SEM secondary- and backscattered-electron image observations were conducted on fossil oreodont teeth to study the distribution, fine structure, and element content in the dentinal imbrications.
Canines and molars were removed from a fossil oreodont, sectioned either longitudinally or horizontally, and then polished to a glass-like finish. The dentin surface was etched with a weak acid, coated with gold or carbon, and then observed and analyzed under a SEM connected to an energy-dispersive X-ray microanalyzer (EDX).
The cut surface of the dentin showed many globular structures composed of concentric rings interconnected with laminated parallel layers, revealing the incremental lines in the oreodont dentin. The SEM study also showed an alternate arrangement of low-contrast, low, and smooth striations measuring 0.9 μm in width, and another component of high-contrast highly elevated, and rough striations measuring 2.3 μm in width in the so-called dentin-ripple. EDX analysis showed the former to have a lower content of both P and Ca than the latter, which finding seemed to indicate a different degree of calcification between them.
Furthermore, the region underneath the mantle dentin of the occlusal surface showed well-developed dentinal ripples. As the dentin shifted pulpally and radicularly, the imbrications became scarce and partially disappeared.

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We applied computer image processing to a silicone occlusal record obtained in the intercuspal position. A video camera was used to record images of this occlusal record for digital input and processing in a computer so that it could be displayed on a video monitor. We were able to observe variations in the number and size of tooth contacts between light and medium occlusal forces by comparing the two images that were processed from records obtained at these forces. Large variations between thc light and medium forces identified premature contacts and showed unstable intercuspation. When this system was tested on two subjects, one with temporomandibular disorders and one with normal occlusion, greater variations were noted in the occlusal contacts of the former.

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The purpose of this study was to investigate the morphological characteristics of the cranio-dento-facial complex of Chinese children with primary dentition and mandibular protrusion. Thirty children with normal occlusion and 30 with mandibular protrusion were selected for cephalometric analysis. The cephalometric measurements were adopted from the analyses of Bjork, Chang, Downs, Northwestern, Steiner, Tweed and the dimensional linear method of Sakamoto, Miura, and Iizuka. Differences in the cranio-dento-facial pattern between Chinese and Japanese children with mandibular protrusion of primary dentition were also studied.
The main conclusions were as follows:
1. While both the lengths of the mandible and the body of the mandible were not significantly different, the mandible was situated further forward in the cases with mandibular protrusion.
2. The maxilla was significantly shorter in the mandibular protrusion group, which may be primarily associated with the shorter anterior cranial base found in this group.
3. The lower incisors were tipped lingually to compensate for the intermaxillary skeletal dysplasia in mandibular protrusion.
4. The only significant difference in the skeletal patterns between Chinese and Japanese children with mandibular protrusion of the primary dentition was the Frankfort mandibular plane angle.
5. Both the maxillary and mandibular dental arch lengths were larger in Japanese than in Chinese children with mandibular protrusion.

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The purpose of the present study was to investigate the relationship between initial blood flow changes and histological changes on the pressure side of periodontal tissue during tooth movement in rats.
Ninety-seven male Wistar rats weighing 220-250g were used. Rubber bands of three different thicknesses (0.65mm×1.0mm×1.0mm, 1.0mm×1.0mm×1.0mm, and 1.5mm×1.0mm×1.0mm) were inserted into the interproximal space between the maxillary first and second molars using the method of Waldo. Gingival blood flow measurements were done with a laser doppler flowmeter, periodontal blood flow measurements were carried out using the hydrogen clearance method, and histological examinations were performed by the quantitative method using photomicrographs. Osteoclasts were stained by the acid phosphatase and tartrate-resistant acid phosphatase methods.
Larger forces induced increasingly larger reductions in blood flow in the pressure area of periodontal tissue. More time was required in the periodontium than in the gingivae to get from maximum blood flow reduction to the base line. Larger forces on the tooth created hyalinized tissue earlier and created a wider hyalinized area. Larger forces introduced many osteoclasts and were transmitted to a wider area of periodontal tissue, creating conditions for future dramatic reorganization of this tissue. Forces beyond this level may create severe damage. Even if the force is not large, severe root resorption may occur due to a concentration of forces in the area. Many osteoclasts appeared in the vicinity of vessels. They seemed to concentrate in areas where tissue blood volume had increased. Osteoclastic activities might be closely related to blood during experimental tooth movement.
Knowledge of blood flow measurements contributes to the proper determination of treatment methods, appliances and optimum forces in clinical orthodontic treatment.

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We investigated the development (calcification) stages of the permanent anterior teeth of Japanese children by classifying them into 13 stages by the criterion of Moorrees, et al., using 11,167 panoramic radiographs, 5,759 of boys and 5,408 of girls, between the ages of 2 years 0 months and 14 years 11 months. The following information was obtained.
1) The development of the anterior teeth was earlier in girls than in boys at every stage. This was particularly true during the middle phases of development.
2) An anterior tooth on one side developed at the same rate as its counterpart on the other side, regardless of differences in sex or arch.
3) In both boys and girls, the development of a mandibular central or lateral incisor was earlier than that of the corresponding maxillary tooth. However, no difference was seen in the development of the canines.
4) When the development of each permanent anterior tooth was compared for Caucasians and Japanese:
a) The developmental age for the central and lateral incisors was considerably later in Japanese than in Caucasians.
b) Although the developmental age for the canine was earlier in Caucasians for the completion of the crown and other early stages of development, it was earlier in Japanese from formation of 2/3 of the root to apical closure.
c) When the developmental periods for each of the permanent anterior teeth were compared with the results of Nolla, Moorrees, et al., and Haavikko, the developmental periods for the central and lateral incisors were longer in Japanese, while those for the canines were shorter.
5) Standardized charts for the development of the permanent anterior teeth in Japanese children were constructed.
Using the above results, we can better understand the developmental age of the permanent anterior teeth of Japanese children. This provides us with new charts which are an improvement over the charts in current use which are for the teeth of Western children. This information can be put to immediate use in clinical practice.

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