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At least 343 records · Page 19Linked to original sources
PubMed1998

Computer aided prediction and control of shrinkage porosity in titanium dental castings.

OBJECTIVES: The main objectives were to investigate the possibility and reliability of quantitative prediction and control of the concentrated shrinkage porosity (macroporosity) in titanium dental castings by means of a numerical simulation technique; and finally to optimize the filling and feeding system design for dental castings. METHODS: A commercial software, MAGMASOFT (Giessereitechnologie GmbH, Germany), was employed to simulate the mold filling and solidification process, and predict the shrinkage tendency in a sample dental casting, two simplified tooth crowns with a connector bar between them. The numerically predicted shrinkages were compared with the experimental results. The experiments were carried out on a centrifugal casting machine. The same geometric and processing parameters of the casting as in the simulations were strictly controlled. RESULTS: The computer predicted shrinkage porosity coincided with the performed experiments, demonstrating the reliability of the numerical model and the thermal physical data chosen for the calculations. Based on the above numerical model, several filling and feeding systems for the same casting were numerically simulated and compared. Finally an optimized design for this sample casting was proposed, and porosity-free castings were obtained. SIGNIFICANCE: It was expected that the numerical simulation technique could be further developed for dental laboratories to aid the real dental casting design.

Computer Simulation↗
PubMed2003

Evaluation of serial casting to correct equinovarus deformity of the ankle after acquired brain injury in adults.

OBJECTIVE: To determine the potential short-term benefit of serial plaster casting in the management of equinovarus deformity associated with acquired brain injury. DESIGN: Prospective uncontrolled interventional trial. SETTING: Inpatient rehabilitation facility in Australia. PARTICIPANTS: Sixteen patients (19 limbs) with equinovarus deformity or deteriorating ankle range of motion associated with severe plantarflexor and invertor muscle overactivity underwent serial plaster casting over an 18-month period. INTERVENTIONS: Below-knee plaster casts were reapplied weekly to increase joint range and muscle extensibility. MAIN OUTCOME MEASURES: Precasting goniometric measures of maximal ankle dorsiflexion range (in knee extension and flexion) were compared with 4 subsequent test occasions (after initial cast, midpoint of casting, after final cast, 1 wk after removal). The amount and type of assistance required to perform a standardized wheelchair-to-bed transfer before and 3 months from commencement of casting were also compared. RESULTS: Subjects who underwent the serial casting regimen had significantly improved ankle range (knee flexed mean, 18 degrees; knee extended mean, 16 degrees; P<.0001); 13 subjects reduced their need for transfer assistance (P<.0015). CONCLUSION: Serial casting appears to be effective, at least in the short term, in reducing the equinovarus deformity that occurs after acquired brain injury. Greater ankle mobility was associated with improved transfer independence in the majority of subjects.

Adolescent↗
PubMedDate not supplied

The treatment of pediatric femur fractures with early 90-90 spica casting.

Twenty-three consecutive children younger than 6 years with a closed femoral shaft fracture stemming from low-energy trauma were treated with an early spica cast. With the patient under general anesthesia, a fiberglass cast was applied in sections. A short-leg cast was applied first, and then the patient was placed on the spica table. The hip and knee were flexed to 90 degrees, and traction was applied to the injured limb via the short-leg cast while the cast was completed. The popliteal fossa was well padded, and a valgus mold was placed at the fracture site. The average number of days in the spica cast was 42 (range, 18-57 days). Average shortening of the fracture at the time of cast removal was 1.0 cm (range, 0.1-2.1 cm). Final patient examinations were performed 18-24 months after the fracture. Overgrowth averaged 1.1 cm in the femur (range, 0.5-1.9 cm) and 0.4 cm (0-0.7 cm) in the tibia. Limb lengths in each patient were within 1 cm of the contralateral limb when measured by scanogram and by blocks. The success of early spica cast treatment in this series can be attributed to strict patient selection and meticulous cast application.

Casts, Surgical↗
PubMedDate not supplied

Buoyancy of synthetic cast and its implications to young patients.

