Stereo fluoroscopy-assisted percutaneous needle puncture of the vertebral body.

The purpose was to determine whether real-time three-dimensional imaging by stereo fluoroscope could alleviate the nuisance of moving the fluoroscope C-arm during needle biopsy of the spine. Fifteen lumbar vertebrae of four beagle dog cadavers were used in a simulation. We used a newly devised portable-type stereo fluoroscope, which alternatively exposes the X-ray from left and right X-ray tubes so that a surgeon can decode left and right images displayed alternately on a monitor by using polarizing glasses. A 2-mm-diameter Kirschner wire was inserted into the vertebral bodies by a posterolateral approach without moving the C-arm. An axial view of the roentgenogram of each vertebra found all 15 wires to be appropriately inserted. This would appear to be a time-saving feature.

Differential termination times of enamel formation on human deciduous anterior-tooth surfaces revealed by tetracycline labelling.

The positional relationships between the cervical-enamel margin and the intersecting point of a fluorescent (tetracycline) line in dentine, with the outer dentine surface or the dentine-enamel junction, were investigated by ultraviolet microscopy of the human deciduous anterior teeth. The results suggest that enamel formation (1) ended earlier on the mesial than on the distal surface in 18 instances and, nearly simultaneously on both of these surfaces in four, (2) ended earlier on the distal than on the labial surface in all 28 specimens and (3) ended earlier on the labial than on the lingual surface in 14 instances and nearly simultaneously on both of these surfaces in eight instances.

Differential rate of dentin formation on human deciduous anterior tooth surfaces deduced from tetracycline labeling.

Distances between the intersecting points of two fluorescent lines with the outer dentin surface were measured on enlarged microphotographs of ground sections of human deciduous anterior teeth. The results suggested that: extension of odontoblast differentiation is greater on the lingual than on the labial side during the 8 months following birth in incisors, and during the first year in canines; it is greater on the distal than on the mesial side during the 3 months following birth in incisors, and during the first year in canines; in the incisors, dentin formation of newly differentiated odontoblasts is more active on the distal than on the mesial side during the 8 months following birth.

The development of the human interradicular dentine as revealed by tetracycline-labelling.

The pattern of labelling of the interradicular dentine that forms the floor of the pulp chamber was studied in human deciduous second mandibular molars from patients who had undergone treatment with tetracycline during the period of formation of those teeth. Six teeth exhibited isolated mineralization centres for the interradicular dentine, indicating that this region in man, unlike in rodents, does not develop as a direct continuation of coronal dentine.

[The lateral dental lamina and the enamel niche. 6th and last paper on the embryology of human teeth]. / La lame dentaire latérale et la niche de l'émail. 6e et dernière contribution à l'embryologie des dents humaines

Up to the cap-stage the lateral enamel strand extends from the dental lamina to the tip of the tongue-like projection of the enamel organ, forming there a swelling. It does not reach the free margin of the enamel organ at the bell-stage. The lateral enamel strand gradually becomes smaller in regard to the tooth germ, changing its relative position to the mesial half of the latter, and finally degenerates. In the molar germ, as the epithelial tongue-like projection at the cap-stage increases in length to become an interradical process, the lateral enamel strand extends as a crest on the buccal interradical process. The direction of the lateral enamel strand is inverse in the maxillary molar germs.