The reactions of ¹¹³SnF₂, Sn¹⁸F₂, Na¹⁸F, and APF (acid phosphate fluoride, labelled with ¹⁸F) solutions on human dental enamel surface under conditions similar to topical application in vivo were investigated.
The experiments supported the following conclusions.
1) A remarkable accumulation of Sn in or on the enamel surface was found after the runs of repetition with SnF₂ solution, whereas a minimum amount of F accumulated as compared with NaF or APF solution.
2) The enamel surface treated with SnF₂ solution aquired more remarkable resistance to acid than treated with NaF or APF solutions.
3) After the treatment wtih SnF₂ solution, the greater part of Sn taken on the enamel rapidly turned into acid-insoluble compounds.
The major amount of these Sn compounds was found on the enamel surface.
4) Fluoride taken by the enamel from fluoride solution diffused immediately into the surface layer of the enamel. The easy release of these fluorides by decalcification indicated that a fair amount of fluoride in the enamel remains in unreacted form.
5) Statistic analyses, however, revealed no significant correlation between Sn or F uptake and increased resistance of enamel to acid.
6) In the analyses of the Sn/F ratio accumulated on the enamel and the amount of F and the Ca/P ratio released by acid, it could not be shown that the Sn compounds on the enamel are either SnPO₄, Sn₄ (PO₄) ₂ (OH) ₂H₂O, or Sn₃F₃PO₄, as had been formerly reported.
7) Although the enamel surface was polished with Al₂O₃, a striking variation of Sn uptake by the enamel was found. This variation of Sn uptake might be dependent on both random difference from place to place in one tooth enamel and on individual tooth differences, both of which consist of unknown factors.
F uptake also varied markedly from tooth to tooth, but variation from place to place in one tooth enamel was negligible.
8) Incipient carious enamel took up Sn more strongly than the intact enamel.

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Japan-from ancient times-has been blessed with an abundance of drinkingwater. The main supply of drinking water for Japanese people was from streams, rivers and wells. However, after the war, construction of water work system was encouraged as these were discovered to be more sanitary. People using tap water also increased rapidly and presently there are over 76.2%, whereas before the war, there were less than 30%.
Examination has found that well water includes fluorine ions (F^-) which is abnormally effective solvent. In areas whose water contains fluorine, this was discovered to be the cause of dental caries. However, other research has proved that with the right level of fluorine, dental caries can be reduced.
Recent years have seen the spread of water work systems in most cities, towns, and counties, and most of the residents depend on them. Generally speaking water supplied through waterwork systems does not include much fluorine. But as it was discovered that the correct level of fluorine prevents dental caries, it was suggested that fluorine be increased to this level. Nevertheless, due to the regulations concerning the usage of fluorine, there were many opponents of this suggestion. As population using tap water, the author and his cooperators made research and experiments to find the relationship between tap water and dental caries to determine what the right level of fluorine should be in drinking water.
1. Research was done in 491 cities, towns, and counties (Tap water was examined in 491 locations, well water in 485 locations). Samples of water amounted to 1657, involving 63, 710, 760 people.
2. In Japan, 76.2% of the areas are supplied by water work systems. Of the areas examined, 87.7% were using tap water.
3. As for pH, 68.5% of the people, among the areas examined, were using alkaline water whose mode was pH 7.1-7.5.
4. Of the areas examined, 69.5% of the people were using water with a fluorine density of below 0.099 ppm. This was the highest. Only 150, 000 people which amounted to 0.2% of the population involved in this research were using water with a fluorine density whose density was greater than that specified by regulation.
5. Geologically, there is a slight relationship between the density of fluorine ions, chlorine ions and pH in water extracted from the same area. However, generally speaking no significant relationship can be found.
6. Relationship between fluorine ion and caries prevalence ratio was proved as follows: when fluorine ion density is between 0.30ppm to 0.39 ppm, the prevalence ratio is 45.5 % which is the lowest, whereas when the density is below 0.20ppm, the prevalence ratio increases rapidly. Likewise, it can be seen that when fluorine density is over 0.40ppm, the prevalence ratio will also increase rapidly.

