An investigation of the dental bioactive proanthocyanidin (PAC) oligomer fractions led to three structurally distinct new PACs (1–3) from pine bark. Pinutwindoublin (1) is the first reported trimer with double A-type interflavanyl linkages (2α→O→5,4α→6 and 2α→O→7,4α→8). Pinuspirotetrin (2) represents the first reported PAC tetramer with a heterodimeric framework consisting of one spiro-type and one A-type dimer. Pinumassohexin (3) was elucidated as a mixed A + B-type hexamer that consists of a peanut-derived tetramer, peanut procyanidin E, and an A-type dimer (5). Compound 3 increased the modulus of elasticity of dentin by an impressive 4.3 times at a concentration of 0.65%
