Is nicotine damaging to oral tissues?

Abstract

Data sources The review included 42 pre-clinical in-vitro studies, published between 1995 and 2017.

Study selection The study selected in-vitro studies which had assessed the effect of nicotine on human gingival and periodontal fibroblasts and epithelial cells. Typically, diluted pure nicotine was added to a cell culture medium in a variety of doses for a variety of time periods and the cells were then compared against a no-nicotine control. Outcomes assessed were: Cell viability, cell attachment or adhesion, cell proliferation or inflammatory mediator production. Studies were restricted to English language and full-text only.

Data extraction and synthesis Two members of the review team screened abstracts and reviewed the full-texts independently. Disagreements regarding inclusion were resolved by discussion and consultation with the third author. Data were also extracted independently using a specifically designed data extraction form which included a quality assessment specifically designed for in-vitro studies. A narrative synthesis of the results was carried out.

Results The included studies were heterogeneous in their designs, with a wide variety of cell types, concentrations of nicotine (1 nM to 100 mM), exposure times (30 minutes to four weeks), and assays used. All studies were assessed at being at high risk of bias due to lack of randomisation, allocation concealment, and blinding. No effect on cell viability was observed when the nicotine concentrations used were within the ranges observed in-vivo in smokers, nicotine replacement therapy users (NRT) and e-cigarette users. Cell viability was adversely affected only when concentrations of nicotine reached those observed in the saliva of smokeless tobacco users (>5 mM). However, periodontal ligament cells are not usually exposed to saliva in-vivo. Effects on cell attachment, cell proliferation and production of inflammatory mediators were reported at a wide range of concentrations, but the effects were contradictory. The authors make several recommendations for future research in this area, to improve the quality of the primary studies.

Conclusions At the concentrations found in smokers and users of NRT including e-cigarettes, nicotine is unlikely to be toxic to human gingival and periodontal ligament cells in in-vitro. Higher concentrations of nicotine, of the levels observed in the saliva of smokeless tobacco users, have been shown to be cytotoxic in vitro.