Morphometrical Study of the Dentino-enamel Junction of the Labial Surface of the Maxillary Central Incisor

The labial surface of the upper central incisor has mesial and distal marginal ridges, and these vary in form and development. We measured the height of the labial marginal ridges of the upper central incisors, which had double-shovel (DS) and no double-shovel (NDS) on the outer enamel surface (OES) and dentino-enamel junction (DEJ) using a 3D scanner. Enamel thickness of the labial surface was also measured in these specimens. Mesiodistal and buccolingual diameters on both OES and DEJ were measured for the comparison of OES and DEJ structures. We obtained the following results ; 1. On the DEJ, DS incisors had more sharp and clear ridges than on the OES. 2. The mesial marginal ridge (MMR) was significantly higher than the distal marginal ridge (DMR) on both OES and DEJ of DS incisors. 3. There were no significant differences of the enamel thicknesses at the three points of the labial surface, such as mesial and distal marginal ridges and the central ridge. 4. The enamel thickness of the DS was significantly thicker than that of the normal incisor at the center of the labial surface, the average of which was 0.91 mm in DS and 0.73 in NDS incisors. 5. No significant differences of both mesiodistal and buccolingual diameters of OES and DEJ were found between averages of NDS group and DS group. 6. Both mesiodistal diameter and buccolingual diameter on OES had a strong correlation to the corresponding diameters on DEJ. The enamel substance at the central labial surface of the DS was significantly thicker than that of the NDS, and marginal ridges in DS observed in OES were clearer and more developed in the DEJ, which was an anatomical base for crown development.