In multiple well-controlled laboratory studies enhancing caries resistance of enamel has been successfully reported using short-pulsed 9.6 µm CO2 laser irradiation. The aim of this study was to prove in a short term clinical pilot trial that the use of the CO2 laser will significantly inhibit the formation of carious lesions around orthodontic brackets in vivo in comparison to a non-irradiated control area. Twelve subjects scheduled for extraction of premolars for orthodontic treatment reasons with an average age of 14.6 years were recruited for the 4-week study. Orthodontic brackets were placed on those premolars with a conventional composite resin (Transbond XT, 3M Unitek, REF 712-035) and a defined area next to the bracket was irradiated with a CO2 laser, Pulse System, Inc (PSI) (Model #LPS-500, Los Alamos, New Mexico), wavelength 9.6 &mgr;m, pulse duration 20 &mgr;s, pulse repetition rate 20 Hz, beam diameter 1,100 &mgr;m, average fluence 4.31 +/- 0.11 J/cm2, 20 laser pulses per spot. Premolars were extracted after four weeks for a quantitative assessment of demineralization by cross sectional microhardness testing. The relative mineral loss &Dgr;Z (vol% x µm) for the laser treated enamel was 402 +/- 85 (SE) while the control area showed a significantly higher mineral loss (mean &Dgr;Z 738 +/- 131; P=0.04, unpaired t-test). The laser treatment produced a 46% demineralization inhibition around the orthodontic brackets in comparison to the non-laser treated areas. This study showed, for the first time that a pulsed 9.6 µm CO2 laser works for the prevention of dental caries in the enamel in vital teeth in human mouths.