Electronic cigarettes have seen a rapid rise in usage since their introduction. A vigorous debate is currently underway in healthcare and regulatory circles with regards to how they should be received. Worldwide regulatory bodies have taken a wide range of stances and there is conflicting advice from several authorities. This paper aims to focus on the oral health aspects of the debate and attempts to answer some of the key questions that face dentists.
What is an electronic cigarette?
Electronic cigarettes (e-cigarettes) are electronic devices that produce an aerosol (often incorrectly referred to as a ‘vapour’) that is inhaled by the user. The e-cigarette contains a solution that comprises three main components: diluents, flavourings and nicotine. The solution is drawn through an atomiser, which heats the liquid to 200°C to produce the aerosol that is inhaled by the user. The process of drawing on the device and the production of the aerosol closely resemble cigarette smoking, making e-cigarettes particularly attractive alternatives to smokers (Fig. 1). Electronic smoking devices are not a new phenonomen, with a patent being recorded in 1965 in the USA.1 The modern rise of e-cigarettes is attributed to Hon Lik, a Chinese inventor, who filed a US patent in 2005 for an ‘electronic atomization cigarette that contains nicotine without tar’2. This was apparently invented after his father, who was a heavy smoker, died of lung cancer.
FIGURE 1. An e-cigarette user ‘vaping’.
What’s in e-cigarettes?
The e-cigarette liquid, sometimes known as e-liquid or e-juice, takes many forms. It can come in pre-loaded cartridges, users can top up their device using bottles of e-liquid or users can mix their own solutions at home using DIY kits. The majority (around 90 percent) of the solution is made up of a carrier or diluent, which is usually propylene glycol or vegetable glycerine and it is this which accounts for the majority of the ‘vapour’ production. Nicotine is available in varying doses from 0 to 36mg/ml. Since both the diluent and nicotine are largely tasteless, flavourings are often added. The range of flavours is quite extraordinary. Common flavours include tobacco, menthol and fruits but can be particularly obscure, e.g. tiramisu and pina colada.
Are there different types of e-cigarettes?
E-cigarettes are now commonly categorised into three generations. First generation e-cigarettes (‘cig-a-likes’ or ‘minis’) typically resemble traditional tobacco cigarettes (Fig. 2). They are often classed as a starter devices due to their low cost. They are usually disposable and claim to deliver between 200-300 puffs, being equilvant to one pack of 20 cigarettes. Nicotine delivery in these first generation devices is often poor and the battery life is limited.
FIGURE 2. A first (left) and second (right) generation e-cigarette with USB charger.
Second generation e-cigarettes (‘tanks’) do not resemble cigarettes and often look like pens. They usually contain a tank that is re-fillable by the user. They have larger batteries and are re-chargeable (Fig. 2).
Third generation e-cigarettes (‘mods’) have more advanced features such as variable voltage systems and digital readouts, allowing ‘vapers’ to customise their experience (Fig. 3).
FIGURE 3. A third generation e-cigarette.
First generation e-cigarettes retail for as little as a couple of dollars, while second and third generation devices require a larger ‘capital investment’, with starter kits retailing at $60 to $70 and $150 to $200 retrospectively (prices correct as of April 2015). A recent study calculated there to be over 466 different brands of e-cigarettes available with 7764 unique flavours.3
How popular are they?
The picture is varied from country to country. Data from Wave 8 of the International Tobacco Control Four-Country Survey4 showed use of e-cigarettes to be 15 percent in the US, 10 percent in the UK, 4 percent in Canada and 2 percent in Australia. This data was collected in 2010/2011 and is now likely to be significantly out of date. The Smoking Toolkit Study (STS) in England is a monthly survey of over 1800 participants, and provides quarterly updates on smoking habits of the population.5 The survey has been running since 2008 with questions on e-cigarettes being asked since 2011. The survey has followed the rise in e-cigarette usage among smokers and recent ex-smokers, with rates doubling year-on-year between 2011 and 2014. Data for the last quarter of 2014 shows ‘ever use’ to be 19 percent and ‘daily use’ at 11 percent. Additional positive changes in smoking habits have been observed over a similar time, with cigarette prevalence smoking rates falling and rates of those trying and being successful in quitting being at its highest level for at least seven years.
Who is using e-cigarettes?
