Fundamentals of Fixed Prosthodontics. James C. Kessler

Fundamentals of Fixed Prosthodontics - James C. Kessler


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      Facebow armamentarium

       Spring-Bow (with bite fork assembly and mounting guide)

       Hanau Wide-Vue articulator

       Plaster bowl

       Spatula

       Laboratory knife with no. 25 blade

       Trimmed maxillary cast

       Pink baseplate wax

       Mounting stone

      Facebow record technique

      A sheet of baseplate wax is softened in hot water, and the bite fork is completely covered with it. The wax-covered bite fork is positioned against the maxillary teeth, and the patient is instructed to close until the mandibular teeth contact the wax on the underside of the fork. The shaft of the bite fork will be to the left of the patient’s midline.

      The wax is cooled in the mouth with an air syringe. The fork is removed from the mouth and placed in a bowl of cold tap water to finish cooling. Excess wax and any areas imprinted by soft tissue are trimmed off. The maxillary cast is seated in the wax record to be sure that it is stable. If there is any rocking of the cast, the occlusal surfaces of the cast should be checked for nodules of stone. If there are none, either the cast or the record is distorted and must be remade.

      If the bite fork assembly is separate from the facebow, the transfer (vertical) rod of the assembly is inserted into the bow socket on the underside of the black centerpiece on the front of the facebow. The flat surface on the rod must be in front when it is placed in the socket. The assembly should be on the right, with the knobs facing the front (Fig 5-57). The thumbscrew is tightened on the front of the centerpiece.

      While the patient grips the bite fork between the maxillary and mandibular teeth, the loosened bite fork clamp is positioned 4 cm (1.5 inches) over the bite fork shaft. The facebow should be pointed upward during this action (Fig 5-58). The bow is opened by pulling outward on the arms and is swung down into position, with an earpiece placed gently into each external auditory meatus. The patient is instructed to adjust the earpieces to the most comfortable seated position (Fig 5-59).

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      The orbitale (infraorbital notch) is marked on the patient’s face with a felt-tip marker to provide an anterior reference point (Fig 5-60). The thumbscrew that holds the orbital pointer is loosened and gently swung in toward the reference mark (Fig 5-61). The front of the facebow is elevated along the transfer (vertical) rod of the bite fork assembly until the pointer is at the plane of the anterior reference point. The bow is grasped to resist torquing (Fig 5-62), and the three thumbscrews are tightened in order from left to right (Fig 5-63):

      1 Transfer (vertical) rod/transverse (horizontal) rod

      2 Transverse rod clamp (upper)

      3 Bite fork clamp (lower)

      They must be tight; an Allen wrench can be used to tighten them if necessary.

      The reference pointer is rotated back over the right temple of the bow, and the thumbscrew is tightened enough to hold it there. While the patient opens, the ends of the bow are grasped, and the earpieces are removed from the auditory meati. It should be held firmly because the bow is made of spring steel and could snap back. The bow is slid away from the patient. The facebow, earpieces, and bite fork are disinfected with a hospital-grade disinfectant before continuing.

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      The reference pointer is rotated back over the right temple of the bow, and the thumbscrew is tightened enough to hold it there. While the patient opens, the ends of the bow are grasped, and the earpieces are removed from the auditory meati. It should be held firmly because the bow is made of spring steel and could snap back. The bow is slid away from the patient. The facebow, earpieces, and bite fork are disinfected with a hospital-grade disinfectant before continuing.

      Mounting the maxillary cast

      The articulator is prepared to accept the casts by setting the inclination of the enclosed condylar track mechanisms at 30 degrees on each side (Fig 5-64). The Bennett angle ring for the progressive mandibular lateral translation should be set at 30 degrees (Fig 5-65).

      Petrolatum is used to lubricate the surfaces of the upper and lower members of the articulator around the threaded mounting studs. Then a clean mounting plate is firmly secured to the mounting stud on the upper member of the articulator. A mounting guide or platform is attached to the lower member of the articulator. The thumbscrew on the front of the facebow is loosened, and the bite fork assembly is removed. The vertical transfer rod of the assembly is placed into the hole at the front of the mounting guide and secured by tightening the screw. The cast support is adjusted to touch the underside of the wax on the bite fork (Fig 5-66).

      The maxillary cast is soaked in a plaster bowl, but the teeth should not be covered with water. The maxillary cast is carefully seated into the imprints in the baseplate wax on the bite fork. The upper member of the articulator is raised, and a golf ball–sized mound


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