Number of aciduric bacteria in a oral specimen from 213 persons, classified into 15 healthy, 11 calculous, 7 gum inflamatory, 10 pyorrhoeal, 35 carious, 17 caries restored, 22 bridge wearing, 30 denture wearing and 66 miscellaneous in combination of above two or three categories, was counted by the method by Onisi and Kondo. According to the general acceptance, it was agreed that average of lactobacillus count in a group of the same number of carious teeth increased proportionally to the damage of tooth, but individual irregularity was too large to estimate the actual destruction of tooth as well as increasing destruction within certain period. In average number, countings from calculous and pyorrhoea patients were lesser than those from healthy mouths, and on the contrary countings from both carious and denture wearing mouth were significantly abundant. The hygienic state in a mouth seemed to have some effect to elimination of this organism. As the resulst, it was stressed that Lactobacilli opportunistically grow in a mouth, once a favorable enviroment is established there in some way, and its numerical increase does not respond to immunological state of dental caries.
The retaining force of inlays cemented with self-curing resin and zinc phosphate cement was studied, testing itself and the surface adhesion as an element of it. The following results and decisions were obtained. 1. The surface adhesions of resin and cement were respectively 1.6 and 7.2 kg/cm2 to dentin, and 8.4 and 18. 8 kg/cm2 to enamel. 2. The retaining force of resin was about one third that of cement. However, that of resin will be kept longer because of its excellent chemical stability. The clinical usefulness of the selfcuring resin as a cementing medium for inlays will be decided in further studies. 3.The adhesion to dentin was considerably weakened by water, though that of resin to enamel was less weakened and that of cement to enamel was reversely stronger in the wet state. Enamel walls are considered as excellent cementing bases. 4. The adhesion to coarser walls was stronger than that to smoother walls. Such a difference was great on enamel but slight on dentin. 5. Upon analysing the retaining force of the simple column inlays tested here, the interlocking force took 83% in the case of resin and 87% in that of cement. The surface adhesion took 17% and 13% respectively 6. The adhesion of resin is very strong in dry state but very week in wet state. The direct resin filling therefore must be kept perfectly dry during its setting to prevent it from separating from the cavity wall by its curing shrinkage. Besides, the cavity for resin filling must be given round undercuts with definite jaws for mechanical retension.
Mechanical properties of commercially pure titanium wires more than 99.4% Ti (KS 70) were tested and the results obtained were compared with those of commercially superior pure titanium wires more than 99.5% Ti (KS 50) previouly reported. The tensile strength and elongation of KS 70 wire were higher than those of KS 50 wire (Fig. 2) . Repeated bending value of KS 70 wire, however, was inferior to that of KS 50 wire (Fig. 6) . Modulus of rigidity and torsion value were little affected by impurities (Fig. 3 and 4) . KS 70 wire was harder than KS 50 wire and was harden remarkably by cold drawing, and surface hardness was higher than center (Fig 7) . From these considerations, the higher purity titanium seems to be suitable for clasp wire.
Tensile strength, grain size and fiber texture of titanium wires which were annealed at 350°—800°for 0.5-1000 min, were examined by means of tensile test, micro-scopy and X-ray diffraction. The titanium wires examined, the one was pure more than 99.4 %Ti and was drawn to 20, 50 and 70 % reduction of area (KS 50) and the other was pure more than 99.5 % Ti and was drawn to 25, 50 and 80 % reduction of area (KS 70) . The results obtained were as follows : (1) In isothermal recrystallization curves, strength was decreased by two stages, the first gradually and the second rapidly. (2) Relations between recrystallization temperature and heating time were shown in Fig. 3. (3) Values of activation energy were calculated from in t-1/T linear relations and were shown in Table 3. (4) Relation between grain diameter D and heating time t was expressed by an equation of the form D=k tn and values of n were shown in Table 4. (5) In drawn wires of both KS 50 and KS 70 titanium, the‹10 1 0›direction was parallel to the wire axis and after full annealing, the texture had the‹11 2 0›direction parallel to the wire axis.
