Molding significantly affects the mechanical properties of Plaster of Paris in orthopaedic use

Background: The use of Plaster of Paris as a means for immobilizing an injured limb has been well accepted for centuries. Although new casting materials are used ever more frequently, Plaster of Paris remains the mainstay of fracture care. Our study is aimed at assessing the effects of water temperature and plastering technique on the mechanical properties of Plaster of Paris casts. Methods: One hundred and twenty preformed casts divided into four equal groups of 30 were evaluated. The first group of casts was applied with use of ice-cold water (cold group). The second was applied with water heated to a temperature as hot as could be tolerated(hot group). The third group of casts was applied with no active molding (no molding group). In the fourth group molding was done (molding group). The no-molding and molding groups of casts were applied using room temperature water. Results: A statistically significant (P<0.05) difference in the mechanical parameters assessed (modulus of elasticity and maximal stress) by the Instron device was found when comparing the molding group with that of all other groups (no-molding, hot, and cold). The molding group out performed the other groups by at least 31% in each of the assessed parameters. No significant difference was found between the other groups. Conclusions: Our findings emphasize that proper molding technique with evenly applied pressure along the sheets of gauze is the makers of a good cast with superior mechanical properties.