The amelocemental junction in young premolar teeth. A replica study by scanning electron microscopy.

To investigate the validity of traditional data on the frequency of various relationships of root cementum to coronal enamel at the amelocemental junction, the relationship in 50 young premolar teeth extracted on orthodontic indications was documented, using replica techniques for scanning electron microscopy (SEM), combined with polarization microscopy of thin ground sections (< 40 microns). Of 200 surfaces, 30 were excluded because of damage during specimen preparation. Replicas of the other 170 surfaces were photographed at 20x and 80x in SEM and classified as having an edge-to-edge relationship of enamel to cementum in 76% and an overlap of cementum onto the cervical enamel in 14%. What appeared to be a gap between enamel and cementum at low magnification (10%) was seen at high magnification to be a ditch or trough in the cementum: no gaps with exposed dentin were observed in SEM. Polarization microscopy of ground sections of the original specimens confirmed the SEM classification. In this material, the edge-to-edge relationship of enamel to cementum predominated: overlapping of cementum onto the enamel was less prevalent than previously reported. The methods applied in this study circumvented some major sources of artefact formation due to shrinkage during specimen preparation, which may previously have caused misinterpretation of 'gap' relationships.