation and, sometimes dramatic expectoration of long, branching bronchial casts. DIsorders associated with bronchial casts either produce an increase in the volume or viscosity of secretions, such as allergic bronchopulmonary aspergillosis, asthma, cystic fibrosis, pneumonia, and chronic bronchitis; or there are obstructions or structural abnormalities that decrease mucous clearance, such as bronchiectasis. The diagnostic evaluation should include serum laboratory studies, specimen cultures, skin tests, chest radiograph and CT scan, pulmonary function tests, and bronchoscopy. Therapy should be directed towards the underlying disorder and should also include maneuvers to facilitate removal of casts to prevent complications, such as secondary pneumonia.

Adolescent↗
PubMed2004

Studies on solution and solution-cast film of polyaniline colloids prepared in the absence and presence of ultrasonic irradiation.

Spectroscopic and voltammetric features for the solution and solution-cast film of polyaniline (PANI) colloids prepared in the absence and presence of ultrasonic irradiation were examined. Significant differences in the color and absorption spectra between the solution of colloids prepared in the absence and presence of irradiation were observed. Effects of ambient atmosphere on the solution of colloids were also studied. A gradual decay in the absorption at approximately 365 nm was occurred upon ageing the solution in air for the colloid prepared under ultrasonic irradiation. PANI film, cast from its colloidal solution, exhibited excellent electroactivity. The films thus cast were applied to electrode modification to control electrochemical reaction. Clear voltammetric response was observed on the electrode modified with the colloid prepared in the presence of ultrasonic irradiation.

Journal Article↗
PubMedDate not supplied

Properties and microstructure of thermo-pressed wheat gluten films: a comparison with cast films.

Wheat gluten films were prepared by thermo-pressing, and their mechanical properties were compared to those of cast films. The stress-strain relationship was established for films with various amounts of glycerol. Both relationships were quite different, revealing a different network organization. Thermo-pressed films presented higher stress values than cast films, but the effect of the glycerol amount was similar in both cases, an increase of the glycerol amount leading to a decrease of both films stress. The glycerol influence on the strain at break of thermo-pressed films was very limited, with strain values reaching a maximum around 200%. The role of disulfide bridges on themomoulded films mechanical properties was investigated, and it was shown that some rearrangements and a significative protein insolubilization occurred during the process. The effective flow porosity of the protein network for thermo-pressed films was estimated by water capillary rise measurements to about 7%. Scanning electron microscopy was used to obtain some information about the microstructure of both cast and thermo-pressed films.

Disulfides↗
PubMed2004

Aging of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene)/toluene solutions and subsequent effects on luminescence behavior of cast films.

Morphological effects in luminescence properties of a representative semiconducting polymer, poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), has recently attracted much attention. Previous studies indicated that short-term heat treatment of solution-cast MEH-PPV films may result in the formation of mesomorphic order that is responsible for the "red" emission around 640 nm, in contrast to the single-chromophore "yellow" emission near 590 nm from the disordered matrix. On the basis of microscopic and spectroscopic evidence for films cast from freshly prepared and aged solutions, here we show that prolonged storage of MEHyellowPPV solutions at room temperature or lower may result in retardation of the thermally induced mesophase formation in the subsequently cast films. According to small-angle neutron scattering and differential scanning calorimetric observations over aged MEH-PPV/toluene solutions, we propose that the suppressed transformation into mesomorphic order is due to further development of nanocrystalline aggregates that serve as physical cross-links among MEH-PPV chains in the solution state upon long-term storage. These solvent-induced nanocrystalline aggregates, however, do not exhibit new spectroscopic features beyond the suppression of "red" emission at 640 nm from the mesomorphic phase.

Journal Article↗