Use of Facebow Device in Prosthodontics

      Define face-bow. Classify face-bows. Mention the parts of the facia type of face-bow. Discuss the use of face-bow.
Answer:

Face – Bow Definition

Face-bow is a caliper-like device that is used to record the relationship of the jaws to the temporomandibular joints or the opening axis of the jaws and to orient the casts in this same relationship to the opening axis of the articulator.

Types Of Face-Bow

1. Arbitrary: Has two types: Earpiece face-bow and Facia type face-bow
2. Kinematic or hinge-bow.

Read And Learn More: Complete Dentures Question and Answers

1. Arbitrary

1. The arbitrary face-bow is placed on the face with the condyle rods located approximately over the condyles.
2. Used in complete denture patients.
3. The condyle rods are positioned on a line extending from the outer canthus to the tip of the tragus and 13 mm in front of the external auditory meatus locating the rods within 5 mm of the                                                                                                                                                           e true center of the opening axis of the jaws. (Facia type) Hanau Model
   • Without clamping the condyle rods, the dentist center the device so equal readings are obtained on both sides and the wing nut of the clamp is tightened to hold the face bow in place on the occlusal fork.
4. The rods of another are designed to fit into the external auditory meatuses (Earpiece type)WhipMix.
   • The fork of the arbitrary face-bow is attached to the maxillary occlusion rim. The transverse axis of the articulator is 5/8 inch (15 mm anterior to the position of the ends of the face-bow).
   • This distance compensates for the distance between the external auditory meatus and the condyle.

Facebow Transfer

2. Kinematic Face-bow

• The kinematic face-bow is so designed that the opening axis of the mandible can be located more accurately.
• The fork of kinematic face-bows is attached to the mandibular occlusion rim.
• As the patient protrudes the mandible and opens and closes the jaws, the movement of the points of the condyle rods is observed.
• As the condyle rods of kinematic face-bows have sharp points, their motion can be observed more accurately.
• When the points rotate only and do not translate, they are on the opening axis of the jaw.
• At this position, the mandible is in centric relation to the occlusal vertical dimension that has been established. After the hinge axis center is located it is marked on the face with an indelible pencil.
  • The face bow is now used in a regular manner by being fastened into place over the previously determined rotational points.
  • This type of transfer will be exact in the positional relation of the cast and will permit a recording medium (such as wax, zinc oxide-eugenol, or plaster) for interocclusal records without usual inaccuracy being produced. This is important when the interarch distance is to be increased or decreased.
• Kinematic face-bow can aid in recording centric relations.
  • The difficulty of attaching the lower occlusion rim to an edentulous mandible and movement of the recording base on the jaw makes determining the exact center of the opening axis difficult hence, preventing its use for edentulous patients.
• Aids in finding the appropriate vertical dimension clinically and does not change in the articulator.

Facebow Transfer

Uses Of Face-Bow

1. It supports the casts while they are attached to the articulator.
2. When cusp form teeth are used.
3. When balanced occlusion in the eccentric positions is desired.
4. When a definite cusp fossa or cusp tip-to-cusp incline relation is needed.
5. Interocclusal check records after face-bow transfer aid in verifying of jaw positions.
6. If the occlusal vertical dimension is changed and the alterations of tooth occlusal surfaces are necessary to accommodate the change.

Parts Of Face-Bow

• It consists of a U-shaped frame or assembly that is large enough to extend from the region of the TMJs to a position of 2 to 3 inches (5 to 7. 5 cm) in front of the face and wide enough to avoid contact with the sides of the face.
• The parts that contact the skin over the TMJs are the condyle rods. The part that attaches to the occlusion rims is the fork.
• The fork attaches to the face-bow by means of a locking device, which serves also to support the face-bow, the occlusion rims, and the casts while the casts are being attached to the articulator.

• For the success of the complete denture, factors such as the evaluation of occlusion, denture stability, retention, and conditions of denture-bearing tissues, together with patient satisfaction and adaptation, apart from an accurate Face-Bow transfer are important.