Supplementary Material for: Mediation effect of dental caries in the relationship between parental locus of control and oral health related quality of life

Objectives
The study aims to assess the direct and indirect effect of parental locus of control (LoC) on child oral health related quality of life.

Methods
As part of the Growing Up in Singapore Towards healthy Outcomes (GUSTO) multicenter longitudinal cohort study, sociodemographic characteristics of parents and their children were obtained at recruitment. Oral health status and dental caries outcomes were assessed at the 5th year post-natal visit and administered alongside the LoC questionnaire. Intra-oral examinations were carried out by 3 trained calibrated dental professionals using the modified International Caries Detection and Assessment System (ICDAS-II) criteria. At the 6th year postnatal visit, the Early Childhood Oral Health Impact Scale (ECOHIS) was administered to mothers to assess the oral health-related quality of life (OHRQoL) of their child. Statistical analysis of direct effects of parental LoC on OHRQoL and causal mediation effects of dental caries were carried out using the potential outcomes approach with 1000 simulations.

Results
A total of 312 parent-child dyads were included in this prospective cohort study. At the 5th year post-natal visit, the median decayed missing and filled surfaces (dmfs) was 2 (IQR 0 – 5), while the median locus of control was 47 (IQR 43 – 50). The total effect of parental LoC on ECOHIS was -2.05 (95% CI -4.03 – -0.08), of which the direct effect through dmfs was -1.45 (95% CI, -3.41 – 0.47). The percentage of the total effect of parental locus of control on ECOHIS that was mediated by the presence of dental caries was 29.5% for dmfs including incipient caries (ICDAS 1-6). The proportion mediated was lower if only active decayed surfaces (ds) were considered (23.7%) and higher if only cavitated lesions (ICDAS 3-6) (30.1%) were considered.

Conclusions
The effect of parental LoC on child OHRQoL was mediated in part through the development of dental caries.