Análise dos componentes volumétricos da linha neonatal e esmalte circunjacente

Abstract

Introduction: The neonatal line is an accentuated incremental line related to physiological stress during the enamel secretion stage, affecting all deciduous teeth and the first permanent molar. Although structural changes have been described in the neonatal line, there are no studies on the enamel component volumes in the neonatal line. Objective: The aim of this study was to analyze the enamel component volumes (mineral, organic and water) in the neonatal line and surrounding enamel (post and prenatal enamel). Methodology: Exfoliated human deciduous incisor teeth (n = 17) were selected and cut for preparing longitudinal histological ground sections. In each section, 5 histological points in the enamel layer (2 prenatal points, the neonatal line and 2 postnatal points), 40 μm apart from each other, where selected for quantification of the component volumes. The mineral volume was determined by digital radiomicrography and the organic and water volumes were quantified by means of the interpretation of enamel birefringence under a polarized light microscope. Data were submitted to normality test, presenting a normal distribution. 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 post natal) had an effect on the mineral (p=2.15x10-4 0.001, η2 = 0.07), organic (p=9.9x10-9, η2 = 0.07), and water volumes (p = 5.8x10-5, η2 = 0.05). 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, power= 99.43%) and prenatal (p=8.44x10-7, Hedge G= 1.88, 95% CI=2.75 / 1.01, power= 99.99%). A negative correlation (coefficient r= 0.451, 95% CI= 0.606-0.283, p=1.48x10-5, power of 99.30%) 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, power= 98.43%) and prenatal enamel (p= 1.75x10-6, Hedge G= 1.77, 95%CI= 2.63/0.91, power= 99.99%) 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,power= 93.27%), and prenatal enamel (p=7.60x10-4, Hedge G= 1.01; 95%CI=1.78/0.23, power= 97.00%). Conclusion: 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.