In vitro evaluation of enamel erosion after Nd:YAG laser irradiation and fluoride application

Previous investigations have demonstrated improved enamel demineralization resistance after laser irradiation. Due to the possibility of a synergistic effect between laser and fluoride, this study investigated the effect of fluoridated agents and Nd:YAG irradiation separately and in combination on enamel resistance to erosion.

One hundred bovine enamel blocks were randomly divided into 10 groups: G1, untreated (control); G2, acidic phosphate fluoride (APF) (1.23% F) for 4 min; G3, fluoride varnish for 6 h (NaF, 2.26%); G4, 0.5 W Nd:YAG laser (250 microm pulse width, 10 Hz, 35 J/cm(2), with uniform velocity for 30 sec in each application); G5, 0.75 W Nd:YAG laser (52.5 J/cm(2)); G6, 1.0 W Nd:YAG laser (70 J/cm(2)); G7, APF + 0.75 W Nd:YAG laser; G8, 0.75 W Nd:YAG laser + APF; G9, fluoride varnish + 0.75 W Nd:YAG laser; and G10, 0.75 W Nd:YAG laser + fluoride varnish. During 10 d the erosive cycle was conducted by immersion of the blocks in Sprite light((R)) for 1 min, followed by immersion in artificial saliva for 59 min. This procedure was consecutively repeated four times per day. In each day, during the remaining 20 h, the blocks were maintained in artificial saliva. The wear was evaluated by profilometry (days 5 and 10). Data were tested by two-way ANOVA and Bonferroni's tests (p < 0.05).

The mean wear at days 5 and 10 was, respectively: G1, 1.83 and 2.67 microm; G2, 1.04 and 2.60 microm; G3, 1.03 and 2.48 microm; G4, 1.13 and 2.47 microm; G5, 1.07 and 2.44 microm; G6, 1.0 and 2.35 microm; G7, 0.75 and 2.27 microm; G8, 0.80 and 2.12 microm; G9, 0.76 and 2.47 microm; and G10, 1.09 and 2.46 microm. At day 5, all the experimental groups presented significant lesser wear when compared to control group. However, at 10 d, only G7 and G8 were still different from control.

The association between APF application and laser irradiation seems to be an alternative preventive measure against dental erosion.