![]() It becomes even worse when it is not broken into small pieces, as there are no guidelines or policies for disposing of such materials in the country. However, the positive cast does not dissolve easily and therefore pollutes the environment. Upon completion of the moulding process, the POP positive cast is often thrown out. At the same time, gypsum contributes to the emission of sulphur dioxide in the environment (Szpadt & Augustyn 1991). The environmental burdens are in the form of limited landfill disposal facilities, and regulated permissions. In many situations, such casts become waste, thus necessitating the repeated preparation of POP powder.įurthermore, huge quantities of plaster have to be used for plastering, and after the bone is set and rejuvenated, this hardened plaster has to be thrown away, thus adding further to waste with consequent burdens on the disposal of such POP plaster casts. Owing to its rapid setting properties, gypsum plaster casts may not be usable if the fractured bone is not properly positioned prior to application of plaster. ![]() Spinal Orthosis molded on a plaster of Paris (POP) positive cast. This transfer of measurement and shape facilitates an optimum alignment of anatomical structure of the teeth and its configurations (Lokuliyana, Petera & Gunawardane 1988). In dentistry, POP is used for mounting casts or models of oral tissues ( Figure 2). However, this is slowly being replaced by fibre glass. When such a cast is applied to support and maintain the corrected position of a fractured segment of a bone, it is referred to as an orthopaedic cast. In medicine, it has been used widely as a support for fractures, that is, broken bones ( Figure 1). It is an excellent source of calcium and sulphur for crop nourishment, especially in crops such as alfalfa, wheat, peanuts and cotton. Owing to its affinity to water, as a soil additive, gypsum improves soil physics and chemistry. One of the advantages of gypsum is that it is not hazardous to humans and plants. Wastes are in the form of improper/untimely setting of gypsum polymer and also from the gypsum polymer removed, for example after the repair of broken bone.Ībundant natural availability of gypsum and its easy response to water, heating and rehydration make it a popular choice in the construction industry. However, there is no information regarding the recycling qualities of calcium sulphate used in waste generated from its use in prosthetics, orthotics, orthopaedics or dentistry. ![]() Gypsum strength evolves during setting because of rapid formation of interlocked matrix of β-dehydrate needles (crystals), followed by internal stress relief and removal of excessive water (Yu & Brouwers 2010). Mechanically, the natural hardened gypsum has a high void level, consequently it is not a very compact solid. Fine dehydrate is usually used to accelerate hydration to the desired setting time by changing the nucleation rates of generated dehydrate. The mechanisms of setting and hardening of gypsum plaster have been explained by the crystalline theory. Yu and Brouwers ( 2010, 2012) reported that the amount of water needed for the hemihydrate is critical in the hydration reaction.
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