Effect of 9.3μm CO2 Laser and Fluoride on Shear Bond Strength, Microleakage, Acid Resistance and Microhardness of Sealants

Objectives: This study aimed to evaluate the effects of a 9.3 μm microsecond short-pulsed CO2 laser and acidulated phosphate fluoride (APF) 1.23% gel on enamel acid resistance, microleakage, failure mode, and shear bond strength of dental sealants. Materials and Methods: 120 extracted posterior teeth were randomly divided into 3 groups (n=40): Group A, resin-based sealant; Group B, moisture-tolerant resin-based sealant; and Group C, glass-ionomer cement. Each group were divided into 4 subgroups (n= 10) treated with: 1) sealant alone, 2) APF 1.23% fluoride gel + sealant, 3) CO2 laser + sealant, and 4) CO2 laser + APF 1.23% fluoride gel + sealant. Sealants were applied on the buccal and occlusal surfaces. Shear bond strength (SBS) test was performed on the buccal surface sealants using the Instron® 5566A, followed by failure mode assessment under a digital microscope. After the SBS test, the teeth were sequentially thermocycled, immersed in a 2% methylene blue solution, and sectioned longitudinally in a buccal-lingual direction. The sectioned mesial halves were examined under a digital microscope to assess dye penetration. The sectioned mesial halves were assessed for baseline Vickers microhardness at four standardized points on mesial surface, and for the microhardness after treatment at four standardized points located 50 micrometers on enamel adjacent to the enamel-sealant interface on the cut surface. The mesial halves were treated to 9 days of pH-cycling of remineralization and demineralization solutions. After acid challenge, the microhardness measurement was performed at four standardized points located 50 micrometers next to the four original points. Results: For the three sealant materials, CO 2 laser + sealant provided higher SBS than other subgroups: 15.5 ± 8.2 MPa for Clinpro, 16.3 ± 7.8 MPa for Embrace, and 4.9 ± 4.7 for Fuji. CO2 laser + sealant also had lower percentage of adhesive failure than other subgroups for Clinpro and Embrace. For Clinpro, microhardness values of subsurface enamel adjacent to the enamel-sealant interface after pH cycling were 202.8 ± 30.1 for sealant, 186.7 ± 39 for fluoride + sealant, 231.4 ± 34.1 for laser + sealant, and 258.3 ± 28.2 for laser + fluoride + sealant. In Clinpro group, subgroup sealant experienced 40% at microleakage score 0, 40% at score 1 and 20% at score 2. Fluoride + sealant subgroup experienced only 20% at score 1 and 80% at score 2. Laser + sealant subgroup experienced 70% of score 1 and laser + fluoride + sealant subgroup experienced 30% at score 1. Conclusion: The 9.3μm CO2 laser had an overall beneficial effect to sealants on the enamel. It increased shear bond strength of dental sealants and reduced adhesive failure for the three sealant materials. For Clinpro, the microhardness of subsurface enamel adjacent to the enamel/sealant interface pre-treated with 9.3μm CO2 laser was higher tha