Sustainability and leaking restorations

Sustainability has, rightly, become a much-addressed subject in relation to clinical dentistry, let alone to the world in general. It is something that has interested me for some time – first addressing the topic in 1998, when it wasn't called sustainability, but a ‘green issue’! Therefore, 25 years ago, published on St Patrick's Day (hence the ‘green’ relevance!), I wrote about ‘green’ problems¹ related to amalgam and the handling of its waste, the very poor biodegradability of latex gloves and polyvinylsiloxane (PVS) impression materials, disposable single-use items used in the surgery, bags of dental surgery waste, the paper mountain, and chemicals used in developing radiographs. At that time, I wasn't able to propose any solutions other than changing from amalgam to resin composite, using early digital radiography, and early CAD-CAM as a potential solution for the PVS mountain, and I wrote that the latter techniques might become increasingly competitive in real cost, to match their reduced cost to the environment.

Move on to 2003,² as well as ‘green’ being a colour in the wavelength range 575–500 nanometres, I suggested that the tooth face was where green issues could be employed, in respect that resin composite could be placed in much less invasive cavities (especially regarding Class IIs) than amalgam, and that minimal-intervention resin-retained bridges held advantages over conventional bridges in terms of ‘greenness’. Regarding prevention, I suggested that the ultimate green cavity was none at all!

Move on to the present, and, principally by way of two research groups, one led by Prof Nicolas Martin in Sheffield, the other by Professor Brett Duane in Trinity College, Dublin, the idea of green dentistry has evolved into environmental sustainability. In that regard, McKeever recently stated that climate change is the greatest anthropogenic threat to human health recorded in history,³ with the impacts of climate change being confirmed by a Climate Change Panel as uncontrolled greenhouse gases.⁴ Groundbreaking research into sustainability and travel related to dentistry⁵ has underlined the fact that reducing patient and staff travel is an important factor to be considered. This might be the case, but I wonder if the latter is something of a non sequitur (for those who did not study Latin at school, it is posh for ‘illogical conclusion’!), given that dental treatment cannot be carried out unless the staff get to where their equipment, materials and dental team are, much the same as when going to a theatre, one needs to get to where the stage and actors are: in other words, many ‘things’ cannot happen without travel to something/somewhere.

In that regard, much of dentistry has to be face to face, or hand to mouth, therefore, including staff travel in the whole sustainability scenario seems to me to have lost the view that life has to go on, and that to keep actually doing anything carries with it an adverse carbon foot print. However, actions such as combining appointments for a family, scheduling an appointment with a hygienist at the same time as a check-up might be ways to reduce the environmental impact of dental appointments. On the other hand, it is shorter appointments, such as examinations, and many orthodontic treatments, that contribute the most, while lengthy appointments, for example for molar endodontics, contribute the least.⁶ In restorative dentistry, one visit direct-placement restorations must surely be more environmentally friendly than the multi-visit appointments needed for indirect restorations. But, perhaps we need to assume that, while commuting is contributory to dentistry-related carbon emissions and it might give an incomplete message not to mention it, this is a necessary evil of modern life. I therefore reflect that dental surgeries, or indeed any specialized activity, generally require a highly specialized unit, therefore staff sustainability costs should be disregarded, unless, of course, they are flying in by helicopter!

Many of the publications on the subject of sustainability address the need for prevention, but few appear to have considered that another way of reducing the environmental impact of dental restorations is to reduce unwarranted replacement of restorations that may be considered to have failed, given that reports have considered that 50%⁷ to 75%⁸ of all restorations are replacements of failed restorations. In the past, this may have been a subjective decision on the clinician's behalf: for example, is the restoration in the upper premolar in Figure 1 defective?

There is groundbreaking research by Professor Edwina Kidd (Emerita Editorial Board member) and colleagues that might help to provide the answer.⁹ In this work, which I feel has never received the publicity it deserves, patients who required replacement restorations were included in their study. A total of 330 sites on 175 teeth in 118 patients were measured for marginal gaps (<0.4 mm or >0.4 mm), with each restoration being removed using a turbine drill and sterile bur: a sample of dentine was removed from the enamel-dentine junction beneath the site, and this was processed microbiologically. Mutans streptococci colonies were counted on agar plates, with lactobacilli and yeasts also being identified. To cut a long story short, the narrow ditch (<0.4 mm) did not have significantly more bacteria than an intact margin. However, the wider ditch (>0.4 mm) presented a different story – there were significantly more micro-organisms present beneath the wider marginal gaps, with a greater proportion of these being lactobacilli, which readers will be aware are favoured by an acidic environment, in other words, conditions favouring the development of active caries.

