From Volume 43, Issue 7, September 2016 | Pages 608-616
This is the second part of this two-part series. The first paper discussed key aspects of case selection, planning and design of resin-bonded bridges (RBBs). This paper outlines the important clinical stages involved in the successful provision of RBBs, including communication with the dental laboratory, clinical protocols and management of the de-bonded RBB.
Shade selection should take place prior to the impression stage to prevent tooth dehydration which can result in transient shade change due to desiccation of enamel, leading to poor shade match of the final restoration.1
The shade-taking procedure should also take into account the use of opaque resin cement where this is planned, which may reduce the translucency of abutment teeth.
The shade-taking protocol is as follows:
Place a cotton wool roll behind the chosen abutment tooth to mimic the effect of opaque resin cement. This may alter the appearance of the abutment tooth, usually giving it a creamier appearance incisally. Therefore, this must be factored in during shade selection and prescribing characterizations for the pontic to the dental technician. In some cases, a metal backing can be bonded to the contralateral tooth if it is not being used as an abutment, to match the altered shade of the abutment tooth.
Good communication with the dental technician and attention to detail are important in the successful provision of RBBs. A pontic design should be prescribed to the technician, as well as the required thickness of the metal framework. An example laboratory card is shown in Figure 1.2
A detailed and prescriptive set of instructions for the dental technician is important to ensure predictability and control over the final result as well as good verbal communication. This includes the specification of the thickness of the retainer, which should be at least 0.7 mm (Figure 1).
As with all indirect restorations, the restoration should be tried in immediately prior to cementation, to assess the marginal fit, seating, aesthetics and occlusion. However, whilst it is essential to check the fit of an RBB, as with any restoration prior to cementation, the minimal/non-preparation nature of anterior RBBs means that there is a lack of inherent retention and resistance form compared to conventional bridgework; therefore it may not lend itself to a trial fit as easily. Aesthetics can be assessed, but it is important to mimic the change in translucency resulting from the retainer wing and resin cement on the abutment teeth in order to give any idea of shade match. A method described by Poyser and Briggs uses Dycal® (Dentsply Ltd, Surrey, UK) on the retainer wing at a try-in which allows the operator and patient to observe the effect an opaque resin cement such as Panavia ‘Opaque’ (Kuraray Co Ltd, Osaka, Japan) is likely to have on the aesthetics, as well as trial the RBB in speech and smiling (although the retention offered by the Dycal® is of course limited, depending on the inherent stability of the bridge).3 Similarly, the unpolymerized base paste (Panavia ‘B paste’) can also be used to mimic the final aesthetics prior to cementation and has the added advantage of being a closer match to the shade of the final cement. Materials containing eugenol should be avoided as this may affect polymerization of the resin composite luting agent.
Once the try-in has satisfied the operator and patient in terms of aesthetics, the try-in cement should be cleaned off and saliva contamination removed from the retainer, ideally by re-abrading using a chairside air-abrasion unit as described above. Abrading the fit surface of the non-precious metal retainer with 50 microns alumina ensures an optimal thickness of oxide layer on the roughened surface of the alloy to improve bonding to resin cements.2 Where a chairside air-abrasion unit is not available, the fit surface of the retainer wing must be cleaned thoroughly and acid-etched to remove surface contaminants such as saliva, followed by a thorough rinse.
