End of the Road for Dental Amalgam?

Readers will be aware of the Minamata Agreement, signed in 2013, in which 147 countries around the world agreed to minimize mercury use in a wide variety of fields, such as, lighting, fertilizers, and, of course, dental amalgam. This resulted in a ban, from 1 July 2018, on the use of amalgam in pregnant women and children under the age of 15 years. Some dental schools had, by then, on the surface, stopped teaching the concepts of resistance and retention form, and, as a result, a proportion of new graduates had no notion of how to retain an amalgam restoration in a tooth!¹ This lack of preparedness is a particular concern in the UK as amalgam is still in widespread use among dental practitioners².

There is some clarity now, in the form of a European Union draft document to phase out all amalgam use by 1 January 2025. These recent EU proposals³ suggest:

The revised Mercury Regulation targets the last intentional remaining uses of mercury in a variety of products in the EU in line with commitments set out in the EU's Zero Pollution Ambition. It sets rules that put the EU firmly on the track to becoming the first mercury-free economy by:

• Introducing a total phase-out of the use of dental amalgam from 1 January 2025 in light of viable mercury-free alternatives, thereby reducing human exposure and environmental burden;
• Prohibiting the manufacture and export of dental amalgam from the EU from 1 January 2025.

If this EU directive is ratified, supply chains will be disrupted and the cost of amalgam will, in all likelihood, rise significantly. This situation will occur against a backdrop of a crisis in access to NHS dentistry, with patients presenting with advanced cavitation of molar teeth where amalgam may be the restoration of choice. This is particularly the case where isolation is particularly challenging, and rubber dam isolation for restoration placement becomes increasingly difficult. The situation may be compounded in Northern Ireland under the Windsor protocol where the EU directive may disproportionately affect colleagues where fees for posterior teeth are generally based on placement of amalgam restorations.

Let's look briefly at the implications of this from an educational point of view and discuss the alternatives.

Amalgam tends to be favoured in posterior teeth where isolation can be an issue, for example where margins are subgingival or the tooth is very heavily restored. While moisture control is still very important, amalgam is more forgiving and compatible with more traditional matrix systems with which most clinicians, across the years, are familiar. Amalgam restorations are not adhesive, so rely on resistance and retention form, with cavities cut to reflect this, often leading to more tooth removal than with preparations for adhesive restorations. Retention can be improved by cutting slots, ledges, grooves and, in the past, pins were used more frequently. All involve removal of tooth substance or creation of further stresses (in the case of pins), so adhesive techniques make sense from a conservation perspective.

With regard to an amalgam replacement, there is not presently a like-for-like material that does not require an intermediate bonding layer and which offers technique insensitivity, but the dental world is getting there. Resin composite is the most frequently used alternative, and, indeed, its use has become widespread in many countries. However, it requires optimal isolation, with rubber dam being the technique of choice, and a bonding stage that takes time and was technique sensitive prior to the introduction of the user-friendly universal bonding agents. In that regard, there is early, but promising, news on a self-adhesive composite that has been used in a clinical trial of posterior teeth.⁴ This might be the closest that we have to a true amalgam replacement, but, for the time being, it looks like we will be using more conventional resin composite materials that have demonstrably good rates of survival⁵ and which approximate those of dental amalgam.

Glass ionomer cements (GICs) are also materials that do not require an intermediate bonding stage, but, in the past, their physical properties have not been considered adequate for loadbearing restorations in posterior teeth. However, a review in the 50^th Anniversary issue of Dental Update⁶ discussed the most recent GIC variant, namely the glass hybrid materials, and cited recent publications in which these were performing satisfactorily in posterior teeth. A research abstract from a CED-IADR meeting in September 2023 has provided us with the most up-to-date information on the performance of EQUIA Forte (GC, Leuven, Belgium) by way of a multicentre 5-year clinical trial⁷ in which this was compared with a resin composite material in ‘moderate to large’ two-surface restorations. The results indicated an annual failure rate (AFR) of 3.6% for the GIC variant and an AFR for the resin composite restorations of 1.9%, with the authors concluding that ‘the success and survival rates of the glass-hybrid restorative system are shown to be satisfactory and comparable to the nano-hybrid resin composite for moderate to large two-surface restorations of molar teeth’. While research abstracts are not peer reviewed, they can provide the most recent information on a particular subject, and an apparent discrepancy between the AFR scores and the conclusion may be explained by the use of a new FDI scoring system⁸ in which repair of a restoration is not classified as a failure. It may therefore be considered that recent GIC materials hold promise, and, for a more complete appraisal of the subject, readers are directed to the 50^th Anniversary issue.

While the EU proposal has not yet been ratified, and some member states may resist this motion – which is where in EU politics, the horse-trading often starts, perhaps with ‘softeners’ being offered in the form of compensation for the fact that amalgam alternatives, such as resin composite, take longer to place and are therefore more expensive. However, even though the UK is no longer in the EU, the direction of travel is to stop use of dental amalgam completely. This leaves us to wonder where clinicians and patients will be left when this comes to pass and we reach the end of the road for dental amalgam.