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PubMed1990

[Investigation of the castings marginal adaptation using investment expansion methods].

The research in the field of metal casting has recorded a continual progress in dentistry. Particularly, due to the economic problems posed by the use of gold alloys relatively inexpensive metal alloys tend to gain increased popularity. Application of such alloys physically in dentistry and their adaptability to various preparations are being studied. In castings where investment expansion methods are employed, and marginal adaptability of castings are evaluated, the results of variance analysis have indicated little significant difference due to the applied methods. However, the hygroscopic method has proved highly successful in terms of marginal adaptability.

Analysis of Variance↗
PubMed1982

The effect of asbestos-alternatives on the accuracy of cast veneer crowns.

The effect of three different lining materials on the investment expansion during the casting procedure, was compared. The accuracy of the castings was assessed by measuring slits at the gingival shoulder of a cast veneer crown. The liners were made of asbestosos, paper and a glassfiber material. They were used with a gypsum bonded and a phosphate bonded investment material using a regular type III and a high-fusing alloy. The glass-fiber material seemed to give a good and reproducible accuracy with both investments. The effect of this liner seemed to be comparable or better than that of the conventional asbest material. The paper liner sometimes allowed a sufficient expansion, but with varying results. Additional problems were connected to this material as it was burnt to ash during the mould heating procedure.

Asbestos↗
PubMedDate not supplied

Description and evaluation of a simplified method to achieve passive fit between cast titanium frameworks and implants.

Because osseointegrated implants have no resilience in bone, passive fit between dental implants and prosthetic superstructures has been identified, both from biologic and mechanical perspectives, as a potential discriminating prognostic factor. Distortion of the metal framework during the casting procedure has been cited as a main cause of misfit. The objectives of the present article were to describe a recently presented method (Cresco Ti Precision method) intended to correct for distortion in cast titanium frameworks, and to elucidate and evaluate the method by photoelastic and strain gauge techniques. The method appears to be an efficient and accurate procedure for correcting for distortion in cast titanium frameworks.

Dental Abutments↗
PubMed1992

Forms of lung lymphatics: a scanning electron microscopic study of casts.

In a recent study, rats given monocrotaline underwent angiogenesis on their pleural surfaces. The rats also had novel structures in their bronchovascular bundles that were detected by scanning electron microscopy of vascular casts. These vessels could have been either new blood capillaries or dilated lymphatic capillaries. To determine if these structures were lymphatics or new blood vessels, specimens from animals that were undergoing angiogenesis were compared to those that were not. Finding similar structures in normal animals would imply that they were lymphatic. The second purpose of this work was to describe the three-dimensional anatomy of the lymphatics of the lung. Cast lymphatics were found in most lungs with edema or angiogenesis, but were rare in other conditions. The vascular structures in question were found in animals not undergoing angiogenesis and were, therefore, lymphatic. Additionally, scanning electron microscopy of casts showed several distinct forms of lymphatics in the lung. Prelymphatics are tissues planes beneath the pleura and around bronchovascular structures. They join reservoir, conduit or tubulo-saccular lymphatics. Reservoir lymphatics are broad ribbon-like structures with textured surfaces and small laterally branching pouches. They occur on the pleural surface, are closely linked with prelymphatics, and join conduit lymphatics. Conduit lymphatics are tubular structures that may contain valves, twist and go great distances without accepting tributaries. On the pleural surface, they may wind around blood vessels and vary greatly in diameter. Sacculo-tubular lymphatics surround arteries, veins and bronchioles. They have thin walls with wide saccular segments. They may be so dense that they form cylinders around the vessels or airways. Different forms of lung lymphatics suggest different function and potential.

Animals↗
PubMed1994

Initial vascularisation in the pig placenta: II. Demonstration of gland and areola-gland subunits by histology and corrosion casts.

Tissues from 10 pregnant pigs between 9 1/2 and 43 days post coitum (p.c.) were prepared for histology and vascular corrosion casts to examine the vascularisation of the gland and areola-gland subunits of the early pig placenta. The endometrial vascular networks shown by casts were equal in both glandular and interglandular fields from days 9 1/2 to 14-15 p.c. This represents a cyclic stage uninfluenced by the early implanting embryo on day 13 p.c. By day 15 p.c., the first areola formation was observed both histologically and on casts. The maternal areolar and glandular capillary network developed into a widely meshed loose type, in contrast to the interareolar type which had a dense and parallel architecture. In some cases extremely large, crooked, and highly anastomosed maternal capillaries developed between these two networks. This specialized transition is thought to form the base for the ring-like seal formation (RSF) of the areolar periphery. A firm materno-fetal anchor therefore "seals" the areola and its glandular secretory contents from its interareolar surroundings. Therefore, the glandular and maternal areolar vasculatures are clearly discernable from that of the fetal areolar vasculature. The former are associated with the known maternao-fetal substance transfer of the porcine areolar-gland subunit. This association, however, seems to remain unspecialized in early placentation, as only the regular roundish areola--not the irregular areola--can be distinctly detected.