One of the authors' young patients suffered near-drowning while being treated with a synthetic below-knee cast, and this intrigued them into examining the buoyancy of waterproof casts and their use in small children. Synthetic and fiberglass casts were fabricated and subjected to immersion testing using lead pellets. Fiberglass casts sank immediately, while synthetic casts stayed afloat. With the addition of weights averaging 221 g, the synthetic casts finally sank. When supine, the casts stayed afloat with more weights. This study shows that synthetic liners are buoyant. Although the weight necessary to sink the casts was small, the weights were lead pellets, which is different from a human limb. Enhanced buoyancy of synthetic casts may pose a potential danger to a small child when not properly supervised in water. The initial buoyant force may be too startling and may place them at a higher risk for near-drowning.

Age Factors↗
PubMed1988

Effects of 'tone-reducing' vs. standard plaster-casts on gait improvement of children with cerebral palsy.

The relative effects of 'tone-reducing' (inhibitive) and standard casts on the gait patterns and functional motor activities of two children with cerebral palsy were examined in a repeated measures (single-subject) design. Both children's stride length improved in the tone-reducing casts, compared with standard casts, but there were no significant difference between the two casts in step length ratio, base of support or foot progression angle. From videotapes, clinicians noted mildly improved gait and function over baseline levels for one child during the tone-reducing cast phase. They also consistently rated this child's performance as being better with the tone-reducing casts than with the standard casts. Parents and therapists also favoured the tone-reducing casts. However, further evidence is needed for the efficacy of tone-reducing casts in the management of children with cerebral palsy.

Casts, Surgical↗
PubMedDate not supplied

Effect of casting procedures on screw loosening in UCLA-type abutments.

BACKGROUND: Screw loosening of implant restorations continues to be a complication in implant prosthodontics. Screw joints are subjected to a loss of initially applied torque because of friction and component misfit. It has been suggested that the loss of applied torque is less in machined metal abutments than in cast plastic abutments. PURPOSE: This study compared the loss of applied torque (detorque) values in machined titanium and in cast UCLA-type abutments for external hex abutment/implant interface. MATERIALS AND METHODS: Four groups of 12 samples each were evaluated: (1) machined titanium abutments, (2) premachined palladium abutments cast with palladium, (3) plastic abutments cast with nickel-chromium, and (4) plastic abutments cast with cobalt-chromium. Each abutment was torqued to 30 Ncm according to the manufacturer's instructions and detorqued three times. The mean loss of applied torque (detorque) was recorded as a percentage of the torque applied. Group means were calculated and compared using ANOVA and Tukey's LSD test. RESULTS: Mean detorque values were (1) 92.3 +/- 2.9%, (2) 81.6 +/- 5.0%, (3) 86.4 +/- 4.6%, and (4) 84.0 +/- 7.0%. Machined abutments demonstrated significantly greater detorque values compared with all cast groups (p < 0.05). No significant differences were found among cast groups. CONCLUSION: Machined abutments retained a significantly greater percentage of torque compared with cast abutments. Casting procedures decrease the percentage of applied torque, which may influence final screw joint stability.

Analysis of Variance↗
PubMedDate not supplied

Cylinder or mobile cast brace after knee ligament surgery. A clinical analysis and morphologic and enzymatic studies of changes in the quadriceps muscle.

Sixteen patients participated in a prospective randomized trial in which a standard cylinder cast was compared with a mobile cast brace. Both were worn for 4 weeks, beginning at 1 week after reconstruction of the anterior cruciate ligament. The athletes that had used a cast brace could return to sports activities in about one-half the time it took for the athletes with a standard cast. The patients with a standard cast showed a significant atrophy of Type I (slow twitch) muscle fibers in the vastus lateralis. The cast brace patients did not show any significant changes in cross-sectional areas of Type I or Type II (fast twitch) muscle fibers. The standard cast patients had a significant reduction of succinate dehydrogenase (SDH) activity in the vastus lateralis whereas the patients with the cast brace did not show any significant changes. No difference in surgical end result was found. A cast brace with a limited range of motion between 20 and 60 degrees of flexion is recommended as the standard postoperative treatment after knee ligament surgery.

Adult↗
PubMed2006

Unloading mechanism in the total contact cast.

