Figure 1. Hazards ratios () and 95% confidence intervals (error bars) for risk of root canal treatment among former cigarette smokers (smoked prior to study baseline, but remained abstinent during follow-up), by length of time since last smoked. The median time since last smoked was 9 yrs. Numbers in each interval are 111 participants/2587 teeth in the 9-year group and 99 participants/2312 teeth in the > 9-year group. Never-smokers (n = 230 participants/5765 teeth) are the reference group. HR are adjusted for age, presence of crown (yes, no), any caries (yes, no), periradicular radiolucency (yes, no), and alveolar bone loss score.