CHAPTER 25 Implant Prosthodontics: Design and Fabrication of a Hybrid Bridge Fixed-Detachable Prosthesis
The hybrid bridge is a fixed bridge made of denture teeth processed to a cast metal barlike framework. The prosthesis must be screw retained, and it usually is used in completely edentulous arches. The prognosis is best when the opposing arch is a complete denture or another hybrid bridge.
Mandibular prostheses require a minimum of five implants; maxillary hybrid bridges require six, or preferably more. The more maxillary root form implants placed (even up to 12), the better the prognosis. The hybrid bridge is a less costly bridge to make, and it is less demanding to fabricate than fixed or fixed-detachable prostheses. It is useful for patients with significant loss of alveolar dimension, whose teeth would appear unrealistically long if a conventional construction technique were used. The most valuable benefit of the hybrid bridge is that it serves well both functionally and cosmetically when implant emergence angles prohibit classic construction techniques.
The completely edentulous jaw can be restored with one of two types of provisional prostheses before and during implant treatment. The provisional restorations may be complete removable dentures or provisional fixed bridges made subsequent to the second stage of surgery. Chapter 21 describes in detail the manner in which any of the designs selected for patient comfort can be fabricated.
A surgical template is necessary to place and position implants accurately and predictably. The surgical template for a hybrid bridge should show what the final prosthesis will look like, including buccal position, incisal edge position, overall height, and cingulum and occlusal areas of the teeth. If the patient is wearing a denture in which tooth positions are to be replicated, this denture is used as a guide for construction of the surgical template. If a change in tooth positioning is planned, a trial denture is constructed that demonstrates the new dental alignment, and it is used for template duplication. Chapter 20 presents the techniques for fabricating surgical templates.
After the implants have been exposed and the healing collars removed, the abutments are chosen. Shouldered, standard, or conical abutments are used for hybrid bridges (see Chapter 22). The abutments act as platforms on which the hybrid bridge framework seats. Abutments of a height that places their interfaces with the hybrid cast framework at the level of the soft tissue should be selected. This allows the prosthesis to be adapted to the soft tissues, blocking out all spaces. It also helps prevent food from becoming lodged beneath the framework, and neither saliva nor air can escape from beneath the ridge lap. The soft tissue beneath the hybrid frame is sufficiently compliant to allow a Proxybrush to perform successful ablutions.
Abutments can be fitted directly in the patient’s mouth or from the master cast after impressions are completed. After the abutments have been firmly placed with a recommended torque wrench, impressions are made using the square or tapered coping techniques described in Chapter 24 (Fig. 25-1, A to K).
FIGURE 25-1. A, Six internal hex implants have become integrated in the parasymphyseal area. Healing collars are left in place for 2 weeks. B, A stone cast is made from an alginate impression of the six healing cuffs. C, Base plate wax is used to block out the entire healing cuff zone to a width of 5 mm and a height of 15 mm. D, An autopolymerizing or Triad tray is made to accommodate the boxed area. E, Nonfluted abutments are selected to be threaded into the implants. These abutments are designed to receive fixed-detachable restorations. F, The abutments are screwed into position. Radiographs must verify proper seating. G, Transfer copings are screwed into the threaded receptacles of the abutments. H, An Impregum impression is made to register the position of the transfer copings. I, Each transfer coping is supplied with a prosthetic abutment analog (left). The coping and the abutment are connected by a threaded feature (right). J, Each transfer coping–abutment analog complex is fitted into the Impregum impression, as can be seen by the positioning of the right central incisor. K, A master cast is poured in stone. The prosthetic abutment analogs are replicated in their true anatomic positions. L, Each abutment has a plastic waxing sleeve available, which is affixed to the analog with a coping screw. M, After the surfaces of the waxing sleeves have been abraded, each sleeve is screwed into position on the cast. N, A verification jig is fabricated using GC Pattern or Duralay resin, which bonds mechanically to the abraded sleeve surfaces. This is used to stabilize the sleeves during the refitting maneuver over the actual implants in the patient’s mouth. O, Placement of a single distal fixation screw should allow the entire complex to fit intimately and accurately into place without torquing or lifting. P, The verification jig and abutment assembly is replaced on the master cast, and a wax rim is made to fit over the GC Pattern resin. Q, Vertical and centric recordings are registered using the rim. R, The casts are affixed to a semiadjustable articulator, and teeth are set in wax with respect to incisal length, midline, labial position, and inclination. S, A silicone impression of the trial bridge is made on the master cast. Each tooth is removed from the wax-up and seated in the silicone index. This guides the location of the waxed superstructure in relation to the teeth borne by it. T, The surface of the completed prosthesis is designed for access and easy cleaning. U, The location of the fixation screws creates an esthetic and functional result. V and W, The hybrid superstructure, both clinically and radiographically, reveals an esthetic prosthesis that has become an integral component of the patient’s masticatory apparatus.
Chapter 24 presents the technique for computer-aided design/computer-aided manufacture (CAD/CAM) fabrication of the abutment-supported bar.
The final casts are completed by using analogs on which the final hybrid bar is fabricated. The guidelines presented in Chapter 21 are followed to convert temporization from a relined overdenture to an interim fixed prosthesis.
Screw-retained provisionals may use temporary cylinders that seat directly on the implant head or on top of a final abutment. A hole is made completely through the provisional restoration to allow the chimney of the abutment cylinder to pass through it or at least to be seen through it; this provides access to the retaining screw. The cylinder is processed to the provisional restoration with self-curing acrylic directly in the patient’s mouth. Care must be taken when luting the cylinders. Using small paintbrush acrylic slurry increments prevents filling of the screw access holes. Also, a cotton pellet is placed in each screw access hole to protect the screw heads from becoming covered. Wax is an unsuitable blocking agent, because it dissolves when the monomer comes in contact with/>