To evaluate the adaptation and penetration into occlusal fissures of two different types of fissure sealants.Extracted third molars (n=10) with evident occlusal fissures were cleaned with a pumice/water slurry and randomly divided into two groups and sealed following the manufacturers' directions as follows: Group 1--Embrace fissure sealant (Pulpdent). Surfaces were cleaned and dried, then etched for 15 seconds. Excess water was removed leaving the surface slightly moist. Sealant was applied from cusp to cusp without covering marginal ridges and light cured for 20 seconds using a halogen light at 500 mW/cm2. Group 2--ClinPro (3M Espe). Surfaces were cleaned and dried then etched for 15 seconds. The etched surface was rinsed and thoroughly dried. Dried surfaces appeared frosty white. Sealant was placed making sure not to go beyond etched area, and light cured for 20 seconds. Teeth were thermocycled (500x) and sectioned with an Isomet in a mesio-distal direction (4 slices per tooth). The sections were examined under the SEM. The marginal adaptation of the sealants was evaluated under the SEM using the following criteria: 1 = Smooth adaptation. Sealant flows with enamel. No ledges; 2 = Sealant is not well adapted. Ledge may be present. The penetration ability of the sealants was evaluated under the SEM using the following criteria: 1 = Sealant penetrated 1/3 the total length of the fissure; 2 = Sealant penetrated 1/2 the total length of the fissure; 3 = Sealant penetrated the total length of the fissure. The results were statistically analyzed using a t-test.Embrace showed consistently more intimate marginal adaptation than ClinPro in fissures of the same approximate width and depth (P < 0.05).