Three dimensional observation of the occlusal grooves in the maxillary first and second deciduous molars with micro-CT

The purpose of this study was clarify the morphological condition of occlusal grooves in the maxillary first and second deciduous molars with micro-CT. We took photographs of the maxillary deciduous molars using a micro-CT device and reconstructed the three-dimensional image of the anatomical crown using a three-dimensional visualization and measurement software. For observation and measurement of the occlusal grooves, twodimensional sliced images were generated 10 images at each groove. On the generated two-dimensional sliced images, we measured the occlusal angle, the depth of the occlusal groove and the enamel thickness at its bottom. The sites which showed smallest angle were distal portions of the central groove in maxillary first deciduous molar, and lingual groove in maxillary second deciduous molar. The occlusal groove in maxillary second deciduous molar was deeper than that of maxillary first deciduous molar in all sites examined, except for distal portion of the central groove. The enamel thickness in maxillary second deciduous molars tended to have thicker enamel than that of first deciduous molars. In maxillary first deciduous molars, most of the occlusal grooves exhibited the shape classified into type P. Whereas in maxillary second deciduous molars, the ratio of type P was relatively low, especially, lingual grooves consisted of type V, whose angle was less than 90 degree, type U and type I, which had the shape looked like a stick. Distal portion of the central groove of maxillary first deciduous molar, and lingual groove of maxillary second deciduous molar tend to be the initiation and predilection sites of dental caries due to the anatomical features of their occlusal fissures. Moreover, it is preferable to apply pit and fissure sealant into the occlusal fissures containing this region at an early point of the treatment.