title: Causal assessment of smoking and tooth loss: a systematic review of observational studies.
abstract: BACKGROUND
  Tooth loss impairs oral function. The aim of the present review was to evaluate the causal association between smoking and tooth loss on the basis of high-quality studies.
  
  
  METHODS
  Relevant literature was searched and screened, and the methodological quality was assessed. Information on the strength of the association between smoking and tooth loss, the dose-response relationship and natural experimental data was collected and evaluated with respect to consistency and study design.
  
  
  RESULTS
  Our literature search yielded 496 citations, and 6 cross-sectional and 2 cohort high-quality studies examining 58,755 subjects in four countries. All studies reported significant associations, although the strength of the association was usually moderate. Four studies reported dose-response relationships between exposure to smoking and the risk of developing tooth loss. A decrease in the risk of tooth loss for former smokers was evident in six studies. Interpretation of evidence for each element was consistent, despite some shortcomings regarding study type and population.
  
  
  CONCLUSIONS
  Based on the consistent evidence found with the existing biological plausibility, a causal association between smoking and tooth loss is highly likely. Further studies using a cohort design and different populations are necessary to confirm this association.
authors.affiliation: Department of Preventive and Public Health Dentistry, Fukuoka Dental College, Fukuoka, Japan. haniokat@college.fdcnet.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Hanioka
authors.forename: Miki
authors.initials: M
authors.lastname: Ojima
authors.forename: Keiko
authors.initials: K
authors.lastname: Tanaka
authors.forename: Keitaro
authors.initials: K
authors.lastname: Matsuo
authors.forename: Fumihito
authors.initials: F
authors.lastname: Sato
authors.forename: Hideo
authors.initials: H
authors.lastname: Tanaka
mesh_terms: D006801:Humans; D012907:Smoking / Q000009:adverse effects*; D016388:Tooth Loss / Q000209:etiology*