Animals↗
PubMed1995

Combined vascular-bronchoalveolar casting using formalin-fixed canine lungs and a low viscosity silicone rubber.

BACKGROUND: Previous work using unfixed or fixed tissues has shown that casts can be made that demonstrate the three-dimensional structure of tissues such as the bronchoalveolar tree or the vasculature. In this report, a new method for creating a vascular-bronchoalveolar cast is described. METHOD: Canine lungs were taken from storage in formalin. Silastic 734 RTV (room temperature vulcanizing) with added red or blue pigments was injected into the pulmonary arteries and veins, respectively, using compressed air. This was followed by filling the airway with clear (translucent) Silastic 734 RTV. The lung tissue was then corroded with potassium hydroxide. RESULTS: Vascular-bronchoalveolar casts were recovered giving fine detail as shown using stereo light microscopy or scanning electron microscopy. CONCLUSIONS: This method may be useful for not only microvascular anatomy studies of lungs, but also for studying the microvasculature of other normal and diseased tissues.

Animals↗
PubMed2004

Three-dimensional arrangement of the vasa vasorum in explanted segments of the aged human great saphenous vein: scanning electron microscopy and three-dimensional morphometry of vascular corrosion casts.

The vasa vasorum of skeletonized and nonskeletonized segments of five human great saphenous veins (GSVs), harvested during coronary bypass grafting, were cannulated, rinsed, and injected (casted) with the polymerizing resin Mercox-Cl-2B. After removal of the dry vascular tissue, the casts were examined using scanning electron microscopy. Stereopaired images (tilt angle, 6 degrees ) were taken, imported into a 3D morphometry system, and the 3D architecture of the vasa vasorum (arterial and venous vasa as well as capillaries) was studied qualitatively and quantitatively in terms of vasa diameters, intervascular and interbranching distances, and branching angles. Diameters of parent (d(0)) and large (d(1)) and small (d(2)) daughter vessels of arterial and venous bifurcations served to calculate asymmetry ratios (alpha) and area ratios (beta). Additionally, deviations of bifurcations and branching angles from optimal branches were calculated for selected arterial vasa. The arrangement of the vasa vasorum closely followed the longitudinally oriented connective tissue fibers in the adventitia and the circularly arranged smooth muscle cell layers within the outer layers of the media. Venous vasa by far outnumbered arterial vasa. Vasa vasorum changed their course several times in acute angles and revealed numerous circular constrictions, kinks, and outpouchings. Due to their spatial arrangement, the vasa vasorum are prone to tolerate vessel wall distension generated by acute increases in blood pressure or stretching of the vessel without severe impact on vessel functions. Preliminary comparisons of data from the bifurcations of cast arterial vasa vasorum, with calculated optimal bifurcations, do not yet give clear insights into the optimality principle(s) governing the design of arterial vasa vasorum bifurcations of the human GSVs.

Aged↗
PubMed2005

Penetration depth into dental casting alloys by Nd:YAG laser.

This study investigated the effect of laser-beam welding conditions [voltage (V) and spot diameter (mm)] on the penetration depth into dental casting alloys. Castings (3.0 mm x 8.0 mm x 50 mm) were prepared from the metals used in this study: commercially pure titanium (CP Ti), Ti-6Al-4V, Ti-6Al-7Nb, cobalt-chromium alloy (Co-Cr) and Type IV gold alloy. Two cast blocks of each metal were butted against one another at the 8.0 x 50-mm surfaces. They were then welded at their interface under the following conditions: voltage of 160-340 V, spot diameter of 0.4-1.6 mm, and pulse duration of 10 ms. After laser welding, the blocks were separated, and the penetration depth into each alloy was measured. The data were analyzed with the use of ANOVA at the p < 0.05 level of significance. The penetration depths were as follows: CP Ti (0.29-6.45 mm), Ti-6Al-4V (0.32-5.24 mm), Ti-6Al-7Nb (0.34-5.65 mm), Co-Cr (0.24-6.15 mm), and Type IV gold alloy (0.12-5.22 mm). The voltage and spot diameter affected the penetration depth into the metals tested. When the voltage increased and the spot diameter decreased, the penetration depth increased for each metal. Selecting suitable conditions for laser welding to obtain sufficient penetration depth for the optimal thickness of the metal is important when welding prostheses.

