Facebow

A facebow (synonyms: transfer bow, transfer arch) is a transfer device used in the fabrication of crowns, bridges or dentures, among other things. The facebow is used to determine the positional relationship of the upper jaw to the temporomandibular joints and to the base of the skull and to transfer this information to the articulator (device for imitating the position of the jaw and the movements of the temporomandibular joints) in which the denture is fabricated. While the plaster models of the jaws must be mounted according to average values without the application of a facebow, the use of the articulator aims to produce the planned dental work on the basis of the most individual values possible according to the anatomical conditions of the patient. The design of articulators is based, among other things, on the mean value of the Bonwill triangle. This is formed by the contact point of the lower central incisors and the center of the condyles (mandibular joint heads of the lower jaw). In relation to the masticatory plane, this triangle forms an angle – the Balkwill angle – which is on average between 20 ° and 25 °. With the help of the facebow, it is possible to individualize this angle and the Bonwill triangle. The plaster model of the upper jaw can thus be mounted in the articulator without any damage. Depending on the articulator system used, the facebow is positioned on the patient at one of two possible planes defined on the skull:

  • Frankfurt horizontal (synonyms: German horizontal, Frankfurt horizontal plane) – running through the lower edge of the orbit (eye socket) and the upper edge of the porus acusticus externus (the external bony auditory canal, the external ear opening) on both sides.
  • Camper’s plane – passing through the spina nasalis anterior (spine at the bottom of the anterior bony nasal opening) and the upper edge of the porus acusticus externus on both sides

The individualization should have a beneficial effect on the static occlusion (final bite), resulting in fewer subsequent occlusal corrections (corrections of the masticatory relief) by grinding in. This, in turn, results in time savings in dental treatment and, consequently, in patient stress. It should be mentioned here that the facebow transfer alone is not sufficient to create occlusal relationships that are as free of errors as possible; rather, the use of the facebow complements a careful jaw relation determination, with which the mandibular model is brought into the correct positional relationship with the maxillary model in the articulator. If the vertical jaw relation (distance between the jaw bases) has to be changed therapeutically, the facebow transfer has a clinically relevant error-reducing effect on the static occlusion (final bite). For the individualization of dynamic occlusion (chewing movements), on the other hand, quite a few other parameters must be recorded.

Indications (areas of application)

  • To reduce errors in static occlusion (final bite), especially when there is a change in vertical jaw relation (distance between the bases of the upper and lower jaws).
  • Better simulation of individual occlusion contacts (tooth contacts in the final bite).
  • To reduce occlusal corrections to new dentures (corrections to the final bite by grinding in).
  • To reduce the adaptation time of prosthetic work (acclimatization period).
  • Time saving of occlusal adjustment (adjustment of the final bite) in the context of splint therapy, especially in the case of major changes in the vertical jaw relation.
  • et al.

Contraindications

There are no contraindications for this procedure.

The procedure

  • Fitting the bite fork of the facial arch to the teeth of the upper jaw – Heated wax or silicone is applied to the metal fork that follows the course of the dental arch, passively positioned (by the practitioner) on the occlusal surfaces (chewing surfaces) of the patient during the plastic phase and fixed until the material hardens.
  • Insertion of the ear olives of the arch on both sides into the external auditory canal – this is located immediately behind the temporomandibular joints, allowing arbitrary (approximate) determination of the hinge axis (connecting line between the temporomandibular joints).
  • Alignment of the facial arch plane to the Frankfurt horizontal or Camper’s plane.
  • Applying the nose support of the face bow at the root of the nose – the weight of the face bow is thus passively borne by the patient.
  • Attaching the bite fork and fixing its position on the facebow via a joint to be locked in place
  • Loosening of the ear olives and removal of the bow – the determined parameters are not changed in this process

After the procedure

In the dental laboratory, the bite fork is placed on a special base. The maxillary model, made from plaster on the basis of a jaw impression, is mounted on the bite fork – according to the impressions (impressions in wax or silicone) – and connected to the articulator by plaster on its base (side facing away from the teeth, towards the skull or upper part of the articulator). In this way, the position of the maxillary model in the articulator largely corresponds to the individual position of the patient’s jaw in the facial skull.

Possible complications

Inaccuracies in facebow placement may result in the occlusal error of the prosthetic work to be fabricated not being reduced to the desired degree.