Fig. 1

Flowchart including adolescents in the preterm group (extremely and very preterm-born) and the full-term control group from the start and then at the ages of 12–14 and 17–19. The adolescents who participated in the study had registered their oral-health related quality of life in OHIP-14 at both occasions as an adolescent. ^* Identified through the Swedish Medical Birth Register ^** Identified through dental clinics. Declined = Declined participation for reasons unknown. Excluded = Excluded owing to intellectual disability. Not fulfilled OHIP-14 § = The study design changed to a longitudinal design, and individuals who did not participate at both 12–14 year and 17–19 years of age were excluded. EPT = Extremely preterm (born in gestational weeks 23–28). VPT = Very preterm (born in gestational weeks 29–32)