RDA Practice Exam – California RDA Test Prep & Free Practice Test (2026)

In this context, viscosity refers to the thickness or flow of the impression material. Light body material has the lowest viscosity, which allows it to flow easily and record fine details of the teeth. Medium body material has a slightly higher viscosity, making it useful for filling in larger areas and providing support for the light body material. Heavy body material has the highest viscosity and is used to create a rigid tray for the other materials to sit in. Putty is a very thick material and is typically used for preliminary impressions. Therefore, light body is the first viscosity applied to the teeth, followed by medium body and then heavy body.