Fundamentals of Fixed Prosthodontics. James C. Kessler
When teeth are prepared at a future date and working casts are mounted on the articulator, it will not be necessary to make new lateral interocclusal records. The recorded information from the diagnostic mounting can be used to set the instrument.
Fig 5-33 The guidance provided by anterior teeth can be recorded in acrylic resin in the dovetail incisal block.
Fig 5-34 The incisal guide pin is 2 to 3 mm posterior to the tip of the retaining screw.
Fig 5-35 Tray resin is placed in the dovetail incisal block.
Anterior guidance
The influence of the TMJ on the occlusal scheme has been noted. The use of lateral interocclusal records in the setting of the condylar guides enables transfer of some of the influence from the TMJ to the semi-adjustable articulator. The influence of the incisors and canines (ie, anterior guidance) on the occlusion during excursive movements must also be taken into account.6,7
The guidance given to mandibular movements by the anterior teeth can be recorded using either acrylic resin or a lightcured material such as Triad (Dentsply) and made part of the setting of the articulator (Fig 5-33). Anterior guidance can, in effect, be transferred from the teeth to the incisal guide block of the articulator. If crowns restoring the lingual contours of the anterior teeth are to be placed, it is extremely important that the anterior guidance be registered on the articulator. If this is not done, the lingual contours or length of the restorations produced may not provide anterior guidance.
The mounted casts are examined on the articulator to assess the anterior guidance. If there are nonworking interferences on the casts, they are removed to enable the articulator to move freely while maintaining contact between the anterior teeth. The anterior guidance is examined to determine its adequacy. If it is not adequate because of wear, fracture, or missing teeth, it is restored to an optimum form with inlay wax or denture teeth on the cast.
The acrylic incisal block is replaced on the articulator with the dovetail incisal block (Whip Mix). The block is positioned so that the incisal guide, with the round end down, is 2 to 3 mm posterior to the tip of the retaining screw (Fig 5-34). The round end of the incisal guide pin and the functioning surfaces of the anterior teeth are lubricated with petrolatum. The interior surface of the dovetail block is also coated. Onehalf scoop of tray acrylic resin is mixed in a paper cup. While it still flows freely, a small amount is placed in the interior of the block (Fig 5-35). The material is allowed to acquire some body before proceeding.
Fig 5-36 The guide pin is closed into the soft acrylic resin.
Fig 5-37 The articulator is moved through all excursions.
Fig 5-38 An anterior guidance record has been formed in the dovetail incisal block.
The articulator is closed into full occlusion so that the guide pin penetrates into the soft tray resin (Fig 5-36). The articulator is moved repeatedly through all the mandibular movements, making sure that the anterior teeth remain in contact at all times (Fig 5-37). The tip of the incisal guide pin molds the acrylic resin to conform to the various movements. Movement of the articulator through all the excursions continues until the tray resin has polymerized.
Excess resin is trimmed off after it has polymerized. The tip of the guide pin has acted as a stylus in forming a registration of the anterior guidance (Fig 5-38). It will now be possible to duplicate the influence of the anterior teeth on the movements of the casts, even if the anterior teeth are prepared and the incisal edges shortened.
Fig 5-39 The components of a Slidematic facebow are (top to bottom) a reference plane indicator, the bite fork assembly, and the facebow with pointer.
Fig 5-40 A reference point is marked 43 mm above the incisal edges of the maxillary teeth.
Fig 5-41 The thumbscrew is tightened to attach the bite fork assembly to the underside of the facebow.
Denar Facebow and Articulator
The Denar Slidematic facebow (Whip Mix) is another self-centering ear facebow that is easy to use (Fig 5-39). The technique for its use is described with the Denar Mark II articulator (Whip Mix), an arcon semi-adjustable articulator. This articulator also allows interchangeability of articulated casts with other Mark II articulators without a loss of accuracy.
Facebow armamentarium
Denar Slidematic facebow (with bite fork, articulator index, reference pin, and reference plane indicator)
Felt-tip marker
Denar Mark II articulator
Plaster bowl
Spatula
Laboratory knife with no. 25 blade
Trimmed maxillary cast
Horseshoe wax wafers
Mounting stone (Whip Mix)
Facebow record technique
The reference plane indicator is used to measure a point 43 mm above the incisal edges of the maxillary incisors on the right side. This point is marked with a felt-tip marker (Fig 5-40). This will form the anterior, or third, reference point for the facebow transfer.
Two horseshoe wax wafers (Surgident Coprwax Bite Wafer) 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. The wax-covered bite fork is placed between the teeth, with the bite fork shaft to the patient’s right. The fork is centered by aligning the index ring on the fork with the patient’s midline. The patient is instructed to bite lightly into the wax to produce shallow indentations of the cusp tips in the wax. The wax is cooled, and the bite fork is removed from the mouth. Any excess wax is trimmed off the bite fork.
The maxillary cast is tried in the wax record to ensure that it will seat without rocking. If the cast fails to seat, the occlusal surfaces of the cast are checked for nodules of stone. If none are evident,