With regard to the material for adhesive bonding, there are many resin cements commercially available that are indicated for RBBs. Much of the evidence published has used variants of Panavia, which is the authors' preferred choice of resin cement for RBB bonding.4,5,6,7,8 The most pertinent recommendation is always to follow the manufacturer's instructions for use as accurately as possible, as they vary even between Panavia 21 Ex (Kuraray Co Ltd, Osaka, Japan) and Panavia F2.0 (Kuraray Co Ltd, Osaka, Japan). Table 1 summarizes the differences between the available variants of Panavia and their clinical implications.9
| Resin Cement | Panavia F2.0 | Panavia 21 Ex |
| Curing type | Dual-cure | Self-cure |
| Shades available | TC (tooth colour), White, Opaque, Light | EX (white), TC (tooth colour) and OP (opaque) |
| Working and setting time | Up to 3 minutes working time. 3 minutes setting time for chemical cure, or 20 seconds of conventional halogen or LED light cure | Up to 4 minutes working time 3 minutes setting time |
| Added benefit | Releases fluoride - although there is no proven clinical benefit of its addition | Easier dispensing of the paste component |
| Clinical implications and tips | The Opaque paste of Panavia F2.0 need not be light-cured as it has no photo-initiator and a low curing depth. Panavia Opaque should be allowed to set chemically for 3 minutes using Oxyguard II® around the margins to prevent oxygen inhibition of setting reaction |
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An intra-oral air abrasion unit is an extremely useful piece of equipment when adhesive dentistry is used and therefore an investment worthy of consideration. Air-abrade the RBB retainer after try-in/prior to bonding with 50 μm alumina. This removes surface contamination, roughens and allows optimal oxide layer formation on the surface of the alloy to improve bonding to resin cements such as Panavia F2.0.
Use an opaque shade of resin cement to eliminate incisal ‘greying’ of anterior RBB abutment teeth where the framework has been extended incisally.
The chemistry of Panavia 21 Ex does not allow complete curing in the presence of oxygen, therefore the use of Oxyguard II is essential. When using Panavia F2.0 Opaque shade, the use of Oxyguard for chemical curing is necessary as this relies on a chemical cure and has a low curing depth.
A review appointment allows the operator to assess the following:
The appointment also provides another opportunity to reinforce the importance of regular maintenance, and extra vigilance where a fixed-fixed design has been used due to the risk of a silent de-bond of a wing described earlier.
Avoid disturbing cement lute immediately after bonding. This includes avoiding the use of an ultrasonic scaler, which should ideally not be necessary if excess cement was removed meticulously during bonding as described above.
Djemal et al defined failure as ‘any significant adverse event related to the restoration requiring remedial treatment or a remake’.5 As with all restorations, RBBs may experience failure mechanically, biologically or aesthetically, separately or, more often, in combination. This can include caries at the retainer margin, periodontal loss of an abutment tooth, and fracture of metal or porcelain. The most common mode of failure (>90%) of RBBs is de-bonding.4,5 Failure by complete de-bonding leaves a cleansable area with a low risk of caries or sensitivity, especially if a non-preparation design was adopted. However, the de-bonding of a RBB may not be an absolute failure, as it may be re-bonded to restore function and aesthetics.
As mentioned previously, de-bond of a fixed-fixed RBB is frequently associated with only one retainer wing and will not result in the bridge becoming dislodged. Such a 'silent' de-bond carries the risk of recurrent caries occurring beneath the debonded retainer wing and it is therefore very important to check for this during routine review appointments and to ensure that the patient is advised to seek advice if he/she notices anything that may indicate unilateral bond failure. However, a minimal preparation technique reduces or eliminates the chance of dentine exposure and therefore reduces the risk of recurrent caries beneath a de-bonded retainer in these circumstances.
It is critical that the cause of de-bonding should be identified and a decision made to re-bond, remake, or to consider an alternative prosthodontic solution outright. Common underlying causes of de-bonding which can be used in the decision-making process have been summarized in Figure 2. If the design of the RBB and abutment selection are acceptable, and the clinical findings suggest a bond failure, re-bonding may be considered with a view to overcoming this failure through an improved adhesive protocol. A design or abutment selection fault may require remaking the RBB to rectify the problem.
There is conflicting evidence regarding the success of re-bonded RBBs after they have de-bonded.10,11,12 When considering the low cost of re-bonding and high patient satisfaction, this should be considered as the first choice where appropriate. Figure 3 describes the sequence for re-bonding RBBs.
Failure due to caries is rare in RBBs, but has been associated with fixed-fixed designs where one wing has de-bonded silently, and may be a greater risk where abutment preparation has resulted in exposure of dentine. In cases where caries is detected early in a unilateral de-bond of a fixed-fixed RBB, the wing associated with the carious tooth can be sectioned and polished to leave a cantilevered RBB in cases where a single unit is being replaced.
