Table 7.

Summary of results to evaluate the causal association between SHS and dental caries.

Tooth type	Element	Description for consistency (number of study)	Evidence synthesis according to study quality	Perceived shortcoming	Evidence synthesis
Deciduous tooth	Strength of association	Strong (2), moderate (5), weak and moderate (2), weak (1), no association (1)	Moderate to strong evidence for weak to moderate association	There was no control group in current smokers in natural experiment.	Possible evidence
	Natural experiment	Smaller effect size and no association (3) in previous exposure group	Strong evidence for natural experiment	Natural experiment and dose-response relationship were reported from two countries. Cohort study was not conducted.
	Dose-response relationship	Obvious relationship between level of exposure and the effect size (5)	Strong evidence for dose-response relationship.
Permanent tooth	Strength of association	Moderate (1), weak (5 a), and no association (2)	Moderate evidence for weak association	Only one study reported results of natural experiment and dose-response relationship.	Insufficient evidence
	Natural experiment	Effect size was similar in previous and current exposure groups (1)	Limited evidence for natural experiment
	Dose-response relationship	Relationship between level of exposure and the effect size was not clear (1)	Limited evidence for natural experiment

^aone study with cohort format.