Main findings

This feasibility study with embedded pilot RCT successfully recruited 80 smokers with periodontitis of whom 58 completed the study, yielding a 73% retention rate, just below the expected 75% rate. Recruitment source affected several aspects with participants from PIC sites having the lowest conversion rates (from being identified to attending and consenting) and retention rates. The vast majority of the participants who did not finish the study failed to attend a visit and were then uncontactable, usually dropping out after the initial periodontal therapy (which was completed at visit 3). Future trial designs should consider whether the number and duration of the study visits can be reduced, and the setting of the research study changed (e.g. more visits in primary care), in order to minimise participant attrition.

The e-cigarette intervention was well received, with 90% of those in the intervention group using it at the quit date and over half using it for the duration of the study. Findings from the process evaluation also suggested that the e-cigarette intervention was acceptable to participants. Several participants chose to diverge from the recommended brand of e-liquid, and an interesting observation is that these individuals made up almost all of the quitters in the intervention group, potentially suggesting that they were particularly determined to quit smoking and engaged more broadly with the process to the extent of exploring the use of other e-liquids. Flexibility and choice may well be important determinants of quit success rates and should be considered when planning future trials. Furthermore, one in five participants in the control group used an e-cigarette, against instructions, an important variable to consider when designing future research, indicating the necessity of a pragmatic research design.

Outcome measures were successfully completed in clinic, but the weekly smoking questionnaire had poor completion rates. The pilot RCT results suggest that the e-cigarette intervention may have the potential to improve smoking cessation outcomes with a greater mean eCO reduction over the 6 months (control group: 6 ppm; intervention group: 12 ppm) and increased rates of eCO-verified continuous 6-month abstinence (control group: 5%; intervention group: 15%), although this needs confirming in an appropriately powered definitive trial. There was almost no difference on average in the change from baseline to 6 months in oral health outcome measures between the groups although the 95% CIs were wide due to the small sample sizes and relatively large between-participant variation in these measures.

The periodontal treatment was successfully delivered to all participants, usually over two visits. However, in a small number of participants (n = 3), due to clinical need or patient anxiety, the treatment was delivered over three or four visits. For three participants, we were unable to collect oral health indices at the 3-month visit (visit 5) as there had been insufficient healing time following the completion of the initial treatment to justify recording the periodontal indices. A proposal for future research is to drop collection of research data at the 3-month time point (although a visit at around 3 months may still be needed for supportive periodontal therapy as part of usual care).

Relationship to previous research

Previous research [34, 35] in this field has rarely provided in-depth descriptions of participant recruitment, although 6-month attrition rates are comparable to those reported in this study.

The eligibility criteria (medical conditions) used in the current study, although more specifically defined than previous research [36,37,38], did not appear to adversely affect eligibility rates (based on the limited data we have from the NDH periodontal new patient clinic in which only one out of 391 patients was ineligible on medical grounds), and similar criteria could be used in future studies.

The minimum number of teeth required to be eligible for this study was reduced from 20 to 16 part way through the study (after 7 months’ recruitment). We found that, due to the severe nature of periodontitis in some smokers, many of the potential participants had suffered from tooth loss previously and had less than 20 teeth remaining. We reviewed the reason for using 20 teeth as a cut-off in previous studies and found this to be arbitrary. We decided to revise our lower limit to 16 teeth which represents half of the dentition of a normal adult, giving a fair representation of the disease profile and enough teeth for the periodontal measures to be useful and for samples to be collected.

The control group in the current study received SCA as part of usual care, achieving a 5% quit rate (RS6). This is similar to the rates discussed in a Cochrane systematic review of brief advice interventions delivered by physicians, which concluded that the brief advice intervention could increase 6-month quit rates to 5% from the 3% unassisted rate [39]. Another Cochrane systematic review focusing on smoking cessation within the dental setting concluded that quit rates could be increased to 7% [40]. It was interesting to note that both of the RS6 quitters in the control group in our study used a self-purchased e-cigarette (against instructions) as part of their quit attempt. The intervention group in the current study achieved a 15% quit rate (RS6) which is similar to previous research (7.3–12%) [37, 38] and comparable to the longer term quit rates seen in specialist stop smoking services [41, 42].

