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At least 19 recordsLinked to original sources
PubMed1997

Skin surface pressure beneath an above-the-knee cast: plaster casts compared with fiberglass casts.

Complications related to immobilization in a cast after an injury or an operation may be related to the materials used for the cast or to the techniques of application, or to both. To evaluate the widely held clinical opinion that the use of a fiberglass cast is dangerous and inappropriate when subsequent swelling of the extremity is anticipated, we studied the skin surface pressures that were generated beneath above-the-knee casts made with different materials and applied with different techniques. A prosthetic model of the lower extremity was designed with an expandable calf compartment to simulate swelling after an injury or an operation. With use of this model, we measured the skin surface pressure beneath a plaster-of-Paris cast, a fiberglass cast that had been applied with a standard technique, and a fiberglass cast that had been applied with a stretch-relax technique. The highest mean skin surface pressure after application of the cast (p < 0.001) and after simulated swelling of the limb (p = 0.04) was generated by the fiberglass cast that had been applied with a standard technique. The lowest mean skin surface pressure after application of the cast (p = 0.006), simulated swelling of the limb (p < 0.001), and all subsequent steps of the experimental protocol (p < 0.001) was generated by the fiberglass cast that had been applied with the stretch-relax technique. The mean skin surface pressure generated by the plaster cast and by the fiberglass cast applied with the standard technique did not return to the value before application of the cast until anterior and posterior longitudinal cuts had been made in the cast and the cast had been spread at those cuts. When the fiber-glass cast had been applied with the stretch-relax technique, the mean pressure returned to the baseline value after only an anterior longitudinal cut and spreading at that cut. The principal pitfall of the use of a fiberglass cast is related to the technique of application. When the fiberglass cast had been applied with the standard technique, it generated a mean skin surface pressure that was higher than that associated with the plaster cast and it accommodated simulated swelling poorly. When the fiberglass cast had been properly applied, with the stretch-relax technique, it generated a mean skin surface pressure that was significantly lower (p = 0.006) than that associated with the plaster cast and it better accommodated simulated swelling without the need to sacrifice the structural integrity of the cast.

Calcium Sulfate↗
PubMed1989

[Casting of pure titanium and high fusing dental alloys by experimental casting machine. 7. Casting procedure for pure titanium denture frame].

The pure titanium cast frameworks were made using an arc-melting pressure and vacuum casting apparatus invented by Sato, and an experimental investment material. The salient features of the method and the cast frameworks were as follows: 1. The casting apparatus used was capable of making both complete and partial denture frameworks with pure titanium. It reduced casting errors and the interaction between titanium and the casting mold, producing less porous casted frameworks with a smooth surface. 2. The experimental investment material made a firm heat-resistant investment model with a smooth surface. It showed appropriate expansion and also excellent strength at room temperature after the burn out of the wax pattern. 3. The titanium casted frameworks fitted to the model and the oral cavity closely, and yielded satisfactory clinical results in more than 15 patients.

Dental Casting Investment↗
PubMed1978

[Casting faults and structural studies on bonded alloys comparing centrifugal castings and vacuum pressure castings].

The casting processes in use today such as centrifugal casting and vacuum pressure casting were compared with one another. An effort was made to answer the question whether the occurrence of shrink cavities and the mean diameter of the grain of the alloy is dependent on the method of casting. 80 crowns were made by both processes from the baked alloys Degudent Universal, Degudent N and the trial alloy 4437 of the firm Degusa. Slice sections were examined for macro and micro-porosity and the structural appearance was evaluated by linear analysis. Statistical analysis showed that casting faults and casting structure is independent of the method used and their causes must be found in the conditions of casting and the composition of the alloy.

Crowns↗
PubMed1984

Functional cast-bracing for Colles' fractures. A comparison between cast-bracing and conventional plaster casts.

The use of Orthoplast cast-bracing to allow early hand function in the treatment of displaced Colles' fractures was investigated in 243 patients. They were randomly allocated into three groups: in the first a conventional Colles' type plaster was used; in the second an above-elbow cast-brace with the forearm in supination; and in the third a below-elbow cast-brace. Radiographic measurements were made at each stage of treatment, and the final anatomical result was scored using Sarmiento's (1975) criteria. Function was assessed at three months and at six months. The anatomical result was not influenced by the method of immobilisation but was related to the efficacy of reduction. Loss of position in the braces was no greater than in plaster. The functional result at three months also was uninfluenced by the method of immobilisation; it was, however, related to the severity of the initial displacement, and (to a lesser degree) to the anatomical result, an effect which was lost at six months. Early hand function and the supinated position advocated by Sarmiento were found to confer no anatomical or functional advantage; we could see no reason to change from the use of conventional plaster casts in the treatment of uncomplicated Colles' fractures.

Adolescent↗
PubMed1975

[The cast structure after vacuum-pressure casting and centrifugal casting].

