Adhesive Dentistry: Strong (R)Evolution in the past years

For the past 50 years, the face of restorative dentistry has totally changed. Numerous innovations have come up and modified the way dentists take care of teeth.

The first big change was the launch of light-cured acrylate composites and their related adhesives. Back in the early days of adhesive dentistry, bonding was quite a challenge, and the outcome was relatively problematic and unpredictable.

Bonding to enamel, a strongly mineralized substrate, would require a prolonged exposure to highly acidic products, etchants, in order to modify its structure so that bonding would be effective and long lasting.

Bonding to dentin would be more complex. Due to its organic structural components (collagen) the etching step would raise even more challenges for an effective bonding. Not to mention the fact that dentin desiccation made bonding rank from fair to totally ineffective.

To be honest, these bonding procedures were challenging for practitioners. First, the procedure itself was very complex: many different products to use in a specific sequence (etchant, primer, mixing bonding A with bonding B), rinsing, light-curing and drying – but without dehydrating – steps in-between… Complexity, longer chair time, lots of bottles, bonding on dentin required a lot of motivation and determination!

On top of that, the bonding values could be completely uneven. In France, in the early 2000s, Prof. Degrange organized several “Battles of Adhesion” during which practitioners could perform bonding on extracted teeth and then measure the bonding values (1). The results were quite surprising: with the same adhesive brand, in a supervised procedure, the bonding values could vary from one dentist to another, and for the same dentist, from one tooth to another, showing that the effectiveness of the bonding was operator dependent as well.

This is when the second big change occurred: the launch of self-etch adhesives. To overcome the difficulties linked to the dentin etching, the acidic level of the primer was increased, making conventional phosphoric acid etching unnecessary for dentin. It was a more dentin-friendly approach. At first, the bonding values with self-etch products were not impressive. But manufacturers did their homework and developed more and more effective self-etch adhesives with reduced numbers of steps and bottles.

To bond to enamel, total-etch was the way to go and to bond to dentin, self-etch was the way to go. Optimal situation? Not quite. More simplicity and versatility were demanded from bonding agents.

The third big change happened a few years ago with Universal Adhesives appearing on the market. One bottle only, usable with or without prior etching, depending on which substrate to bond to; also featuring selective etching, whenever a cavity involves both enamel and dentin for bonding.

Calcium Silicates: A Different Substrate To Bond To

This sounds absolutely perfect if you stick to enamel and dentin. But what about bonding to other substrates? Since composite resin are not supposed to be placed directly on or close to the pulp, for biological reasons, Septodont launched in 2010 a calcium silicate-based cement – Biodentine™ to mimic sound dentin both mechanically and biologically, thereby introducing the concept of Biobulkfill.

Biodentine™ shows a wide range of benefits: it releases calcium ions and calcium hydroxide, which will elevate the pH to contribute to remineralization of the adjacent dentin, while at the same time limiting bacterial development as bacteria need an acidic environment to grow. Studies have shown that Biodentine™ triggers stem cell differentiation to odontoblast-like cell that create tertiary dentin; that it may feature anti-inflammatory properties explaining therefore the clinical observation of lower pain in patients.

Since it is a water-based cement, Biodentine™ doesn’t show any depth of cure limitation. It can fill a very deep cavity, e.g. a full pulpotomy in a molar, in only one single increment. It therefore allows to work faster, deeper while maintaining the pulp vital. Hence the Biobulkfill concept, which represent another innovative breakthrough in restorative dentistry: Biodentine is placed from the pulp to the top of the cavity, regardless how deep.

Yet, the question remains: how to bond to Biodentine™? It doesn’t have any organic parts; it is 100% mineral. So, should Biodentine™ be considered as enamel and be total-etched? Or in the contrary, should it be considered as dentin – which is Biodentine™ claim – and be self-etched? How to make sure the bonding will be effective? Should we look at the bonding strength values only? Since Biodentine™ features a high pH, will it interfere with the acidic pH of adhesives?
Well, many questions that can cause hours of hellish perplexity if not sleepless nights!

As a matter of fact, bonding a resin composite to Biodentine™ is quite simple as long as its basic chemistry is made clear.

The calcium silicate-based cements have an evolution cycle in their hardening of about one month. After one month, they will reach their final hardness and can be considered as a 100% mineral material, just like enamel – but with a different hardness and wear resistance. Right after placement in the tooth, they are still in their hardening process and care should be taken that nothing interferes with it or inhibits it; they therefore should be considered as dentin and receive less acidic treatments.

When used as a replacement for damaged dentin in a restorative cavity, Biodentine™ offers the possibility to receive the final composite restoration in the same session or in a subsequent session – if, for example, the pulp needs a few weeks monitoring.

So, if the final composite is bonded in the same session, a self-etch adhesive will be preferred, since it is less acidic than a total-etch adhesive, and therefore will not interfere with the proper setting of Biodentine™. Studies have shown that when doing so, the bonding strength is similar to bonding to a glass-ionomer cement.

If the final composite is bonded to Biodentine™ in a subsequent session, between 2 weeks and 6 months, then either a self-etch or a total-etch procedure can be carried out.

In fact, a staircase to heaven

From a clinical standpoint, in deep cavities the need for Biodentine™ is obvious: the closer to the pulp, the higher it needs protection. But Biodentine™ is not a passive protection as other dental materials. It is highly biocompatible with the pulp to maintain its natural defenses, i.e. tertiary dentin & dentin bridges (2), against bacterial attacks.

In such big cavities, carious tissue will be removed but sound enamel and dentin will, of course, be left in place. So, the cavity in which the composite needs to be bonded to is a mix of Biodentine™, dentin and enamel. The use of a universal adhesive with selective etching is in this case advisable!

Whether the practitioner decides to place the final composite in the same session or in a subsequent session, the selective etching adhesive allows to use etchant only where required: The enamel. This will optimize the bonding strength to all substrates, which nature is different.

Bonding a composite in a deep cavity where Biodentine™, dentin and enamel are present, will clearly become easy, comfortable, and effective: patients will be pain-free, even happier than before, about their beautiful restorations and restored smiles!