Fourth Clinical Appointment
The trial dentures are evaluated intraorally for esthetics (Figure 11), phonetics, and OVD. The occlusal contacts are checked to ensure a bilateral balanced occlusion. The patient’s partner (or significant other person in their life) must be present during this appointment. They should be asked to opine about the esthetics and phonetics with the wax trial dentures and changes should be made as necessary. Approval from both of them, prior to proceeding with the next step is crucial, since, the same tooth set up will be used as a guide to fabricate the frameworks and will also be replicated in the definitive prostheses.
Figure 11. Evaluating patient esthetics during the try-in procedure.
Next external impressions may be made to develop appropriate contours of the polished surface of the maxillary trial denture.39 Baseplate wax/material apical to the prosthetic teeth on the trial denture is carefully removed, VPS tray adhesive (Caulk tray adhesive, Dentsply Caulk) is painted on the area where the wax/material is removed (Figure 12A) and low viscosity VPS impression material (Aquasil Ultra LV fast set, Dentsply Caulk) is applied to the same area (Figure 12B). The trial denture with the impression material is inserted in the patient’s mouth. The patient is instructed to make orofacial movements such as pucker their lips, smile, cough, suck, open and close the mouth and move the jaw from side to side to make the maxillary external impression. The trial denture is removed from the mouth following the complete polymerization of the impression material and evaluated. Excess impression material is trimmed with scissors (Figure 12C).
Figure 12A. VPS tray adhesive painted on the area where the wax is removed.
Figure 12B. Low viscosity VPS impression material applied to the same area.
Figure 12C. Trimmed external impression.
Verification of the Restorative Space, Selection of Attachments, and Framework Fabrication for The Maxillary Prosthesis
Ideally, restorative and esthetic spaces should be evaluated in the diagnostic phase before the placement of implants.40-43. Nevertheless it must be verified and re-verified before selecting the attachments and processing the denture. An occlusal or facial matrix of the wax trial denture may be used for re-assessing the restorative space. All the factors discussed in Part I of this course should be taken into consideration while making the attachment selection.
When inadequate vertical restorative space is present, locator abutments are the attachments of choice. They are selected for each implant based on the height of the mucosal cuff. Incorporation of the metal framework in the design of the overdenture aids in increasing its strength (especially important when restorative space is inadequate), decreasing its flexure (when the open palate design is planned) and fracture susceptibility.44,45 The locator abutment assembly (abutment and their retentive element) is attached to the implant analogs on the maxillary casts. The maxillary master cast and the trial denture are sent to the laboratory for fabrication of the metal framework. The restorative dentist should provide the design of the framework to the laboratory (Figure 13A). The framework is examined and adjusted to ensure complete seating on the cast (Figure 13B).
Figure 13A. Framework design.
Figure 13B. Maxillary framework.
Designing and Fabrication of the Milled Framework for the Mandibular Prosthesis
The mandibular master cast and the trial denture are sent to the laboratory for the fabrication of the CAD/CAM milled titanium framework (more accurate compared to a cast framework) for the “all-on-5” prosthesis. Precision of fit (passivity), durability, simplicity, and ability to use biocompatible and/or esthetic materials such as titanium and zirconia are some of the advantages of CAD/CAM framework (however, they are more expensive compared to casted frameworks.)21 It is important to be involved in the designing process of the framework. The technician should be asked to send screenshots of the design for approval. While reviewing the software images, there should be adequate distance between the framework and the tissue to perform oral hygiene. The framework should extend posteriorly up to the distal-most prosthetic teeth and it should be within the confines of the prosthetic teeth in all 3 dimensions (Figure 14). A short dental arch is planned for this patient based on the position of the implants. Increasing the number of posterior teeth will increase the cantilever length and the stresses on the implants.
Figure 14. The framework extends posteriorly to the posterior-most teeth.