Evaluation of polished sections revealed the following: 1. Grain size in marginal areas of the crown is, in general, smaller than it is in the occlusal region. 2. Grain size varies depending on the casting method applied. Differences in hardness were found only to a limited extent. They were not always in line with the grain structure. This phenomenon deviating from the rule cannot satisfactorily be explained. The piping distribution was in accordance with observations made so far.

Crowns↗
PubMed2000

Effect of ring liner and casting ring temperature on the dimension of cast posts.

STATEMENT OF PROBLEM: If a post does not fit passively, binding with the radicular tooth structure occurs, possibly increasing the risk for root fracture. Therefore, it is necessary to fabricate slightly undersized cast posts to allow for passive fit and cement placement. Shrinkage of the mold cavity may be a desired effect during the casting of posts. PURPOSE: This study evaluated the influence of: (1) a cellulose ring liner, and (2) a lower casting temperature of the metal ring, on the dimensions of a cast post. MATERIAL AND METHODS: Eighty plastic posts were divided in 4 equal groups (group 1, 815 degrees C, liner; group 2, 815 degrees C, no liner; group 3, 600 degrees C, liner; and group 4, 600 degrees C, no liner), invested in phosphate-bonded investment and cast with a noble alloy. Posts were measured at 2 locations, the tip and base, before and after casting. RESULTS: Investing in a lined metal ring and using a casting ring temperature of 815 degrees C (group 1) resulted in markedly oversized posts (tip: +25.8 microm; base: +20.3 microm). The absence of the cellulose liner in the casting ring (group 2) decreased the expansion of the investment producing slightly oversized castings (tip: +9.75 microm; base: +4.52 microm). Lined rings that were heated to a final temperature of 600 degrees C (group 3) produced posts that were oversized (tip: +16.65 microm; base: +11.05 microm). Final casting ring temperature of 600 degrees C and the absence of a cellulose liner (group 4) resulted in posts slightly undersized (tip: -4.1 microm; base: -2.2 microm). CONCLUSION: The use of 2 casting ring temperatures (815 degrees C or 600 degrees C) and the influence of a ring liner were investigated. Decreasing the casting ring temperature from 815 degrees C to 600 degrees C and the absence of a ring liner significantly decreased the dimensions of a cast post.

Analysis of Variance↗
PubMed1992

The fit of gold-alloy full-crown castings made with ceramic casting ring liners.

Measurements were made of the fit of gold-alloy full-crown castings produced with dry ceramic ring liners. When used with vacuum investing, these liners absorb relatively large amounts of water from the investment mix (thereby reducing its original W/P ratio) and then function as wet liners, thus increasing the investment's potential expansion and giving castings which are consistently larger than when air investing is used. With four of the five liners tested, investing in air produced many castings which were unacceptably undersized (inaccuracy worse than -0.2%). The fifth liner, an industrial material 2 mm thick, gave only one casting out of 12 which was outside this limit, although all castings were undersized to a lesser extent. Vacuum investing gave improved casting accuracy; with four of the five liners, the improvement was highly significant (p < 0.001), and with the fifth, probably significant (p < 0.05). Even with vacuum investing, however, with only two of the liners did all castings show inaccuracies within +/- 0.2%. With the other three liners, some castings (ranging from 2/10 to 7/9) had inaccuracies worse than -0.2%. With both air and vacuum investing, changing from one liner to another caused changes in relative casting accuracy which were often significant (p < 0.01) or highly significant (p < 0.001). In casting techniques where a ceramic ring liner is used, the choice of specific lining material and the choice between investing in air or under vacuum are important factors which can have a major effect on the fit of castings.

Absorption↗
PubMed1998

Biochemistry and biomechanics of healing tendon: Part I. Effects of rigid plaster casts and functional casts.

PURPOSE: Traditional treatment of surgically repaired Achilles tendons includes complete immobilization of the joint in rigid casts for 6 to 8 wk. We tested the use of functional polyurethane casts as an alternative to rigid plaster casts after experimental tenotomy and repair of the rabbit Achilles tendon. METHODS: After repair the limbs of 15 experimental rabbits were immobilized in a functional polyurethane cast for 15 d, while those of 14 controls were immobilized in traditional rigid plaster casts for the same period. RESULTS: Functional casting resulted in a 60% increase in total collagen in the neotendon compared with that in rigid casting (P < 0.05). Mature collagen cross-links declined 8% in the tendons with functional casts. The biomechanical parameters of the tendons changed with functional casting, showing a 20% increase in maximum load and 21% increase in maximum stress. CONCLUSIONS: These changes were noted without any cases of tendon re-rupture in either type of cast. Thus, functional casting following surgery of Achilles tendons appears to improve healing without significant risks of re-rupture.

Achilles Tendon↗
PubMed1998

[Mechanical properties of titanium casting obtained using short-time cast procedure].