BACKGROUND: The effectiveness of total contact casts is postulated to be due to the reduction of plantar pressure. We investigated plantar loads to evaluate the mechanism by which total contact casts off-load the plantar surface of the foot to determine if it is the intimate molding of the weightbearing plantar surface or if a below-knee cast is necessary. METHODS: Plantar pressures and forces in a total contact cast (TCC) were recorded in 12 healthy subjects, using the Pedar (Novel GmbH, Munich, Germany) pedobarographic system. The measurements were repeated after removal of the 'shank' portion of the cast (proximal to malleoli), leaving in effect, a well-molded shoe-cast (SC). Measurements included average force and peak pressure. All parameters were measured under two different loading conditions: single-leg standing balanced on the casted limb and over-ground walking. To assess the contribution of calf geometry, the 'calf ratio' was calculated by dividing the largest by the smallest circumferences of the calf. All parameters were compared between TCC and SC for each subject in each of the two conditions. Paired t-tests were used to evaluate significance, which was set at a level of p < 0.006 due to the Bonferroni Correction. RESULTS: Removal of the shank portion of the TCC significantly increased the average plantar force by 31% during walking. The force only increased 9% during standing, which was not significant. Peak pressure increased 53% after removal of the shank portion of the TCC during walking. Peak pressure was not significantly different during standing on one limb. No correlation was found between the calf ratio and the magnitude of change in the measured values. CONCLUSIONS: These results help to partially explain the widely recognized clinical observation that molded insoles and shoes, no matter how well conformed to the foot, do not reduce plantar loads as effectively as a total contact cast. The mechanism appears to be a critical unloading function of the proximal, 'shank' portion of the cast, presumably due to reduction in ankle motion.

Adult↗
PubMed2001

Focused rigidity casting: a prospective randomised study.

Focused rigidity casting was compared with standard casting in a randomised prospective study. Two hundred consecutive patients attending a fracture clinic were assigned to have either a standard cast consisting of synthetic or plaster of paris, or a focused rigidity cast of synthetic material. Patients were assessed using a specially developed scoring system termed the Bradford Plaster Index. In patients with fractures of the base of fifth metatarsal, focused rigidity casting proved superior to traditional techniques for ability score (p=0.0001), satisfaction score (p=0.0023), overall impairment of function (p=0.019), limitation of movement following cast removal (p=0.024) and in limitation of muscle strength following cast removal (p=0.001). In fractures of the distal radius, focused rigidity casting was superior for ability score (p=0.0002) and satisfaction score (p=0.00009). Patients with scaphoid fractures were better for satisfaction score (p=0.0483). Compared with the standard technique, focused rigidity casting has been shown to be superior to traditional methods with regard to satisfaction and functional scores without any detriment to clinical results.

Ankle Injuries↗
PubMed1999

Castability of Ti-6Al-7Nb alloy for dental casting.

Castability of Ti-6Al-7Nb alloy, CP Ti, and Co-Cr alloy was examined for mesh type and plate type specimens. The casting was carried out with a pressure type casting machine and commercial molding material. The castability of the mesh type specimen was evaluated in terms of the number of cast segments (castability index), and that of the plate type was evaluated by the area of the specimen (casting rate). X-ray images processed by a digital imaging technique were used to identify the casting porosity. The casting rate of the specimens increased with increasing thickness of the specimens. It was concluded that the castability index and the casting rate of Ti-6Al-7Nb alloy was slightly lower than that of CP Ti, and higher than that of Co-Cr alloy, were as Ti-6Al-7Nb alloy showed fewer casting porosities than CP Ti and smaller ones than Co-Cr alloy, which was advantageous for increasing the reliability of the casting properties.

Dental Alloys↗
PubMed1990

[Studies on application of pure titanium for cast plate].

Pure titanium produced by a commercial pure titanium casting system was studied for use as a cast plate for clinical application. The mechanical properties, elemental analysis, castability, adaptability of pure titanium and adhesion to denture base resin were investigated. The interfacial zone of the pure titanium castings was composed of a layered structure obtained by reaction with phosphate bonded Al2O3/SiO2 investment material. Vicher's hardness at 100 microns thick from the surface was higher than that in the inner part by oxidation. Cast pure titanium showed tensile strength, elongation and hardness close to those of the type III or IV dental gold alloy. The castability of pure titanium was lower than that of Co-Cr alloy and pure titanium castings also had large casting defects. Adaptability between pure titanium cast plate and the working model was satisfactory when reversible hydrocolloid impression material was used with heating-bath treatment in the refractory model. The tensile and compressive shear bonding strength of pure titanium to heat-curing or self-curing resin were similar to that of the Co-Cr alloy, and surface treatment using a solution containing 2-vol% 3-methacryloxypropyltrimethoxysilane produced a higher bonding strength than non-treatment, MKV treatment and 4-META treatment. These findings suggest that pure titanium castings produced by this system have suitable mechanical properties, adaptability and adhesion to denture base resin, and is available for cast plate in clinical application.

