CO2-LASER INHIBITION OF ARTIFICIAL CARIES-LIKE LESION PROGRESSION IN DENTAL ENAMEL

Several studies during the last 30 years have demonstrated the potenti al of laser pre-treatment of enamel or tooth roots to inhibit subseque nt acid-induced dissolution or artificial caries-like challenge in the laboratory. The overall objective of ongoing studies in our laborator ies is to determine, systematically, the optimum sets of parameters fo r carbon dioxide laser irradiation that will potentially effectively i nhibit dental caries in enamel and tooth roots. The aim of the present study was to examine the roles of wavelength and fluence in the preve ntion of caries progression in vitro in enamel by means of a pH-cyclin g model. The hypothesis to be tested was that the highly absorbed 9.3- and 9.6-mu m wavelengths would be efficiently converted to heat, crea ting a temperature sufficiently high to reduce the acid-reactivity of the mineral and inhibit caries-like lesion progression in dental ename l. One hundred and sixty caries-free tooth crowns were cleaned and var nished with acid-resistant varnish, leaving one exposed window of enam el. Twelve groups of 10 enamel samples were irradiated in their indivi dual windows by one of the four wavelengths (9.3, 9.6, 10.3, or 10.6 m u m) of a tunable CO(2 )laser. Energy per pulse was 25, 50, 100, 200, or 250 mJ (25 pulses). Repetition rate was 10 Hz, and beam diameter wa s 1.6 mm. Fluence conditions of 1 to 12.5 J/cm(2) per pulse were produ ced. AU teeth, including 40 non-irradiated controls, were subjected to pH-cycling to produce artificial caries-like lesions. Results were as sessed by cross-sectional microhardness testing. Inhibition of caries progression of from 40% to 85% was achieved over the range of laser co nditions tested. At 9.3 and 9.6 mu m, 25 pulses at absorbed fluences o f 1 to 3 J/cm(2) produced inhibition on the order of 70% with minimal subsurface temperature elevation (< 1 degrees C at 2 mm depth), compar able with inhibition produced in this model with daily fluoride dentif rice treatments. Safety and efficacy studies will be required in anima ls and humans before these promising laboratory results can be applied in clinical practice.