The purpose of this study was to investigate the mechanical properties of titanium casting obtained using short-time cast procedure. A commercial phosphate-bonded investment for titanium casting were used. And dumbbell-shaped specimens with phi 2 mm x 14 mm parallel portion were cast according to manufacture instruction and by way of three different short-time cast procedures. Then, micro vickers hardness test and tensile test were performed with these specimens. In the hardness test, the micro vickers hardness of 50 approximately 250 microns deep location from specimen surface was ranged from 192.8 to 259.0 Hv; there were significant difference among both the location factor and the casting procedure factor by the two-way ANOVA (p < 0.05). In the tensile test, tensile strength, yield strength, elastic modulus and elongation were obtained: these tensile properties of short-time cast procedures were not significantly different from those of manufacture instruction. These results indicated that the short-time cast procedure for titanium casting was available in the point of mechanical properties. It was, however, not obvious that how the short-time cast procedures effected the dimensional accuracy of titanium casting. Therefore, further investigation was needed for the practical usage of this method.

Dental Casting Technique↗
PubMed1988

Casting of electron field defining apertures: casting with the metal mold kits.

Cerrobend alloy casts are made to define the desired electron field shapes. These custom casts are fabricated for the selected electron applicator size that has been chosen for the patient. When the cast is placed into that selected electron applicator, it will block out areas that are not to be treated. When an all metal mold assembly was used for the fabrication of these casts, the lip region of the cast which is used to accurately align the cast in the actual treatment applicator, had an irregular edge that prevented an accurate alignment of the cast. To eliminate the irregular edges on the lip region of the cast, the metal mold assembly was heated to approximately 80-85 degrees C before the molten cerrobend alloy was poured into it. The heating of the metal mold assembly helps eliminate the irregular edges on the lip region of the cast. Unfortunately it also created new flaws such as holes, dents, cracks and/or crystallization of the cast as it solidified. These flaws were controlled by cooling the metal mold assembly and the cast immediately after the pouring of the molten cerrobend alloy, evenly with water.

Alloys↗
PubMed1995

Casting shrinkage of thin-walled castings.

OBJECTIVES AND METHODS: The casting shrinkage of thin-walled castings was measured using a tungsten die method. The thickness and the surface area of the casting were simulated to those of either partial veneer crowns or complete denture frameworks. Gold alloys were cast at two different pressures (0.35 and 0.49 MPa) and the shrinkage measurement was made at different locations on the castings to investigate the effect of these factors. RESULTS: Both overall and local shrinkages were significantly influenced by size and casting pressure. These shrinkages were significantly lower for the denture-sized (DS) specimens than for the crown-sized (CS) specimens, and significantly decreased with the increase of the casting pressure. The effect of location on the local shrinkage significantly varied with the change of the other two factors, size and pressure. At the higher casting pressure, the DS specimens sustained a significantly smaller shrinkage at the margin than at the centre, whereas the CS specimens had a significantly smaller shrinkage at the centre than at the margin at the lower pressure. CONCLUSIONS: The results suggest that the casting shrinkage of a thin-walled casting is influenced by the temperature gradient in the alloy and the resultant time difference in alloy solidification as well as the volume supply of the molten alloy in the mould.

Crowns↗
PubMed1992

The fit of gold-alloy full-crown castings made with pre-wetted casting ring liners.

Measurements were made of the fit of full-crown gold-alloy castings produced with two types of pre-wetted ring liner (asbestos and cellulose) and a typical gypsum-bonded investment (Cristobalite Inlay, Sybron/Kerr Products, Romulus, MI; W/P = 0.40). Laboratory measurements were made of the effects of the liners on potential investment expansion, and properties of the lining materials considered relevant to casting accuracy were also measured. There was a wide variation in values for mean dimensional inaccuracy. One liner produced a series of castings all of whose inaccuracies lay within the range +/- 0.1%, with a mean value of + 0.01%. With the other five liners, all or most castings were undersize. With three, all or most castings showed inaccuracies worse than -0.2%. The values for casting inaccuracy with the various liners showed a probable correlation with potential investment expansion (p < 0.05); however, no correlation was found between casting inaccuracy and any apparently relevant liner properties, alone or in combination. In casting techniques which use a pre-wetted ring liner, the choice of a specific lining material is an important factor which has a significant effect on casting inaccuracy. With at least three of the six liners tested, a higher investment expansion was needed for accurate full-crown castings to be ensured.

Absorption↗
PubMed1994

[Variables effecting casting accuracy of quick heating casting investments].

Recently, several new products of investments for "quick heating" have been put on the Japanese market. The total casting procedure time for this quick heating method involves only one hour; 30-minutes waiting after the start of mixing before placing the mold directly into the 700 degrees C furnace and 30-minutes heating in the furnace. The purpose of this study was to evaluate two variables effecting casting accuracy using these new investments. The effect of thickness of the casting liner inside the casting ring and the effect of waiting time before placing the mold into the 700 degrees C furnace were evaluated. A stainless-steel die with a convergence angle of 8 degrees was employed. Marginal discrepancies of the crown between the wax patterns and castings were measured. The size of the cast crown became larger when the thickness of the ring liner was thick and when the waiting time before placing the mold into the furnace was long. These results suggest that these new investments have the advantage of providing sound castings using short-time casting procedures. However, it is necessary to pay careful attention to the casting conditions for obtaining reproducible castings.

Dental Casting Investment↗