A laboratory investigation of the bactericidal effect of a NdYAG laser.

Laser irradiation produces bactericidal effects which may be of use in dentistry. The aims of this study were to investigate the effect of pulsed NdYAG laser irradiation on bacteria in a laboratory model, in the presence and absence of a black dye, Suomi ink. The experiments were carried out in small capillary tubes containing a measured volume of Enterococcus faecalis broth culture. This model simulated the number of organisms that could be expected to occur in an infected root canal. Laser irradiation was delivered from a NdYAG laser via a 320-microns fibre. Powers of 0.3 to 3.0 W were used for 20 to 60 s. Controls received no irradiation. The effect of the black dye was investigated by the addition of a fixed volume to the culture before lasering. The treatments were evaluated for bactericidal effect by comparing the number of viable bacteria remaining in the irradiated and the control specimens. At energy doses of 54 J and above, without black dye, a reduction of 10,000-fold or greater occurred. A similar reduction was achieved at energies above 25 J when black dye was added. These results indicate the energy levels which should be investigated to assess the potential role of the NdYAG laser in endodontics.