E-cigarettes are primarily being used by smokers or ex-smoker and data from the Office of National Statistics (UK) from 2014 shows e-cigarette usage at 11.8 percent for current smokers, 4.8 percent for ex-smokers and 0.14 percent for ‘never smokers’.6 Data from the STS concurs that use among ‘never smokers’ is negligible.5
Concerns have rightly been raised about the potential for e-cigarettes to act as a gateway to burnt tobacco smoking, particularly among the young. Some studies have shown that significant numbers of young people are trying e-cigarettes7 (one in five in Britain) but progressing from ‘ever trying’ an e-cigarette to ‘regular use’ amongst non-smoking children is very rare or entirely absent.8,9 Further research is needed in this area.
How are they regulated? (Internationally)
The regulation of e-cigarettes varies hugely across the world and is
changing on a regular basis. Table 1 details the current picture.
What’s happening in Canada?
In March 2009, Health Canada advised Canadians not to purchase or use electronic smoking products, as they may pose health risks and have not been fully evaluated for safety, quality and efficacy.10
Canada currently has a two-tier system of regulation, i.e. a system that separates nicotine and non-nicotine products. The hardware and non-nicotine containing refills are permitted, whereas nicotine containing refills require a medical licence.
This system has caused some confusion and debate as to whether e-cigarettes are illegal in Canada. Health Canada considers e-cigarettes to fall within the scope of the Food and Drugs Act, thereby necessitating market authorization before they can be imported, advertised or sold.11
The counterargument to this is that e-cigarettes are not a drug or medicine.12 It is claimed they are a recreational consumer product and as , do not fall under the Food and Drugs Act. Nicotine replacement therapies approved by Health Canada, such as patches and gums, make therapeutic claims and are therefore covered under the Act. E-cigarettes, however, make no such therapeutic claims and it is argued that they cannot lawfully be required to seek approval as a medicine.
In order to demystify e-cigarette use, the Canadian House of Commons Standing Committee on Health produced a report in March 2015, which set out a number of recommendations.13 The first being that they are to support research on the health effects of e-cigarettes and the impact on uptake on nicotine products. The government plans to consult with the public, provinces/territories and stakeholders regarding the regulation of e-cigarettes, with a view to protecting the health of the Canadian public.
The government is intending to work with all affected stakeholders to establish a new legislative framework for regulating e-cigarettes and related devices. Within their recommendations, they have outlined that this framework should:
Address both e-cigarettes that do and do not contain nicotine.
Require that e-cigarettes be visually distinct from tobacco products.
Establish a maximum level of nicotine.
Establish safety standards of all of the components and also require manufacturers and importers to disclose information regarding ingredients.
Require that e-cigarette components be sold in child-resistant packaging that clearly and accurately indicates nicotine concentration and appropriate safety warnings.
Prohibit manufacturers from making unproven health claims.
Prohibit sale to persons under 18 years of age.
Prohibit use in federally regulated public spaces.
Restrict advertising and promotional activities for these products.
Prohibit cross-branding practices, which can involve tobacco industry logos being used on e-cigarettes.
Prohibit use of flavourings in e-liquids that are specifically designed to appeal to youth.
Are they useful for smoking cessation?
Although further large scale randomised controlled trials are needed, there is now a growing body of evidence to show e-cigarettes are an effective smoking cessation aid. A Cochrane Collaboration Systematic review published in December 2014 concluded that14:
Nicotine containing e-cigarettes increased the chances of quitting long term compared to e-cigarettes without nicotine.
Using an e-cigarette with nicotine helped more smokers reduce the amount they smoked by at least half, compared to using an e-cigarette without nicotine or a nicotine patch.
There was no evidence that short-term e-cigarette usage is associated with health risk.
The concept of ‘harm reduction’ is worthy of specific consideration. E-cigarettes may prove to be a particularly effective harm reduction tool in those ‘unwilling to quit’. A small observational study provided 40 smokers who were ‘unwilling to quit’ with an e-cigarette – 22.5 percent quit, 12.5 percent were heavy reducers (reducing from an average of 30/day to three/day) and 32.5 percent were reducers (reducing from an average of 25/day decreasing to six/day).15 Further full scale trials are needed to confirm these encouraging results.
What are the potential oral health side effects?
The potential oral health effects of e-cigarettes has received very little attention, which is surprising considering the intimate relationship of tobacco smoke with several pathogenic processes in the oral cavity and also, the fact that e-cigarette aerosols will contact the oral tissues first when they are at their hottest and most concentrated.
