A dental impression tray assembly includes an upper tray and a lower tray operable with the upper tray, and the lower tray includes a first piece configured to measure jaw relations of a patient's mouth and a pair of second pieces detachably attachable to the first piece. The first piece of the lower tray is inserted into the patient's mouth independently of the pair of second pieces of the lower tray to measure the jaw relations and to obtain a bite registration. After the first piece is connected to the pair of second pieces, the assembly allows a final gum impression of the patient's lower gum to be obtained.