In order to give more strength-especially high elastic limit-to Kroll titanium as dental use for clasps and bars, zirconium, aluminium, chromium and silver were added to Kroll titanium up to about 2%. Tensile test, hardness test and corrosion test were taken on these alloys and these results are shown in Table 1 and 2 and Fig. 2 in this paper.
In dental practice, whether brazing is easy or not is important. A brazing process for titanium in air was studied using town-gas as a heat-source. Due to the gas-active properties of titanium, it seems to be necessary to braze it at a low temperature. The alloys and the fluxes for low temperature brazing were studied by us and it was found that some alloys in Table 1 and 2, and fluxes in Fig, 3-7 were satisfactory for this purpose.
Brazing of titanium in air was studied, by using these alloys and fluxes which have been discussed in the previous report. Table 1 shows the results of tensile tests under the combination of these alloys and fluxes.Most of them were ruptured at the brazed part by shear stress, however some were broken by tensite stress. Alloys containing Ag 34-36%, Cu 17-19 %, Zn 5-15% and Cd 34-38% and fluxes I or IV were excellent as shown in Table 1. The micro-structures of brazed specimens were also studied. Finally, these results stated above were compared with those of Dececco et al. The brazing processes which were studied in this paper were excellent in various points because of low brazing temperature utilized.
Thermal expansion (Table 2, 3, 4, 5 Fig, 1, 2), strength (Fig. 4, 5), transparency (Table 6. Fig. 3) and spalling resistance of porcelain teeth in K-feldspar-quartz, K-feldspar-sand, and in K-feldspar-quartz-kaolin systems were studied. The properties vane considerably according to the mixing ratios of raw materials, and a good result was obtained from the sample containing 60% of K-feldspar and 40% of quartz in quartz-K-feldspar system. The mixture of sand or kaolin and K-feldspar base did not give a satisfactory result.
This study was proceeded to compare the chemical composition, strength and microstructure of porcelain tooth in the market. The composition of the samples are falling mainly on the K-feldspar-quartz-kaolin system. The choiced of the method of mixing and baking is important for the improvement of the porcelain teeth.
The use of acrylic resin teeth in dentures to replace the usual porcelain teeth has gained considerable favor during recent years in Japan. But very little is known about the physical characteristics of the resin teeth produced in our country, so we have studied about their properties with other countries products. 1) The composition of resin teeth are essentially polymethylmethacrylate, but some of teeth contain a cross-linking agent (sample 1, 7, 8) . 2) The construction of resin teeth were consider in view of the sagittal section of resin teeth (Photo 1) . Many of the teeth were processed by the powder-liquid method, and some were processed by an industrial injection molding process (sample 2, 4) . 3) The knoop hardness number of resin teeth are about 17-18 except the sample 5 of K. H-N. 19. The abrasion resistance of the resin teeth are measured by mean of a dropped carbolundum method, and it is estimated that he wear down amount by the dropped carbolundum on resin teeth surface are approximately treble amount of polyurethan teeth (sample 11) . The result of experiments it found that the resin teeth on the market exhibit desirable physical properties as a polymethylmethacrylic resin teeth, but the aim of artificial plastic teeth must be to improve the hardness and abrasive resistance by the application of new plastic materials.
A 14-month-old half-blood boy, whose father is an American, is presented. The erupted deciduous teeth, permanent tooth-germ and alveolar bone were studied both histologically and physico-chemically. Marked incisal attrition was observed in the deciduous incisors. A decrease in microhardness of the enamel and dentin was observed. Although a decrease in amount of inorganic materials were found, the chemical composition of the dentin was similar to that of normal dentin. The pulp chamber did not decrease in its size. The tooth germ of permanent incisor showed hypoplasia and hypocalcification of the dentin. The pulp chamber was wide. The remodeling process of the alveolar bone seemed to be disturbed.