Comparison of demineralisation rates in pre- and postnatal enamel and at the neonatal line

Abstract

AimsThe neonatal line, which is an exaggerated incremental layer line, separates pre- and postnatal enamel. It has been suggested that this layer may be a barrier to the progress of a carious lesions. The objective was to measure the rate of demineralisation in pre- and postnatal enamel and within the neonatal layer using scanning microradiography (SMR). Permanent enamel and compressed permeable hydroxyapatite samples were used as controls. Methods and resultsEnamel specimens from deciduous incisors were cut into mesiodistal blocks of 2mm thickness without altering the labial surface and located within SMR cells. Permanent enamel and hydroxyapatite specimens were similarly prepared. Artificial caries-like lesions were created by exposing the specimens to 0.1moll−1 acetic acid (pH 4.0) within the SMR cells. SMR was used to measure the rate of mineral loss at 10 points either side of and at the neonatal line in the deciduous enamel, and 20 points across in the control specimens.The rate of demineralisation was almost the same in pre- and postnatal enamel ((6.0–8.0)×10−4gcm−2h−1), but much lower in the vicinity of the neonatal line (2.0×10−4gcm−2h−1). The rate of demineralisation was lower in permanent (5.0×10−4gcm−2h−1) than in deciduous enamel, and even lower in the permeable hydroxyapatite specimen (2.5×10−4gcm−2h−1). ConclusionsThis study showed no difference in the rate of demineralisation between pre- and postnatal enamel, but a reduced rate within the region that contained the plane of the neonatal line. This supports the hypothesis that the neonatal line may act as a barrier to the propagation of carious lesions.