Composite Monomer Conversion Required to Resist Acetone Solvation

Objectives: To measure percent of maximal monomer conversion (PMMC) value required to resist to acetone solvation.
Methods: Two optical transition layers of sectioned, acetone-solvated resin composite specimens have been identified that infer solvent resistance: (1) depth to porous layer, (2) thickness of solvent resistant composite. Mean transition layer depths were determined after 5-20 min of acetone sonication (n=20). For the current research, uncured shade A2 composite discs (5mm dia, thicknesses between 0.5 and 5.0mm in half-mm increments of Herculite Ultra, Kerr and Tetric EvoCeram, Ivoclar) were placed on an infrared spectrometer and covered with Mylar (n=5). Spectra were obtained before light curing (16 scans, 2cm^-1 resolution) as well as 3-min following a 10s exposure (Demi Ultra, Kerr; Bluephase Style, Ivoclar, respectively). Spectra of top, irradiated surfaces were also obtained (n=5) (maximum conversion). Monomer conversion was calculated from ratio changes of aliphatic-to-aromatic C=C absorbance peaks in uncured and cured states. Bottom surface PMMC values for each specimen were determined relative to that of the top. Specimen thickness was measured using a micrometer (±0.01mm). Polynomial regression analyses were used to predict PMMC at any thickness for each composite brand from which PMMC values at the mean depth of each transition layer [(1) and (2)] were determined.
Results: Table presents results. The depth each transition occurred was different between composite brands, however, within a given transition layer, PMMC values between composite brands were not different, showing overlap at their 95% CI. For each composite brand, the porous layer occurred at 20% to 27% of top-surface conversion, and depth of solvent resistant composite occurred at 34% and 40% of maximum, top value.
Conclusions: An acetone-solvated DOC specimen can be sectioned and, by measuring the depth of these two transition levels, the relative value of maximum composite cure that provides solvent resistance can be determined.