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The relationship between periodontal diseases and osteoporosis were examined between farm and fishing villagers with different prevalences of periodontal diseases. The correlation coefficient between the periodontal indices and the number of the lost tooth is significant (r=0.343, P<0.01). An increment of the periodontal indices of the subjects was observed to parallel osteoporotic changes of the lumbar vertebra (0, I, II type).
Both the periodontal index and the prevalence of the osteoporosis were higher among the farm villagers than among the fishing villagers.

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One of the changes resulting in carious infection of the dental tissues is considered to be decalcification by acids which bacteria produce. The decalcification would proceed under the neutralization process of a small quantity of acids by dissolution of the dental tissues surrounding the infected site.
The reaction was investigated using equipment capable of recording pH changes in suspension of dental tissue powder after addition of a certain amount of acid. Dentin or enamel powder was suspended in 100 ml of CO₂-free distilled water, 1 ml of acid was added, the mixture was stirred at 37°C and the pH movement of the suspension was measured. The pH value dropped immediately after addition of the acid, and thereafter increased slowly to return to the constant value. According to the curve of pH change, the pH value at 2 hrs. afer acidification was defined as this final constant pH. Effect of powder size, the concentration of suspension, kind and amount of acids on the pH change was investigated, and dissolved Ca and P in the suspension were estimated.
The results were as follows:
Smaller particles of tooth powder and higher concentration of the suspension caused a slighter drop and a faster recovery of pH. Lactic acid had the strongest decalcification capacity as compared with other acids: acetic, formic, propionic, succinic, and butyric acid. The solubility of enamel is less than that of dentin because the final pH of enamel is lower and recovery time is longer than that of dentin.
Assuming that acids were produced at the dentino-enamel junction, acids would be immediately neutralized by the dissolution of dentin which dissolves ealier than enamel and enamel would hardly be affected. These results also explain the formation of the half-moon shaped decalcification which is observed only at the dentin site of rat molars in the early stage of experimental caries described in a previous report. (Onisi et al. 1968).

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In the present study, the authors concerned themselves with the application of a 3-grade contour line plotter (commercially known as the M-3 plotting device) for analyses of the morpholgies of the teeth and palates as well as antagonistic relationships of the upper and lower teeth in terms of stereoscopic photographs. In basic considerations of the plotting device, particular attention was here given to its accuracy. By way of material, three threecornered columns with angles of 60°, 90° and 120° were manufactured of yellow hard plaster. These specimens were stereoscopically phothgraphed at three different distances of (i) 350mm, (ii) 400mm and (iii) 450mm.
Tow stereoscopic photographs taken under each condition were then subjected to the plotting of contour lines by the use of the M-3 plotting device.
Measurements consisted of the length of vertical and horizontal arcs of the column base, the product of basal area and sectional area at a height of 5 mm from the base, and the angles. The actual measurements of the plaster specimens were compared with those of contour line plottings so as to compute differences between the two sets of values.
As a result, it was established that differences between the two were reasonably small within the inevitable bounds of the plotting device. For this reason, this plotting device can be used for future analyses with a tolerable degree of accuracy.

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For the study of dental occlusion in the light of oral hygiene, it is necessary to elucidate fully the antagonistic relationships between the upper and lower teeth and their contact conditions. Although there is a relative abundance of published research literature on these matters, what is to be accepted as conclusive is still scanty. A proper understanding of the relationships between the upper and lower teeth is particularly important for the determination of masticatory efficiency but, so far, many methods of determination are by no means uniform and reported data are at variance with one another.
As a first step toward a better understanding of the masticatory efficiency from a hygienic point of view, the author studied the antagonistic and occlusal relations of teet in terms of cast models and carefully reproduced their curved planes on sheets of paper by the use of a contour map technique. The present study consequently brought out the following conclusions.
1. A comparison of the plane and stereoscopic photographs in terms of the precision of measuements revealed that errors were much fewer in the latter. Therefore, stereoscopic photography is recommended for the photographic measurement of cast models.
2. A benchmark axis was established for the upper and lower molars for the determination of their observational direction.
Efforts were made made by a projection to find out how much inclination of this axis would occur to the buccloingual side at the eruption. As a result, it was found that, on the average, the upper first molar inclined to the buccal side by 8.0° and lower first molar to the lingual side by 15.0°.
As there is a difference of 7.0° betweem the two, it can be seen that these two teeth invariably erupt in the same direction.
3. The section sheets of contour lines were prepared with certain standards by overlapping the contour planes of the lower and upper first molars at the centric occlusion. In terms of the section sheets of contour lines thus prepared, there were, on the average, 6.3 contacts between the two including the point and suface contacts.
4. When the antagonistic distances were compared between 2 lingual cusps of the upper first molar and 3 buccal cusps of the lower first molar, the measurements were as follows.
Lower cesial buccal cusp top 0.15mm
Upper mesial lingual cusp top 0.28mm
Upper distal lingual cusp top 0.38mm
Lower distal buccal cusp top 0.42mm
Lower distal cusp top 0.58mm
As is seen from the above values, the top of the lower mesial buccal cusp is in the most intimate occlusion.
5. By the application of a contour line technique, it has been possible to portray graphically various spots of the teeth that are in intimate occlusion, in partial occlusion and those spots which are not in occlusion at all. At the same time, destances and antagonistic relationships can be numerically given.

