Dw. Coffelt et al., DETERMINATION OF ENERGY DENSITY THRESHOLD FOR LASER-ABLATION OF BACTERIA - AN IN-VITRO STUDY, Journal of clinical periodontology, 24(1), 1997, pp. 1-7
The Nd:YAG and CO2 lasers have been shown to be bactericidal at relati
ve low energy densities. However, at energy densities exceeding 120 J/
cm(2) (CO2) and 200 J/cm(2) (Nd:YAG), laser irradiation also causes ir
reparable root surface damage. The purpose of this study was to determ
ine, in vitro, the energy density threshold at which microbial ablatio
n could be achieved while inflicting the least amount of damage to the
root surfaces of human teeth. Pairs of Escherichia coli colonies cult
ured on broth agar were treated with a CO2 laser using a pulsed wavefo
rm at approximate energy densities ranging from 3 to 110 J/cm(2). One
of each colony-pair was then examined by scanning electron microscopy
(SEM) and the other subcultured for viable microbes. Roots of extracte
d teeth were lightly scaled and treated by CO2 laser, again with pulse
d beam using approximate energy densities of 3 to 110 J/cm(2): and exa
mined by SEM. Regardless of the level of energy density, residual bact
eria could be subcultured from al laser treated microbial colonies. Th
e inability of the laser to completely obliterate microbial colonies w
as likely due to: depth of energy penetration, difficulty in precisely
overlapping beam focal spots, irregular beam profile, and presence of
microbes at the periphery of the beam focal spot. The threshold energ
y density for bacterial obliteration was determined to be 11 J/cm(2) a
nd that for root damage was 41 J/cm(2). Root damage was evident by cha
rring, crater formation, meltdown and resolidification surface mineral
, and increasing surface porosity. The results of this in vitro study
indicate that when used at an energy density between II and 41 J/cm(2)
the CO2 laser may destroy microbial colonies without inflicting undue
damage to the tooth root surface.