Determination of energy density threshold for laser ablation of bacteria An in vitro study

Abstract

The Nd:YAG and CO2 lasers have been shown to be bactericidal at relative low energy densities. However, at energy densities exceeding 120 J/cm2 (CO2) and 200 J/cm2 (Nd:YAG), laser irradiation also causes irreparable root surface damage. The purpose of this study was to determine, in vitro, the energy density threshold at which microbial ablation could be achieved while inflicting the least amount of damage to the root surfaces of human teeth. Pairs of Escherichia coli colonies cultured on broth agar were treated with a CO2 laser using a pulsed waveform at approximate energy densities ranging from 3 to 110 J/cm2. One of each colony-pair was then examined by scanning electron microscopy (SEM) and the other subcultured for viable microbes. Roots of extracted teeth were lightly scaled and treated by CO2 laser, again with pulsed beam using approximate energy densities of 3 to 110 J/cm2: and examined by SEM. Regardless of the level of energy density, residual bacteria could be subcultured from all laser treated microbial colonies. The inability of the laser to completely obliterate microbial colonies was 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 energy density for bacterial obliteration was determined to be 11 J/cm2 and that for root damage was 41 J/cm2. Root damage was evident by charring, crater formation, melt-down and resolidification surface mineral, and increasing surface porosity. The results of this in vitro study indicate that when used at an energy density between 11 and 41 J/cm2 the CO2 laser may destroy microbial colonies without inflicting undue damage to the tooth root surface.

Clinical efficacy of semiconductor laser application as an adjunct to conventional scaling and root planing

“…Laser applications in the field of periodontology have been of enormous scientific interest throughout the last decade and a variety of laser systems have been investigated in numerous in vitro [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and in vivo studies [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. In the treatment of inflammatory periodontal diseases, lasers may contribute to the bacterial reduction in periodontal pockets as well as to the removal of calculus and granulation tissue and can be used for contouring hyperplastic gingiva.…”

In vitro laser ablation of laboratory developed biofilms using an Nd:YAG laser of 532 nm wavelength

“…Even though there are several nontoxic abating techniques under investigation (Matsunaga et al, 1998;Sreekumari et al, 2002), better and more environmentally safe methods are needed. The laser's ability to inflict bacterial mortality (Coffelt et al, 1997;Nandakumar et al, 2002a) has been exploited to devise a laser-based sterilization technique of surgical tools (Andrian and Gross, 1979;Powell and Whisenant, 1991) and in surgery in medical and dental fields (Deckelbaum, 1994;Lee et al, 1999). The research in laser-microbe interaction so far is aimed for a quick bacterial mortality by using highpower laser irradiation (Rochd et al, 1998;Ward et al, 2000;Yeo et al, 1998).…”

Laser Radiation as an Adjunct to Nonsurgical Treatment of Periodontal Disease

“…Since ablation is basically produced by heat generation, unlike other laser systems such as Er:YAG laser, carbonization occurs easily on the irradiated surface (Sasaki et al, 2002). When used with relatively low energy output in a pulsed and/or defocused mode, CO 2 l a s e r s h a v e b e e n u s e d t o a c h i e v e root conditioning, detoxification, and bactericidal effects on contaminated root surfaces (Coffelt et al, 1997). However, at low energy outputs in a continuous mode, it is unable to remove subgingival calculus and when used with high energy outputs, especially in a cw mode, it is inappropriate for calculus removal due to major thermal side effects, such as carbonization, melting and cracking on the cementum and dentin (Misra et al, 1999).…”