A dental impression tray assembly comprising: an upper tray adapted to be inserted into a patient's mouth to obtain an impression of the upper gum; and a lower tray operable with the upper tray, wherein the lower tray comprises, in turn, a center piece and a pair of second pieces: the center piece having end portions and being configured to be inserted in the patient's mouth independently of the pair of second pieces to measure jaw relations of a patient's mouth and to obtain bite registration; the center piece being sized to allow obtaining a first impression of approximately two-thirds of a patient's lower gum including a lower anterior gum, the pair of second pieces being detachably connectable to the center piece, each of the second pieces being respectively attachable to each end portion of the center piece, the second pieces being sized to allow obtaining a second impression including the rest of the lower gum when connected to the center piece, thus the lower tray allowing to obtain the first final gum impression including the first impression and the second impression; wherein the assembly is configured to allow a first final gum impression of the patient's lower gum to be obtained after the center piece is connected to the pair of second pieces, characterized in that the dental impression tray assembly further comprises an intra-oral tracer and a cover, the intra-oral tracer being insertable into an upper surface of the center piece and comprising a screw, the cover being placeable on a lower surface of the upper tray; wherein the intraoral tracer and the cover are configured to allow, after taking impressions of the upper and lower gums, measurement of jaw relations by lowering or raising the screw in the mouth to contact the cover. an upper tray adapted to be inserted into a patient's mouth to obtain an impression of the upper gum; and a lower tray operable with the upper tray, wherein the lower tray comprises, in turn, a center piece and a pair of second pieces: the center piece having end portions and being configured to be inserted in the patient's mouth independently of the pair of second pieces to measure jaw relations of a patient's mouth and to obtain bite registration; the center piece being sized to allow obtaining a first impression of approximately two-thirds of a patient's lower gum including a lower anterior gum, the pair of second pieces being detachably connectable to the center piece, each of the second pieces being respectively attachable to each end portion of the center piece, the second pieces being sized to allow obtaining a second impression including the rest of the lower gum when connected to the center piece, thus the lower tray allowing to obtain the first final gum impression including the first impression and the second impression; wherein the assembly is configured to allow a first final gum impression of the patient's lower gum to be obtained after the center piece is connected to the pair of second pieces, characterized in that the dental impression tray assembly further comprises an intra-oral tracer and a cover, the intra-oral tracer being insertable into an upper surface of the center piece and comprising a screw, the cover being placeable on a lower surface of the upper tray; wherein the intraoral tracer and the cover are configured to allow, after taking impressions of the upper and lower gums, measurement of jaw relations by lowering or raising the screw in the mouth to contact the cover. the center piece having end portions and being configured to be inserted in the patient's mouth independently of the pair of second pieces to measure jaw relations of a patient's mouth and to obtain bite registration; the center piece being sized to allow obtaining a first impression of approximately two-thirds of a patient's lower gum including a lower anterior gum, the pair of second pieces being detachably connectable to the center piece, each of the second pieces being respectively attachable to each end portion of the center piece, the second pieces being sized to allow obtaining a second impression including the rest of the lower gum when connected to the center piece, thus the lower tray allowing to obtain the first final gum impression including the first impression and the second impression; wherein the assembly is configured to allow a first final gum impression of the patient's lower gum to be obtained after the center piece is connected to the pair of second pieces, characterized in that the dental impression tray assembly further comprises an intra-oral tracer and a cover, the intra-oral tracer being insertable into an upper surface of the center piece and comprising a screw, the cover being placeable on a lower surface of the upper tray; wherein the intraoral tracer and the cover are configured to allow, after taking impressions of the upper and lower gums, measurement of jaw relations by lowering or raising the screw in the mouth to contact the cover.