Polyurethanes have been recognized as a resin having a characteristically rubbery elasticity. This study aimed to evaluate the possibilities for application of polyurethanes as pit and fissure sealants.
Experiments were conducted on two-component polyurethane systems in which two components are mixed together immediately before use. MDI (Diphenylmethanediisocyanate) was used as the isocyanate component, and three kinds of polyether and two kinds of polyester as the OH component.
The tests for prepared polyurethanes were performed on (1) water absorption, (2) hardness, and (3) tensile strength. The tensile strength on bovine enamel etched with 3M phosphoric acid for 30 sec. was tested after curing the samples at room temperature for 3 days and immersing them in tap water at 37°C for a week. Bubble formation and marginal leakage were also tested. The bubble formation was examined on the etched occlusal surface of human molar teeth. In order to evaluate marginal leakage, penetration of fucsin dye was observed after thermal shock treatment (4°C-60°C) for 3 hrs. followed by the immersion in 0.2% fucsin solution for 24 hrs.
The results obtained in this study were as follows:
1) Water absorption during 5 days was approximately 1-3mg/cm². It was found that the water absorption of polyester-polyurethanes was less than that of polyether-polyurethanes.
2) The hardness value of the material, even that of the material which had the highest hardness among the five kinds of polyurethanes prepared, was only about half that of bis-GMA pit and fissure sealant (Nuva seal).
3) The highest values of tensile strength were obtained at NCO/OH molar ratios of 8/1 and 10/1 in the polyether-polyurethanes, and a ratio of 3/1 in the polyester-polyurethanes.
4) Bubble formation of polyurethanes which occurrs during the curring reaction was minimized by using 30%-50% solids (w/w) in ethyl acetate, since this material could be applied as a very thin film because of its low viscosity and consequently, carbon dioxide gas from the curing reaction could be discharged easily.
5) Using 50% solids in the solvent at an NCO/OH molar ratio of 1/1, the marginal leakage after thermal shock was scarcely noticeable when using MDI/Castor oil of polyester-polyurethane, in contrast to the results obtained with polyether-polyurethane.
6) Using the materials prepared at the NCO/OH molar ratios which showed the maximal tensile strength, marginal leakages after thermal schock were less in the case of the two kinds of polyester-polyurethane consisting of 50% solids in the solvent than in the three kinds of polyether-polyurethane.
7) It is suggested that the material consisting of MDI/Castor oil is promising as a pit and fissure sealant in the two component polyurethane systems.

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As part of a series of studies on polyurethane sealant, this study was done on one-component polyurethane systems which consist of a prepolymer with terminal isocyanate groups and are cured by moisture in the air after evaporation of solvent. A two-component polyurethane system can prepare a variety of elastic materials by changing the NCO/OH molar ratio, whereas the one-component polyurethane system is a prepolymer which is already prepared for application.
Two types of the one-component polyurethane system were chosen for this experiment: polyether type prepolymer (K-0312) and polyester type prepolymer (T-1011) which were supplied for testing by the Nippon Polyurethane Industry Co.. Experimental methods were similar to those of Part I except for the hardness and water absorption tests.
The results of tensile strength showed that, after 3 days curing at room temperature, the values of K-0312 and T-1011 were 58±20 and 85±37 kg/cm², respectively, and after further exposure to tap water at 37°C for a week the former kept nearly constant (61±25) and the latter decreased to 55± 35 kg/cm². These values were lower than the maximum values of tensile strength (90-135 kg/cm²) at each different NCO/OH molar ratio for the two component polyurethane systems. However, they suggest that this type of polyurethane might be useful as a pit and fissure sealant. The observation on marginal leakage showed no appreciable difference between one- and two-component polyurethane systems after thermal shock treatment for 3 hrs.
In conclusion, it was difficult to determine which of both polyurethane systems is more suitable as a sealant, but the one component polyurethane system has an advantageous characteristic which can be used with simplicity from the viewpoint of clinical application. Furthermore, the one-component polyurethane system has the possibility that the curing time could be shortened by the use of proper catalyst.

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To examine the three dimensional morphology of tag-like extensions which are believed to be significant in the formation of bonds between resin sealant and etched human enamel, the present study was made using light microscopy and scanning electron microscopy.
The tag-like extensions formed in many etched labial and occulusal enamel surfaces of permanent teeth showed a honeycomb-like structure due to enamel prisms when observed by SEM and the tag length observed by light microscopy was 2 to 5 times longer than that by SEM. The results suggested that even if sealant was lost from etched enamel surfaces by fracture or/and abrasion, the enamel surfaces retain the part of sealant occluding the micropores of the etched enamel surface, providing a protective barrier against caries.
A three dimensional model of tag formed in etched enamel surface where prism peripheries were demineralized preferentially, consisting of a crater-like foundation with a filamentous or filmy extension on it, was proposed to explain the difference observed in tag length between light microscopy and SEM.

