Impact of hydrophilicity and length of spacer chains on the bonding of functional monomers

Objectives. 10-Methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) is currently considered as one of the most effective functional monomers for dental bonding, this in part thanks to its long and relatively hydrophobic spacer chain, adequately separating the polymerizable from the phosphate functionalities. This study compared functional monomers with different spacer chains' length and hydrophilicity to 10-MDP on their dentin and enamel bonding performance. Methods. Atomic absorption spectroscopy (AAS) was used to characterize the chemical interaction. Micro-tensile bond strength (mu TBS) and fractographic analyses were performed after 24 h and one year. Confocal micro-permeability and SEM nanoleakage assessments were also undertaken. The tested functional monomers were 2-MEP (2-carbon spacer), 10-MDP (10-carbon), 12-MDDP (12-carbon), MTEP (high hydrophilic polyether spacer chain) and CAPP (intermediate hydrophilic ester spacer). Results. AAS revealed clear differences (p < 0.05) in monomer-calcium salt formation in this order: 12-MDDP = 10-MDP > CAP-P > MTEP > 2-MEP. The highest initial dentin mu TBS was obtained using 10-MDP or 12-MDDP. After 1-year aging, a significant drop (p < 0.05) in mu TBS was observed for the adhesives with MTEP (enamel and dentin), 2-MEP (enamel) and CAP-P( enamel). MTEP presented the highest micro-permeability, while 2-MEP, CAP-P and MTEP showed increased nanoleakage after aging. Significance. These outcomes showed that more hydrophilic and shorter spacer chains may compromise the chemical interaction with calcium and the dentin/enamel bonding performance. (C) 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.