Timing of primary maxillary tooth eruption in preterm compared to term infants: a retrospective longitudinal cohort study

Background Reported eruption times of primary teeth in term and preterm infants are largely based on detection of visible tooth structure at the gingival level by parents, paediatricians, or dentists. Furthermore, there is a lack of quantitative data on primary tooth eruption velocity in the literature. This study aimed to compare eruption timing, eruption velocity, and maximum crown length by modelling longitudinal crown eruption trajectories in term and preterm infants. Methods This retrospective longitudinal cohort study included 100 infants (51 preterm, 49 full-term) who were followed from the first weeks after birth with quarterly assessments over four years. A total of 626 serial maxillary plaster casts were obtained as part of a prospective clinical trial registered at clinicaltrials.gov (NCT00408746). The crown length of 1,885 primary teeth (central and lateral incisors, canines, first molars) was measured by one investigator on digitised casts using Blender software. Intrarater reliability was evaluated using intraclass correlation coefficients (ICC). Timing and velocity of eruption were estimated using a non-linear asymptotic growth model. Results Measurement reliability was excellent (ICC = 0.996). Comparing chronological age revealed that preterm infants had a mean eruption delay of 2.7 months compared to full-term infants, with a significant delay observed for canines (4.5 months). However, when corrected age (chronological age minus days born before 37 gestational weeks) was used, a mean delay of only 1.4 months with no significant differences was found. Model-derived eruption preceded commonly reported clinical eruption ages by 6.2 months in preterm and 7.7 months in full-term infants. The model-estimated maximum crown lengths were slightly smaller in preterm infants, though these differences were not statistically significant. Eruption velocity followed a non-linear pattern, with preterm infants showing a tendency towards higher eruption rates, suggesting catch-up growth. Conclusions Based on our model, eruption timings reported in the literature likely correspond to clinical observations made when primary teeth have attained about half of their final crown height. Consequently, crown exposure through gingiva appears to occur on average about six months prior to clinically visible eruption. Although preterm infants show a delay in tooth eruption when assessed by their chronological age, this difference resolves after correction for prematurity.