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An enzyme which possesses lytic activity against cariogenic streptococci was obtained from strains of streptomyces in soil and sewage. The strains of streptomyces which produced a highly active enzyme in the culture supernatant were identified as Streptomyces griseus strain H-402 and Streptomyces gloaisporus strain 1829. The enzyme of S. globisporus strongly lysed the strains of cariogenic streptococci in the tris acid malate-NaOH buffer, pH 7.0.
This study is concerned with the estimation of the bacteriolytic activity of the enzyme derived from S. globisporus on cariogenic microorganisms such as the strains of Streptococcus mutans, Lactobacillus casei and Actinomyces viscosus, and also deals with the effect of fluoride ion, sodium N-lauroylsarcosinate and sodium dehydroacetate on the activity of the bacteriolytic enzyme.
Twenty seven strains of S. mutans employed in this experiment were all sensitive to the bacteriolytic enzyme. Dergrees of bacteriolysis were compared with each of 5 serological groups of S. mutans. Strains of group a and b were more sensititive to the enzyme than group, c, d and E. Cariogenic L. casei ATCC 4646 and A. viscosus T₆ were also extremely sensitive, whereas 4 strains of Streptococcus sanguis were less sensitive to the enzyme.
Strains of S. mutans and S. sanguis which showed the least sensitivity to the enzyme were significantly lysed by prolonged incubation with the enzyme.
The bacteriolytic activity was apparently enhanced by the presence of 20 μg/ml of lysozyme or 0.3% of sodium N-lauroylsarcosinate. 0.2% of sodium dehydroacetate was also effective in enhanceing of the enzyme activity. The enzyme activity was not influenced by fluoride ions with a concentration of less than 200 ppm, whereas 40% of the enzyme activity was supressed in the presence of fluoride ions with a concentration of more than 400 ppm. The enzyme activity was also supressed by halide ions such as F^-, Cl^-, Br^-, and I^-.

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Since movement of the body are controlled by a feedback mechanism of sensations it is reasonable to consider that this mechanism also takes part in controlling toothbrushing.
The present study was started on a suggestion that difference in individual toothbrushing force might be related with a feedback mechanism for the sensations of the oral mucous, periodontal membrane, and of muscles and joints of the arm and hand which held a toothbrush.
Twelve people 21-28 years of age were studied under three conditions, 1) the oral mucous membrane only anesthetized, 2) the oral mucous and periodontal membrane simultaneously anesthetized, 3) neither the oral mucous membrane nor the periodontal membrane anesthetized, as to relations between stiffness of a toothbrush and brushing force in reference to change in sensations in the oral mucous and periodontal membrane.
The results obtained were as follows:
When the oral mucous and periodontal membrane were anesthetized, the use of a soft bristle toothbrush decreased brushing force from 100-1, 100g to 100-700g; the use of a hard bristle toothbrush decreased only from 100-700g to 100-600g.
The above difference in decrease indicated that cutaneous sensations of the oral mucous and periodontal membrane were related with a feedback mechanism governing toothbrushing force when a soft bristle toothbrush was employed or over 700g of force was given, and sensations of the muscles and joints of the arm of hand which held a toothbrush were related when a ard bristle toothbrush was employed or less than 700g of force was given.
Since toothbrushing force which greatly influences plaque removal effect is related with sensation which is a physiological factor very difficult to change, an attempt to increase the plaque removal effect needs a great deal of effort.
The next best requirement would be an attempt to make the brushing force as large as possible, or. to increase the number of brushing strokes (prolongation of brushing time) or to improve radically the present brushing methods. So long as a manual toothbrush is being used, it is almost hopeless to increase the plaque removal effect with the present methods.