Dental Alloys↗
PubMed2006

Grindability of cast Ti-Hf alloys.

As part of our systematic studies characterizing the properties of titanium alloys, we investigated the grindability of a series of cast Ti-Hf alloys. Alloy buttons with hafnium concentrations up to 40 mass% were made using an argon-arc melting furnace. Each button was cast into a magnesia-based mold using a dental titanium casting machine; three specimens were made for each metal. Prior to testing, the hardened surface layer was removed. The specimens were ground at five different speeds for 1 min at 0.98 N using a carborundum wheel on an electric dental handpiece. Grindability was evaluated as the volume of metal removed per minute (grinding rate) and the volume ratio of metal removed compared to the wheel material lost (grinding ratio). The data were analyzed using ANOVA. A trend of increasing grindability was found with increasing amounts of hafnium, although there was no statistical difference in the grindability with increasing hafnium contents. We also found that hafnium may be used to harden or strengthen titanium without deteriorating the grindability.

Biocompatible Materials↗
PubMed2002

Vascularization of the brains of the Atlantic and Pacific hagfishes, Myxine glutinosa and Eptatretus stouti: a scanning electron microscope study of vascular corrosion casts.

The microvascularization of the brains of the hagfishes, Myxine glutinosa L. and Eptatretus stouti, were studied by scanning electron microscopy (SEM) of microvascular corrosion casts. Sections of these casts were used to determine the vascular territories of defined brain areas. Histological serial sections (10 microm) of the brains served for correlation of findings. Analysis of the microvascular casts of both species revealed that the blood supply to and from these brains arose ventrally and dorsally, respectively. Neither species possesses an arterial circle (Circulus Willisi) and both have similar microvascular patterns. The only difference between Myxine and Eptatretus was that the posterior cerebral artery in Myxine divides into mesencephalic and rhombencephalic branches, and in Eptatretus a third branch, termed telencephalic branch, arises from the posterior cerebral artery. 3D-morphometry revealed that luminal diameters of: 1) intracerebral arteries and arterioles range from 35.11 +/- 5.66 microm (mean +/- SEM) in the hypothalamus to 92.69 +/- 14.48 microm in the thalamus; 2) capillaries range from 17.8 +/- 0.44 microm in the olfactory bulb to 21.70 +/- 0.87 microm in the basal ganglia; and 3) intracerebral venules and veins range from 49.38 +/- 4.17 microm in the hypothalamus to 75.58 +/- 6.59 microm in the rhombencephalon. Interbranching distances of arteries and arterioles range from 179.19 +/- 11.32 microm in the optic tectum to 235.19 +/- 94.64 microm in the hypothalamus. Capillaries range from 91.07 +/- 6.22 microm in the hypothalamus to 116.15 +/- 9.45 microm in the thalamus, and venules and veins range from 137.30 +/- 18.11 microm in the hypothalamus to 189.83 +/- 17.47 microm in the optic tectum. Intervascular distances range from 70.58 +/- 3.58 microm in the olfactory bulb to 89.52 +/- 5.74 microm in the optic tectum. Branching angles of arteries and arterioles range from 38.39 +/- 10.9 degrees in the olfactory bulb to 100.73 +/- 9.4 degrees in the optic tectum, and the branching angles of capillaries range from 74.40 +/- 5.42 degrees in the optic tectum to 90.24 +/- 4.66 degrees in the olfactory bulb. Finally, the branching angles of the venules and veins range from 67.84 +/- 6.83 degrees in the tegmentum of the mesencephalon to 92.30 +/- 6.35 degrees in the optic tectum.

Animals↗
PubMed1983

Observations concerning the limited mobilisation cast after anterior cruciate ligament surgery.

A limited mobilisation cast (LMC) with hinges locked at 20 and 60 degrees has been advocated for the care after anterior cruciate ligament (ACL) surgery. The brace presumably limits motion to 20 and 60 degrees and prevents straining of the ACL. Extension of more than 20 degrees as well as anterior drawer forces are known to strain the ACL. We have therefore tested whether the LMC reliably limits the desired range of motion: Extension of more than 20 degrees was found in 11 of 12 patients and averaged 12 degrees. The long leg cast reduced a 30 degree anterior drawer in unstable knees by 70%, a Lenox-Hill-Derotation Brace by 53% and the LMC by only 14%. It was concluded that a modified Lenox-Hill Brace locked at 30 and 60 degrees of flexion provides better stress-protection of the ACL than a LMC and that the safety of the conventional long leg cast should be remembered in legs with unfavourable soft tissue configurations. If a LMC is used, it should be fixed to the trunk with a waist- or shoulder-strap and the hinges must be freely adjustable.

