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Dentine Bonding with Optibond FL


This protocol and explanation is specifically for dentine bonding. It can also be applied to enamel bonding in the same way because the ‘prime’ stage does not weaken the bond to enamel at all. However, there are more significant considerations and challenges with dentine bonding, like a relatively high organic content, the presence of water and considerably less mineralisation than enamel. Dentine bonding is therefore mostly significant for adhesive restorations in the posterior teeth as they consist of mainly dentin. (I have heard that the hard tissue in a molar crown is 80% dentin, but haven’t been able to find any research to confirm this.)

To fully appreciate the problems inherent with dentine bonding we need to consider the composition of dentine. Dentine is 70% mineral by weight, but only 40-45% by volume. The rest of the composition is 20% organic by weight, which is 30% in volume, and 10% water which is 20-25% in volume. In other words more than 50% by volume of the dentine we are trying to bond to is not mineral, compared with 97% in enamel.

One of the main problems this creates is that our resins/composites are hydrophobic. Therefore, as the surface of the dentine is wet, it rejects the hydrophobic resin. To get around this a wetting agent, or a hydrophilic material is necessary. Back in the nineties the manufactures produced a 3 stage bonding system (4th generation) which comprised of etch, prime (hydrophilic), and bond (hydrophobic). The main example of this Optibond FL. Subsequent generations of bonding agents have tried to reduce the stages and simplify the entire process for dentists. To get the hydrophilic and hydrophobic compounds to mix together they had to use various additional chemicals such as HEMA.

This led to four problems:

Those systems that were self-etching did not remove the smear layer, but incorporated it into the hybrid layer. The result is a weaker bond than using an etchant which is effective at removing the smear layer and creating the dentine/collagen tags of the hybrid layer.
The hydrophilic content of the bond is permeable and absorbs water over time. This causes the bond to break down.
The resin has to be very thin to allow penetration into the dentine/collagen tags. Bearing in mind that oxygen can inhibit curing by up to 40 microns (the oxygen inhibition layer) this means that the hybrid layer is not cured properly before further further layers or restorations are added.
In addition this low viscosity of the bonding agent means that it cannot be filled, which results in reduced strength and increased polymerisation shrinkage.

The clinical implications are:

Weaker dentine bonds.
Inadequate bond/seal of the hybrid layer means bacterial leakage under the composite, air gaps and polymerisation shrinkage which all contribute to post-op sensitivity and early failure of the restoration.
Ongoing degradation of the bonding layer over time through water absorption. I am seeing this increasingly in Bite Wings when I look at composite fillings that were done as recently as 5 years ago.

Advantages of Optibond FL Over Standard One Bottle Systems

The systems requires proper etching which is the best way to prepare dentine for bonding.
The prime is hydrophilic so it acts as a wetting agent and penetrates into the dentine, and thus forms the hybrid layer. The prime is a monomer so it will interact chemically with the resin.
The bonding agent, or resin, is hydrophobic and so can bond with both the prime layer and the composite.
Together the prime and bond not only bond to the dentine, but they seal it as well. This is called ‘immediate dentine sealing’ which greatly improves bond strength when we come to doing indirect composite restorations.
The resin is 48% filled. This greatly reduces polymerisation shrinkage and increases the viscosity.
This increased viscosity means that firstly the resin layer will remain thick enough to avoid oxygen inhibition of the hybrid layer and also it spreads evenly like a flowable composite over the base and walls of the cavity.
The resin is radiopaque. This is very significant as it means you can check the bond on an x-ray and see any resin flashes. This is very important when we come to doing Deep Margin Elevation.

This all translates into a very predictable, stable and strong bond. Anecdotally, I seldom get problems with post-op sensitivity and have seen very, very few fillings nor indirect restorations (Belleglass) fail. Those that have failed are generally down to operator error or impossible situations when I was trying to be the hero!

Useful facts about Optibond FL:

The bond strength is around 50MPa, which is comparable to the DEJ, which is measures at 51.5MPa. (This is an important fact to remember in presenting ‘white fillings’ as an option to patients. But more on that later)

The bond degradation rate was measured in a study involving class V restorations with no mechanical retention over 13 years. Optibond FL proved to be superb with 94% retention rate.



Etch with 30% to 40% Phosphoric acid – if possible stage the etching with 20 seconds on the enamel and 10-15s on the dentine.
Rinse the tooth for at least 20s. Dry, but do not over-dry! Do not desiccate the dentine.
Apply Primer (bottle number one) with a microbrush. Do not leave the lid off the bottle – very volatile. Dab and scrub the wet microbrush over the dentine for 15s; air dry to remove the solvent GENTLY! Do not rub the enamel as it will reduce the enamel tags for bonding.
Surface of dentine should be shiny and not wet.
Apply bond/resin – bottle number 2. Lightly rub the resin around the dentine and over the enamel. Do not allow pooling and remove excess around occlusal enamel margin. Shouldn’t need to air-blow to disperse. Do not over-thin the resin layer.
Cure for 20s.


Over-etching of dentine leads to the removal of too much mineral weakening the bond strength.
Etching dentine is no longer considered to be harmful to the tooth/pulp. There is absolutely no need for an insulation layer, especially not CaOH and neither GI. The majority of post-op complications are better explained by poor/failed bonding.
Don’t be impatient with rinsing the cavity. You have just created a porous surface and even when it looks clean there can still be etchant in the dentinal tubules. ALWAYS check in your mirror if you have not got direct line of sight to the entire cavity to make sure all etchant is washed away, especially in undercuts, proximal boxes and around the matrix band if using one.
Do not over-dry. The prime is hydrophilic and if you desiccate the dentine the collagen of the tubules lies flat and you don’t get the penetration of the monomer into the tubuli and demineralised spaces.
The monomer of the primer is dissolved into ethanol. You ‘pump’ it or ‘scrub’ it to encourage penetration into the dentine. But you do not want ethanol in your bond space, so LIGHTLY blow it to get rid of the ethanol, but without drying out the prime layer. Alternatively you can get your nurse to use the high volume suction to get rid of the solvent.
The bond is very viscous, a bit like flowable composite, so it is very easy for the nurse to put too much on the brush. Dab any excess off on your paper tray liner.
NB: the resin contains 48% fillers which can settle in the bottle. DO NOT SHAKE as this introduces air bubbles, but teach the nurse to stir it by rotating the bottle in both directions.
Don’t worry too much if you get a little extra thickness in the corners where the matrix band and tooth meet. The bond has a high filler content and will not degrade at the margins of the proximal and vertical surfaces. But it does not have the same resistance to wear as the composite so do not allow a thick layer at the occlusal enamel margins. If it is too thick then remove with a clean micro-brush.
Remember you are curing not just the outer layer of the resin, but the dentine hybrid layer as well. Make sure that when curing there are no shadows especially in deep proximal boxes.

One last tip: use a different coloured microbrush for the prime and the bond, like blue for bond or pink/purple for prime. That way you can use the bond brush to squash/press your composite down into the nooks and crannies between increments, as well as smooth the outer margins over. As the bond has a high filler content, this does not weaken the filing.

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