Modular apparatus for installation of multiple dental prostheses formed of a plurality of implants inserted in the patient's maxillary or mandibular bone and of a corresponding number of cylindrical stumps associated with the implants in order to protrude from the bone, the apparatus is composed of two main elements, which are regularly alternated between the various stumps to be connected, the first element consists in a substantially cylindrical extensible rod being provided with a ball (30, 30') at each end, said extensible rod being formed of some cooperating elements (2, 2', 4, 30, 30') that, being mutually connected by means of helical coupling, provide the entire rod with a variable length that can be selectively chosen according to the specific user needs, the second element consists in a joint, the joint consists in a ring adapted to be exactly inserted into a stump, as well as externally provided with a radial fork having a basically semi-circular profile, adapted to exactly receive one of the balls (30, 30') mounted at the ends of the rod, allowing for free rotation and providing an articulated "spherical joint" coupling, wherein said cooperating elements consist in - at least a first specimen of a short tube with circular section that is internally provided, at approximately half of its length, with a vertical partition that separates two identical cylindrical ducts (20b, 20c), provided with internal threaded walls, - at least a second specimen of a short tube with circular section that is provided, at one of its ends and for approximately half of its length, with a cylindrical duct with threaded walls and, at the other end, with a threaded stem adapted to be helically coupled with a threaded cylindrical duct (20b, 32), - at least two specimens of a threaded stem ending with the ball at one side, the diameter of each threaded stem corresponds to the section of the ducts (20b, 20c) of the short tube (2, 2'), - at least two specimens of the ball provided with nozzle internally provided with the cylindrical duct that is adapted to be helically coupled with the threaded stem, - at least one specimen of a pin formed of a central cylindrical body with substantially the same diameter as the short tube and provided at each end with a threaded axial pin having the same diameter as the threaded stem; wherein each of said threaded pins is adapted to be helically coupled with the cylindrical ducts (20b, 20c, 20b') of two specimens of said short tube (2, 2') between which the pin is disposed. - at least a first specimen of a short tube with circular section that is internally provided, at approximately half of its length, with a vertical partition that separates two identical cylindrical ducts (20b, 20c), provided with internal threaded walls, - at least a second specimen of a short tube with circular section that is provided, at one of its ends and for approximately half of its length, with a cylindrical duct with threaded walls and, at the other end, with a threaded stem adapted to be helically coupled with a threaded cylindrical duct (20b, 32), - at least two specimens of a threaded stem ending with the ball at one side, the diameter of each threaded stem corresponds to the section of the ducts (20b, 20c) of the short tube (2, 2'), - at least two specimens of the ball provided with nozzle internally provided with the cylindrical duct that is adapted to be helically coupled with the threaded stem, - at least one specimen of a pin formed of a central cylindrical body with substantially the same diameter as the short tube and provided at each end with a threaded axial pin having the same diameter as the threaded stem; wherein each of said threaded pins is adapted to be helically coupled with the cylindrical ducts (20b, 20c, 20b') of two specimens of said short tube (2, 2') between which the pin is disposed.