In vitro study of the effect of a pulsed 10.6μm CO2 laser and fluoride on the reduction of carious lesions progression in bovine root dentin

The aim of the present study was to evaluate the combined in vitro effects a pulsed 10.6 μm CO2 laser and fluoride on the reduction of carious lesion progression in root dentin. Sixty five slabs of previously demineralized bovine root dentin were assigned into five groups (n=13): control (no treatment), acidulated phosphate fluoride gel 1.23% (FFA), CO2 Laser (L), FFA+L, L+FFA. The lasered groups were irradiated with 4.0J/cm2. After a 7 day pH cycling regime, the knoop hardness number (KHN) was determined by cross-sectional microhardness testing (5g, 5s, 10-60 μm, 10 μm interval). The data was analyzed by ANOVA and Student's t-test (α= 0.05). A significant interaction between KHN and the indentation depths was found (p<0.05). At 10-20 μm, FFA+L (KHN:12.12±0.95/13.07±1.03) and FFA (KHN:12.86±4.54/12.60±3.93) inhibited caries progression when compared to control group (KHN:8.76±0.95/9.50±1.03) (p<0.05), but did not differ with neither each other nor from group L (p>0.05). At 30 μm, the KHN was significantly higher than the control only in the FFA group (KHN:15.35±1.16). At 40 μm, the groups FFA (KHN: 15.87±3.76), L (KHN: 15.57±5.71) and L+FFA (KHN:15.50±5.08) were capable of significantly inhibiting caries progression, however they did not differ each other (p>0.05). At depths of 50-60 μm, only group L (KHN:17.05±1.29/18.26±1.30) differed statistically from the control (KHN:13.43±1.24/13.81±1.25), but not from the other groups. In conclusion, CO2 laser alone was able to inhibit caries progression in the deepest layers. However, no synergistic effect was obtained when CO2 laser irradiation and FFA application and were combined.