Influence of Irradiance and Exposure Times on the Mechanical and Adhesive Properties of Universal Adhesives with Dentin

Abstract

SUMMARY Objectives: This study evaluated the influence of irradiance/exposure time on the Knoop hardness (KHN) and polymer cross-linking density (PCLD), as well as microtensile bond strength (μTBS), nanoleakage (NL), and in situ degree of conversion (DC) of universal adhesives. Methods and Materials: Two universal adhesive systems, Clearfil Universal Bond Quick (CUQ) and Scotchbond Universal Adhesive (SBU), were light-cured using various irradiance/exposure times: 1400 mW/cm2 for 5 s (1400*5); 1400 mW/cm2 for 10 s (1400*10); 3200 mW/cm2 for 5 s (3200*5); and 3200 mW/cm2 for 10 s (3200*10). Adhesive disks from each group were used to measure PCLD by KHN. One hundred and twenty-eight human molars were randomly assigned to 16 groups according to the following variables: adhesive system vs adhesive strategies vs radiance/exposure times. After restoration, specimens were sectioned into resin-dentin sticks and tested for μTBS, NL, and DC. The data from PCLD (%), KHN, μTBS (MPa), NL (%), and DC (%) data were subjected to ANOVA and Tukey’s test (α=0.05). Results: Significant reductions in KHN, μTBS, and DC (p=0.00001) values and an increase in NL and PCLD (p=0.00001) values were observed for 3200*10 when compared with other groups. Higher KHN, μTBS, and DC (p=0.000001) values were observed for 3200*5 in comparison with the other groups. The 1400*5 (7 J/cm2) and 1400*10 (14 J/cm2) groups showed intermediate values (p=0.000001). Conclusion: Although similar results in terms of hardness, polymer cross-linking density and nanoleakage were observed when 5 seconds at 3200 mW/cm2 and 10 seconds at 1400 mW/cm2 groups were compared, the use of higher irradiance (3200 mW/cm2) for only 5 seconds showed better results in terms of bond strength and degree of conversion for both universal adhesives to dentin. The prolonged exposure time (10 seconds) at the higher irradiance (3200 mW/cm2) showed the worst results.

Effect of Simulated Dental Pulpal Pressure Using Fetal Bovine Serum for the Bonding Performance of Contemporary Adhesive to Dentin

“…Additionally, the presence of 4-MET is related to a lesser capability to create stable monomer-Ca salts [25]. SBP and Scotchbond Universal, its predecessor, have been extensively studied, and their DC has been reported high [27,32,[34][35][36]. Scotchbond Universal's high DC has been ascribed to its relatively low solvent content [36] and application mode, which requires a gently air-blowing until the adhesive film no longer moves on the dentin surface to promote sufficient solvent evaporation and guarantee an appropriate polymerization [2].…”