Adhesiveness↗
PubMed1977

[Origination of casting porosity on high fused dental alloys by use of Bio-X X-ray unit (MRO-10R) (author's transl)].

Experiments were carried out clarify internal defects in dental casting with high fused dental alloys, as cobalt-chromium alloy or nickel-chromium alloy by use of Bio-X X-ray unit (MRO-10R for dental castings), exploited by KAWAHARA and TSK international corporation. Satisfactory radiographic observations were obtained with the following results; 1. In any of castings, a large amount of porosity was found on X-ray clearly. 2. On the castings in this experiment, porosity, round and bubble like in shape was markedly observed in the location right below the sprue attachment and its neighborhood. But in regions far from sprue, porosity was decreased, it came gradually to be present on the surface of castings. 3. Radiographically some defects were of a clack type and a shrinkage type in castings, although castings seemed to be quite sound in appearance. These types of defects were considered to become a weak point when external force was applied. 4. In regard to the completeness of castings, especially large round shape, clack type and shrinkage porosity can be prevented by a rapid removal of the air or gas from a mold and by improving the casting system to obtain better efficiency.

Chromium Alloys↗
PubMed1995

Resin dental casts as an aid in bite mark identification.

Two techniques are presented for the fabrication of resin dental casts to aid in bite mark analysis. The first technique produces visible light cured dental casts of the suspected biter's dentition. These casts can be compared to the victim's bite marks or photographs of the bite marks. The technique is rapid and casts of the suspected biter's dentition can be made in less than thirty minutes, which is advantageous when the elimination of possible suspects must be accomplished in a timely fashion. The second technique involves the fabrication of crystal clear epoxy resin dental casts of the suspected biter's dentition. The dental casts are translucent and permit visualization through the teeth when comparisons are made to the bite marks or to tracings or photographs of the bite marks. The casts can also serve as an educational tool for a jury or juries in trials involving bite mark evidence. The resin dental casts are less brittle than dental stone casts permitting storage without concern for breakage for periods of years.

Bites, Human↗
PubMed1993

Evaluation of master cast techniques for multiple abutment implant prostheses.

This study compared the accuracy of three techniques used to fabricate master casts for implant prostheses. A metal model with six implants and standard abutments and a matching template were fabricated. Impressions of the model were made in Impregum and cast in Die Keen. The casts were divided into three groups of 15 casts: group A--solid casts; group B--Pindex; and group C--Zeiser system. Each cast was visually evaluated for fit of the template. Positional accuracy of the abutments was numerically assessed using an optical comparator. Visual analysis showed that only casts sectioned with the Zeiser system allowed a passive fit of the template. Statistical analysis of numerical findings indicated that casts made with the Zeiser system were significantly more accurate than solid casts, which in turn were more accurate than those made with the Pindex system.

Dental Abutments↗
PubMed1996

Pressure generation beneath a new thermoplastic cast.

A new cast immobilizer that is heat-shrunk to conform to an injured extremity was examined. The purpose of these studies was to compare pressures beneath the thermoplastic cast with those beneath fiberglass casts on a laboratory model and on the forearms of human volunteers. Pressures measured beneath fiberglass casts on metal cylinders averaged 36 mm Hg. Thermoplastic casts on the smaller cylinder that allowed 42% shrinkage produced a mean pressure of 25 mm Hg; those placed on the larger cylinder that allowed 17% shrinkage produced a mean pressure of 39 mm Hg. Pressures measured on the forearms of healthy volunteers averaged 22 mm Hg beneath fiberglass casts and 31 mm Hg beneath the thermoplastic casts. These pressures were considerably less than pressures that have been shown to occlude the microcirculation of the skin. Acute compartment syndromes result from swelling within a limited space and remain a serious concern clinically when swelling is anticipated under any type of constraining cast. The results of these studies indicate that the new cast should not produce a greater risk of circulatory compromise to the limb than previously used fiberglass materials.

Analysis of Variance↗
PubMed1998

Effect of different full-limb casts on in vitro bone strain in the distal portion of the equine forelimb.

