Bottom-to-Top Conversion Values Among Biocompatible Resin Composites

Objectives: To compare the ability of new biocompatible composites, and a variety of contemporary composites, to provide 10-minute bottom-surface monomer conversion (MC) values, which approach that of the top, 4-hour old irradiated surface (percent maximum monomer conversion (PMMC)).
Methods: Composite materials were used in recommended, 2-mm thick increments, or as bulk-fill materials (4mm) (see Table). The biocompatible materials are said to contain no Bis-GMA-like monomers, and one states no leachable monomeric component (Table (*)). Uncured composite discs (2 or 4 mm thick) were placed on the surface of a horizontal attenuated total reflectance unit in an FTIR spectrometer, and bottom surface spectra were collected over time (1 scan/s for 10 min, 2 cm^-1 resolution). The first 5 scans collected uncured spectra, the curing light was the activated (Table), and data continued to be collected. MC was calculated at 10 min by comparing changes in the ratio of aliphatic-to-aromatic C=C peak absorbances between uncured and cured states. (N=5) Spectra of the top, irradiated surfaces were obtained 4-hours after exposure, MC was calculated (N=3), and the mean top MC was determined. The percentage of maximum, 4-h top surface MC that each bottom surface attained after 10min (PMCC) was determined. Percentages were compared using a 1-way ANOVA, and Tukey’s post-hoc test at a pre-set alpha of 0.05.
Results: Table presents results. Bottom surface PMCC of Tetric EvoCeram was significantly less than all 2-mm thick products, which were not significantly different from each other. Two bulk-fill, 4-mm thick products had bottom surface PMCC values not significantly from many of those of the 2-mm thick products, but the remainder were all significantly less.
Conclusions: One of the new biocompatible composites demonstrated high proportion of bottom surface conversion values with respect to that of the top, irradiated surface, and also performed well at 4-mm thickness.