Resin-Bonded Fixed Dental Prostheses

Buonocuore's20 development of the acid-etch technique for enamel 60 years ago provided the basis to achieve high and durable enamel bonding using dental resins (Fig 1-1). In the 1970s, artificial teeth were initially bonded with composite resin to adjacent abutment teeth for anterior tooth replacement37 using the acid-etch technique. However, the longevity of these purely resin-based restorations was rather limited.

Today, extracted natural or artificial teeth can still be adhesively bonded in the same way to serve as long-term provisional restorations, e.g. when inflamed tissues in the alveolar ridge need time to heal prior to the fabrication of the final prostheses. It requires no great effort to shorten an extracted tooth by cutting off its root and to bond it back adhesively. However, after removing the root the remaining crown should be sealed on its cervical end using a dentin adhesive, and by using a tooth-colored composite resin, an ovate pontic basis is formed. The ovate pontic should reach 2 to 3 mm into the extraction socket and support the marginal gingiva circumferentially (immediate pontic technique, compare with Fig 5-11). In this way, the blood coagulum in the extraction socket is also protected. In the presented case (Figs 1-2 to 1-9), the resin bonding of the extracted and shortened tooth was reinforced using a polyethylene fiber net (Ribbond). Figure 1-9 presents the restoration after 14 years of clinical service. This case is an example of the excellent durability of bonding to enamel. Mostly, such long-term provisional restorations will fail after several years of clinical service due to a fracture of the elastic fiber-reinforced resin bonding. However, at this stage the hard and soft tissues have healed, so that either a final resin-bonded fixed dental prosthesis or a single tooth implant can be used for the final prosthetic restoration.

Fig 1-1Enamel etching pattern after etching with phosphoric acid (scanning electron microscopic photo at 1000× original magnification).

Fig 1-2Labial view of the hopeless tooth 32 (situation after repeated unsuccessful apicoectomies done elsewhere).

Fig 1-3Fabrication of an incisal-positioning splint prior to extraction of tooth 32.

Fig 1-4Situation after extraction of tooth 32. Care was taken to ensure complete filling of the extraction socket with blood.

Fig 1-5Basal view of the removed tooth revealing an untreated lingual root canal, and a crack in the labial canal wall.

Fig 1-6Reshaping the root portion with adhesive techniques and composite resin into an ovate pontic shape.

Fig 1-7Occlusal view of tooth 32 that was adhesively fixed with composite resin reinforced with a lingual fiber net under rubber dam isolation.

Fig 1-8Labial view of tooth 32 after complete healing.

Fig 1-9Status 14 years after reinsertion of the extracted reshaped tooth [Source: CDT Matthias Hasselberg, Eckernförde, Germany].

These composite resin fixed teeth did not provide good long-term results on a regular basis. To improve longevity, Rochette80 suggested using metal-based resin-bonded fixed dental prostheses (RBFDPs) with two retainer wings for anterior tooth replacement. Macromechanical retention for the metal retainer wings was provided by means of tapered pinholes into which the luting cement would flow, acting as a resin rivet to secure the RBFDP to acid-etched enamel. Howe and Denehy35 and, in particular, Livaditis and Thompson65, from the University of Maryland, Baltimore, USA, advanced the use of metal-based RBFDPs, resulting in the well-known name Maryland Bridge. A significant advancement indicated the use of the electrolytic etching technique for non-precious metal alloys (Fig 1-10), which provided micromechanical retention of the retainer wings for composite resin luting agents, making macromechanical retention holes unnecessary. The introduction of mechano-chemical bonding systems, especially silica coating with subsequent silane application, and the development of modified luting resins containing adhesive phosphate monomers in the mid-1980s, resulted in significant improvements to resin-metal bonding. These advances significantly improved the long-term prognosis of metal-ceramic RBFDPs (Figs 1-11 to 1-14).

Fig 1-10Etching pattern of a cobalt-chromium alloy after electrolytic etching (scanning electron microscopic photo at 200× original magnification).

Fig 1-11 Two-retainer metal-ceramic RBFDP replacing tooth 12.

Fig 1-12Metal-ceramic RBFDP from the lingual view.

Fig 1-13Status 10 years after insertion from the lingual view.

Fig 1-14.and from the labial view. The slightly grayish shine-through of the metal retainer wing is clearly recognizable, especially in comparison to the non-restored left side.

Fig 1-15Unilaterally debonded two-retainer metal-ceramic RBFDP, replacing tooth 21.

Fig 1-16Clearly visible caries at the debonded abutment tooth 11 after removal of the RBFDP.

Fig 1-17Metal-ceramic RBFDP replacing teeth 31 and 41 with four splinted metal retainer wings. Retainer wings on teeth 32 and 42 are debonded.

Fig 1-18After removal of the RBFDP without retentive tooth preparation, massive caries is recognizable under the debonded retainer wings. Splinting of multiple retainers should be avoided. Principle: Less is more!

One of the most frequent and dreaded complications with two-retainer RBFDPs with a metal framework was the unilateral debonding of one retainer wing, which was often not noticed by the patient, or even ignored.

Such unilateral debondings in multiple-retainer RBFDPs almost inevitably resulted in caries (Figs 1-15 to 1-18). Among the causes for these unilateral debondings of metal-based RBFDPs were errors regarding indication, clinical procedures, and bonding methods. However, unilateral debondings also occurred when everything had been done correctly. In part, this can be explained by the fact that metal retainer wings with their relatively high flexibility in thin cross-section can bend during loading. This bending results in high peeling forces in the marginal area of the retainer wings, causing a progressing debonding that starts at the retainer margins. When the pontic or the abutment teeth are functionally loaded, minimal and differential tooth movements will always occur. For example, when replacing a missing maxillary lateral incisor or canine with a classic two-retainer RBFDP, the incisors will be deflected anteriorly during protrusion, while during lateral excursion the canine will be deflected laterally. Without retentive abutment tooth preparation, unilateral debonding of one retainer wing could be predicted with some certainty (Figs 1-19 to 1-27).

Fig 1-19Two-retainer metal-ceramic RBFDP replacing tooth 13.

Fig 1-20During laterotrusion and protrusion, differential tooth movements (excursions) occur.

Fig 1-21Unilaterally debonded retainer on abutment tooth 12 prior to removal of the RBFDP.

Fig 1-22Clearly visible caries in the area of the lingual tubercle of tooth 12.

Since the mid-1990s it has been recommended to routinely attach RBFDPs unilaterally. The single-retainer wing reduces peeling and shear forces resulting from the differential loading forces, preventing the dreaded complications caused by unilateral debondings experienced with two-retainer RBFDPs16,36. In the meantime, the concept of metal-based single-retainer RBFDPs with superior longevity compared with multiple-retainer RBFDPs was confirmed by various clinical studies14,15,27,59,83,102. Therefore, in the case of a unilateral debonding of a two-retainer RBFDP, one should not try to debond (disconnect) the still attached retainer; instead the debonded...