Fiberglass is harder to apply, although the more recently introduced bias stretch material is an improvement. They are harder to contour than plaster of paris, and the polyurethane may irritate the skin. These materials are strong and lightweight, and resist breakdown in water they are also available in multiple colors and patterns.
WORKING WITH A PLASTER BANDAGE CAST MASK SKIN
Fiberglass casts provide lower skin pressure when compared with plaster casts when properly applied. 2, 5, 6 These materials are preferred for most orthopaedic applications except in acute fractures in which reduction maintenance is critical.
The exothermic reaction does not place the patient’s skin at risk for thermal injury. The prepolymer is methylene bisphenyl diisolynate, which is converted to a nontoxic polymeric urea substitute. Most of these are a fiberglass fabric impregnated with polyurethane resin.
Two decades ago, a number of companies developed materials to replace plaster of paris as a cast material. Additives are used to alter the setting time three variations are available: (1) Extra fast setting takes 2 to 4 minutes, (2) fast setting takes 5 to 6 minutes, and (3) slow setting takes 10 to 18 minutes.ī. Plaster is available as bandage rolls in widths of 8 in, 6 in, 3 in, and 2 in and splints in 5- × 45-in, 5- × 30-in, 4- × 15-in, and 3- × 15-in sizes.Thick casts take longer to dry than thin ones. The evaporation from the cast surface is influenced by air temperature, humidity, and circulation about the cast. Cast drying occurs by the evaporation of the water not required for crystallization. The interlocking of crystals (the critical setting period) begins, when the plaster reaches the thick creamy stage, becomes a little rubbery, and starts losing its wet, shiny appearance. Motion during the critical setting period interferes with this interlocking process and reduces the ultimate strength by as much as 77%. The interlocking of the crystals formed is essential to the strength and rigidity of the cast. 3, 4 The more plaster and the hotter the water, the more heat is generated. The amount of heat given off is determined by the amount of plaster applied and the temperature of the water.1, 2 When this material is dipped into water, the powdery plaster of paris is transformed into a solid crystalline form of gypsum, and heat is given off: Plaster bandages and splints are made by impregnating crinoline with plaster of paris.
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