What is facebow transfer and registration?

April 11, 2016

  

The facebow is a device used by prosthodontics to measure the relationship between the jaws and the temporomandibular joint with special emphasis on the axis of rotation. It is used to transfer this relationship accurately to the articulator thereby ensuring proper orientation of the casts. This ensures that the treatment is compatible with the individual patient’s anatomy and helps to achieve functional efficiency along with esthetic results.

Uses of face bow

The utility of the facebow lies in the fact that it mimics the position of the patient’s upper arch in relation to three different points of reference of the head. This three dimensional measurement, when transferred to the articulator replicates the jaw movement of the patient and authentic anatomic relationship exactly. It is therefore used along with an articulator for

1. Diagnosis of tooth contact that hinders smooth jaw movements (occlusal interference).
2. Treatment in accordance with the patient’s anatomy, therefore providing maximal functional performance and comfort.
3. Clear standardized communication of functional issues to laboratory.
4. Baseline records.

 What does it consist of?

1. U-shaped frame - main frame to which all other parts are attached
2. Condylar rods/ear pieces - purpose is to locate hinge axis
3. Bite fork - u-shaped plate which is placed inside the mouth
4. Locking device - fixes the bite fork to the main frame after measurements
5. Third reference point - a reference point on the face in line with condylar points

How do you put a facebow on a patient

Wax or the registration material for taking the impression is placed on the maxillary side of the bite-fork and softened in hot water. The bite-fork is then put in the patient’s mouth to obtain accurate impression of the upper teeth.  

The patient is asked to hold the arms of the cross bar and the ear pieces are inserted in the ears. Then the thumb screw is used to tighten and lock the width of the facebow. The front portion of the facebow is adjusted till the nasion relator touches the bridge of the nose and locked in place with the locking device. The double-toggle clamp is the placed on the stem of the bite fork and tightened to secure it in place. The single toggle clamp is then secured to the vertical attachment. The nasion relator and the thumb screw are loosened so that the patient can open his mouth. Having taken out the ear pieces, the facebow is removed from the face. After this the bite-fork is separated from the facebow frame and sent to the laboratory.

Which measurements in the facebow registration are important?

Measurements that are essential in a facebow registration are the reference points, intercondylar distance, terminal axis and the condylar path.

The three reference points consist of two points that are at the back of the upper jaw and one that is at the front of the upper jaw. The use of three points ensures accuracy so that the position of the upper jaw can easily be replicated. The terminal axis points on both sides of the face are taken as posterior points. Terminal axis is an imaginary line that is formed on opening of the mouth to the extent that it no longer remains a simple hinge movement. The front reference point is either the nasion or the orbitale.

Equally important is the measurement of the condylar path and the intercondylar distance. The condylar path is the arc of circle followed by the condyles during various lower jaw movements. It depends on the shape of the condylar head and the mandibulat fossa(glenoid fossa).The intercondylar distance is the distance between the two condyles at either side of the face and has an effect on the radius of movement as well as the arc formed by the cusps of the teeth during sideways movements of the lower jaw.

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