Background/rationale: Systematic reviews on the effects of pacifiers on occlusion have highlighted the need for quality RCTs.

Trial design: Single region, three parallel-armed, prospective, randomized controlled trial.

Objectives: To investigate the correlations between early childhood non-nutritive sucking habits and malocclusion. Specifically to test whether the use of a study pacifier has differing effects compared to other pacifiers and control, and whether the duration of pacifier use or digit sucking influence the occlusion.

Participants: The subjects were firstborn children, born in 2008 in Vantaa, Finland.

Intervention: One-third of participants were offered study pacifiers, free of charge, from birth up to 2 years of age. The history of the subjects' sucking habits, including pacifier use was screened in a questionnaire at the age of 2 years, and clinical examinations were performed at the age of 7 years. In addition, the subjects were divided into groups that were equally matched regarding their mother's level of education.

Outcomes: Posterior crossbite, anterior crossbite, overjet, deep bite, open bite, and crowding.

Randomization method: Three districts were randomly allocated to three study groups by drawing lots.

Blinding: It was not possible to blind the clinicians or parents from the intervention. Blinding during data analysis was performed.

Results: From the original cohort of 2715 children born in the town of Vantaa, 1911 were excluded and 353 were lost to follow-up. The remaining 451 children were divided into three groups according to the use of pacifiers. The prevalence of posterior crossbite at the age of 7 years was higher if a non-study pacifier had been used (P = .005) even when matched for the mother's level of education (P = .029). The prevalence of posterior crossbite was higher if the pacifier habit had continued for 12 months or more compared to 11 months or less, 7% and 1%, respectively, (P = .003). Digit sucking for 12 months or more was associated with crowding (P = .016). The prevalence of crossbite in the study pacifier group was less than in control pacifiers.

Harms: No adverse harms were reported other than effects on the dentition.

Conclusion: The use of pacifiers is associated with the posterior crossbite, especially if their use continues for a year or more. Parents/guardians should be advised to stop the use or reduce the use of pacifiers to a minimum after their child's first birthday.

Trial registration: ClinicalTrials.gov NCT01854502.