5. McHorris WH. Centric relation defined. J Gnathol 1986;5:5–21.
6. Dawson PE. Temporomandibular joint pain-dysfunction problems can be solved. J Prosthet Dent 1973;29:100–112.
7. Dawson PE. Evaluation, Diagnosis, and Treatment of Occlusal Problems. St Louis: Mosby, 1974:58.
8. Perry HT. Muscular changes associated with temporomandibular joint dysfunction. J Am Dent Assoc 1957;54:644–653.
9. Weinberg LA. Physiologic objective of reconstruction techniques. J Prosthet Dent 1960;10:711–724.
5 Articulation of Casts
To properly evaluate a patient’s occlusion, it is mandatory that diagnostic casts be placed in an articulator in approximately the same relationship to the temporomandibular joints (TMJs) as that which exists in the patient.1 A facebow registration is used to mount the maxillary cast on the articulator so that it is properly located both anteroposteriorly and mediolaterally.2,3 To be used enough to make a real contribution to the improvement of quality dentistry, a facebow and articulator that possess reasonable accuracy, are simple to assemble and use, and can be set up relatively quickly should be selected.
Information collected in an informal manufacturer’s survey of the 67 North American dental schools indicated that 31 schools were using a Whip Mix articulator, 29 were using a Hanau (Whip Mix), 4 were using a Stratos (Ivoclar Vivadent), and 3 were using a Panadent. Models used varied among the schools, and some schools used one brand of articulator for one discipline and another brand for a different discipline. Each of the following sections on a facebow-articulator combination is meant to stand alone (ie, everything the reader needs to know about the use of a system is contained in that respective section). The one exception lies in the description of a mechanical anterior guide. Although similar devices are available for all three articulators, use of the mechanical anterior guide is described only for the Hanau articulator.
Whip Mix Facebow and Articulator
The technique for the QuickMount facebow with Quick Lock Toggle (Whip Mix) (Fig 5-1), an ear facebow that possesses the qualities previously described, is presented. Following that is the technique for the use of the Whip Mix 2200 series articulator, a semi-adjustable instrument. Casts mounted on one of these articulators can be transferred accurately to another instrument of the same type that has been set to the same parameters.4 There are many advantages to this feature, including the ability to send casts to the laboratory without sending the instrument.5
Fig 5-1 The components of a QuickMount facebow are (left to right) a bite fork, the facebow with the nasion relator, and the Quick Lock Toggle assembly.
Facebow armamentarium
QuickMount facebow (with bite fork, nasion relator, and Quick Lock Toggle assembly)
Whip Mix articulator
Plaster bowl
Spatula
Laboratory knife with no. 25 blade
Trimmed maxillary cast
Horseshoe wax wafers
Mounting stone (Whip Mix)
Facebow record technique
Two horseshoe wax wafers (Surgident Coprwax Bite Wafer, Heraeus Kulzer) are heated in warm tap water until they become soft and flexible. A wafer is adapted to each side of the bite fork so that it is uniformly covered (Fig 5-2). The wax-covered bite fork is placed against the maxillary teeth. The attachment portion of the fork is centered on the patient’s midline. The bite fork is supported, and the patient is instructed to close lightly into the wax to obtain shallow impressions of only the cusp tips (Fig 5-3). The wax is cooled, and the bite fork is removed from the mouth. Excess wax is trimmed away. Any areas where soft tissue was registered on the wax must be completely removed.
Fig 5-2 A wax wafer has been adapted to each side of the bite fork.
Fig 5-3 The bite fork is placed against the maxillary teeth and supported by the dentist as the patient closes lightly for a shallow impression of the cusp tips.
Fig 5-4 The patient guides the earpieces (a) as the dentist places them into the external auditory meati (b).
The maxillary cast is set in the bite fork registration to confirm that the cast seats firmly in the index with no rocking or instability. If the cast does not seat, first the occlusal surfaces of the cast are checked to make sure there are no nodules of stone. If there are none, then either the registration or the cast is distorted and should be remade.
The bite fork is placed back in the mouth, and the patient is instructed to close to hold it securely between the maxillary and mandibular arches. The patient is then asked to grasp both arms of the facebow and guide the plastic earpieces into the external auditory meati, much as one would guide the earpieces of a stethoscope (Fig 5-4). The shaft of the nasion relator is extended while the facebow is adjusted up or down to center the plastic nosepiece on the patient’s nasion, and the thumbscrew is tightened (Fig 5-5). Next, the thumbscrew is tightened on the top of the facebow (Fig 5-6).
The Quick Lock Toggle is slipped into the slot on the bite fork with the head of the thumbscrew facing downward, and the screw is tightened (Fig 5-7). The Quick Lock Toggle is stabilized, and the T screw is tightened (Fig 5-8). The facebow record is now complete (Fig 5-9).
Fig 5-5 The shaft of the nasion relator is extended, and the thumbscrew is tightened.
Fig 5-6 The thumbscrew on the top of the facebow is tightened.
Fig 5-7 The Quick Lock Toggle is slipped into the slot on the bite fork (a), and the thumbscrew is tightened (b).
Fig 5-8 The Quick Lock Toggle is stabilized, and the T screw is tightened.
Fig 5-9 Completed facebow record.