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Studies were made of 15 women 18-22 years of age having a daily tooth cleaning habit with the rolling method. Each surface of the six blocks of the dental arch was brushed for 10, 15, 20 and 30 seconds; measurements were made of brushing force, brushing strokes, and plaque removal effect on each surface; the relations between the time required for brushing and plaque removal effect, the brushing force and the number of brushing strokes, between the brushing force and the brushing strokes, and the plaque removal effect during brushing, in an effort to clarify the significance of the time required for brushing in reference to brushing strokes and plaque removal effect with the following results:
1) Increase of brushing time from 10 to 15 and then to 20 seconds increased brushing force and brushing strokes with an increase of plaque removal effect.
But the increase from 20 to 30 seconds did not result in an increase of the plaque removal effect.
2) A rate of increase in plaque removal effect accompanying an increase of brushing time showed no difference between the upper and lower jaws. But the increase from 15 to 20 seconds resulted in more increase in the labial and buccal surfaces than in the lingual surface.
3) It was found that the plaque removal effect was marked in the labial and lingual surfaces of the anterior teeth in the upper and lower jaws, and very slight in the lingual surface irrespective of the length of brushing time.
Thus, it was revealed that an optimal length of brushing time with a manual toothbrush following the rolling method for the tooth surfaces in one block proved to be 20 seconds, an optimal brushing force being 650-800g, and an optimal number of brushing strokes 30-35/20 sec.
The data presently obtained of brushing time and the number of brushing strokes are to be recommend for those who give instruction in toothbrushing.

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Increase in the use of a manual toothbrush results in deformation of the brush's bristles. Therefore, it is reasonable to consider the relations among the deformation force, the number of brushing strokes, and the plaque removal effect.
Thses influences were studied on a correlative basis with 13 people 22-28 years of age whose use of a toothbrush (4 minutes once daily for 45 days) was experimentally increased.
The results obtained were as follows:
The degree of deformity of bristles of a toothbrush accompanying an increase in the use of bristles was correlated with brushing force, and brushing force with the number of brushing strokes. Accordingly, an increase in the use of brushing was followed by an increase in plaque removal effect. While a toothbrush was new, the degree of skill in brushing in individuals was hardly recognizable, but it revealed itself after the toothbrush was used for several days.
It was recommended to use a new toothbrush in order that individual difference in the degree of skill of brushing might be eliminated. Among the examinees whose plaque removal effect was 100%, brushing force and the number of brushing strokes were in inverse proportion. Plaque removal effect was found to be high in the upper anterior teeth and low in the lingual surfaces of the lower right and left molars irrespective of the use of a new or an old toothbrush.
Thus, to obtain a higher plaque removal effect it is necessary to use a new toothbrush, or change the brushing method, or pay special attention in brushing those sites which have been low in plaque removal effect. The present results recommend the use of a toothbrush three times daily, for three minutes, three minutes after a meal (3-3-3 formula of toothbrushing) for 13 days. If the optimal time period for brushing obtained in the present study is adopted, about a week's practice will be sufficient.

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In an oral health instruction program it is very important to elevate the plaque removal effect by adequate guidance of toothbrushing. The toothbrushing of an individual is accompanied by manners and customs which are reflected in the brushing force, and the number of brushing strokes is related with the plaque removal effect. Guidance in toothbrushing is reasonably expected in order to improve the plaque removing effect.
Thirteen women 18-20 years of age who had never been instructed as to adequate toothbrushing were trained with the rolling method. Day to day observations were made of the influences of the brushing force, the number of brushing strokes, and the plaque removal effect in these women with the following results:
After instruc tion brushing force was increased, while the number of brushing strokes showed a sudden temporary increase and more decrease than the pre-instruction stage, followed by a gradual increase.
Immediately after instruction, individual differences among the trainees in the brushing force and the number of brushing strokes were slight, because of little familiarity with the training.
This indicated that instruction in a certain brushing method might level off individual technical differences. Several days after instruction individual differences grew larger. This resulted from individuals' degree of adaptation to guidance leading to the establishment of their own habits.
The above changes observed in the brushing force and the number of brushing strokes after instruction tended to be similar in all sites of brushing. In other words, the merit of instruction was reflected in all sites with a resultant increase of plaque removel effect.
Throughout the pre- and post-instruction period it was found that the examinees with a 100% plaque removal effect had an inverse proportional relationship between brushing force and the number of brushing strokes, that the labial surfaces of the upper and lower frontal teeth showed high plaque removal effect, and that the lingual surfaces of the right upper and lower molars showed low effect. This finding indicated that the fundamental principles of toothbrushing could not be changed so long as a manual toothbrush was employed. In carrying out a toothbrushing training program it is important to take into consideration individual trainees' manners and habits in brushing.

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Hydroxyapatite, having a crystallinity similar to biological apatites, is required for X-ray crystallographic and other studies in biological apatites.
Our studies were made on synthesized compounds having a crystallinity similar to human enamel prowder. Hydroxyapatite was prepared by a modification of the alkaline precipitation method of Napper.
The synthetic hydroxyapatite X-ray powder diffraction patterns were similar to human dental enamel and suggested a similar degree of crystallinity.
Analysis of the composite hydroxyapatite sample showed that the Ca: P ratio was 1.62±0.02. The sample was thus calcium-deficient hydroxyapatite, but here too, it was similar to human dental enamel.

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