presents the subject characteristics by case status. The study design matched case and control subjects on sex, age, and neighborhood, which induced a degree of matching on ethnic group, so we saw no differences in these factors. We found a significant difference between ESCC cases compared to controls in that a higher percentage of cases reported ever using tobacco and/or opium.
Subject characteristics by case status in the GEMINI case-control study of ESCC
We fit a linear regression model using only the control subjects to assess what confounders we should consider when building our multivariate models for tooth loss and the results are given in . As expected, age had the strongest association with number of teeth and the model predicted that for every three years of age after 65 the subject would lose another tooth. This model had only two other significant predictors of tooth loss, sex and alcohol drinking. It predicted that women would have lost 1.69 more teeth than men and that alcohol drinkers would have lost 4.84 more teeth on average compared to never drinkers. Since only 2% of cases and 3% of controls reported alcohol consumption, the beta coefficient for alcohol had wide confidence intervals. The total model r2 was 18%, little more than the 15% found when using age alone in the model, so the model had low explanatory power.
Predictors of the number of teeth lost using a linear regression model in controls from the GEMINI case-control study of ESCC
presents the differences in oral health variable distributions by case status. The median number of teeth lost in subjects diagnosed with ESCC differed significantly from the median number in controls, 29 in cases and 25 in controls (P=0.0045), and there was a significant trend across categories of tooth loss. We calculated the DMFT score and found that this median differed significantly as well, 31 in cases and 28 in controls. The age of first adult tooth loss also differed significantly when tested as a trend across categories, but the medians did not differ significantly, 27 years of age versus 30 in cases and controls respectively. We found a significant difference in oral hygiene habits, with 78% of cases and 58% of controls reporting no regular oral hygiene practices such as tooth brushing or rinsing with salt water. We found no difference in the percent of subjects using dentures, 34 % of both cases and controls.
Oral health variables by case status in the GEMINI case-control study of ESCC
presents age- and sex-adjusted and multivariate-adjusted models for the association between tooth loss and ESCC. Increasing tooth loss led to increasing risk of ESCC, and edentulous subjects had an OR (95% CI) of 1.90 (1.12-3.23) compared to subjects that had lost fewer than 13 teeth. Since we found few predictors of tooth loss () the multivariate adjusted models were quite similar to the crude models and for edentulous subjects the OR (95% CI) changed only to 1.79 (1.03-3.13). Using DMFT produced similar results and the ORs became smoothly monotonic across categories, with ORs of 1.31, 1.62, 1.89, and 2.10 and a P of 0.0058 for the trend test.
Odds ratios and 95% confidence intervals for the association between tooth variables and ESCC in the GEMINI case-control study
We also estimated the effects of age of first adult tooth loss. We only present OR (95% CI) adjusted for all considered factors, including the number of teeth, because the age of first tooth loss strongly correlates with the number of teeth lost. We found increasing risk of cancer with lower age of first tooth loss up to the second lowest category, ages 20-25, with an OR (95% CI) of 1.57 (1.02-2.43). The category which included subjects who began losing adult teeth below the age of 20 showed no significant association with ESCC risk, with an OR (95% CI) of 1.27 (0.73-2.19).
Compared to daily tooth brushing, subjects who did not practice any oral hygiene had significantly increased risk of having ESCC, with an OR (95% CI) of 2.37 (1.42-3.97). Subjects who brushed less than daily or who used other oral hygiene methods (rinsing with salt water, etc.) did not differ in their risk of ESCC from those who brushed daily.
As shown in tobacco use had no significant association with tooth loss in our population, but to further remove the potential for confounding by tobacco use, we recalculated each of our models after excluding subjects that reported ever using tobacco. This reduced the power of our tests, but we found no meaningful changes in our results (). Alcohol use was uncommon and not associated with ESCC in this population and we found no meaningful changes to our results after removing subjects that reported ever consuming alcohol ().
Finally, we fit a single model that included DMFT category, age of first adult tooth loss, and oral hygiene practices and found that each of these three exposures retained independent associations with risk of ESCC. Compared to those in the lowest category, subject with a DMFT of 32 had an OR (95% CI) of 2.15 (1.19-3.91) and those never performing regular oral hygiene had an OR (95% CI) of 2.31 (1.38-3.89), but the OR (95% CI) for an age of first loss of 20-25 dropped to 1.36 (0.86-2.14).