Facebows: The Facebow Recording
Subir Banerji and Shamir B. Mehta
This chapter focuses on the facebow, a rigid but adjustable device that relates the maxillary occlusal surface to an anatomical reference point. The facebow recording is often the first procedure undertaken when mounting study casts on a dental semi-adjustable articulator. Its primary purpose is to permit mounting of the maxillary cast on the articulator. In addition, the facebow also provides a guide to the width between the condyles, referred to as the intercondylar width, which has further practical significance, as discussed in Chapter 3.4. Facebows are also referred to as hingebows in the literature; the indications for the use of a facebow therefore indirectly relate to the need to use a dental articulator and are discussed in Chapter 3.4.
Typically, two reference points are chosen when attaining a facebow record: a posterior one, typically the terminal hinge axis, an imaginary line that runs between the heads of the mandibular condyles (which relates to the condylar elements of the articulator). A second, more anterior reference point is also usually selected, which may vary between different articulators. Both anterior and posterior reference points should be replicable during further subsequent appointments. Typical anterior reference points include the nasion or the inner canthus of the eye.
Facebows generally fall into the category of being either arbitrary or kinematic. Arbitrary facebows, as the name perhaps suggests, are less accurate in the manner in which they relate to the terminal hinge axis. However, they are suitable (and have been proven to be so) for most routine restorative dental procedures. They effectively approximate the position of the terminal hinge axis, typically to the position external to the auditory meatus (which is erroneous by definition). Facebows that utilise the external auditory meatus as the reference point are commonly referred to as earbows.
In contrast, the use of a kinematic facebow requires the terminal hinge axis to be more accurately determined, which may be more relevant where there is a need to copy the precise opening and closing movements of the mandible on the dental articulator, such as in a complex restorative reconstruction involving an alteration of the existing vertical and horizontal occlusal relations.
The facebow fork or bite fork is an item of equipment that is used to record the maxillary occlusal surfaces using a variety of different media. These materials should offer dimensional stability, a suitable working time and ease of use. Typically applied recording materials include impression compound, greenstick, polyvinyl siloxane (PVS) bite-registration materials (such as Stonebite, Dreve Dentamid GmbH, Unna, Germany) or extra-hard wax, such as Moyco beauty wax (Integra Miltex, Rietheim-Weiltheim, Germany). The record attained using the bite fork is then inserted into the facebow, permitting attainment of the registration required.