What are minimal preparation (resin retained) bridges and when are they used?

Minimal preparation bridges have also been referred to in the literature as resin retained bridges, adhesive bridges and resin-bonded bridges. In this text the term minimal preparation (resin retained) bridge will be used. These are bridges that require minimal preparation of tooth tissue and rely on adhesive cements for their primary retention, unlike conventional bridges that require significant tooth reduction to make retentively shaped preparations which provide the primary retention and then rely on a cement lute for secondary retention.

Minimal preparation (resin retained) bridges are therefore used when the potential abutment teeth are unrestored or minimally restored and there is a need to reduce unnecessary tooth preparation. Consider the 22-year-old patient in Figure 18.1: preparation of the vital upper right central incisor tooth for a metal–ceramic retainer has been destructive of tooth tissue as this tooth only had a small fractured incisal edge. A cantilevered minimal preparation (resin retained) bridge using the central incisor as an abutment tooth would have been much more conservative. However, in this patient both lateral incisors are missing. Conventional bridge retainer preparation of the non-vital upper left central incisor tooth has been necessary not only to retain a pontic but also to disguise the appearance of the discoloured tooth. Furthermore, this patient had orthodontic treatment to close a midline diastema and since this treatment tends to be unstable, the conventional retainers were linked to also act as an orthodontic retainer.

Figure 18.1 This is the patient seen in Figure 19.2, Chapter 19. Preparation of the upper right central incisor for a metal–ceramic retainer has not been conservative of tooth tissue.

History of resin-bonded bridges

It is useful to understand the history of the development of minimal preparation (resin-bonded) bridges as some principles and applications can be useful in contemporary practice.

Macromechanical retention

Natural tooth pontic

This technique can be used for a tooth that needs to be extracted. Once extracted, the root is resected and then the crown is cemented to the adjacent tooth/teeth using composite resin cement. At the resected root end the root canal should be opened and restored with either a glass ionomer or composite resin to prevent food and plaque stagnating within the tooth. To bond the extracted tooth the corresponding approximal surfaces are acid etched, bond applied and then composite used to cement the crown in place. Figure 18.2 illustrates diagrammatically how this procedure is carried out and Figure 18.3 shows an example where this has been done. In the author’s opinion this technique has been remarkably successful for the patient in Figure 18.3 as this ‘temporary’ measure had been carried out many years previously.

Figure 18.2 Diagrammatic representation of the patient seen in Figure 18.3. The teeth are periodontally involved and the lower right central incisor requires extraction. Following extraction the root is resected (top right), the root canal is cleaned from the resected end and the canal restored with composite resin or glass ionomer (bottom left). The tooth is then bonded to the adjacent tooth with composite resin cement (bottom right).

Figure 18.3 Lower central incisor resin retained natural tooth pontics cantilevered off the lateral incisors.

If a patient presents with a missing tooth, which is either lost or not reusable, a replacement tooth can be made from composite resin using a crown former or simply an appropriately sized acrylic denture tooth can be used. Additional retention can be obtained, if required, by embedding a contoured orthodontic wire, wire mesh or fibre-reinforced ribbon in composite to the lingual surface of the extracted tooth and the tooth or teeth to which it is being bonded.

Laboratory-made bridges using macromechanical retention

Rochette bridges

A Rochette bridge consists of a pontic connected to a metal wing retainer which covers the lingual surface of the abutment tooth. Within the wing, countersunk holes are cut which allow retentive composite plugs or rivets to form when the bridge is cemented in situ (Figure 18.4). When Rochette bridges were originally described, they were designed to act as permanent fixed prosthodontic restorations (Figure 18.5). However, to achieve composite plugs of adequate strength they had to be of a significant diameter and depth, the latter necessitating a thick wing which caused problems in relation to the occlusion, especially when placed in the upper anterior region. In addition, occlusal stresses were concentrated on a limited number of composite plugs, predisposing to them to fracture and, as such, retention rates were often poor in the long term.

Figure 18.4 Diagrammatic representation of a Rochette bridge. The cross-section shows the countersunk holes and retentive composite ‘rivets’.

Figure 18.5 An example of a fixed–fixed Rochette bridge. This bridge had been in situ for over 20 years.

Today, Rochette bridges can still be considered as an immediate provisional tooth replacement when ease of removal is a benefit. For example, if a patient was unable or unwilling to wear a removable prosthesis and an upper central incisor required extraction, its immediate replacement with a cantilever Rochette bridge, using the contralateral central incisor as an abutment, could be considered. The tooth could be extracted, rubber dam applied and the Rochette bridge cemented without any blood contamination from the socket.

Provided the bridge is cemented in place with a non-adhesive, dual or chemically cured composite resin luting cement, such as Nexus luting cement (Kerr/SDS), removal is achieved by simply removing the composite from the holes within the wing. It is important to note that if the permanent tooth replacement is to be a minimal preparation (resin-bonded) bridge using the same abutment tooth, the superficial enamel will be impregnated with resin and this will also have to be removed, otherwise the subsequent bond for the permanent bridge will be compromised. Therefore, this technique is preferred when either a different tooth is to be used as an abutment for the definitive bridge or if the final replacement is an implant which is not reliant on a tooth for support and retention.