Indiana University-Purdue University Indianapolis (IUPUI) / Occlusal pits and fissures are ideal places for caries development. Placement of dental sealants has been reported to be effective in preventing this process. However, the effectiveness of dental sealants has been reported to be influenced by clinical factors, such as preparation and placement techniques. A report recently published by the American Dental Association on the clinical recommendations for use of pit-and-fissure sealants included critical evaluation and a summary of relevant scientific evidence on the use of sealants aimed at assisting clinicians. The report addressed concerns such as: Does placing sealants over early (noncavitated) lesions prevent progression of the lesions? Are there any techniques that could improve sealants’ retention and ffectiveness in caries prevention? The investigators concluded that there is limited and conflicting evidence to support that mechanical preparation with a bur results in higher retention rates in children and recommend that pit-and-fissure sealants should be placed on early (noncavitated) carious lesions. The purpose of this in vitro study was to evaluate two methods of fissure treatment before sealant placement on different caries levels. In this study, 135 extracted human molars (ICDAS codes 0 to 2) were collected and ranked by a calibrated examiner into three groups. These were further divided into three subgroups (nine total). Occlusal surfaces were prepared with: 1) a ¼-mm round bur, 2) air abrasion, and 3) no treatment as a control. All groups were etched with 3.0- percent phosphoric acid for 15 seconds, rinsed thoroughly, and dried with an air water syringe. Opaque dental sealants were placed on the etched occlusal surfaces according to the accepted clinical standards and light-cured for 30 seconds. All groups were thermocycled for 5000 cycles. The roots of the teeth were painted with nail varnish, root apices were sealed with wax, and the occlusal surfaces were immersed in 1.0-percent methylene blue for a full 24 hours. The next day the teeth were cleaned, and the roots were sectioned to expose the crowns. Crowns were cut along the occlusal surfaces in the buccolingual direction. The sectioned surfaces were examined under the Nikon SMZ 1500 microscope for sealant penetration in the fissure and microleakage along the sealant enamel interface. The analyses were performed on a transformation of the sealant penetration percentage commonly used for calculated percentages: sin-1(p1/2). The effects of the type of group, the ICDAS code, and the fissure type on sealant penetration percentage were compared using ANOVA. The effects on microleakage and bubbles were compared using GEE methods applied to logistic regression. The effects on dye penetration were compared using GEE methods applied to cumulative logistic regression to account for the ordered categories of the dye penetration scale. In the findings of sealant penetration, the group type did not have a significant effect on sealant penetration (p = 0.195). ICDAS codes had a significant effect on sealant penetration (p = 0.0113) where ICDAS Code 0 had greater penetration than ICDAS codes 1 and 2. Fissure type had a significant effect on sealant penetration (p = 0.0001) where fissure types V and U had greater sealant penetration than Fissure types Y and W. In the findings of microleakage, the type of group had a significant effect on microleakage (p = 0.0004) where the abrasion group had increased microleakage as compared with the 1/4 round bur and control groups. ICDAS code had a significant effect on microleakage (p = 0.0022) where ICDAS code 0 had less microleakage as compared with ICDAS code 1 and 2. Fissure types V, U, Y, and W did not have a significant effect on microleakage (p = 0.721).