Face Bow PDF

By Dr/Mohammed A. El-Sawy BDS, MSc, PhD (Mansoura University) FACE BOW Lecturer of Prosthetic Dental Science Faculty of Dentistry Menoufia University  The terminal hinge axis (horizontal axis, transverse axis, inter-condylar axis) is an imag...

By Dr/Mohammed A. El-Sawy BDS, MSc, PhD (Mansoura University) FACE BOW Lecturer of Prosthetic Dental Science Faculty of Dentistry Menoufia University  The terminal hinge axis (horizontal axis, transverse axis, inter-condylar axis) is an imaginary line around which the mandible rotates. This rotation averages about 12° or ranges between 10-25mm of incisal opening and occurs in centric relation. It is assumed that the movement of the condyle during this early opening is pure rotation around this axis. Facebow The facebow is a caliper like device that is used to record the relationship of the jaws to the hing axis and to orient the casts in this same relationship to the hing axis of the - articulator. Zarb.Hobkirk.Eckert.Jacob.Prosthodontic treatment of edentulous patients.Edition 13 :196-97 3 Types of face bows: 1- Maxillary (arbitrary) face bow 2- Mandibular or kinematic face bow (Hinge axis face bow)  Maxillary (arbitrary) face bow (Fig. 5-9): It is a caliper like device consist of: It is a U-shaped bow. The following parts are connected to it: A bite fork which is attached to the bow by a universal joint and a clamp. Two posterior reference point indicators: At each end of the bow, there is a graduated condylar rod and a clamp. They are placed on the assumed condylar position An anterior reference point indicator. It relates the whole assembly to a fixed cranial reference point.  Types of maxillary facebow: Maxillary face bow is an instrument used to record the position of the maxillary arch relative to opening and closing axis (hinge axis) A. According to the posterior reference indicator: 1-Facia facebow: The posterior reference point indicators are placed on the patient's skin over the position of the hinge axis. The hinge axis can be either determined kinematically or arbitrary (11-13)mm anterior to the external auditory meatus. 2-Earpiece facebow: The posterior reference point indicators are inserted into the external auditory meatus. According to the anterior reference point: 1-Infra orbital pointer: The third point of reference is the lowest margin of the infra-orbital rim on one side. The articulator is designed with a curved infra- orbital pointer plane indicator that allows for proper vertical orientation of the facebow 2-Nasion pointer: The third point of reference is the nasion. According to mechanism of intercondylar distance equilibration: A certain mechanism should exist to guarantee that the maxilla is centralized mediolaterally within the bow: 1-Calibrated condylar rods: The condylar rods are graduated. They are adjusted bilaterally until equal reading are achieved on both sides 2- Spring facebow: made of spring steel and simply springs widening and narrowing of the bow till the two condylar rods contact the posterior reference point 3- Slidematic facebow: The anterior horizontal arm is composed of two sliding arms that allow for medio-lateral movements of the bow till the condylar rods contact their posterior reference points. 2- Mandibular or kinematic face bow (Hinge axis face bow). It consists of U-shaped bow. The bow is attached to the mandible by means of a clamp that fits under the chin and fixes the lower occlusion block in place. The clamp is attached to the bow by means of a universal joint. Two pointed condylar rods are attached to the bow (Fig. 4). Uses: 1. Locate the exact terminal hinge axis before using of Maxillary face bow. 2. Record the centric relation.  Determination of the exact terminal hinge axis: 1-Arbitrary: The terminal hinge axis is arbitrarily located by placing it 11 - 13 mm. anterior the tragus of the ear on a line extending from the outer canthus of the eye to the upper margin of the external auditory meatus (Fig.3). 2-Kinematically: 1. Arbitrarily determine the location of the hinge axis to place the rods. 1. The Kinematic face-bow is attached to the mandible 2. The patient is asked to open and close his mouth slightly while the mandible is in the most retruded position at the proper vertical dimension of occlusion. Each condylar rod will draw an arc on the paper attached to the skin. The position of the condylar rods is adjusted toward the center of these arcs. With further repetition of this procedure, the size of the arcs drawn by the condylar rods will be progressively decreased in size, until the rods rotate in a point. This point represents the terminal hinge axis of the condyles which is termed the "Still point".  Registration of a Maxillary Face Bow Record 1.The condylar axis is located accurately by the mandibular face bow or arbitrary by drawing a line on the patient's face on each side from the upper margin of the external auditory meatus to the outer canthus of the eye. On this line, a point is drawn 11-13 mm anterior to the meatus. 2.The bite fork is attached to the maxillary occlusion rim parallel to the occlusal plane while the central notch coincides with the central line of the wax rim. It is than inserted in the patient's mouth. The mandibular occlusion block is also inserted to support the maxillary block. 3.The stem of the bite fork is slipped in the universal joint and the clamp is left open. 4. The condylar rods are adjusted so that their ends lie on the points representing the condylar axis. Both condylar rods should show equal calibrations with slight tension. Then the clamps are tightened. 5.The clamp of the bit fork is tightened. 6. The 3rd reference point (infra-orbital notch or nasion) is placed. 6.The condylar rods are released, and the entire assembly is removed taking care that the fork is firmly clamped to the face bow.  Mounting the maxillary cast on the articulator using the maxillary face bow record The articulator and the face bow are placed on a flat surface, and the graduated condylar rods of the face bow are adjusted to show equal calibrations when fitted onto the extended condylar rods of the articulator. The anterior part of the bow is adjusted until the lower edge of the occlusion rim is in the level with a notch present on the incisal pin of the articulator. The maxillary occlusion block is supported with a device called cast support(Jig) to prevent sagging of the maxillary cast during its mounting. The top of the incisal pin should be in level with the surface of the upper member of the articulator.