The Use of a Face Bow for Function and Esthetics
Results include better efficiency, stability, and patient comfort
Most oral healthcare practitioners agree that interferences in the dentition are harmful and can create destructive occlusal forces, as well as lead to occlusal disease and many other problems.1,2 Every dentist checks the “bite” with marking ribbon and then adjusts the teeth for equal, simultaneous, and bilateral contacts. However, the evaluation of how the teeth fit and function in relation to how the temporomandibular joints fit and function is often overlooked. The use of a face bow and articulator to articulate dental casts is taught in every dental school in this country and has been available for more than 100 years.3 However, approximately 90% to 95% of all restorations and prostheses are fabricated and other dental procedures are performed using either no articulator or a disposable articulator without a face bow because of misunderstood concepts, complex instrumentation, and time-consuming procedures.
The purpose of a face bow is to register the relationship of the patient’s maxillary arch in three planes of space and transfer this information into an articulator that can be adjusted to simulate the patient’s jaw movements (Figure 1 and Figure 2).1,4-7 The relationship is two-fold: to establish the functional relationship of the maxillary arch to the axis of rotation for proper function (Figure 3) and to analyze the esthetic relationship of the maxillary arch to the patient’s face for optimal esthetics (Figure 4).
Functional and Esthetic Considerations
Currently, all ear-bow techniques transfer an arbitrary, or average, hinge axis location by referencing an approximation using the patient’s ears. Although somewhat imprecise mathematically, this approximation is within an acceptable range for dental articulation,4-6 particularly when minimum-to-moderate changes are necessary in the dentition. However, there are greater concerns when extensive changes are required in the dentition or when the occlusal vertical dimension needs to be altered. In addition, esthetic information may be transferred improperly using an ear bow. If the third point of reference is inappropriate, the maxillary arch will be slanted incorrectly front to back in the sagittal plane or profile view (Figure 5). If the patient’s ears are uneven upward or downward, the maxillary arch will be canted incorrectly left to right in the coronal plane or frontal view (Figure 6).8,9
The use of “stick bites” has been advocated to capture the esthetic reference plane to communicate with the dental laboratory. However, by referencing to the patient’s eyes, which can also be uneven, the relationship can be inaccurate esthetically. Using an adjustable nasion relator and level gauge on the face bow will enable the face bow to be adjusted to a horizontal level in relationship to the patient’s postural head position (Figure 7).8 The face bow will now transfer the esthetic relationship of how the patient’s teeth look in the face to mount the maxillary cast into the articulator (Figure 8).
Face Bow Procedures
Place Bite-TabsTM (Panadent Corp., www.panadent.com), wax, or other suitable registration material onto the maxillary side of the bite fork, and then place into hot water to soften registration material. Place the bite fork in the patient’s mouth in order to obtain registration of the maxillary teeth (Step 1). With the nasion relator and bite-fork stem assembly attached to the cross bar of the face bow, have the patient grasp the side arms of the face bow and insert ear pieces firmly into their ears. Tighten the large thumb screw to lock the face-bow width (Step 2). Raise or lower the anterior end of face bow until the nasion relator makes contact with the bridge of the patient’s nose (nasion) and tighten the nasion-relator thumb screw (Step 3). Slide the double-toggle clamp over the protruding stem of the bite fork and tighten the double-toggle clamp securely to the stem of the bite fork (Step 4).
Tighten the single-toggle clamp securely to the vertical attachment post. Loosen the nasion relator and large thumb screw to have the patient open the mouth, and then retract the side arms away from the ears to remove the face bow with the bite-fork assembly from the patient’s face. Remove the bite-fork assembly from the face bow, and send to the laboratory for mounting procedures.
Mounting Procedures
Set the incisal pin on articulator to zero. Remove the plastic incisal table and attach the mounting fixture to the articulator. Place the bite-fork assembly in the mounting fixture and tighten in place (Step 5). Seat the maxillary study cast into the bite-fork registration. Add plaster or stone into the mounting plate and on the maxillary cast (Step 6). Close the articulator until the incisal pin contacts the surface on the mounting fixture, connecting the mounting plate to the maxillary study cast (Step 7). After the plaster has set, open the articulator to remove the mounting fixture with the bite-fork assembly and replace the plastic incisal table (Step 8). Mount the mandibular cast using an inter-
occlusal record.
Summary
Most oral healthcare workers would agree that some basic treatment goals would be to:
- Eliminate destructive occlusal interferences or forces and prevent occlusal disease
- Fabricate anatomy compatible with the biologic system for chewing efficiency, occlusal stability, and patient comfort
- Create a beautiful smile and enhance facial esthetics
Therefore, the rationale for using a face bow and an articulator is for:
- Diagnosis of destructive occlusal interferences and occlusal disease
- Treatment planning with anatomy compatible with the biologic system for chewing efficiency, occlusal stability, and patient comfort
- Laboratory communication of functional and esthetic concerns or goals
- Baseline records to document procedures performed
Conclusion
The use of a face bow and mounting study casts on a full-size articulator in order to diagnose and develop a more predictable treatment plan that results in better efficiency, stability, and patient comfort, as well as being able to communicate with other specialists or the laboratory technician of both functional and esthetic concerns, is critical to clinical success.
References
1. Lee RL. Esthetics and its relation to function. In: Rufenacht C. Fundamentals of Esthetics. Chicago, IL: Quintessence;1990.
2. Dawson PE. Evaluation, Diagnosis and Treatment of Occlusal Problems. 2nd ed: St. Louis, MI: C.V. Mosby Co., 1989.
3. Snow GB. Articulation. D Cosmos. 1900;42:531-535.
4. Weinberg LA. An evaluation of the face-bow mounting. J Prosthet Dent. 1961;11(1):32-42.
5. Weinberg LA. An evaluation of basic articulators and their concepts: part I. Basic concepts. J Prosthet Dent. 1963;13(4):622-644.
6. Weinberg LA. An evaluation of basic articulators and their concepts: part II. Arbitrary, positional, semi adjustable articulators. J Prosthet Dent. 1963;13(4):645-663.
7. Christiansen RL. Rationale of the face-bow in maxillary cast mounting. J Prosthet Dent. 1959;9(3):388-398.
8. Lee RL. Standardized head position and reference planes for dento-facial aesthetics. Dent Today. 2000;19(2):82-87.
9. Stade EH, Hanson JG, Baker CL. Esthetic considerations in the use of face-bows. J Prosthet Dent. 1982;48(3):253-256.
About the Author
Thomas Lee
President, Panadent Corporation
Colton, California
