In this blog, we cover the indications/contraindications, advantages and disadvantages, designs, impression taking and the bonding workflow of Resin Bonded Bridges!
This is a summary of the full webinar presented by Dr. Kushal Gadhia on Student ACE courses. If you are a student, you can sign up to watch the full webinar among loads of other webinars on topics such as occlusion, periodontics, dentures and much more by following this link:
Indications and Contraindications, Advantages and Disadvantages
We won’t bore you by reading what you can see on the screen now, so if you would like to have a look at the advantages and disadvantages or the indications and contra-indications for a resin bonded bridge, feel free to pause the video now. It’s also interesting to note that the survival rate for resin bonded bridges are 80% at 5 and 15 years but the most important factors were the operator’s experience and the bridge design being a cantilever.
Design + Occlusal considerations
Moving on to the design, there are mainly 3 types that you can use: A cantilever which is a pontic from 1 abutment tooth. A fixed-fixed bridge which as the name describes is attached to 2 abutment teeth and finally a hybrid which has a resin bonded wing, or a retainer, on one abutment tooth and a crown or conventional designed retainer which sits on the other abutment tooth.
Starting with a cantilever, these are good when you have 1 missing tooth and want to replace the gap. It also has a reduced risk of secondary caries as compared to a fixed fixed design. The reason for this is because if you just have 1 winged retainer and that de-bonds, then that’s that, the bridge will just come out. In terms of survival rates, cantilevers last about 10 years and fixed-fixed bridges last about 8 years. Also, when you have a fixed-fixed design, if one retainer de-bonds, the other wing will keep the bridge in place and food and plaque will build up and get trapped under your de-bonded wing and cause secondary caries.
However, a cantilever is not preferred post orthodontic treatment because cases have been seen where the teeth adjacent to the pontic have rotated which of course effects the aesthetics. Because of this, it might be better to either use a fixed-fixed design or to use a night time retainer more often than what the orthodontist has prescribed for you to wear it.
The second design we mentioned was the fixed-fixed and this is option of choice when you have a longer span and need to replace multiple teeth. For example if you had your premolars missing in the upper arch, you could place a wing on the 3 and an occlusal coverage retainer on the 6 with the 4 and the 5 as a pontic as shown on the screen now. Again they’re also good post-orthodontic treatment but they have a higher chance of secondary caries if you get a partial de-bonded retainer.
For the hybrid design, they can come with a male and female component which allows for some freedom in movement. It also benefits us in that if one retainer de-bonds, then you can just remove the male component, remake the new pontic with a new retainer and slot it back in to the crown without having to take the crown off.
A fourth design that we’ll quickly mention is called a spring cantilever and these are useful when the adjacent teeth to the gap that you want to replace are compromised.
One ideal feature that you should aim to incorporate into your bridge design is maximum coverage for a better bond strength and you can do this by extending your retainer just short of the incisal edge, mesially, distally and right down only just supragingivally to allow cleansable in the area.
Posteriorly, we should be doing a fixed-fixed design and we should be aiming for full occlusal coverage. The reason is because when you do partial occlusal coverage, the occlusal forces in lateral excursion can cause the retainer to sheer off.
Another ideal feature is to ask for the retainer to be a minimum of 0.7mm thick to prevent the warping of the retainer. The design should ensure that it is cleansable which means the patient should be able to feed some superfloss under the pontic. And In terms of the occlusion, we want to have a holding contact on the retainer which means they do contact in ICP but we want to avoid all protrusive or lateral excursive contacts.
Tips and Other considerations
You may come a across cases where an opposing tooth has over-erupted into the space of the missing tooth. This is why it is important to check the occlusion, how would we create space in this area? The options are to use the dahl approach, orthodontic intrusion, enamel-plasty or a combination of these together to create the space needed to restore the missing space.
You also want to look at the abutment teeth and check them both radiographically, with a peri-apical, and clinically with sensibility testing. You need to consider the patients lip line at rest and when they smile. And Is this treatment post-orthodontics?
And finally for the abutment selection, which tooth would you cantilever from? Let’s say you are replacing an upper lateral incisor, would you use the central incisor or the canine? The answer is, if both are not compromised in anyway, you would choose the one with more enamel surface area to bond to. Although this is less important, you should also consider the wrap around from mesial to distal of the tooth.
