Neonatal lines in the enamel of primary teeth--a morphological and scanning electron microscopic investigation.
OBJECTIVE
The neonatal line (NNL) is in principle found in all primary teeth and the line represents the time of birth. Earlier findings of the appearance of the NNL in light microscope and in microradiographs have shown not only changes in the prism direction of the enamel, but that the NNL has a hypomineralized character.


METHODS
The neonatal line was analyzed in un-decalcified sections of primary lower and central incisors, collected from individuals of different ages utilizing polarized light microscopy, microradiography, scanning electron microscopy (SEM) and X-ray analysis (XRMA).


RESULTS
In polarized light the NNL appeared to have a more porous structure than the enamel in general. The appearance of the NNL as a dark line in microradiographs is interpreted as the NNL being less mineralized than neighbouring enamel. Analysis with ImageJ visualized the reduction of the amount of grey value, indicating that the NNL is less mineralized. Analysis of the NNL in SEM showed a reduction of the diameter of enamel prisms, the more narrow diameters continued through the postnatal enamel. A change of the growth direction of the prisms was also observed at the NNL. In a three-dimensional image the NNL appeared as a grove, however, in non-etched enamel no grove was seen. The elemental analyses with XRMA showed no marked changes in the content of C, Ca, P, N, O or S in the area around the NNL.


CONCLUSIONS
The NNL is an optical phenomenon due to alterations in height, and degree of mineralization of the enamel prisms.
Sabel
Nina
N
Department of Pedodontics, Faculty of Odontology, Göteborg University, Göteborg, Sweden. nina.sabel@vgregion.se
Johansson
Carina
C
Kühnisch
Jan
J
Robertson
Agneta
A
Steiniger
Frank
F
Norén
Jörgen G
JG
Klingberg
Gunilla
G
Nietzsche
Sandor
S
D003743:Dental Enamel / Q000000981:diagnostic imaging / Q000648:ultrastructure*; D006801:Humans; D007180:Incisor / Q000000981:diagnostic imaging / Q000648:ultrastructure; D007223:Infant; D007231:Infant, Newborn; D008852:Microradiography / Q000379:methods; D008855:Microscopy, Electron, Scanning; D008859:Microscopy, Polarization / Q000379:methods; D008963:Molar / Q000000981:diagnostic imaging / Q000648:ultrastructure; D014083:Tooth Germ / Q000000981:diagnostic imaging / Q000648:ultrastructure; D014094:Tooth, Deciduous / Q000000981:diagnostic imaging / Q000648:ultrastructure*