Dye‐mediated bactericidal effect of He‐Ne laser irradiation on oral microorganisms

Abstract

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.

The Possible Application of He-Ne Laser for Dental Plaque Control

“…Clearly, the plaque on the irradiated surface of the tooth was found to occupy a smaller area than that which formed on the unirradiated surface. been studied in our laboratory [1]. Of the various dyes screened, when blue or purple dyes were mainly used together with He-Ne laser irradiation, a killing effect was manifested.…”

“…We have previously reported that mutans streptococci, used as a representative of oral bacteria, were briefly killed by He-Ne laser irradiation [1].…”

“…The number of investigations into the effects of low-power lasers has been extremely limited [1][2][3].…”

“…There have been several reports on the effects of laser irradiation on microorganisms [1][2][3][4][5][6][7][8][9], but most of these reports have been concerned with the bactercidal action of high-power lasers which arises from the heat they produce. However, such high-power lasers cannot be applied for plaque (Received February 25th 1993, Accepted April 12th 1993 control, because the heat produced would adversely affect either the dental pulp or the periodontal tissue.…”

The current status of low level laser therapy in detistry. Part 2. Hard tissue applications

“…Streptococcus sobrinus is sensitive to LLP under these conditions, while Escherichia coli, a Gram-negative enteric micro-organism, is resistant. 25 The effect on the cariogenic micro-organism S. sobrinus is rapid, with leakage of the bacterial membrane detectable after 2 minutes of laser exposure. The bactericidal action of LLP can be obtained with a range of blue, purple, and green dyes within the phenylmethane family, all of which are strong absorbers at 632 nm.…”