Why do so many class II restorations have post-op sensitivity?
A lot of dentists and dental therapists tell me they get patients returning with post-treatment sensitivity following a class II restoration.
I remember the same thing before I changed how I restore teeth.
The good news is that every cause (except where a pulp is already necrotic or irreversibly inflamed) is something we can control. These days, post-op symptoms from restorations don’t exist at The Gentle Touch and we guarentee them for ten years. We do expect them to last for decades, but this is more difficult to guarentee in a large practice.
Causes are likely to be due to the following:
1. A gap at the bond
This is the big one. If the compsoite shrinkage stress is stronger than an immature dentine bond, the bond fails and a gaps form. Dentine tubules are exposed, fluid moves, and the patient feels it.
Hayashi et al. (2017) actually imaged gaps forming in real time, during and after curing. And as I covered in the last blog, the deep box is the worst place for this: high C-factor, cusps can’t compensate, and this area happens to be the weakest bonding substrate in the tooth.
2. Micro-fractures
If the bond holds, the shrinkage stress goes into the tooth instead. Enamel is strong but brittle, and Belli et al. (2001) found shrinkage stress can cause cracks within the enamel itself.
3. The adhesive
Universal adhesives have a part to play, and as I mentioned in my last newsletter, they can still work. They’re just less forgiving on your worst day. They contain less resin and more solvent; the film is very thin (maximum 10 microns), oxygen inhibition affects the cure, and they absorb water over time. If you use one, if possible air-abrade first and use two coats to thicken the film.
We use Kuraray Clearfil SE Protect, a two-step self-etch. It gives a film of around 20 microns; the MDP forms a stable chemical bond with hydroxyapatite (it needs about five minutes to do this), and MDPB adds an antibacterial benefit.
4. Bulk-fill, or composite placed too thick or too quickly
This is one of the most common causes I hear about.
If the increment is >2 mm, it behaves like a bulk-fill. Extra stress builds at the centre and pulls away from the bonded surfaces.
Going too quickly does the same kind of damage. Join the walls before the dentine bond has matured, or cure everything at full power straight away, and you load the bond too early.
Our first layer over deep dentine is horizontal, around 1 mm, and connected to the floor only. That turns a high c-factor area into a low one for that increment (it’s cunning and it works!). We use a slow-start cure, and we give the dentine bond at least five minutes before connecting the walls.
5. No lining required
Instead, paint a coat of flowable composite, approx. 0.5 mm thick, all over the sealed dentine. It’s thick enough to form an effective buffer, and thin enough to polymerise towards the adjacent dentine. We use Majesty Flow.
6. Fiber stress mitigation
For anything deeper than 3 mm, we use Ribbond. El-Mowafy et al. (2007) found significantly less gingival microleakage in class II composites with fibre inserts. Ribbond also acts as a buffer, and also a fail-safe if something further up the restoration is under stress.
7. Cracks and caries left at the margin
The peripheral seal zone (the outer 2 to 3 mm of enamel, DEJ and superficial dentine) has to be completely clear of caries and cracks (Alleman and Magne, 2012). Caries left there means an automatic poor bond. A crack left there keeps flexing, and the patient is likely to feel something.
8. The pulp was already irritated
Sometimes the sensitivity has nothing to do with the restoration. If a tooth was symptomatic beforehand, or vitality is questionable, it may continue to be symptomatic afterwards. No matter how good your bond is, a pulp compromised by bacteria can’t be reverse engineered. Vitality test before you start, and if you’re concerned inform the patient beforehand.
So what?
The dentine bond is the most important part of the restoration. As David Alleman would say: “get bonded, stay bonded!”
Any questions, get in touch!
Thanks, Amber.
