Enamel Component Volumes in the Neonatal Line and Adjacent Enamel

Objectives: This study aimed at analyzing the enamel component volumes (mineral, organic and water) in the neonatal line and surrounding enamel.
Methods: Ground sections of exfoliated human deciduous incisor teeth (n = 17) were prepared. In each section, component volumes were quantified in 5 enamel histological sites (2 prenatal, the neonatal line, and 2 postnatal), 40 μm apart from each other. The mineral volume was determined by digital radiomicrography and the organic and water volumes were quantified by means of the interpretation of enamel birefringence. One-way repeated measures ANOVA followed by paired T test (2-tailed significance of 5%) were applied. We also tested the hypothesis that mineral volume decreases as it approaches the neonatal line using Pearson's Correlation.
Results: The histological location (pre, neonatal, and postnatal) affected the mineral (p=2.15x10-4 0.001), organic (p=9.9x10-9), and water volumes (p = 5.8x10-5). The neonatal line had the following mean values for volumetric components: 85.88% (mineral volume), 6.44% (organic volume) and 7.68% (water volume). The mineral volume in the neonatal line was smaller than in the postnatal enamel (p=1.38x10-4, Hedge G=1.20, 95% CI=2.00/0.42) and prenatal (p=8.44x10-7, Hedge G= 1.88, 95% CI=2.75/1.01,). A negative correlation (r= -0.451, 95% CI= 0.606/0.283, p=1.48x10-5,) between neonatal line distance and normalized mineral volume was verified. The organic volume in the neonatal line was higher than in the postnatal (p= 3.80x10-4, G= 1.09, 95% CI= 1.86/0.31) and prenatal enamel (p= 1.75x10-6, Hedge G= 1.77, 95% CI= 2.63/0.91) and the water volume in the neonatal line was higher than in postnatal (p= 1.96x10-3, Hedge G= 0.90, 95% CI= 1.66 / 0.13) and prenatal enamel (p=7.60x10-4, Hedge G= 1.01; 95% CI=1.78/0.23).
Conclusions: It is concluded that the neonatal line is a hypomineralized enamel with higher organic and water contents compared to pre and postnatal enamel. The mineral volume decreased as it approaches the neonatal line.