Facebows … Optimizing the Data

It is nearly impossible to find a textbook related to prosthodontics or restorative dentistry that does not mention the facebow as a technique to orient the upper cast to the articulator of choice. The general inference is the more sophisticated and involved the treatment —the better the results (or the fewer adjustments required) when using a facebow.

What you need to know about facebows

Are you getting what you are looking for? Early published “research” on the use of a facebow can be found in Dental Cosmos from WGA Bonwill in 1878 basically pertaining to the construction of complete removable denture prostheses. The idea is to begin the process of establishing a point reference for setting teeth.

Why make a facebow record? The facebow is used to relate the maxillary cast to the condylar elements of your instrument or articulator of choice. The overall goal is to use this information to minimize the amount of adjustment at the time of delivery. One advantage of making a facebow record is the visible cue to the patient that there is something different going on in your office all part of the process of creating value for the treatment provided.

At what point do we need more accuracy? In general, an earbow oriented facebow is an estimated measurement of the hinge axis position provides enough information for the majority of restorative treatment, particularly if our goal is to provide a mutually protected occlusal scheme with anterior guidance and shallow cuspal inclines in the posterior segments. Certainly, if the restorative goal includes a group function occlusal scheme, then more information is required. The additional information related to the functional pathways of each temporomandibular joint complex is obtained with something like a pantographic tracing with a fully adjustable articulator that optimally has customizable condylar elements. Specifically, if our interocclusal record is made with a leaf gauge or Lucia Jig to record a repeatable hinge axis position, then it is safe to assume the bite registration is made at a vertical dimension of occlusion that is open from maximum intercuspation position (MIP). It is with this information whether as a close estimate (earbow) or more precise measurement (pantographic tracing) that we then feel comfortable altering the vertical dimension on the articulator by moving the pin up or down on the instrument.

Can we get by without a facebow? Challenge yourself with this point. Talk to your laboratory technician to gain some insight on what is done on a regular basis and how they manage without the information gained from a facebow record. The goal is to plan our restoration based on the facial features of our patient … the final result must fit the patient's face to be truly esthetic.

Think about what we do to coordinate the position of the anterior teeth: a stick bite, a digital facebow showing facial features, and more specifically — modifying the position of the facebow/earbow to fit the horizontal plane that we are looking for in order to position the maxillary cast in a way to communicate the occlusal plane. What if the ears are asymmetrical? What if we have to “tug” the earbow element up, down, forward or back on one ear in order to make the record parallel to the desired horizontal plane? Are the estimates of the facebow record in terms of hinge axis position accurate at this point? How does this affect or influence the impact of the condylar elements on the articulator? Think about this a little more.

A Randomized Controlled Trial (RCT) published in the Journal of Prosthetic Dentistry (Hickey, et. al.) compared two methods of denture construction: One with hinge axis location and facebow transfer to an “advanced” articulator, and the other with arbitrary mounting to a simple articulator. The results after 20 year follow up (Ellinger et. al.) stated that were no significant difference between patient groups. Is that for real?

One technique that is used to teach laboratory technicians how to make dentures without the information gained by a facebow involves the use of a set up template. The idea is to make use of average value articulator settings using shallow denture teeth. The critical factor here is that the most important piece of information is an interocclusal record must be made at the anticipated vertical dimension of occlusion. This little detail minimizes the error attributed to the articulator. The set up template is used to serve as a reference point based on the information provided by a properly contoured maxillary wax rim. The idea is that the clinician is able to see the wax rim clinically and is able to modify it to fit the esthetic landmarks of the patients face. The midline and the arch width are recorded so that if changes in tooth position are required, then it becomes a much more precise endeavor. A huge benefit when thinking about how wax alters tooth position three-dimensionally based on temperature changes.

The clinical photos (Figs. 1, 2, 3, 4) included show a denture tooth set up at the wax evaluation appointment. The desired changes include a slight modification of the midline position at the incisal as well as modification of the occlusal plane – bring the right side down and the left side up. How would you communicate this to the lab? How would you check the modifications that were made after the case is returned?

Does this apply to natural dentition?

Dr. Kinzer demonstrates a technique in the Worn Dentition Workshop where we can get the best of both – a facebow record to mount the maxillary cast and a custom made plane of reference … a set up template. The technique provides the opportunity to facilitate communication, and, more importantly, track changes that are made while working with the dental laboratory. This type of information is useful during a diagnostic wax up based on the mounted study models. How do you use the facebow record?

Douglas G. Benting, DDS, MS, FACP, Spear Visiting Faculty and Contributing Author.

References

1. Bonwill, WGA. The science of articulation of artificial dentures. Dental Cosmos 1878;20:321.
2. Hickey, JC, et. al. Patient response to variations in denture technique. I. Design of a study. Journal of Prosthetic Dentistry 1969;22:158-170.
3. Ellinger CW, et. al. Patient response to variations in denture technique. Part VII: twenty-year patient status. Journal of Prosthetic Dentistry 1989;62:45-48.