This in vitro study determined the penetration depth of a fissure sealant into an empty fissure system and into a conditioned enamel surface, using different sealing procedures.48 extracted, non-carious human molars were sealed with the unfilled sealant (Heliobond) using the enamel adhesive technique (35% phosphoric acid gel, 120 s etching time, bond application, light-curing for 60 s). The following factors were tested in comparison to the control group (1): influence of a precuring time lapse of 20 s after sealant application (2); ultrasound application with a plastic tip during the etching procedure (3); a wetting agent in an acid vehicle (4); enamel drying with acetone after the etching procedure (5); and finally, the combination of ultrasound during etching; a drying procedure with acetone; and a 20 s precuring time lapse (all applied to the same sample). The sealed teeth were sectioned and evaluated by conventional light microscopy to determine the penetration depth into the fissure, and by confocal laser microscopy to investigate the quality of the adhesion zone.Strict adherence to a specified penetration time, an intensified etching procedure with ultrasound, and the use of a drying procedure with acetone each showed a positive effect on the fissure penetration depth of the sealant and on the adhesion zone. The combination of these measures improved significantly the quality of the fissure sealing. Penetration depth increased to 92% of the fissure depth. From 95-100% of the total length of the analyzed adhesion zone shows excellent tags of sealant in the conditioned enamel surface.Simple changes in the application technique of fissure sealants, such as ultrasonic treatment during etching procedure and drying the etched fissure system by acetone, improved the quality of the fissure sealing, which is a noninvasive preventive measure.