If necessary, a partially debonded F-F bridge can be removed using a straight enamel chisel and a sturdy instrument, such as a pair of Adams pliers, to use as a mallet. The chisel should be placed at the margin of the retainer wing to be debonded, such that shear force is directed along the cement lute. The ‘mallet’ is then used to tap firmly on the end of the chisel handle to break the cement bond, removing the bridge intact. It is extremely important to ensure sufficient purchase at the retainer wing margin before applying force to the chisel to prevent slippage and resulting trauma before any force is applied. Gauze should be placed behind the bridge and floss tied around the pontic/connector area to protect the airway, ensuring that the dislodged bridge is not displaced towards the oropharynx. Following removal, the bridge and tooth surfaces can be cleaned and the RBB re-bonded as described.
The presence of spacing presents a challenge when restoring with RBBs, which usually require an intimate contact between the abutment and the pontic via a connector, thereby closing any spacing or diastema. In such cases, where there is spacing between abutment teeth and pontic spaces, the use of a modified spring cantilever design of RBB, as described by Gibson,13 can maintain a diastema. Alternatively, resin composite build-ups to eliminate spacing may be considered, which can be accomplished prior to impression, or at the fit appointment by altering the framework design to incorporate the altered contour of the abutment, as illustrated in Figure 4. An implant-supported crown is also a viable option to maintain spacing, providing that adequate 3-dimensional space and bone exists for this.
The scope of this article is limited to traditional adhesive bridges using non-precious metal to manufacture the framework, although the use of ceramics for this technique is growing in popularity. There is little published evidence in relation to the use of ceramic as the framework material for adhesive bridgework compared with metal alloys.14 The advantage of an aesthetic, metal-free framework is countered by the need for an increased cross-sectional area of the connector to maintain strength and rigidity, which itself may hinder the final aesthetic potential of the pontic and the embrasure spaces. This may mean that using ceramics may not be feasible in some cases due to a lack of strength of the framework. The most common cause of failure of all-ceramic RBBs is fracture of the framework, which is a less favourable mode of failure compared to metal RBBs where a complete de-bond is observed more commonly.14 Furthermore, the overall thickness of the ceramic framework necessary to maintain strength and rigidity would necessitate an over-contoured framework, which may compromise ultimate cleansability, aesthetics and interocclusal space. The alternative is to create the space for the required thickness of framework by tooth preparation, which may be more invasive. The removal of tooth structure to create enough space for an appropriately rigid ceramic framework may expose dentine, which would compromise the bond to abutment teeth. However, in cases where there is plentiful interocclusal space, or where the labial contour needs to be adjusted, there may be an indication. For example, in some cleft cases, the ceramic framework may be bonded labially, allowing modification of labial tooth contour for aesthetics incorporated in the bridge design. This may require no preparation yet still achieve the required cross-sectional framework thickness (Figure 5). The required minimal critical dimensions for the connectors are dependent on the type of core ceramic material being used,15 although these materials are an area where much development is ongoing. Based on the limited studies available, the success of all-ceramic RBBs has been estimated at 72.5% at 3 years, compared to 82.8% for metal RBBs for the same period, but the latter is based on more research.14 Therefore, in view of the relative scarcity of published evidence at present, the authors are cautious in recommmending this as a routine mode of treatment compared to metal framework designs.
Resin-bonded bridges are a conservative and potentially non-invasive treatment modality used to replace missing teeth. This two-part series has outlined the fundamentals of successful RBB provision and shared the authors' experiences and tips for success (Figure 6). The clinical steps involved in RBB provision are relatively simple compared to conventional bridgework and implants. However, this does not preclude the need for careful case selection and design, which are critical factors in their success as for all restorations. The economics of RBB provision are favourable in comparison with implants, conventional bridges and metal-framed dentures due to lower laboratory costs and reduced chair time. The relatively low financial cost and reasonable longevity means that RBBs are good value for money, as well as being predictable and aesthetic if undertaken carefully and appropriately. The minimally invasive nature of RBBs means less tooth tissue being sacrificed, which is arguably the most significant benefit.
