The end of amalgam fillings
Metal amalgam fillings containing mercury have in use in the developed world for over 125 yrs. For previous generations it was the predominant material used to restore cavities in decayed teeth due to its strength, durability, easy of use and cost effectiveness. However, more recently there has been a progressive move away from its continuing use.
A significant step towards the declining use of amalgam came in October 2013 at the Minamata Convention on mercury in which a global treaty was agreed to and signed by the UK and over one hundred other countries. The intention of this agreement was to protect human health and the environment from the adverse effects of mercury by limiting the use of mercury from all sources, including LED light bulbs, fluorescent tubes, vaccines, fertilizers, thermometers and, of course, dental amalgam.
Following on from this, the current UK regulations now state that as of July 2018 dental amalgam should not be used for dental treatment of deciduous teeth, of children under 15 years of age and of pregnant or breastfeeding women, except in exceptional circumstances specific to the patient.
This marks the first step in an absolute reduction in dentists placing amalgam and eventually is aiming towards a completely phasing out of this filling material altogether.
There are strict guidelines which outline the safe handling, collection and disposing of amalgam waste which commonly occurs when these old amalgam fillings need to be removed.
It is important to recognize that the use of dental amalgam is being phased out primarily because of environmental reasons. Research has shown that existing dental amalgam fillings are safe for patients. There is no evidence that amalgam fillings cause any health issues. Regardless, patients often request the replacement of their old silver fillings as part of cosmetically improving their smile to a more natural appearance.
Alternative metal and mercury free tooth coloured filling materials have been developed and used for many years including various resin composite and glass ionomer based filling materials. Glass ionomer fillings have good adhesive properties but their limited long term durability mean that they are best utilized for provisional fillings or for small fillings that are under minimal load.
Composite resin however has much more ideal strength and aesthetic properties, so has become the filling material of choice for both dentists and patients. There are other good reasons why composite resin is preferred by dentists. Previously when amalgam fillings were placed, due to a lack of any physical adhesion between amalgam and tooth tissue, the shape of cavities needed to be prepared such that the filling was mechanically retained by whatever remained of the tooth. This often meant the cavity preparation was more invasive and damaging to the teeth and the fillings tended to be larger than necessary. Since the introduction of composite resin and improved immediate dentine bonding systems, tooth coloured fillings are bonded in place instead, so less preparation of the teeth is needed and more of the natural tooth is retained. Compared to amalgam though, the placement of composite fillings require more time and are technically more demanding.
The use of a protective rubber shield (rubber dam) to isolate the teeth being treated should ideally be used to a create a moisture free environment to maximize bonding to the teeth whilst improving patient safety and minimizing patient exposure to amalgam waste products when removing the old fillings.
This more conservative approach of restoring teeth allows dentists to rebuild decayed and worn teeth and improve smiles without having to damage healthy tooth tissue unnecessarily. This may be particularly useful when we are trying to restore cases of pathologic tooth wear which most commonly occurs due to acidic erosion and/or parafunctional bruxing (grinding,clenching). In these instances, where there is already some loss of healthy tooth tissue, it is imperative we are able to find a solution without compromising the remaining natural tooth any further.
Brad Ngan BDS (Otago)