Aim: Assessment of dental health in the primary dentition of preterm infants (PTI) including investigation of mother- and infant-related risk factors in a case-control study design. Material and Methods: One hundred twenty-eight infants aged 3-4 years were included. Sixty-four PTI (27 males) were randomly selected from the preterm registry of the Jena University Hospital. As a control group served 64 full-term infants (FTI) recruited from the Department of Paediatric Dentistry, matched for age and sex. Dental examinations were provided by one dentist under standard clinical conditions. Caries was scored using the International Caries Detection and Assessment System (ICDAS II) and the DMFT, gingival health using the Periodontal Screening Index, and developmental defects of enamel using the DDE index. Mother- and infant-related factors were collected via a questionnaire and from medical records. Results: The caries prevalence was 50.0% (ICDAS II >0) in PTI and 12.5% (ICDAS II >0) in FTI. The caries experience was higher in PTI (DMFT 1.0 ± 3.1) than in FTI (DMFT 0.3 ± 1.0). PTI had a higher risk of caries (OR 7.0), initial lesions (OR 6.2), DDE (OR 7.5), and gingivitis (OR 6.5) than FTI. The highest risk occurred in PTI with an extremely low birth weight (<1,000 g). A higher risk of DDE was present when mothers suffered from illness during pregnancy (OR 3.9). A higher risk of caries was revealed in infants with respiratory syndrome (OR 6.2) or when their mothers had a lower socioeconomic status (OR 6.3). Conclusions: PTI had less healthy teeth than FTI and are at a higher risk for DDE, caries, and gingivitis. The poorer dental health in PTI is associated with a low birth weight, a low socioeconomic status, and mothers' illness during pregnancy.