Adolescent↗
PubMed1990

Vascular canals in bovine cortical bone studied by corrosion casting.

The architecture of vascular canals in cortical bovine bone was studied by a corrosion casting method. Prior to perfusion of the casting polymer, both cellular and nonmineralized components were removed to ensure proper impregnation into vascular canals--haversian and Volkmann's canals within secondary osteons and the vascular canals of periosteal circumferential lamellae. The resulting castings revealed an anastomotic system of canals within and between these two regions of cortical bone. The nature of these arborizations, their varying degrees of interconnectiveness, and their spatial, three-dimensional ordering are clearly demonstrated in this study.

Animals↗
PubMed2006

Molar and canine occlusal changes in study casts before and after treatment with cervical headgears.

AIM: We carried out a retrospective study on 246 pairs of casts to compare the extent of changes in occlusal relationship and overjet reduction induced by cervical headgears. MATERIAL AMD METHODS: Molar-canine occlusal relationships and overjet were determined from study casts made immediately before headgear treatment. Those findings were then compared to another cast made immediately after headgear monotherapy and before multiband-appliance administration. Headgear treatment lasted at least 6 months. Only patients whose upper first molars were distalized by at least 4 mm were included. RESULTS: Strikingly, the distalization and overjet reduction induced by headgear treatment were most pronounced in posterior positions and decreased progressively toward more anterior positions along the arch. The mean amount of distalization was 6.87 mm at molar, and 1.87 mm at canine positions. The mean reduction of initial overjet was 0.78 mm. No significant differences resulted by grouping the data based on upper anterior tooth inclinations before treatment. Significant differences, however, were obtained by grouping the data based on initial overjet. Significantly greater changes in molar-canine occlusal relationships and overjet reductions were observed in patients with a major initial overjet of > 6 mm than in those with a relatively minor overjet of < 4 mm.

Child↗
PubMed2000

[Is a general pharmacologic thromboembolism prophylaxis necessary in ambulatory treatment by plaster cast immobilization in lower limb injuries?].

Selected patients with minor lower limb injuries and low risk for deep vein thrombosis (DVT), who required cast immobilizing and did not receive medical thrombosis prophylaxis, were included in a prospective study. The decision to give not medical thrombosis prophylaxis depended on an concept of individualised prophylaxis for patients at risk for thromboembolism. From March 1994 to March 1996 in 178 outpatients (118 men, 60 women, mean age 25.8 [16-39] years) a clinical examination and a colour-coded duplex sonography were performed after removal of the cast for detection of DVT of the lower limb. A phlebography was performed when thrombosis was suspected. Two patients developed a one bundle thrombosis of the calf. Clinical appearance of lung embolism was not observed. These results suggest, that low risk patients with minor injuries of the lower limb and plaster cast immobilisation do not need a medical thrombosis prophylaxis.

Adolescent↗
PubMed2000

Response of Charcot's arthropathy to contact casting: assessment by quantitative techniques.

AIMS/HYPOTHESIS: This study used two different methods of quantitative bone scanning to study the relation between activity of Charcot's arthropathy and clinical variables over 12 months. METHODS: Skin temperature of affected and unaffected feet was measured at baseline and every 3 months for 12 months in 17 subjects. Eight subjects underwent a three-phase quantitative bone scan at baseline and 3 monthly for 12 months. Bone isotope uptake in a standard rectangular area over the foot and tibia was analysed by the bilateral scan method (the ratio of isotope uptake of affected and unaffected feet) and the unilateral scan method (the ratio of isotope uptake of affected foot and ipsilateral tibia). The affected foot was placed in a contact cast for an average of 8 months. RESULTS: At presentation the affected foot was hotter than the unaffected foot but the temperature became progressively cooler over 12 months. Median isotope uptake in the affected foot was 2.1% of the injected dose (interquartile range, IQR 1.9-3.0). In both scanning methods the ratio of uptake decreased after casting but at 12 months the affected foot still had more isotope uptake. There was a strong correlation between temperature difference and the ratio of uptake in the bilateral scan method (r = 0.90; p < 0.0001) but when using the unilateral scan method this relation was not significant (r = 0.1;p = 0.6). A strong relation existed between perfusion of the affected foot in the dynamic phase and isotope uptake in the delayed phase of the scans (r = 0.92; p < 0.0001). CONCLUSION/INTERPRETATION: Bone activity and skin temperature of Charcot's arthropathy can be measured quantitatively and both improve over 12 months with contact casting. There is a strong relation between perfusion and disease activity in this condition.

