SD rats were continuously given only lactobacillus drinks (Calpis or Yakult) for 9 or 12 weeks from 5 weeks of age. After that, the occlusal surfaces of the lower molars were observed by microscopy, microradiography, and scanning electron microscopy.
Calpis and Yakult accelerated the attrition of left or right molars with the aid of occlusal functions and because of the habit of taking the water bottle in the mouth. The occlusal surfaces of the dentin showed remakable changes which were considerd the effects of acid erosion. In the fissures of enamel and dentin, decalcified zones resembling early caries were frequently observed. These lesions were more clearly recognized in the molars of recieving Calpis than in those recieving Yakult.

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Dextranase-producing microorganisms were isolated from the dental plaque formed in 3 hr on the cleaned buccal surface of the maxillary molars of adult volunteers by the Blue Dextran agar plate method. Dextranase producers were detected in 5 of 8 plaque samples and their proportion varied ranging up to 2.57% of the total number of colonies recovered. Three representative isolates possessing higher dextranase activity were tentatively identified as Streptococcus mitis. Cells of the isolates agglutinated upon addition of human whole saliva supernatant and were adsorbed on uncoated and saliva-coated hydroxyapatites. In the mixed culture with a Streptococcus mutans strain in sucrose broth, two of the isolates inhibited the sucrose-dependent strong adherence of S. mutans cells on glass and enamel slabs, whereas one isolate did not affect the cellular adherence. The in vivo role (s) of the dextranase-producing plaque flora is discussed with respect to the establishment and persistence of cariogenic S. mutans on tooth surfaces.

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A short-term rat experiment was carried out in order to investigate the time course of the incidence of rat molar caries and the variation in the number of the oral cariogenic microorganisms or their biochemical properties. From the results obtained, an attempt was made to clarify the oral environment at the time of incidence of initial caries.
In the time course of the caries incidence, carious lesions appeared as soon as rat were introduced to a sucrose diet and increased quickly. At day 15, carious lesions were found in about 80% of all the fissures. Moreover, the rate of caries incidence was unchanged for the first 6 days. According to the caries score, the mean number of carious lesions of the rat group which were fed a non-sucrose diet was lower than that of the experimental group, so that a difference in caries incidence was seen even in short-term experiments.
As to the bacteria existing in the teeth, according to the incidence of the initial fissure caries, variation in the quantity of some microorganisms occured. Regarding S. mutans, the isolation rate and the number were not lower in the rats fed a non-sucrose diet than in the rats fed a sucrose diet.
In biochemical tests, the strains of S. mutans derived from sucrose diet group strongly fermented sucrose, while a strain from the non-sucrose diet group had lower final acidities from glucose or starch than those of sucrose.
From these aspects, regarding the incidence and progress of incipient caries, I suggest that biochemical factors of the various bacteria have stronger influence than their mere numbers, and it seems likely that the oral environmental factors, especially sucrose, have an important effect upon the biochemical behavior of oral microorganisms, and then the biochemical properties are changed to cariogenic. I believe that the early establishment and evaluation of oral environment factors such as diet and microorganisms are very important in caries prevention.

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Since the first report of Goldman describing an early investigation of laser effect on carious lesions in 1964, there has been considerable interest in the use of lasers in dental research. Kinersly reported in 1965 that a ruby laser can ablate stains but leaves a chalky spot in the area of impact.
The purpose of this study was to determine the effect of a Q-switched Nd-YAG laser in removing dental deposits safely and easily, and especially in removing intrinsic enamel pigmentations and pit & fissure contents which could not be bleached by cleaning with an ultrasonic scaler.
Thirty-nine human teeth with dental deposits or pigmentation were irradiated with a Q-switched and pulsed Nd-YAG laser at a wavelength of 1.06μm using an articulating optical manipulator. In this connection the giant pulse laser was expected to have an ability to increase the acid resistance of enamel as reported by Yamamoto in 1974.
Numbers of teeth provided in the present experiment were 5 for intrinsic stain, 9 for calculus, 11 for extrinsic stain, 8 for plaque, and 6 for pit & fissure contents. Energy density was 1.2-2.7J/cm²/pulse, repetition rate 40 pps, and power output 85-100 mJ/pulse.
Impact of the Q-switched Nd-YAG laser caused bleaching of stains and removal of deposits and pit & fissure contents. No chalky spots or craters were found microscopically on the enamel surface. These results strongly suggested the clinical applicability of Q-switched Nd-YAG laser in removing dental deposits, intrinsic pigmentation, and pit & fissure contents.