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The present study is part of a series of research activities, conducted by the Department of Hygiene, Nihon University School of Dentistry, for many years, concerning the occupational, human engineering and environmental aspects of the dental clinician in the light of hygiene.
The author was concerned here with the effects of various postures, cutting operations and the noise of the dental air-turbine engine on the dentist in his routine clinical environment.
For the prescribed purpose, a sample of six dentists who ranged from 24 to 39 in years and were in good health was selectively used. These subjects were measured as their maximum blood pressures and heart beats in connection with the following 3 items: (i) changes that would take place when on operator moved from the supine position to sitting and standing postures, (ii) influences on an operator of exposure to the rotary noises of dental air-turbine engines and cuttiong operatins, and (iii) vital changes in an operator between dental work in standing and sitting postures. For the measurements, use was made of the Shimazu maximum blood pressure automatic serial recording apparatus (Scs-301).
As a result, the author arrived at the following salient conclusions.
1. The maximum blood pressures were, in order, in the staning, sitting and supine postures. The heart rates revealed an identical tendency, being in the order of standing, sitting and supine postures. There was computed a significant difference among these values.
2. The exposure of subjects to the rotary noise of the dental air-turbine engine did not directly affect the maximum blood pressure and heart beat on their part.
At the time of cutting operations, the maximum blood pressure registered a definite increase. On the other hand, the heart rate registered a decrease though to a very slight degree.
3. In common with the operations both in standing and sitting postures, tendencies of increase in the maximum blood pressure and heart beat were difinitely observed in connection with the treatment of root canals and the preparation of abutment teeth. These tendencies were particularly manifested in operations in the sitting posture.

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A sample of 100 lower secondary school pupils was carefully selected from those in whom all the upper and lower teeth had erupted with the exception of third molars by excluding those pupils who were defective in normal arch, suffered from the caries greater than C₃ or those who did not show any symptom of the gingivitis at all. PMA indices obtained of these subjects were put to the computation of correlative coefficients (r) to find out what tooth or teeth would be most representative of PMA findings of the anteriors, molars and jaws.
As the result, it was found that the correlation between 16 teeth consisting of the upper and lower first molars and 12 anteriors, and jaws gave r=0.96, the coefficient being satisfactorily representative of the jaws. We call this the AM method of PMA indices.
The correlative coefficient between 12 upper and lower anterior and jaw PMA indices was r=0.74 with 1% less risk than the above AM method. Further, the correlative coefficient between upper and lower 12 anteriors and either 1||1, 21||12, 31||13 or 32||23 and between them and six teeth in 321||123 was respectively 0.76, 0.88, 0.80, 0.82 and 0.89.
The correlative coefficient between PMA findings of the upper and lower first molars to which 1||1, 21||12 or 321||123 was added and those of jaws was respectively 0.82, 0.84 and 0.85.
From these measurements, it is to be concluded that for epidemiological purposes, PMA findings of the upper and lower first molars to which those of the anteriors are added may be reasonably taken as representative of the jaws. For the purpose of school dental examination for pupils, on the other hand, those of the upper and lower first molars to which either 1||1 or 21||12 is added may serve as a reliable guide.