In this case, of course the canine would have more wrap around. But if the central incisor had a larger enamel surface area to bond to, you would use this. Make sure to be cautious of the metal retainer showing through the incisor. To prevent this make the incisal edge of the retainer just short of the incisal edge of the tooth so that we don’t compromise the aesthetics. We can also use an opaque cement like panavia to block out the colour of the metal wing.
Preparation vs no preparation
The evidence by king et al 2015 leans towards not preparing teeth at all and says that there is little benefit in doing so. Tooth preparation is irreversible and so should be avoided in the name of minimally invasive dentistry. It is justifiable if you need to make mesial and/or distal guide planes so that you have a path of insertion for the retainer. Some people prepare a margin but the enamel is thin and removing it may very easily expose dentine, reducing the bond strength massively.
It would be better to stick the retainer in high by adding 0.7mm of thickness than to remove tooth tissue. The surrounding teeth will very quickly adapt to this new occlusal height by dahling in. This is a case example of this happening. You can see in this photo that the canines are in contact and so adding the 0.7mm retainer will open up the bite. You can see this on the study cast here and then 6 months later when the occlusion was re-assessed, the posterior teeth dahled in and closed this posterior separation.
One example of when you should prepare a tooth is if it had an old restoration. Let’s say you wanted to replace a gap in the UL5 by using the UL4 and the UL6 as fixed-fixed abutment teeth. And lets say the UL6 had a class 2 mesio-occlusal restoration. You should replace that restoration with another composite ensuring there are no secondary caries and then create a mesial rest seat, like you would for a removable partial denture. This would increase the rigidity of the connection between the retainer and the pontic by increasing the thickness of the metal in that area. This will also allow more favourable bonding to the resin cement and enhance the retention of the bridge.
Something else to consider is the preparation of the pontic site with electrosurgery or a dry high speed bur when there is excess gingiva in the area. You can draw an imaginary line between the gingival margin of the central incisor and the canine and the gingival margin of this pontic should lie 1mm below this imaginary line. If this excess tissue isn’t removed, the pontic would look really small and you won’t have the most aesthetic result. The alternative is to do a ridge lap design but these would be really difficult too clean for the patient which is also not ideal.
When taking your impressions, ideally you should take both your working impression and the opposing impression in light and medium bodied silicone. rarely you will need to use a retraction cord palatally or lingually to expose the maximum area of enamel. And when you’re doing anterior work or multiple units posteriorly, then a you should be using a facebow.
You can also use an intra-oral scanner and the benefit of this is that you can send the image to the lab and keep your articulating markers present to demonstrate where the patient is occluding.
You want to send the lab a set of instructions in the prescription and they are as follows: Please construct a cantilevered RBB replacing the UR3 from the UR4 using Ni-Cr alloy. Full occlusal coverage with metal covering all occlusal, mesial and palatal surfaces. Minimum thickness of wing equal to 0.7mm. Bridge will be cemented high. Thick connectors with minimum height 3mm. Modified ridge lap pontic. Please sandblast fitting surface. Pontic to have a light shimstock hold on ICP, pontic to have no contact in lateral excursive mandibular movements. you also need to sent them the shade that you need the pontic to be.
When you come to try the bridge in, you can do this using non-egenol temp bond and you can check the fit of the retainer, the occlusion and the aesthetics. If any adjustments need to be made, now is the time to make them.
A: Once you’re happy with the try in, you want to bond it in and we need to consider 3 things. The RBB retainer, the tooth itself and the cement we’ll use.
So starting with the RBB retainer we want to sandblast the wing immediately before cementation with 50 microns of alumina to increase the surface area and micromechanical retention. Then you need to steam clean it to remove any alumina or metal deposits, or you could alternatively etch with phosphoric acid for 20 seconds and wash it off. Finally you need to apply a metal primer for bonding and make sure you don’t cure it yet.
On the tooth itself, we need a rubber dam with floss ligatures for moisture control. Then you use a polishing disc to clean any debris before sandblasting, etching and rinsing with water. Then you need to follow the bonding protocal of the cement you’d like to use.
As for the cement itself, you could use a dual cured resin cement like Panavia or Variolink, but there are loads to choose from.
Once bonded in, you want to check the occlusion, clear excess cement, teach the patient how to clean under the bridge and between the retainer and the pontics. Then you should review the patient and use an ultrasonic or bur to remove any more excess cement and make sure the dahl is working. If they had orthodontic treatment, you would provide new retainers once the their teeth have dahled in and ensure they have regular visits to ensure continued periodontal stability if needed.
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