The functionally generated path (FGP) technique enables the restoring dentist accurately to capture the mandibular eccentric movements of a patient without the use of complicated or expensive instrumentation.55,56,68 The eccentric movements are recorded after the dentist establishes the OVD and anterior guidance. The technique has been used for all types of occlusal schemes but is most useful for bilateral balanced occlusion, especially when the occlusal plane is not ideal. The dentist may use the FGP concept to fabricate the maxillary complete denture opposing natural dentition or to reset posterior teeth with rebasing or relining procedures.
The most common indication for the FGP in the implant practice is a maxillary complete or RP-5 overdenture opposing natural or previously restored fixed restorations (Figure 33-52). Bilateral balanced occlusion is especially difficult to establish when one of the arches presents natural dentition. Compounding the problem are patient treatments that do not permit complete occlusal rehabilitation of the natural arch. Implant dentistry often presents treatment options that combine the restoration of the maxillary arch with a traditional complete denture with an implant-supported fixed mandibular prosthesis.
FIGURE 33-52 A maxillary denture occasionally is made to opposing natural teeth or an implant-supported fixed restoration without an ideal occlusal plane. Bilateral balance is difficult to achieve under these conditions.
The eccentric movements of the mandible are dictated by the condylar disc assembly paths and the anterior incisal guidance. Because the FGP technique first establishes the vertical and anterior guidance, all necessary information is already available for an accurate customized recording of mandibular movements.
An occlusal plane analyzer may be used on diagnostic casts to evaluate pretreatment conditions of the mandible and assist in intraoral occlusal plane correction. Occlusal analyzers may be fabricated in several sizes. The average size corresponds to a 4-inch sphere and provides a starting point for ideal curves of Wilson and Spee. Any discrepancy observed on the cast may be corrected in the mouth. Misch has designed a laboratory-assisted template with this intent.14 In the laboratory, a vacuum or press fit of an acrylic shell is prepared over the cast. The occlusal plane analyzer is then used to evaluate and correct an improper occlusal plane. A handpiece is used to grind the acrylic shell and protruding occlusal cusps on the duplicate diagnostic cast. The clear acrylic shell is then taken intraorally and inserted over the teeth. Any cusp extending through the acrylic shell is recontoured to the level of the surrounding acrylic. As such, the occlusal plane is rapidly corrected to an ideal condition (Figure 33-53).
FIGURE 33-53A, A Misch occlusal analyzer with a 4-inch curve is placed on the mandibular cast to evaluate the curves of Wilson and Spee. B, A clear vacuum form is placed over the teeth, and the mandibular cusp is selectively recontoured to fit the occlusal analyzer. C, The modified cusps are marked on the cast. D, The clear template is placed in the mouth, and the appropriate cusps are modified.
The first step in the FGP technique for a maxillary removable prosthesis is the determination of maxillary anterior tooth position after fabrication of final impressions and stable base plate records. The dentist uses the guidelines previously discussed for esthetics, contour, and phonetics. The dentist then addresses the mandibular arch. If the mandibular arch is a RP-4 overdenture and the restoring dentist selects the position of the teeth, one determines the maxillary occlusal plane in the occlusogingival, buccolingual, and A-P directions. If the mandibular arch already is restored with a fixed prosthesis or natural teeth, the dentist also recontours the mandibular anterior teeth as necessary to eliminate irregularities in height or labial position. The dentist recontours the buccal contours of the mandibular posterior teeth to permit a more medial position of the occlusal contacts and often reduces the lingual cusp height to prevent lateral prematurities.
The dentist establishes the OVD using facial measurements. The dentist obtains a record of vertical centric occlusion relation after determining anterior teeth position and OVD. The dentist may or may not use a face-bow registration to mount the maxillary cast base plate with anterior teeth in final position. The dentist mounts the opposing cast of the natural fixed mandibular teeth with the centric registrations and uses a “verticulator” or articulator with condylar protrusive settings greater than 60 degrees as the articulator for FGP techniques (Figure 33-54).
