Effects of CO sub(2) laser irradiation on tooth enamel coated with biofilm

Background and Objectives CO sub(2) laser irradiation of tooth enamel can inhibit demineralization of tooth enamel, by changing enamel composition and resistance to acid attack. The aim of this work was to examine these effects of CO sub(2) laser irradiation on enamel covered by biofilm. Materials and Methods Streptococcus mutans was grown on bovine enamel surfaces for 48hours to form a mature biofilm. Samples were irradiated by CO sub(2) laser (wavelength of 10.6 mu m) at a power of 0.08W in a super-pulse mode for 1second and 24pulses/second, with an energy density of 0.77J/cm super(2) per pulse. Untreated controls and laser treated samples with and without biofilm were examined for the morphology of the biofilm and the enamel surface by scanning electron microscopy (SEM). Structural biofilm viability was assessed using confocal laser scanning microscopy with live/dead staining. The biofilm was removed in a sonication water bath and the non-treated and irradiated enamel samples were chemically analyzed using energy dispersive X-ray spectrometry (EDS) and Fourier transform infrared spectroscopy (FTIR). Results Irradiated samples showed a melt zone with micro-cracks in the center of the irradiating beam position, which was smaller when irradiated enamel was covered by biofilm. Confocal microscopy images demonstrated higher proportion of dead bacteria at the margins of the irradiated spot area, while at the spot center the bacteria were evaporated exposing the enamel surface to direct laser irradiation. EDS analysis showed an increase in Ca/P ratio after irradiation of enamel covered with biofilm. FTIR analysis showed an approximately 40% carbonate loss in the irradiated enamel samples, including those with biofilms. Conclusion Biofilms protect enamel surfaces from possible morphological irradiation damage without interfering with the resultant chemical changes that may increase the enamel resistance to acid attack. Therefore, under certain exposure regimens that are thermally and mechanically safe for enamel, CO sub(2) laser irradiation of biofilms on dental hard tissues is suggested as a potential novel preventive treatment for controlling dental caries. Lasers Surg. Med. 46:216-223, 2014. copyright 2014 Wiley Periodicals, Inc.