Childhood Factors Shaping Adolescent Oral Health: A causal-inference analysis of the Longitudinal Study of Australian Children

Abstract

Dental caries is the most common chronic disease of childhood and one of the most steeply socially patterned. Australian guidelines recommend twice-daily toothbrushing from the first tooth, yet the evidence that establishing this behaviour early prevents disease is almost entirely cross-sectional, has rarely been followed into adolescence, and has seldom asked whether any benefit is shared equally across the social gradient. This thesis brings modern causal-inference methods to the Longitudinal Study of Australian Children (LSAC) birth cohort to ask whether, and for whom, early childhood conditions shape adolescent oral health.

Using a shared, DAG-informed analytic pipeline, the thesis estimates the causal effect of early twice-daily brushing on caries at age 14–15 through target-trial emulation; tests whether that benefit differs by area-level socioeconomic position; widens the lens to the multilevel structural and behavioural determinants of caries; and validates the carer-reported outcome on which the whole program rests against clinical photographs. Three findings converge. 

Early brushing causally lowers adolescent caries, robustly across ten estimators. But the benefit is concentrated in advantaged areas and small where disadvantage is greatest; and across the whole system, structural and material conditions, chiefly sugar and dental access, dominate over individual behaviour. A measurement-validation study, the first of its kind in this cohort, confirmed that these conclusions are robust in direction to plausible outcome misclassification. Together the results argue that individual behaviour is necessary but not sufficient for children's oral-health equity, and that closing the gap requires structural action, not behavioural advice alone.

Speaker

Hesham Al-Sharani is a PhD candidate at the National Centre for Epidemiology and Population Health (NCEPH), the Australian National University, supervised by Dr Tehzeeb Zulfiqar, Dr Nicole Stormon, Prof Alice Richardson, and Dr Yuehan Zhang. Originally from Yemen, he completed a Bachelor of Dentistry at Ibb University and a Master of Dentoalveolar Surgery at Jinzhou Medical University and worked as a lecturer in the Faculty of Dentistry at Ibb University before commencing his PhD. His doctoral research applies modern causal-inference methods, target-trial emulation, propensity-score and doubly-robust estimation (IPTW, G-computation, TMLE), and quantitative bias analysis, to the Longitudinal Study of Australian Children, examining how early childhood behaviours and social conditions shape adolescent oral health and its inequalities. Half of the work has been published in BMC Oral Health, with further papers under review with other journals. His research interests include the social determinants of child health, health equity, and measurement in observational epidemiology.