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Little attention has been given to the bactericidal effect of laser irradiation, particularly using low-power energy lasers. It has been demonstrated that He-Ne laser light has an inhibitory action on dental plaque. The purpose of this study was to investigate the bactericidal effect of He-Ne laser irradiation on cariogenic microorganisms. The bactericidal effect was determined by the formation of a growth-inhibitory zone or by the counting of viable bacterial colonies. Streptococcus sobrinus AHT that is a Gram-positive microorganism was sensitive to He-Ne laser light, but Escherichia coli, a Gram-negative microorganism, was resistant. The effect of several dyes necessary to instigate a bactericidal action was also examined. A growth-inhibitory zone was observed using 10 kinds of blue, purple, or green dyes, which were mainly phenylmethane dyes. The leakage of potassium from S. sobrinus AHT following laser irradiation was determined using an atomic absorption spectrophotometer. The leakage began to increase following irradiation for 2 min, and reached a plateau following irradiation for 30-60 min. Moreover, to examine some changes in the dye itself following laser irradiation in the absence of bacteria, ultraviolet-visible absorption spectra and 1H NMR spectra were recorded. In this study, it was indicated that the bactericidal effect on cariogenic bacteria by He-Ne laser irradiation was efficient only in the presence of specific dyes. It is suggested that this laser may be suitable for clinical applications in preventive dentistry.

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Abstract:The purpose of this study was to investigate the incidence of congenital abnormalities of deciduous teeth including fused teeth, congenitally missing teeth, peg-shaped teeth, and supernumerary teeth, and their relation to maternal and child conditions during pregnancy or delivery. The abnormalities were also studied from the hereditary aspect. The subjects were 12,812 children aged three years who visited the East Health Center in Fukuoka City for dental health examination during [1983][1984][1985][1986][1987][1988][1989][1990].Fused teeth had the highest incidence. The incidence of fused teeth was 4.77%, including the incidence of congenitally missing teeth. Fusion of central and lateral incisors was observed with the highest freqency. Total rate of incidence of congenital abnormalities was 4.89%. No significant longitudinal changes in the rate of incidence were seen during the period of investigation. However a marked elevation of the rate of incidence of abnormalities during the past 50 years was suggested by comparison with data reported previously in Japan. Most of the abnormalities (91.5%) were found in the lower teeth. Incidence on the right side was significantly higher than on the left side. Incidence of abnormalities in deciduous teeth has no significant relation to maternal abnormalities during pregnancy, maternal age, or the weight of the child at birth. Bilaterally occurring abnormalities and fusion of canine and lateral incisors showed stronger hereditary influence than other types of abnormality.

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