FIGURE 33-54 During the maxillary wax rim and try-in appointment, the position of the maxillary anterior teeth has been confirmed and the occlusal vertical dimension, and centric occlusion records have been obtained. The articulator reproduces this clinical situation, and the condylar settings on the articulator are selected greater than 60 degrees.
After the maxillary anterior teeth and OVD are established, the maxillary posterior wax rim is designed to occlude with the opposing cast or denture teeth on the articulator. The dentist cuts a narrow slot into the maxillary posterior occlusal rim directly over the central fossa of the mandibular posterior teeth. This slot extends to the acrylic base plate and forms a 3-mm-wide groove. The dentist adds monomer to the base plate in the groove and fills in the area with acrylic. The dentist coats the opposing cast with petroleum jelly or separating medium and articulates the casts. The dentist then removes the remaining wax rim after the acrylic polymerizes. This procedure results in an acrylic fin occluding with the central fossa of the posterior cast at the recorded vertical occlusal dimension (Figure 33-55).
FIGURE 33-55 An acrylic fin on the maxillary base plate is made to occlude with the central fossa of the mandibular teeth at the occlusal vertical dimension position.
The dentist places the maxillary base plate in the patient's mouth and confirms the anterior tooth position and vertical occlusion (Figure 33-56). The dentist adds Iowa wax or soft wax around the posterior acrylic fin and then guides the patient first into centric occlusion and makes a record of the occlusal surfaces of the mandibular teeth with the wax. The dentist softens the wax in warm water and instructs the patient to bite in centric occlusion, and then the dentist guides the patient into a left lateral movement until the maxillary and mandibular canines are in the same plane. After the dentist registers the extent of the movement, the patient opens the mouth and occludes back into centric occlusion. This recording is repeated. The dentist removes the maxillary base plate and examines it (Figure 33-57). The posterior wax should not be unsupported at the base. If the wax extends wider on the occlusal table than on the base, the dentist adds wax below the occlusal registration table until it is supported.
FIGURE 33-56 The maxillary base plate and anterior teeth try-in are evaluated intraorally. The posterior fin occludes in the central fossa of the posterior teeth.
FIGURE 33-57 Iowa or soft wax is placed around the posterior fins of the base plate. The patient is guided through left and right border movements, keeping the jaws in contact.
The dentist reinserts the maxillary base plate and guides the patient into centric relation occlusion and guides the mandible into a right lateral border movement. The patient opens when the mandibular movement has aligned the maxillary and mandibular canine facial surfaces and closes back into centric occlusion. The movement is repeated. The dentist removes the maxillary base plate and examines it for accurate occlusal patterns and supported occlusal wax contour.
The dentist inserts the base plate again, this time guiding the patient into centric relation occlusion and asking the patient to make one protrusive movement until the maxillary and mandibular anterior teeth are aligned. The patient then opens the mouth, and the dentist removes the base plate. Protrusive movements are not border movements and may vary slightly with repeated records. Therefore the dentist records only one protrusive movement in the posterior occlusal wax.
The dentist places a moist, cold towel around the posterior wax to prevent distortion, boxes the region, and pours it with dental or die stone (Figure 33-58). The cold towel helps prevent distortion of the wax when the stone generates heat during setting.
FIGURE 33-58 A moist, cold towel is positioned around the posterior soft wax regions of the base plate, and stone is poured onto the wax.
When the stone is set, the dentist repositions the maxillary base plate on the articulator, removes the mandibular cast of the teeth or dentures from the mandibular component, and joins the posterior stone patties to the mandibular articulator frame with plaster (Figure 33-59). The dentist then separates the mandibular occlusal casts from the maxillary base plate. The occlusal aspect of the mandibular cast does not appear as teeth; instead, the cast is the representation of the border and protrusive movements of the mandibular cusps (Figure 33-60).