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I chose Shodo island as aclosed system, because it is separated from other areas geographically and geologically, so that I might define the relationship between fluorine ion density and dental caries in drinking water in one area.
Shodo island has three towns, Uchinomi-cho, Ikeda-cho, and Tonosho-cho. For my research on this occasion, I had the cooperation of the three town offices, and was able to collect tap water and well water in all villages.
In the drinking water, I measured the factors that would seem to have a relation to dental caries. They are pH, fluorine ion density and chlorine ion density.
I examined the relationship between these factors and the prevalence of dental caries in elementary school children, who are the most easily influenced, by these three factors.
As a result, an obvious relation was seen between fluorine ion density and the prevalence of caries. The prvalence is the lowest when the fluorine ion density is 0.300-0.399 ppm. Chlorineion density has a tendency to increase together with flurorine ion density.
I found that both fluorine ion and chlorine ion content is large in drinking water in the western part of the island, and that this content decreases in the eastern part.
As for the pH, almost all the drinking water had a pH of less than 7.0, so that most people on this island drink acidic water.

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In our epidemiological investigations of the gingivitis in school children in the past few years, it has been our experience that a certain subjective judgment is bound to occur in the assessment of findings by different individuals.
The present survey was undertaken with the thought that the elucidation of thses individual differences would put our data in better perspective and, at the same time, would provide a useful tool for comparing our own data with others.
Five examiners were instructed to work on a total of 81 school children without any previous training to bring their respective PMA findings into standardized ratings. The examiners were given a simple briefing at a meeting and left to their own devices. The result was that there was seen a wide degree of individual differences; some found a larger incidence of PMA in the anterior region, while others found the upper jaw more frequent than the lower.
It was definitely revealed that data collected by a more experienced examiner gave more stable findings than the inexperienced.
It is concluded that, in comparing our data with others, it is necessary that sufficient care be given to the degree of individual differences on the part of the examiners.

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We examined the relationship between fluorine ion density, pH, and chlorine ion density in drinking water and dental caries in the Nominoo area, Kurose-cho, Kamo-gun, Hiroshima, from the information about people who came to the School of Dentistry, Tokyo Medical and Dental University Hospital, with mottled teeth. I chose the Shimokurose elemetary school area, which is situated the west end of Kurose-cho, as a control area for the examination of the Nominoo area.
It was found that the area of high fluorine ion density was an area of alluvial soil near Nominoo along the Kurose river, 1, 000m in north-south diameter, and 400m in east-west diameter. Fluorine ion density is comparatively low, 0.1-0.8ppm, in the water of a shallow well where the depth of underground water is less than 10m. In the water of a deep well more than 10m pleep high density, 1.00-8.60ppm, was detected.
Between Nominoo elementary school area where fluorine ion density is high in drinking water and Shimokurose elementary school area where it is compatively low, it is hard to get an exact comparative value of prevalence ratio of pupils statistically because of few examples. But for the pupils of the higher grades, it was found obviously that their prevalence ratio has a tendency to increase in rather high fluorine ion density area. The same tendency is seen between people who use drinking water of high fluorine ion density and people who use drinking water of low fluorine ion density. And as for fluorine ion density and Ph, fluorine ion density is high on the alkalin side and decreases toward the acid side. That value is almost a straight line relation and a recurrent straight line is shown by the equation:
y=2.58x-14.45
The coefficient of correlation is:
ρ=0.7718
In this straight-line relation, chlorine ion density is highest at Ph 6.2-6.7, and fluorine ion density at 0.25 ppm-1.50 ppm.

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In the present survey, the authors examined a total of 426 boys and girls from the 2nd to 6th grades, using prepared questionnaires, concerning their intelligent understanding of oral health according to grade, at the same time, the relationship of this understanding to dental instruction contained in school curricula. A similar survey made by Fukui of our Department before the revision of the elementary school curriculum in 1959 was used for comparative analyses.
As a result, it was found that, compared with boys and girls of other grades, those in the 5 th grade had a much better understanding of oral health. These findings can be attributed to the relatively high frequency of instruction regarding teeth in the natural science and physical education curricula for this particular grade.
In the elementary school curriculum for 1969 in which natural science subjects were mainly taught in the 2nd, 4th and 6th grades, Fukui found that boys and girls in the 4th and 6th grades had much better understanding than those in the 5th grade. The present survey findings present a marked contrast to those of Fukui in this regard.
As for the understanding of other related dental matters, on the other hand, the degree did not vary any appreciably from grade to grade but it was more or less in proportion to the advance in grade. As a possible reason for this, it may be concluded that extracurricular activity as well as home instructions exerted a more beneficial influence than school subjects directly.

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