In our study, there was contamination of the control group, with 20% of participants in the control group using an e-cigarette at some point. Previous studies [37, 38] have not reported on this, which has likely become more of an issue with the widespread availability and popularity of e-cigarettes in recent years. Future research should utilise a highly pragmatic design, accepting a level of e-cigarette use by participants in the control group.

There were 56 AEs mainly associated with the sequelae of severe periodontitis, e.g. toothache, dentine hypersensitivity, tooth loss and abscesses. Direct comparison with previous research is difficult as AEs have rarely been reported. Five of the AEs reported in the intervention group could have been associated with e-cigarette use or smoking cessation (mouth ulceration and intra-oral soft tissue soreness). The Cochrane review on e-cigarettes [9] found that the most frequently reported adverse events were mouth and throat irritation.

Strengths and limitations

Strengths

To the best of our knowledge, this is the first RCT of e-cigarettes in the dental setting or focusing on oral health. This study was feasibility in scale, with 58 participants completing it. However, this compares favourably to the previously conducted prospective studies in this field, which reported completion numbers of 26 (12-month follow-up) [34] and 63 (6-month follow-up) [35]. The feasibility study and pilot RCT complied with reporting guidelines; the CONSORT checklist for pilot and feasibility studies [13] has been used, and the study complies with all the relevant checklist items. Similarly, the interventions provided in this study were reported in detail using the Template for Intervention Description and Replication (TiDieR) checklist, enhancing transparency and reproducibility [43]. Our findings will allow for a well-designed and efficient definitive study in order to answer a research question evaluating the effectiveness, cost-effectiveness and safety of an e-cigarette intervention for smoking cessation delivered alongside periodontal therapy and if this leads to improved periodontal outcomes.

Limitations

The contamination rate of the control group (using e-cigarettes, against instructions) was an important finding of the current study. On the one hand, this adds to the reasons why these pilot RCT results should be interpreted cautiously, but on the other, it is an important feasibility outcome that will shape the design of a future definitive study.

The current study was conducted in a single specialist DCRF within a secondary care environment (NDH), in which the chief investigator and principal investigator were based. This allowed for dedicated experienced research teams to conduct high-quality research, but applicability to primary care may be reduced compared to a study conducted in a primary care environment. Future studies should consider this in their design. Additionally, the SCA was delivered by a single clinician in this pilot RCT, unlike a future trial which would have multiple operators.

The control group in the current study appeared to have more severe periodontitis at baseline than the intervention group. Ideally, the groups should have balanced disease profiles, and hence, a future definitive study should stratify for periodontitis severity.

Blinding was not possible for the collection of the smoking outcome measures, mainly for practical reasons, e.g. staffing limitations. West et al. [18] discuss the concern that lack of blinding may lead to differential efforts being devoted to contacting subjects in different treatment groups, and they recommend that follow-up rates should be reported by group. We reported detailed follow-up rates by group and found that equal numbers of participants (29 in each group) completed the study. Those participants lost to follow-up appeared to have higher eCO and FTND readings and more severe periodontitis. It is noteworthy that similar studies have also not employed blinding [37, 44].

A common challenge with all e-cigarette research is the rapidly moving pace of the field, particularly with regard to product development and use. The product we used in our study, although still available for sale at the end of the trial, had largely been superseded. The rapid changes in popularity and usage of e-cigarettes also potentially make the applicability of the findings challenging. In order for the findings of the current study to remain of optimal relevance, it is important that a definitive study is instigated rapidly.

Implications for future research

Overall, this feasibility study with embedded pilot RCT demonstrated that the offer of an e-cigarette starter kit by a dentist to smokers with periodontitis was feasible and acceptable. Its evaluation within this context was possible, and there are several design implications for a future definitive study. These include expected recruitment and retention rates; conducting part of the research in primary care; eligibility criteria in relation to numbers of teeth; not including willingness to quit as an inclusion criterion; study design to be highly pragmatic (broad inclusion criteria, conducted in primary dental care and the e-cigarette intervention having a range of flavour choices, including tobacco and non-tobacco flavours); stratification based on periodontitis severity; not collecting research data at the 3-month time point; reducing the number of outcome measures collected; not using the weekly smoking questionnaire (or collecting such data less frequently); having co-primary outcomes (smoking abstinence rates and a measure of oral/periodontal health); and a sample size based upon the pilot RCT data.