At first glance, there is no obvious connection between a modest fishing village on the west coast of Japan and a series of international dentistry symposia held Dalhousie’s Faculty of Dentistry. But, in fact, events that took place over 60 years ago in that Japanese village are having a dramatic impact on modern dentistry all over the world.
In the 1950s, residents of Minamata, Japan, began to see cats “dancing” in the streets. Humans, as well, started to exhibit strange symptoms. The cause was mercury poisoning. Industrial waste from a manufacturing plant was flowing into Minamata Bay, and mercury had made its way into the food chain via the fish and shellfish that were a major food source for local residents.
Although the effects of significant exposure to mercury have been well known ever since, there are still some products that use mercury: compact fluorescent lamps, switches and relays, soaps and cosmetics, thermometers and blood pressure devices, for example.
Replacing mercury fillings
In 2013, representatives from over 100 countries signed the Minamata Convention on Mercury. This United Nations treaty, designed to protect human health and the environment from mercury releases and emissions, banned new mercury mines and called for the phasing out of many products containing mercury by 2020. The convention will enter into force 90 days after it has been ratified by at least 50 countries; so far, 15 countries have ratified the convention, and the number of signatories is up to 128 countries including Canada, the US, and the European Union.
Mercury has been an ingredient in amalgam tooth fillings for over 150 years, and it will now need to be phased down in the ratifying countries. An alternative, composite resins (tooth-coloured fillings), have been used in dentistry for several years, but some studies have shown that these resin fillings need to be replaced more often, particularly the larger fillings in molar teeth. That means more fillings — and more cost — for the patient, the insurance companies and, in some cases, the government.
If composite resins are to fill the gap left by the phasing out of amalgam fillings, it will be important to improve their durability. This durability depends to a large extent on the skill of the dentist. Conventional resin fillings are applied in 2 mm layers and “cured” at each stage with blue light. If the final cure is inadequate, the filling will not last as long.
Leading a global conversation
Dr. Richard Price, a professor of prosthodontics in Dal's Faculty of Dentistry, has organized three international conferences at the university, bringing world experts together to discuss curing dental resins, light research, best practices and education. A fourth conference that will focus on bulk filling and bulk curing of resin fillings will take place at Dal November 4-5, 2016.
The first conference, held in October 2012, gathered together academics from Canada, Germany, the UK and the U.S. They looked at the problems associated with light curing in the mouth and started to develop guidelines on technique. The outcomes from the first conference were published in a number of peer-reviewed articles and short videos on YouTube.
At the second conference in 2014, delegates from industry, as well as academics, assembled to develop the guidelines further and reach a consensus that was published in four leading dental journals.
The third conference, in June 2015, focused on developing additional guidelines on how to choose and use a curing light. A consensus statement from this conference will be published in Brazil and Canada this July.
“The objectives for the conferences were to ensure that, when complying with the Minamata treaty, the dental profession will be well equipped with the tools, knowledge, and skills it needs to deliver high quality and durable light-cured restorations,” says Dr. Price. “These conferences enable us to share information and best practices, and give members of the profession videos and publications that can help them provide the best treatment for their patients.”
The conferences have not only resulted in numerous papers, articles and videos [PDF], but have also served to inspire the development of a new curing light. After hearing Dr. Price present his research on the importance of light homogeneity on the quality of the cured resin filling, 3M scientists recognised an opportunity and designed a new curing light, the Elipar DeepCure-S. “This could really have a significant positive impact on improving clinical outcomes of light curable dental materials,” says 3M scientist Dr. Joe Oxman.
For more information on the conference taking place in November, please contact Dr. Richard Price at firstname.lastname@example.org.
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