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ePaper created 2017-05-10, 16:12:25 | version 1.38.0
restoration of the edentulous maxilla case report | of rotation. These implants should also be posi- tioned so that future implants may be considered should the patient wish for an implant-supported alternative. The hybrid prosthesis The screw-retained hybrid prosthesis is a fully implant-supported structure and, therefore, is not affected by incremental resorption of the residual ridges. It has gained in popularity as the technically difficult and costly gold frameworks have been re- placed by CAD/CAM titanium structures, and by proven success of angled implant placement to increase the AP spread. Because the restoration has a metal substructure, it is possible to cantilever pos- terior to the terminal abutment, increasing the length of the functional arch. However, the aesthetic component of the restora- tion—namely the denture teeth and acrylic resin ma- trix—are inherently weak materials originally in- tended for use in complete and partial dentures where functional load is comparatively low. If insufficient interarch space is available, the risk of fracture or dis- placement of denture teeth or resin base is high as the materials will be too thinned to withstand forces gen- erated during function and especially parafunction. Unfortunately, this is an increasingly common oc- currence, especially in restoration of the maxilla with a fixed hybrid prosthesis. Inconvenient screw-access holes may further weaken the prosthetic teeth. Repair of a fractured or lost tooth requires removal of the hy- brid prosthesis and correction in the dental laboratory. The dentist must be prepared to remove the structure and later re-seat it once the repair is completed. The patient must accept they will be without “teeth” for the length of time required for the technician to fix the problem. Attempts to prevent fracturing by increasing the thickness of the resin is limited by the space avail- able to do so. If inadequate interarch space is encoun- tered, correction cannot be achieved by adding more material. Rather a change in design to a different and possibly more expensive restoration may be needed. When hybrids are used in the maxilla, conflict may arise in attempting to improve the aesthetic and pho- netic result by use of ridge lapping and the limitations such shapes impose on proper oral hygiene. The benefits of the fixed hybrid prosthesis are clearly improved function and minimal post-treat- ment complications as long as the patient is able to properly clean it and breakage is avoided. Because it is fixed, the patient cannot remove it to clean away entrapped debris and properly remove plaque. Repair or replacement of the resin teeth requires removal and re-seating by a dentist. Atlantis Conus concept: the removable implant-supported bridge As described above, the tissue-supported overden- ture performs best with only two implants placed in the anterior region. When more than two implants are placed, the goal should be to provide a completely im- plant-supported result.4, 5 The Atlantis Conus concept (Dentsply Sirona) provides the optimal functioning convenience of a fixed hybrid, but also allows patient retrievability for unobstructed oral hygiene practice, regardless of the degree of ridge lap. It is, in effect, a prosthesis that can be removed by the patient, with the stability of a fixed bridge. The concept centres around patient-specific abut- ments, each milled to a 5-degree convergence, and parallel to each other in the dental arch. Recommen- dation is for at least four implants in the mandible and four to five implants in the maxilla. These uniquely designed, conical abutments are fit- ted by corresponding metal SynCone caps (Dentsply Sirona), which are incorporated into the prosthesis. The result is a friction-fit, stable, retentive and fully implant-supported bridge that remains removable by the patient.6 No special latches or plunger attach- ments are necessary to retain it. The patient merely slides the bridge in vertically onto the abutments and removes it in the opposite way. Because the abut- ments are a part of the Atlantis (Dentsply Sirona) portfolio, it is available for all major systems. In addition, because each abutment is custom- made, correction of angled implant placement is pos- Fig. 3: Duplication of an acceptable denture serves as a custom tray. Holes of sufficient diameter to accommodate impression copings have been prepared. Fig. 4: Open tray impression copings seated on the dental implants. One implant is selected for disuse and covered with a transmucosal abutment. Fig. 3 Fig. 4 CAD/CAM 2 2017 11