We conducted a systematic review of the literature in 2014 to establish if there was any evidence for oral health effects from e-cigarette usage.16 This identified a handful of relevant studies. There were multiple user questionnaires/surveys that repeatedly detailed ‘mouth and throat dryness and irritation’ as one of the most common reported side effects of e-cigarette use.15,17,18 An in vitro study on periodontal ligament fibroblasts demonstrated decreased fibroblast proliferation rates with menthol additives.19 A five-year multicentre prospective observational cohort study is currently underway in France and one of the outcome measures is hospital admission for cancer of the oral cavity.20 A pilot study investigating oral mucosa perfusion in intraoral free flaps was referred to in a publication but the results are currently unpublished.21
The smoking cessation and harm reduction ability of e-cigarettes has significant potential to reduce tobacco smoke related oral diseases, such as oral cancer and periodontal diseases. Achieving smoking cessation is notoriously hard and within the dental setting, one-year cessation rates are around 15 percent when using intensive interventions.22,23 E-cigarettes provide an exciting opportunity to improve on these rates but may also be particularly effective as a ‘harm reduction’ tool in the 85 percent of patients who failed to quit.
The potential negative effects of e-cigarette aerosol on the oral tissues need to be considered and balanced with the benefits of reducing overall burnt tobacco smoke exposure. Much of the research to date examines tobacco smoke as a whole and confusingly uses the terms ‘nicotine’ and ‘smoking tobacco’ interchangeably. Specific research into the effects of the e-cigarette aerosol need to be completed and indeed, the National Institute of Dental and Craniofacial Research (NIDCR) in the USA announced this as a research theme for 2016: ‘Effects of E-cigarettes Aerosol Mixtures on Oral and Periodontal Epithelia’.24
The topical effects of nicotine are worthy of specific consideration. Interestingly, the nicotine in the aerosol is primarily absorbed in the buccal and pharyngeal mucosa, rather than the alveoli, demonstrating the potential to have effects on the oral tissues.25,26 Nicotine has been shown to have angiogenic and wound healing properties27 potentially suggestive of useful therapeutic indications within the oral cavity, including the management of osteonecrosis and post-surgery healing, especially when using free-flaps. Concerns have been raised regarding its ability to promote tumour growth (in lung cancers) through several suggested mechanisms (cell proliferation, angiogenesis, migration and invasion).28,29 The research to date is largely in vitro and clinical studies have failed to show an appreciable effect of nicotine (i.e., in patients using nicotine replacement therapies).30,31
Is the ‘vapour’ safe?
Burnt tobacco smoke contains an estimated 10,000 to 100,000 chemicals, including 70 known carcinogens.23 E-cigarette aerosol has been studied in detail and a review of the research on the topic by Cahn and Siegel24 concluded that we already have a much better knowledge of e-cigarette aerosols than we ever have of cigarette smoke.
Toxins have been found in e-cigarettes in several studies including diethylene glycol (used in anti-freeze), lead, nickel and chromium. These are found in much lower levels than in burnt tobacco smoke. A study by Goniewicz et al32 investigated 12 brands of e-cigarettes, finding levels of toxicants to be nine to 450 times lower than in burnt tobacco.
It is beyond the remit of this paper to discuss each constituent in detail, however, we will touch upon a few areas of recent media attention. A letter in the New England Journal of Medicine reported discovering hidden formaldehyde in e-cigarette aerosols.33 The authors reported discovering formaldehyde in the aerosol from their experiment, and went on to calculate the human cancer risk, concluding it was five to 15 times higher than long-term smoking. Many commentators have criticized this research as being highly unrealistic with the devices running at extreme temperatures producing so called ‘dry puff’ conditions that no user would ever be able to palate. Without overheating, no formaldehyde was detected. Furthermore, the cancer risk calculations have been described as ‘back of the envelope’ calculations, based on several unsupported assumptions and reported out of context.34 Professor Peter Hajek, director of the Tobacco Dependence Research Unit at University of London, commented: “When a chicken is burned, the resulting black crisp will contain carcinogens but that does not mean that chickens are carcinogenic. Without overheating the e-liquid, no formaldehyde was detected. Vaping may not be as safe as breathing clear mountain air, but it is much safer than smoking. It would be a shame if this study persuaded smokers who cannot or do not want to stop smoking and contemplate vaping that they might as well stick to their deadly cigarettes”.35
In 1976, Professor Michael Russell classically wrote: “People smoke for nicotine but they die from the tar” and this has become particularly pertinent with e-cigarettes.36 Estimates have calculated that for every million smokers who convert to an e-cigarette, 6000 lives a year could be saved.37
Another area of interest has been one particular flavouring ingredient, diacetyl, which is used in some butterscotch flavoured e-liquids. Diacetly is a chemical that is safe to eat, but perhaps not to inhale. It has been linked to a respiratory condition; bronchiolitis obliterans, or popcorn lung, owing to the increased incidence in workers at microwave popcorn factories caused by long-term exposure to high concentrations of diacetyl. Inflammatory obstruction of the bronchioles in this condition causes restriction of air flow, leading to wheezing and coughing. It is not known if the reduced levels of diacetly found in e-liquids would pose a similar risk to vapers, as to those with high level chronic exposures. Nevertheless, some manufacturers have withdrawn certain flavours to negate the possible risk.
