Results. Mean values 6 SD for Lucitone 550 (16.52 6 0.94 VHN) and QC-20 (9.61 6 0.62 VHN) demonstrated a significant (P,.05) decrease in hardness after disinfection, regardless of material and disinfectant solutions used (Lucitone 550: 15.25 6 0.74; QC-20: 8.09 6 0.39). However, this effect was reversed after 15 days of storage in water. Both materials exhibited a continuous increase (P,.05) in hardness values for up to 60 days of water storage, after which no significant change was observed.