Through most of the two decades period after the 2nd World War. a remarkable growth accerelation has been observed in the phisique of primary and middle school pupils residing in Kokura Ward, Kitakyushu city, although it seems that a stationary phase of the growth rate has already set in by around 1963. The growth accerelation in those years was especially marked in the middle school pupils, while it was less marked in the primary school pupils, and especially least marked in pupils of lowest grade. It was characteristic of the post-war growth pattern that the growth accerelation with respect to the body length and body weigh was larger than of the prewar form toward a slim form has been taking place. In parallel with the above change, the tooth exchange in those pupils, and tooth growth itself was likewise accerelated. In addition to this, however, much increase in the incidence of tooth caries obserbed through those years, the rate of increase, however, being leveled off since 1963. The high incidence of tooth caries obserbed may be caused mainly by a asudden change of post-war mode of living increased consumption of sugar products, especially of a variety of sweat juices. In view of these observation, more powerful effort shuld be exerted to promote the dental health education program toward both parents and their children, for the prevention of dental decay and for complete treatment means to cope with the present dental health problem for these young population may be the earliest possible therapeutic treatment of the teeth to be conducted at least 3 times annualy.

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A study was conducted on the possible effect of AH-26, a root-canal filling material having an epoxy-resin basis toward the connective tissues of rats, with reference to Yoshida Paste, N_2, and Homosfuran Triozinc Paste as control materials. 1. Immediately after the mixing, a definite amount of all four filling materials was respectively introduced into subcutaneous connective tissues of the back of adult rats, and the animals were sacrificed on the 1st, 3rd, 7th, 14th and 21th postoperative days. The materials introduced and their surrounding tissues were exciced from the animals and prepared for the microscopic examination. 2. The study revealed that throughout the experimental period, Yoshida Paste produced a slight inflammatory response only in earliest period of experiment, which could be readily brought to normal by the formation of newer granular tissues. Such favorable effect was also observed in AH-26, although in lesser degree. Homosfuran Triozinc Paste was worse than Yoshida Paste and AH-26, and N_2 produced so severe inflammation in the tissues that it could no longer be repaired. Consequently we consider that Yoshida Paste and AH-26 are more compatible with living connective tissue than Homosfuran Triozinc Paste and N_2.

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The size of ordinary dentinal tubules is in the range from 1.0 to 4.0 microns in diameter, except for those dentinal tubules of 5.0 micron^<6)> found occasionall in the crown part of molars. So far dentinal tubules over 6.0 micron in diameter have not been reported. On the other hand, with regard to occurrence of capillaries of dentine, it is well known that are present in secondary dentine in calcified state, and in certain species of fish they occur as the vasodentine serving as nutritive channels. The present authors found unexpectedly in the crown dentine of a third molar (horizontal semi-impacted) occurrence of dentinal tudules of enormous size and capillaries, which were thought to represent considerable deviation from the normal. The fin ling are as follows. A material tooth was decalcified with Plank and Rychlo's^<7)> mixture consisting of 2.0 g. of AlCl, 8.5 ml of HCl, 5.0 ml of formic acid, and distilled water to a total of 100 ml. Following the routine procedure, the tooth were embedded in celloidin, and serial cross-section from 10 to 15 microns were prepared, and these were stained with hematoxylin-eosin, Gomori's silver methods. As shown in Diagram, in the crown portion of dentine (canopy dentine), there were found the tubules of enormous size approximately 8.0 to 12.5 microns in diameter sparsely distributed. These abnormal forms were not seen throughout the entire length of the dentinal tubules, but they were only local enlargement of the tubules occurring in the middle layer of crown dentine, and in the range from 100 to 300 microns in length. The dentinal fibers in the tubules shrinked considerably. On the other hand, there were in the vicinity of the tubules also capillaries, approximately 10 to 16 microns in diameter, a part of which still showing vascular appearance, and another part calcified, and still another showing rudimentary appearance. Also, the capillaries dwindled progressively toward the pulpal direction, and no connection thereto was observed.

