The isolation efforts focused on 12.1 g of enriched tri-and tetrameric PACs, obtained upon combining 6.5 g of fraction A and 5.6 g of fraction B that were prepared from 200 g of pine bark extract by centrifugal partition chromatography (CPC) as described previously. Dentin treated with both fractions A and B presented statistically higher apparent moduli of elasticity compared to control (p<0.001), with an approximate 7-and 9-fold increase in the apparent modulus of elasticity values, respectively. As no statistically significant differences occurred among the PACtreated groups (p<0.05; Figure ). Considering a certain degree of overlap in constituents as per HPLC and TLC analysis, the materials were combined for the isolation of individual PACs. Compounds 10 and 17 are the most abundant tri-and tetrameric PACs, respectively, in the investigated pine bark. Their structures are identical with those of the peanut procyanidins D and E, as established by comparison of their C NMR data (Tables ).