Evaluation of the effects of initial water temperature and curing time on fiberglass cast strength

Objective: To determine the effects of water temperature and cure time on cast strength. Study design: Prospective randomized experimental study. Methods: Two water temperatures were tested, 23°C (cold) and 42°C (warm). Cast constructs were made of 4-inch fiberglass casting material over a rubber mandrel. Each construct was divided into 3 segments and tested in 4-point bending at 0.5, 1, and 24 hours. Stiffness and bending moment, cumulative energy, and angular deformation at yield and failure were recorded and analyzed by using repeated measures ANOVA. Results: Mean time ± SD to complete the construct was 2.2 ± 0.8 and 2.3 ± 0.6 minutes for warm and cold water, respectively. Warm water and longer cure times produced constructs with greater stiffness (23.05 vs 20.88 newton-meter degrees [Nm°] at 0.5 hours), bending moment (121.75 vs 107.31 Nm° at 0.5 hours), and cumulative energy (557.33 vs 428.89 Nm° at 1 hour) at yield and failure. Longer cure time significantly increased angular deformation of rods at failure; however, water temperature did not. In general, the strongest casts were produced with warm water and after curing for 24 hours. Conclusion: Fiberglass casts continued to gain strength for at least 24 hours. Use of warm water increased the rate of curing, resulting in stronger constructs at earlier time points. Clinical significance: Use of warm water is recommended to initiate fiberglass cast curing, especially if the casted limb will be loaded soon after cast application.