OBJECTIVE: To determine the ability of a full-limb transfixation pin cast to protect the distal portion of the equine forelimb from weight-bearing forces by measuring bone strain in vitro on cadaver limbs loaded in a mechanical testing machine. SAMPLE POPULATION: 6 forelimbs from 6 horses. PROCEDURE: Each limb was instrumented with 3 unidirectional metal foil electrical resistant strain gauges. Gauges were placed on the dorsal aspect of the distal portion of the radius and the mid-dorsal portion of the cortex of the third metacarpal bone and the first phalanx. Each limb was tested 3 times, once supported with a transfixation pin cast, once supported by a standard full-limb cast, and finally, uncast. The limbs were tested in a mechanical testing machine under axial loads ranging from 100 to 1,000 lb, and bone strains were recorded at each load. RESULTS: Compared with values for the uncast limb, the transfixation pin cast and the standard full-limb cast significantly (P < 0.001) reduced bone strain on the distal portion of the radius, third metacarpal bone, and first phalanx. Compared with the standard full-limb cast, the transfixation pin cast significantly (P < 0.001) reduced bone strain on the first phalanx. CONCLUSION AND CLINICAL RELEVANCE: Compared with the standard full limb cast, the full-limb transfixation pin cast is more protective of the first phalanx.

Animals↗
PubMed2002

Effect of wax melting range and investment liquid concentration on the accuracy of a three-quarter crown casting.

STATEMENT OF PROBLEM: Dental casting accuracy is influenced by the setting expansion of investment materials. Although setting expansion can help compensate for casting shrinkage, it cannot be fully realized under a confined wax pattern. Exactly how soft a wax pattern should be to ensure optimum setting expansion has not been determined. PURPOSE: In this study, the relationship between wax characteristics and the casting accuracy of a three-quarter crown was investigated. MATERIAL AND METHODS: Four different wax materials were used: paraffin 135 with a softening temperature of 37.5 degrees C (P38), paraffin 1080 with a softening temperature of 63.5 degrees C, Shofu Red with a softening temperature of 41.5 degrees C, and Shofu Hard with a softening temperature of 51 degrees C. Two mixtures of phosphate-bonded investment were prepared: one with 100% special liquid and another with 75% special liquid plus 25% distilled water. For both, the liquid/powder ratio was 16:100. A type IV gold alloy was cast into a three-quarter crown mold. The discrepancy at 6 locations (1 lingual, 1 mesial, 1 distal, and 3 facial) was measured with a traveling microscope. Five readings were collected. Means and standard deviations were calculated for all data. A 2-way analysis of variance followed by the Student-Newman-Keuls test for multiple comparisons was used to identify significant differences between groups at the 95% confidence level. RESULTS: For the gingival measurement sites (lingual, mesial, and distal), there was no significant difference in cast adaptation when Shofu Hard and paraffin 1080 waxes were used. However, the results with these 2 waxes were different than with Shofu Red and P38. For the 3 facial measurement sites, significantly different measurements were found for each wax; P38 demonstrated the best results. Casting shrinkage was smaller with the use of 100% special liquid. CONCLUSION: Within the limitations of this study, casting shrinkage was affected by the type of wax used and was sensitive to the site at which dimensional measurements were performed. The higher the softening temperature, the larger the casting shrinkage.

Analysis of Variance↗
PubMed1995

Dopaminergic parameters in the striatum and substantia nigra of seven strains of mice: higher density in striatum of CAST compared to BALB mice.

Tyrosine hydroxylase activity was assayed in microdissected substantia nigra and striata from seven strains of mice (BALB, CBA, YBR, WB, IS, MOLG, and CAST). In the substantia nigra where tyrosine hydroxylase activity is thought to be proportional to dopaminergic neuron number, only CBA had a different (lower) enzyme activity compared with BALB. However in the striatum, tyrosine hydroxylase activity was larger for IS, MOLG and CAST compared with BALB. Further investigation of the CAST striatum showed that dopamine content and dopamine uptake activity were also higher in comparison with BALB. All three dopaminergic parameters were larger because of lower protein levels in the CAST striatum. A lower absolute amount of glutamic acid decarboxylase activity in CAST versus BALB striatum was consistent with the possibility of a smaller CAST striatum. In contrast to dopamine, the serotonin content in CAST striatum was reduced in proportion to the decrease in protein content. We suggest that the CAST striatum is smaller than BALB striatum and is innervated by proportionally fewer serotoninergic terminals, but the amount of dopaminergic innervation of the CAST striatum is not altered by the size of the target.

Animals↗