A small number of case reports of exogenous lipoid pneumonia have also been publicised in recent years, potentially linked to e-cigarette use.38 This is a rare chronic inflammatory reaction caused by the presence of lipid substances in the lungs. The exogenous form develops from inhaling or aspirating lipids. Due to the limited number of case reports and insufficient research a causative link has not yet been proven.
Passive smoking is always a hot topic, and so concerns have also been raised regarding ‘passive vaping’. E-cigarettes do not produce ‘smoke’, so the well-documented effects of passive smoking are not applicable. Exposure of non-smokers to e-cigarette ‘vapour’ is said to create nicotine at levels about one tenth of that generated by a cigarette,39 and as nicotine itself does not cause serious adverse health effects and it is not carcinogenic, the risks of ‘passive vaping’ is therefore likely to be extremely low.40
Overall, the hazards associated with e-cigarette use are low compared to traditional cigarette smoking but despite this, they could be reduced further by implementing appropriate product standards and regulation.
What’s next for e-cigarettes?
The upcoming few years will be an interesting time for e-cigarettes. Daily usage rates (in England) have seen a plateau in growth and slight downturn during 2014.5 This could simply be due to the fact that ‘early adopters’ have now all converted and remaining smokers need more convincing. It is also possible that the percentage of smokers/recent ex-smokers using an e-cigarette is reducing because they are successfully quitting, and hence, moving from this group. Additionally, and most likely, e-cigarettes have suffered from some negative press during 2014, undermining consumer confidence in the products.
The technology of e-cigarettes has developed considerably since their introduction in 2008 and this will no doubt continue as investment is poured in from tobacco companies wanting a piece of the action.
The regulatory picture will continue to change as research and opinions develop over the coming years.
What should we tell our patients?
With so many controversies and a lack of long-term studies, it is not surprising that as health care professionals, we are naturally cautious and that no definitive guidelines exist. Indeed, even the term ‘cigarette’ is particularly unnerving and terms such as ENDS (Electronic Nicotine Delivery Systems) have been suggested. Many would advocate a defensive position, such as that taken by the European Association of Dental Public Health, who suggest ENDS users should be encouraged to switch to licensed products. For dentists operating in Canada, there would appear to be little other options, given the unclear legal situation around e-cigarettes.
For dentists operating in other jurisdictions, such as the UK where e-cigarettes are legal, freely available and soon due to be regulated under an EU directive, a more open approach can be considered and this is what is recommended by several authorities, including the National Centre for Smoking Cessation and Training (NCSCT).41 Current smokers should be encouraged to quit using a brief intervention strategy such as the 3A’s technique: Ask, Advise and Act.42 If they enquire about or are currently using an e-cigarette, the pros and cons need to be explained, and ultimately, they need to make the decision based on the best evidence available. E-cigarettes should ideally be used as a smoking cessation aid, with ultimate cessation of the e-cigarette.
It is worth bearing in mind that the comparator to e-cigarette ‘vapour’ is burnt tobacco smoke. We know from seminal studies that smokers of burnt tobacco smoke have essentially a 50 percent mortality rate (half of smokers die from smoking related diseases and half of those will die in middle age [35-69]).23,43
To summarize, e-cigarettes have many good features and a few potentially concerning features but as of yet, very few, if any, ugly ones. We should encourage a level headed, yet cautious approach to e-cigarettes, which could be a game changer in the fight against tobacco. We should push for further good quality long-term clinical trials, as well as much needed studies into the oral health interactions.
Conflicts of interests
The authors of this paper have no links and have never received any funding from e-cigarette or toba
cco manufacturers. They have a research interest in e-cigarettes and oral health and plan to conduct a clinical trial in the near future, funded through traditional (non-tobacco related) funding bodies.OH
Richard Holliday, BDS (Hons), MFDS RCSEd, MFDS RCSEng. National Institute for Health Research Academic Clinical Fellow/ Specialty Registrar in Restorative Dentistry. He can be reached at email@example.com.
Claire Stubbs, BDS, MFDS RCPSGlas. General Professional Trainee. Centre for Oral Health Research (COHR), Newcastle University, Newcastle Upon Tyne, United Kingdom.
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