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At the two laboratories (Shofu Dental Laboratory and G. C.'s Chemical Manufacturing Company), we have made 3 series of investigation, and the results obtained were summarized as follows : 1) The setting time of the copper amalgam specimens was 145.3 minutes on an average with the hand pressure of 3 kilograms and final hand pressure of 3 kilograms, as shown in Table 3. The setting time of the copper amalgam specimens with the hand pressure of 3-8 kilograms, was 129.5 minutes on an average. The compressive strength of specimens obtained under these two different conditions was respectively 1001kg/cm^2 in the former condition, and 1610kg/cm^2 in the latter condition. 2) The setting times and the duration of plasticity with the hand pressure of 3 kilograms and final hand pressure of 3 kilograms for G. C.'s non-zinc-amalgam and their cobined alloys of copper amalgam were obtained respectively as 10.5 minutes and 5.5 minutes for No.1 specimen, 10.0 minutes and 9.0 minutes for No.3 specimens, 8.5 minutes and 8.0 minutes for No.4, as shown in Table 3. 3) The setting time and the duration of plasticity of test specimens with the hand pressure of 3 kilograms and final hand pressure of 8 kilograms for "Pre-non-zina amalgam" and their combined alloys of copper amalgam are obtained with the use of the mechanical amalgamator and the hand mortor and pestle, and the results were shown in Table 4. 4) The setting times of "Pre-non-zinc amalgam" and their combined alloys of copper amalgam obtained by the use of the mechanical amalgamators, were slightly accelerated than those obtained by the use of hand mortar and pestle. 5) The setting time and the duration of plasticity of G. C.'s non zine amalgam specimens with the hand pressure of 3-8 kilograms is illustrated in Table 5. In view of our results, it seems that the proper specimens to be selected for clinical dental use for their ideal dimensional change may be reprsented by no. 1-A, C, D, as listed iu Table 5. 6) As shown in Table 5 and 6, there was no appreciable correlation between alloy-copper ratios and setting times, in contrast to the copper amalgam, where the greater the alloy-copper ratios, the longer the setting times. In order to extend the duration of plasticity further than 8 minutes and to raise the compressive strength above 4100 kilograms per square centimeter, the alloy-copper ratios should be increased to above 6.0 per cent in a single specimen. 7) The flow rates of No.1 to 4 alloys were within the limits of JIS (Japan Industrial Standards) as shown in Table 3. 8) The dimensional changes with hardening were least in No.2 alloys, followed by No.4, No.3 and No.1 alloys in this order as shown in Table 3 and Table 4. 9) The porosities of the copper amalgam alloys are markedly larger and fewer than are observed with other alloys. This would probably be caused by the greater viscosity of the alloy, which tends to trap the air bubbles very firmly within the alloy during manipulation for mixing and filling the material. 10) The mixing times of non-zinc-amalgam alloys and their combined alloys with copper amalgam by mechanical amalgamator should be reduced to about 5 minutes to prevent an excessive contraction due to the over-mixing.

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Marked variations of tooth forms were encountered in two subject's mouths which strongly suggested some degenerative changes. The first case was a female aged 24 who had the upper 1st molars in both sides of jaw with a diminutive size, and these teeth appeared to have 3 cusps, because of the lack of the disto-lingual cusp, apparently by degeneration. The 2nd molars of both dental arches were more pronouncedly reduced in size than the 1st molars, and appeared flattened mesio-distally. These teeth were also three-cusped by the lack of disto-lingual cusp, and, in addition, their disto-buccal cusps showed a sign of degeneration. In this subject, the 3rd molars of both dental arches were congenitally missing and all the other upper molar teeth showed more or less general picture of degeneration. However, the remaining dentition appeared normal in the development. The 2nd case was a male of 38 years of age in whom the upper left 2nd molar was extremely diminutive like a dwarf tooth, and its crown assumed a bud-like form. The same tooth on the opposite dental arch was normally contoured except that its mesio-distal width was slightly reduced. His 1st premolar and the remaining members of whole dentition showed no sign of degeneration, and appeared rather slightly larger sized than the normal.

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