Acetone Immersion Time and Internal and External Measurements of Depth-of-Cure

Objectives: To study effects of acetone immersion time on thickness of composite specimens as well as depths of internal optical layering depicting depths of cure.
Methods: Uncured composite (Herculite Ultra, Kerr; Tetric EvoCeram, Ivoclar) was placed into opaque cylinders (5mm-dia, 10mm-long) and light-cured 10s (Demi Ultra, Kerr; Bluephase Style, Ivoclar). Cylinder contents were ejected, uncured composite removed using manual scraping (control;ISO4049), or entire contents placed in acetone and sonicated for various times: 5, 10, 15, 20, 30, 45, 60, 120 min. Recovered, cured composite specimens were embedded in epoxy, sectioned top-to-bottom, and hand-polished to 600 grit SC. Digital images of specimens were obtained at 20X using a 10MP camera in a stereomicroscope. Using software (ImageJ), (1) the top-to-bottom length of each specimen was measured, as well as the depth from the top surface to 2 internal optically identifiable transition zones: (2) depth to porous layer, and (3) depth of solvent resistance (a discontinuous layer of voids). For a given composite, and within a depth measurement, a 1-way ANOVA and Tukey post-hoc test was performed among depth values at a pre-set alpha of 0.05. N=5 per test group.
Results: Table presents results. Within each composite brand, manual composite removal thickness (1) was not significantly different from acetone-sonicated specimens through 20 minutes. Within each composite brand and within each internal identifiable layer (depth to the porous layer (2) and depth of solvation resistance (3)) no significant differences were found between 5 and 20 minutes of acetone sonication.
Conclusions: Acetone sonication between 5 and 20 minutes provided similar total specimen height as does manual removal of uncured composite (ISO4049). In addition, discovery of 2 internal optically identifiable transition zones were measured in solvated specimens, and each was found to provide depth values not significantly different between 5 and 20 minutes of acetone sonication.