Root concavity are always in evidence at the root surfaces of lower premolar, arenoted for a long time. The frequency of the concavity was different with the kinds of teeth andthe mesio-distal and bucco-lingual surface. The concavity on the mesial surface of lower firstpremolar and the buccal surface of lower second premolar are widely noted.
One thousand and one hundred twenty one-first lower premolars, 546 Japanese and 575 Indianteeth were examined for the incidence of the concavity.
The results were as follows:
1. The deep fissure was found on the mesial surface of the lower first premolar root. Accountedfor 10.39% in Japanese and 25.61% in Indian.
2. On the buccal surface of the lower second premolar root accounted for 3.36% in Japanese, for 21.68% in Indian.
3. Frequency of the concavity and the difurcate root of lower premolar were found greaterin Indian than in Japanese.
4. In the most cases the root concavity of lower premolar occurred (appeared) at the identicalsurface of the same jaws.
5. No correlation was found between the root form and the traits of crown shape (tubercules, number of the cusp, etc.)

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Scanning electron microscopy of early carious lesions of the labial and proximalsurfaces of deciduous front teeth demonstrated two distinct patterns in the progression of incipientcaries.
The variable patterns could be related to the differences of the enamel surface structure between the prismatic enamel and prismlessenamel. The breakdown of the prismatic enamel surface developed continuously through rod end depressions. The prismless enamel showed rough surfaces with channels and cracks extending from the surface to the decalcified subsurface area. Microscopically scattered and dissolved portions of the enamel surface were detected and this may suggest multi-occurrence of carious lesions.
Artificially produced carious lesions showed the characteristic demineralization at the prismaticenamel surface of cervical region. This phenomenon revealed an important factor ofthe prismless enamel layer in the resistance to carious progress.

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Among the 82 skull specimens (33 males, 28 females and 21 unknowns) in the 1 st Department of Oral Anatomy, Kyushu Dental College, of raccoon dogs (Nyctereutes Procyonoides Viverrinus TEMMINCK), nine supernumerary teeth were observed in six cases (2 males, 1 females and 3 unknowns).
1. Supernumerary teeth were found in the maxilla in two cases with a total of three teeth and in the mandible in fivecases with six teeth. A greater number of incident occurred in the mandible.
2.In a maxillary case, eruptions of two teeth at the third anterior molars region, side by side from the lingual to the buccal sides, were observed. The buccal one was regarded as being the probable supernumerary tooth. Another case showed an incident of symmetrycal eruptions at the first anterior molars region on eachside of the maxilla. In addition, a supernumerary tooth was also observed at the first molars region of the left mandible.
3. All the mandible cases showed eruptions at the first anterior molars region, along the line of dentition. The tooth on the mesial side was smaller in each case and was regarded as being of the supernumerary tooth germ.
4. Among the mandible cases, there was a case of symmetrical eruptions. Comparison between the right and left sides showed that more incidents occurred on the left side.
5. Incident of supernumerary teeth is notsignificant phylogenetically and it is considered to occur due to division of the tooth germ. However, the fact that incident occur frequently at the first anterior molars region suggests instability at this region in connection with the tooth being in the process of reduction.

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A study was made of the distribution and type of inactive collagenase in the bo -vine gingiva, pulp and periodontal membrane of teeth in the stage of mixed dentition. Inactive collagenase was directly extracted with KC1 from tissue, activated with NaSCN, trypsin and both of them, and from the activity of activated collagenase the content of inactive collagenase was calculated.
The results obtained were as follows:
1. There were two types of inactive collagenase in the bovine gingiva, the pulp and periodontal membrane of unerupted and erupted teeth. One was a complex of collagenase and a 2-macroglobulin, and the other was activated by trypsin but not by NaSCN.
2. Distribution of the two types of inactive collagenase in tissue was individually different.
3. No relationship was found between the distribution of inactive collagenase and dry tissue weight, the content of RNA, uncollagenous protein and collagen in each tissue.
4. A correlationship was found between the distribution of inactive collagenase and the content of DNA in the bovine gingiva, the pulp of unerupted and erupted teeth and the periodontalmembrane of unerupted teeth, but not in the periodontal membrane of erupted teeth.
5. In tooth eruption, the pulp showed no difference or decrease in the content of inactive collagenase, while the periodontal membrane was increased.

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The time course change on the toxicity and components of formalin-guaiacol (FG) preserved in a closed bottle at room temperature was investigated in this report.
In acute toxicity test, the oral LD₅₀ for FG was determined in male mice.
As the change of components of FG, the detection of guaiacol resolution was done by thin-layer chromatography.
Results
1. The LD₅₀ value for control group of FG was 996mg/kg, and the value after three months or six months was 1152mg/kg or 1071mg/kg, respectively.
Thus, the acute toxicity is seemed to decrease gradually with time course.
2. New spots assumed to be the resolvents of guaiacol in any months samples were not found by the thin-layer chromatography.
3. FG may be regarded as the chemically stable preparation, comparing with formocresol.

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Longitudinal, transverse or tangential sections of the tooth enamel wereground smoothly in order to obtain the longitudinal or transverse planes of enamel rods. They were then etched with 0.01 mol lactic acid at pH 2.8, or 0.01 mol phosphoric acid at pH 2.4 and the cross striations of enamel rods and Retzius lines were observed under a reflection microscope and a scanning electron microscope.
The cross striations of enamel rods are considered to appear not only in the regular changes of acid resistance, but also in the successional fan-shaped arragement of crystals within the enamel rods.
The regular Retzius line begins where the crystal orientation changes abruptly which is noted as a remarkable cross striations. In this zone enamel rods bend toward the root of the tooth and thereafter bend again to regain the orginal orientation. Such double bending of the enamel rods gives three subdevisions to the crystal arrangement of the enamel rods.
Irregular Retzius lines are not one and all the same. They may be eecognized as forms which are similar to regular Retzius lines, or as a zone where a clear cross striation occur in succession. They may as well be suggestive of a dynamic change of calcification or may be observed as an extreme disorder in the orientation of the enamel rods.

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In order to elucidate the mechanisms of writhing syndrome induced by intraperitoneal injection of acetic acid in mice, a study was made in relation to the motility of gastrointestinal tract.
Judging from the facts that the inhibition of the passage of charcoal meal in digestive tube, the relaxation of isolated intestine and the decrease of excretion of stool, the marked inhibition of the motility of gastrointestinal tract in acetic acid induced writhing mice were recognized. Furthermore, a close relationship between the motility of gastrointestinal tract and stretching movement was observed.
α-Adrenergic blocking agents such as tolazoline, phentolamine, dibenamine, phenoxybenzamine and hydergine inhibited stretching movement strongly in conjunction with recovery of depressive motility of gastrointestinal tract in writhing mice. The stretching movement was inhibited markedly by serotonin (s. c.) administration and facilitated by dopamine (s. c.) administration. While 35 % of the decrease of total catecholamine contents of gastrointestinal tract was observed at 1 hour after administration of acetic acid intraperitoneally.
These suggest that adrenergic system is concerned with the motility of gastrointestinal tract, and which is very important factor in writhing syndrome.

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