FIGURE 33-59A, The maxillary wax try-in and occlusal patties of set stone. B, The mandibular cast is removed from the articulator and is replaced with the stone patties and joined to the mandibular articulator frame with plaster.
FIGURE 33-60 The stone patties do not appear as natural teeth. They are the representations of the mandibular teeth tracings during border and protrusive movements of the mandibular occlusal surfaces.
The dentist increases the articulator vertical relation pin 1 mm, positions the maxillary posterior fully anatomical denture teeth in the maxillary base plate, and places the premolars for esthetics and function. The first molar is often more medial in position in divisions C and D bone, and the maxillary second molar may be set in crossbite if the posterior ridge has severe resorption. The posterior teeth are set 1 mm too high at the present step because the articulator vertical incisal pin was increased.
The dentist then repositions the vertical relation pin to the original vertical dimension. The articulator is used only in the vertical position. No excursions are made. Articulating paper marks the portions of the teeth in occlusion, and the dentist recontours these until obtaining the original vertical dimension (Figure 33-61). This procedure results in a bilateral balanced occlusal scheme.
FIGURE 33-61 The incisal pin of the articulator is raised 1 mm, and the posterior teeth are set in the wax rim. The pin is returned to its original position, and the vertical movement of the articulator is used to equilibrate the maxillary teeth until the original occlusal vertical dimension is restored.
The dentist tries the maxillary prosthesis with waxed-in teeth in the patient's mouth. The patient makes the left and right border movements along with a protrusive movement. The dentist evaluates occlusion and adjusts as needed. The dentist also evaluates esthetics and phonetics. The final denture then may be processed and delivered at the following appointment (Figure 33-62).
FIGURE 33-62 The maxillary denture is processed, and final delivery of the prosthesis is made. The patient is reminded about continued bone loss and the need to remove the prosthesis during sleep to slow the bone loss process until implants may be inserted.
One may use an alternative technique for a FGP denture if the mandibular arch also may be restored. This technique first finishes the maxillary denture to ideal esthetics, contour, comfort, and occlusal plane depending on the amount of maxillary ridge resorption. The mandibular arch is then restored to the final maxillary prosthesis.
The dentist positions the final maxillary denture in the patient's mouth, positioning the mandibular anterior teeth first and evaluating for esthetics and phonetics at the desired vertical dimension. Anterior contact in centric relation occlusion usually is not indicated for a maxillary removable prosthesis. The dentist places an incisal stop or index on the anterior teeth to record the vertical dimension at centric condylar position. A centric vertical occlusal recording permits the mounting of the maxillary denture cast and mandibular base plate on an articulator.
After the maxillary cast and mandibular occlusal records are mounted on an articulator, the dentist fabricates the acrylic fin connected to the mandibular base plate in a manner similar to the previous technique. During the next patient appointment, the dentist makes intraoral wax recordings similar to those of the previous procedure. The setting of the posterior teeth, occlusal grind-in procedure, and delivery of final prosthesis are also similar.
For a maxillary RP-4 overdenture opposing natural teeth, one should use mutually protected occlusion or canine guidance. The dentist also may use an FGP concept for this occlusal scheme. However, after processing, the dentist selectively removes occlusal nonworking contacts to eliminate all interferences.
The maxillary denture becomes a source of complaint when opposing natural teeth or a stable mandibular overdenture. Many removable denture concepts have been developed to make the mandibular prosthesis more stable. After implants are placed in the mandible and attached to a superstructure, the maxillary denture becomes the least retentive and stable member. Methods to improve maxillary denture stability include careful evaluation and treatment of the maxillary soft tissue, ridge HA augmentation and shape enhancement, raising of the posterior occlusal plane in relation to the bone support, and establishing a balanced “medial-positioned lingualized occlusion.” The result is reduced moment forces and improved maxillary denture stability.
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