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The purpose of this study was to investigate the sensory response of dental pulp in vivo and the threshold of the occurrence of any subjective symptoms when living human teeth were irradiated with a Q-switched Nd-YAG laser. These experiments were carried out with the cooperation of two volunteers from our dental school. The subject teeth were sound premolars which were expected to be extracted for orthodontic purposes.
In preliminary experiments with extracted teeth an increment of temperature at the tooth surface and at a side wall of the pulp chamber was measured during exposure to radiation under various conditions. An estimated optimal energy for the in vivo experiment was obtained from the preliminary experiments.
The results from the experiments in vivo were the following. 1) Unpleasant subjective symptoms did not occur with a laser energy of less than 10.83J/cm²/pulse at a repetition rate of 28 pps. 2) A clinical pulp examination such as the electric pulp test, the thermal test and/or the response to percussion revealed that no sensory abnomality occurred in any of the irradiated teeth under the experimental conditions.

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Two kinds of sewing needles (Sokyu), No. 1 (Diameter 1.14 mm) and No. 4 (Diameter 0.89mm), were used to examine the dental caries of 295 children in elementary schools. Caries was detected at occlusal pits and fissures of permanent molars (including buccal surface pits of 1st and 2nd molars) and at lingual pits of permanent anterior teeth, and cavity detection rates were calculated. Cavity detection rate by No. 4 needle was higher than by No. 1 needle, and No. 4 needle detected 1.7 to 2.5 times more cavities than No. 1 needle in each school grade. There were statistically significant differences at a probability of less than 0.001 in each school grade.

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The effect of fluoride ion (NaF) on proliferation was examined in Vero cells derived from kidney tissue of Cercopithecus aethiops. Fluoride ion concentrations in the growth medium of 0.1, 1, 10, and 100 ppm were employed in the first experiment and of 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, and 100 ppm in the second. Simplified replicate cultures were prepared and cultivated for about five days. After cultivation, cell growth was estimated by enumerating cell nuclei concentration. A relationship between cell proliferation and fluoride concentrations in the growth medium was confirmed statistically and details from control and experimental cell growth were investigated.
Cell growth was accelerated by 17-18% with increasing fluoride ion concentrations of 1-10 ppm in first experiment. Maximum proliferation occurred at 2 ppm in the second experiment with a 22.6% rate of increase. Thereafter cell growth was reduced with increasing fluoride ion concentrations until near 100 ppm, at which concentration cell growth was completely stopped in both experiments.

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The purpose of this study was to investigate the effect of the solutions of titanium fluoride compounds on human enamel. Experiments were performed in vitro, and solutions of (NH₄) ₂TiF₆ (ammonium titanium fluoride, 9000ppmF^-, pH 3.4) and SrTiF₆·2H₂O (strontium titanium fluoride, 9000ppmF^-, pH 3.2) were applied to powdered enamel and intact enamel. APF solution was used for comparison with the titanium fluoride solutions.
In the experiments with powdered enamel, the fluoride uptake from fluoride solutions and the estimation of the Ca/P mol ratio in enamel were examined by means of chemical analysis. X-ray diffractometry was performed by the use of an automatic recording X-ray diffractometer to observe the crystallinity and identify the reaction products in enamel following the application of fluoride solutions.
In the experiments with intact enamel, electron probe X-ray microanalysis was carried out to determine the distribution of Ca, P, Mg, F, Ti and Sr in fluoride-treated intact enamel surfaces. An acid solubility test and scanning electron microscopic study were performed on these enamel surface.
In the chemical analysis, the fluoride concentrations in powdered enamel were increased by the application of highly concentrated fluoride solutions. However, the Ca/P mol ratio of titanium fluoride-treated enamel was similar to that of control enamel. The chemical analysis and X-ray diffractometry showed that no CaF₂ was present in the titanium fluoride-treated enamel, while a large amount of CaF₂ was Produced in the APF-treated enamel. Furthermore, no other reaction products were found in the titanium fluoride-treated enamel and the enamel retained its hydroxyapatite structure. The crystallinity of enamel apatite was increased by the fluoride.
In the electron probe X-ray microanalysis, the uptake of fluoride and titanium by the enamel surface was investigated in titanium fluoride-treated enamel and the uptake of strontium was seen in the strontium titanium fluoride-treated enamel. The acid solubility test proved the acquisition of high acid resistance by the enamel. Scanning electron microscopic study showed that there was glaze formation on enamel surfaces caused by the effect of titanium and that the acid-etched enamel surfaces after treatment with the titanium fluoride solutions had an acid-resistance picture.
From these findings, it is suggested that ammonium titanium fluoride and strontium titanium fluoride seems are useful as agents for fluoride topical application in clinical use.

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