On 2017 Nov 23, Richard Holliday commented:

The oral health risks of tobacco smoking are well known and it is critically important we continue to build the evidence base around novel nicotine products so we can accurately inform our patients of the relative risks. It is great to see more research published on this topic.

After reading this paper, I was left confused with regards to tobacco smoking within the e-cigarette (EC) consumer group. The study population is described as being made up of ‘former cigarette smokers’ and ‘current EC users’.

The ‘former smokers’ groups were defined as:

• Smoked >100 cigarettes in their lifetime.
• Been abstinent (self-reported) for at least 6 months and not more than 2 years.

The ‘EC consumers’ group were defined as:

• EC consumers were ‘smoking’ EC for at least 6 months.<br>

My concern with the study design and interpretation is that there has been inadequate control of confounding factors, particularly tobacco smoking. ‘Dual use’ (i.e. using both combustible tobacco and EC) is very common, currently around 45% in the UK. The study inclusion criteria do not specify that those in the EC consumer group need to be abstinent from tobacco smoking nor do they include any method of biochemically validating this (e.g. expired air carbon monoxide or salivary/urine biomarkers).

This confounding factor makes the interpretation of the results very challenging. The comparison is between ‘former smokers’ and ‘users of combustible tobacco and EC’. Unfortunately, you can’t differentiate out the effect of the EC with this design. The papers conclusions ‘Our results show that e-cigarettes are linked to three types of inflammatory lesions in the oral cavity’ hence appear invalid.

I also felt it would have been useful to have a ‘tobacco smoking (without EC)’ comparator group and I was unsure why this was not included or presented. This would have allowed relative risk to be communicated to tobacco smokers.

I encourage the authors to clarify these points. Many thanks.

On 2017 Nov 23, Richard Holliday commented:

The oral health risks of tobacco smoking are well known and it is critically important we continue to build the evidence base around novel nicotine products so we can accurately inform our patients of the relative risks. It is great to see more research published on this topic.

After reading this paper, I was left confused with regards to tobacco smoking within the e-cigarette (EC) consumer group. The study population is described as being made up of ‘former cigarette smokers’ and ‘current EC users’.

The ‘former smokers’ groups were defined as:

• Smoked >100 cigarettes in their lifetime.
• Been abstinent (self-reported) for at least 6 months and not more than 2 years.

The ‘EC consumers’ group were defined as:

• EC consumers were ‘smoking’ EC for at least 6 months.<br>

My concern with the study design and interpretation is that there has been inadequate control of confounding factors, particularly tobacco smoking. ‘Dual use’ (i.e. using both combustible tobacco and EC) is very common, currently around 45% in the UK. The study inclusion criteria do not specify that those in the EC consumer group need to be abstinent from tobacco smoking nor do they include any method of biochemically validating this (e.g. expired air carbon monoxide or salivary/urine biomarkers).

This confounding factor makes the interpretation of the results very challenging. The comparison is between ‘former smokers’ and ‘users of combustible tobacco and EC’. Unfortunately, you can’t differentiate out the effect of the EC with this design. The papers conclusions ‘Our results show that e-cigarettes are linked to three types of inflammatory lesions in the oral cavity’ hence appear invalid.

I also felt it would have been useful to have a ‘tobacco smoking (without EC)’ comparator group and I was unsure why this was not included or presented. This would have allowed relative risk to be communicated to tobacco smokers.

I encourage the authors to clarify these points. Many thanks.