Alternatives To Amalgam

The Minamata Convention on Mercury is a global treaty which was signed by the UK and over one hundred countries from all over the world in October 2013 with the intention of protecting human health and the environment from the adverse effects of mercury.

As a result of this treaty amalgam was banned in many industries, however dentistry wasn’t hit with an outright ban, but with a “phase down”. From July 2018, amalgam use was banned in the UK for children under the age of 15 years and for pregnant or nursing women. This leaves us with the need to find an amalgam “replacement”.

Nothing currently exists which possesses the same properties of amalgam and it’s likely nothing ever will. It’s unlikely that we will ever use a metal alloy again to restore teeth directly, but to have a material that could be bulk placed; is quick and easy to use; has good physical properties and is cariostatic would be brilliant. As well as replicating the properties of amalgam, our wish list could also be extended to include the ability to be self-adhesive and aesthetic.

White filling materials started life in the sixties with dual cure paste / paste composite systems. This was well before the invention of light curing so these could often be placed in some degree of bulk and then allowed to cure by themselves. The physical properties and aesthetics of early materials were not great, but the last fifty years has seen much research into this area and the modern materials that exist today have overcome many of the issues which plagued the early restoratives.

Until recently shrinkage has probably been the number one issue that we have learnt to deal with over time. Shrinkage isn’t too much of an issue in an anterior cavity, but in the classic box shape preps often associated with Class I and II cavities, shrinkage can be a big issue. By adopting a herring bone type layering pattern and using small increments has shown us that the stresses caused by shrinkage can be minimised. This brings us onto the main issue here as it’s not really the shrinkage that causes the problems, it’s the physical stress that the shrinkage induces which is our enemy. Shrinkage stress can pull on our adhesive layer and, in some cases, remove it physically from the tooth. This can lead to microleakage, which in turn can lead to secondary decay and often sensitivity. Cuspal deflection is another stress related issue which can often lead to cracking of the enamel and sometimes even failure of the cusp itself.

Bulk fill flowable composites were probably the first materials to arrive that went some way to alleviate stress and by increasing the translucency, these materials can be cured to greater depths than the existing paste type composites. Having been around for around ten years now, bulk fill composites have really found a place in the dental market and are loved by many as a variable depth liner in difficult posterior cavities.

Being flowable in nature means that they don’t have the strength of your average paste type composite simply because they contain less filler. To ensure appropriate curing to deeper depths (typically around 4mm), these materials are usually made to be translucent. Translucency is good from a light curing point of view but isn’t always ideal when great aesthetics are required. Translucent materials may often look grey to the observer.

A simple solution to both these limitations is to cap the flowable restoration with at least 2mm of a normal (non-flowable) composite thus giving it a strong capping layer and appropriate aesthetics. The capping layer means that in theory you are still building the restoration in two layers and to have a material where we could just bulk place in one lump would be less technique sensitive and more desirable.

The arrival of 3M™ Filtek™ One Bulk Fill in 2017 has given then market the most versatile bulk fill composite yet. Several major innovations have allowed this material to be used simply and quickly in cavities where historically we would have reached for amalgam.

• An appropriate amount of translucency allows Filtek One to be cured to 4mm in a Class I and 5mm in a Class II. During the curing process the resin has been designed to change its refractive index giving a result which is as opaque as a traditional composite restoration. This clever switch from translucent to opaque provides a material that can be used both in the anterior and posterior.
• Filtek One is the only bulk fill composite to contain 100% nano-filler. The nanoclusters provide the strength for a posterior composite, but also the appropriate wear. Wear data has shown that the nano-filler technology has similar wear to that of enamel over a five-year period.
• Filtek One utilises a new resin molecule called an addition fragmentation monomer. This clever innovation essentially measures the stress build up in the composite as the resin cures. If the stress levels become too high these fragmentation monomers physically break apart to relieve the stress and then reform in a lower stress orientation.
• Filtek One is not only BPA free, but it is BPA derivative free too.

With great aesthetics, great long-term wear, and stress relieving chemistry, Filtek One Bulk Fill is possibly the closest alternative to amalgam that currently exists. Used in combination with 3M™ Scotchbond™ Universal Plus Adhesive (the first radiopaque universal adhesive), you have an adhesive which is proven to bond and seal caries affected dentine.

Whilst bulk fill resin composites provide us with most of the desired properties for an amalgam replacement, there are some situations where a resin composite would not be suitable. In these circumstances, a glass ionomer restorative may be the next best alternative. Glass ionomer restoratives offer self-adhesive one step placement and aesthetics superior to amalgam, however wear resistance and longevity of the restoration are not comparable.

3M™ Ketac™ Universal Glass Ionomer is a strong, radiopaque glass ionomer restorative which comes with two major advantages; It doesn’t need to be used with a conditioner, and it doesn’t need to be used with a protective glaze to finish. The removal of these two steps provides a glass ionomer which is less technique sensitive to use as well as saving time.
The last thing to touch on when considering posterior cavities is the getting adequate isolation and moisture control. Isolation can be a challenge and the obvious solutions of rubber dam, and an appropriate matrix system will be required but this is out of scope for this article as much has already been written on this topic.

Moisture and bleeding control can again be achieved in many ways, but clinicians have found that 3M™ Astringent Retraction Paste may help in these situations. Designed predominantly for gingival retraction prior to impression taking, Astringent Retraction Paste is also indicated for use during the preparation of Class II and V restorations. The paste can give good gingival control and haemostasias while making access and moisture control feasible. This was concluded in the published clinical article by Dr Dawett (Gingival Control, The Dentist, 98, March 2017).

As was discussed at the beginning of this article, we don’t currently have a material which is an exact alternative to amalgam, and we probably never will. The recent advancements in composite and glass ionomer technology have certainly taken us closer to finding an appropriate alternative and will see us take even larger strides towards the ultimate posterior restorative.