Abstract
INTRODUCTION: Secondhand smoke (SHS) exposure is a risk factor for early childhood caries. Here we examined the association between SHS exposure and early tooth eruption (ETE) to clarify the additional etiology of an increased chance of contact between the tooth's surface and acid produced by fermenting oral bacteria. METHODS: Data of 388 child-mother pairs who attended health checkups at public health centers were assessed for children aged ≥18 months. SHS exposure was reported as maternal smoking during pregnancy and household smoking after birth. Associations between SHS exposure and ETE (≥3 canines in the oral cavity) were tested using multivariable analyses of the dose-response relationship. Subgroup and sensitivity analyses were performed for birth-weight subgroups and SHS exposure variables, respectively. RESULTS: ETE prevalence was 65.5%, 68.1%, and 76.9% in the no, medium-dose (ceased partway and sometimes), and highest-dose (every day) exposure groups, respectively, during pregnancy, and 61.5%, 75.0%, and 75.5%, respectively, after birth. The association between the highest dose exposure during pregnancy and ETE was not significant (OR=1.42, 95% CI: 0.34-5.96, p=0.631), whereas that between highest dose exposure after birth and ETE was significant (OR=2.13, 95% CI: 1.06-4.31, p=0.034); this association was distinct in the subgroup of children with smaller birth weights (<3000 g) (OR=3.19, 95% CI: 1.08-9.44, p=0.036). The dose-response relationship was consistently significant for exposure after birth (p<0.05). The sensitivity analysis that employed no SHS exposure, as a reference, revealed that exposure after birth but no exposure during pregnancy was significantly associated with ETE (OR=2.29, 95% CI: 1.19-4.40, p=0.013). However, the association between exposure during pregnancy and ETE was consistently non-significant (p>0.05). CONCLUSIONS: When controlling for variables of birth weight and exposure type, SHS exposure after birth was independently associated with the early eruption of deciduous canines. Further studies are warranted to examine the trajectory of SHS exposure after birth, ETE, and early childhood caries incidence. ABBREVIATIONS: ETE: Early tooth eruption, SHS: Secondhand smoke.