Which is an improper procedure to disinfect impression materials before sending them to a laboratory?

Immersing impression materials in disinfecting agents for an excessive duration, such as one hour, can be considered an improper procedure. This is primarily due to the potential alteration or degradation of the impression material. Many impression materials are designed to be chemically sensitive, and prolonged exposure to disinfectants can lead to changes in their physical and dimensional stability. This could compromise the quality and accuracy of the impressions, impacting the final restorations or prosthetics produced by the laboratory.

In contrast, rinsing off blood and saliva, using an EPA-registered disinfectant for the recommended contact time, and employing a soft brush to remove debris are all appropriate and effective practices to ensure that impressions are disinfected without damaging the material. These procedures help maintain the integrity of the impression while ensuring it is safe to transport to the laboratory.