The aim of this study was to evaluate the effects of different techniques of surface treatment on the microleakage of a fissure sealant in molar teeth. A total of 50 freshly extracted noncarious human third molars were randomly assigned to one of five groups. Occlusal fissures were treated with one of the following: acid etching with 35% orthophosphoric acid (group 1); fissurotomy with a Fissurotomy Micro NTF metal bur (group 2); laser etching with an Er,Cr:YSGG laser at 2 W and 20 Hz (group 3); laser etching with an Er,Cr:YSGG laser at 2 W and 40 Hz (group 4); and air abrasion for 20 s with 30-A mu m Al2O3 particles via a CoJet Prep device (group 5). After surface pretreatment, a resin-based sealant was applied to the fissures. The sample teeth were subjected to thermocycling and stored in distilled water at 37A degrees C for 1 month. Following immersion in 0.5% basic fuchsin solution for 24 h, three buccolingual slices of each sample tooth were scored under a stereomicroscope, and the morphological appearance of the area between the enamel surface and fissure sealant was examined under a scanning electron microscope. The Kruskal-Wallis test and one-way ANOVA revealed significant differences in marginal leakage, as follows: group 1 showed significantly lower scores than groups 2 and 5, the scores of groups 1, 3 and 4 were not significantly different, and group 2 showed significantly higher scores than groups 3 and 4. Laser irradiation, the metal bur, and the CoJet Prep device did not eliminate the need for acid etching of the enamel prior to placement of a fissure sealant. Laser etching at 2 W (20 Hz or 40 Hz) may be an alternative to conventional acid-etching.