The authors, Kidd et al,⁹ stated that they chose the marginal defect widths in their study because they equated to the tip of a BPE probe, whereas choosing a wider variety of defects would have been too complicated to apply in routine dentistry. According to this work, therefore, the restoration in Figure 1 should be replaced if the margin defect that is visible is greater than the width of a BPE probe tip, and if it is less, then monitoring or repair is indicated, because the authors stated that ‘it might be prudent to replace restorations where marginal gaps exceeded 0.4 mm’. They added that colour change adjacent to an amalgam restoration should not trigger its replacement.

However, colour change around resin composite restorations tells a different story.¹⁰ Another research study involved 197 discrete sites in 72 patients who had tooth-coloured restorations requiring replacement. Thirty sites (12 on enamel and 18 on dentine) were carious, and 167 sites were clinically non-carious. After giving local anaesthetic and applying rubber dam, margin sites were selected for microbiological sampling around the margin of the restorations. For example, if in a single restoration where part of the margin was stained and part not, both sites were sampled. The colour of the margin was noted and the tip of a local anaesthesia needle was used for the removal of plaque from the tooth-restoration interface, and the restoration was then removed using an air turbine and sterile bur. A sample of dentine was taken, and all the samples processed microbiologically. The results indicated significantly more bacteria in samples from carious than from non-carious sites: that may not be a surprise, but more bacteria were found in dentine beneath stained margins. As in the previously quoted research, plaque samples from ditched margins yielded more microorganisms as the width of the ditch increased, but only margins >0.4 mm yielded more micro-organisms in dentine.

What is the message from this work? Soft dentine beneath tooth-coloured restorations is heavily infected, but where the margin is not frankly carious, no clinical criteria (not even margin staining) will reliably predict the presence of this soft dentine. Therefore, in the absence of a patient concern about a discoloured margin around a tooth-coloured restoration, there is no indication from a caries viewpoint to replace a tooth-coloured restoration that has a stained margin.

It is my view that the lessons from these research studies provide useful information from the sustainability point of view in relation to unnecessary replacement of restorations whose margins may be considered defective.

While Dental Update generally tries to publish articles that are high on practical, useful information for clinicians, the year 2023 has seen two outstanding examples of excellent, sound, contemporary clinical advice in the shape of the special issues published this year, one being the 50^th Anniversary issue, the other being the Tooth Wear special issue published last month. Much thanks are due to all the contributors of these issues. However, from time to time, we receive an article that describes a treatment technique that not many of us will aspire to ever carry out, but which may, nonetheless, be considered to present a treatment modality that might benefit some of our patients. The article on zygomatic implants falls into that category.

Finally, as we approach the end of another year of Dental Update, I wish all readers, everywhere, Season's Greetings. I also thank you, the readers of Dental Update, for continuing to subscribe to our journal during these challenging financial times – I hope that you have enjoyed this year's issues, and also to have found the contents valuable. I also wish to thank the Editorial Board for their input and wisdom, our superb authors for sifting through the voluminous dental literature and telling us what it really means by way of the review articles that they write, our peer reviewers for their advice and, finally, the excellent team at Guildford, namely, Fiona Creagh and Lisa Dunbar, Rob Yates and Stuart Thompson, for producing each super issue. And, if readers who may indulge in some alcoholic refreshment over the festive time missed the warnings in the 2017 article ‘Advice for Festive drinkers’,¹¹ the reference to it is below, please spare a thought for the wine tasters who have to try the drinks before they get to market and the hazards that they face, as detailed in the article starting on page 923! Finally, may I wish all readers a happy and peaceful, and above all healthy, 2024.

PS: Editorial Board member, Damien Walmsley was recently highly commended in Landscape Photographer of the year for one picture with another commended. The picture of the tree stumps is from Washington state and was one of his photographs in the monovisions, international black and white competition. I am pleased, as part of our festive relaxation, to publish some of his work in this issue of Dental Update and on its cover.