Aged↗
PubMed1999

The development of the endotheliochorial mink placenta: light microscopy and scanning electron microscopical morphometry of maternal vascular casts.

The development of the mink endotheliochorial placenta has been studied by means of light microscopy and scanning electron microscopy of maternal vascular corrosion casts. The placental blood vessels of three groups of mink, representing early, intermediate and near-term gestational ages were either perfusion fixed for histology, or instilled with liquid plastic in order to prepare vascular casts, which were examined qualitatively and/or quantitatively. The maternal component of the placental vascular system evolves from preimplantation blood vessels between the endometrial glands, into which the initial feto-maternal contact is made. The influence of highly invasive syncytiotrophoblast provokes a transition of the maternal capillaries into extensively anastomosing sinusoids with a subsequent modification of their endothelial cells into large cells with luminal protrusions. Three-dimensionally, the sinusoids are arranged as vascular crypts. This implies a villous-crypt type of interdigitation for the mink, but since the fetal capillaries surround the maternal sinusoids as a dense network a labyrinth is formed. The vascular crypts are supplied by very short arterioles, branching from maternal stem arteries, which arise from branches of the uterine artery and move straight to the surface of the endometrium. Venous outlets of the sinusoids converge onto venules and large stem veins in the deepest portion of the endometrium. This architectural pattern persists until term. Morphometry was used to confirm the qualitative observations in vascular casts. The diameter of maternal vascular crypts significantly increased from 137.3+/-21.9 microm in early gestation up to 217.8+/-80.9 microm in the intermediate stage and 431.8+/-119.5 microm near-term, when compared to the paraplacental zone in early gestation (82.2+/-19.5 microm). The capillary or sinusoidal diameter also increased significantly from intermediate stage (42.9+/-11.8 microm) to near term (60.1+/-16.7 microm), whereas the difference in the paraplacental zone (7.3+/-2.1 microm) and early gestation (13.0+/-3.2 microm) was not statistically significant.

Animals↗
PubMed1998

Radiographic inspection of dental castings.

Underdimensioning may adversely affect the clinical use of a crown or bridge. Insufficient dimensions may be due to inadequate modelling or deficiencies caused by the casting process. The dimensions of cast objects are measured mechanically using a calliper. This method has often proved to be insufficient in detecting areas of too small dimensions. This paper presents a non-destructive method of inspecting dental castings using radiography. The occlusal thickness of a random sample of 150 crowns made during regular clinical treatment in our department was inspected mechanically and radiographically. We found that 19% of the crowns were only 0.1 mm thick or less at the thinnest spot, 18% were between 0.1 and 0.2 mm and 9% were between 0.2 and 0.3 mm. In comparison to mechanical examination, radiographic inspection usually showed smaller values.

Crowns↗
PubMed2007

Fatigue limits and SEM/TEM observations of fracture characteristics for three Pd-Ag dental casting alloys.

The fatigue limits and fracture characteristics for three Pd-Ag dental casting alloys (Super Star, Heraeus Kulzer; Rx 91, Pentron; W-1, Ivoclar Vivadent) were studied. Specimens meeting the dimensions for ADA Specifications No. 5 and 38, and having the as-cast surface condition, were subjected to heat treatment simulating dental porcelain firing cycles and fatigued in air at room temperature under uniaxial tension-compression at 10 Hz. A ratio of compressive stress amplitude to tensile stress amplitude (R-ratio) of -1 was used. Alloy microstructures and fracture surfaces were examined with a scanning electron microscope and a transmission electron microscope. Fatigue limits for the three alloys had low values of approximately 15% of the yield strength for 0.2% permanent tensile strain. Complex fracture surfaces with characteristic striations were observed for all three fatigued alloys. Planar slip of dislocations occurred in the Pd solid solution matrix, along with dislocation-precipitate interactions and dislocation networks in the interfaces between the precipitates and surrounding matrix. Twinning occurred in the Pd solid solution matrix of Rx 91, and within discontinuous precipitates in Super Star and Rx 91. The low fatigue limits for these alloys are attributed to their complex microstructures and perhaps to casting defects.

Dental Alloys↗