Effect of nanolayering of calcium salts of phosphoric acid ester monomers on the durability of resin-dentin bonds

• Published in: Acta biomaterialia Vol. 38; pp. 190 - 200
• Main Authors: Tian, Fu-cong, Wang, Xiao-yan, Huang, Qi, Niu, Li-na, Mitchell, Jan, Zhang, Zheng-yi, Prananik, Chandrani, Zhang, Lu, Chen, Ji-hua, Breshi, Lorenzo, Pashley, David H., Tay, Franklin R.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.07.2016
• Subjects: 10-MDP; Adhesives; Analog; Bond durability; Bonding strength; Dentin; Dentin - chemistry; Durability; Durapatite - chemistry; Durapatite - pharmacology; Esters; Humans; Methacrylates - chemistry; Methacrylates - pharmacology; Molar - chemistry; Monomers; Nanolayering; Nanostructure; Organic-inorganic hybrid calcium salt; Phosphoric acid; Phosphoric acid ester resin monomer; Resins, Synthetic - chemistry; Resins, Synthetic - pharmacology; Thiazolidinediones - chemistry; Thiazolidinediones - pharmacology; Nanolayering; Phosphoric acid ester resin monomer; Bond durability; 10-MDP; Analog; Organic-inorganic hybrid calcium salt
• ISSN: 1742-7061; 1878-7568
• DOI: 10.1016/j.actbio.2016.04.034

[Display omitted] To investigate the contribution of nanolayering on resin-dentin bond durability, two phosphoric acid ester resin monomers, 10-methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) or its analog, methacryloyloxy-penta-propyleneglycol-dihydrogen-phosphate (MDA), were examined for their affinity for mineralized dentin powder in a column chromatography setup. Hydroxyapatite (HA) powder was dispersed in experimental primers consisting of 10-MDP or MDA solvated in ethanol/water and examined with FTIR, 31P MAS-NMR and XPS. Light-curable 10-MDP or MDA primers were used for bonding to dentin, and examined after 24h or one-year of water-aging by TEM for evidence of nanolayering, and for microtensile bond strength evaluation. Primer-bonded dentin was examined by thin-film XRD to identify short-range order peaks characteristic of nanolayering of resin monomer-Ca salts. Although 10-MDP had better affinity for mineralized dentin than MDA, both monomers completely eluted from the mineralized dentin powder column using ethanol-water as mobile phase, indicating that the adsorption processes were reversible. This finding was supported by chemoanalytic data. XRD of 10-MDP-bonded dentin showed three diffraction peaks hat were absent from MDA-bonded dentin. Nanolayering was identified by TEM in 10-MDP-bonded dentin, but not in MDA-bonded dentin. Significant drop in bond strength (in MPa) was observed for both groups after one-year of water-aging compared with 24-h: 10-MDP group from 48.3±6.3 to 37.4±4.6; MDA group from 50.7±5.0 to 35.7±3.8 (P<0.05), with no significant difference between the two groups at the same time-point. Because both functional monomer-primed, resin-bonded dentin exhibited similar bond strength decline after water-aging, presence of nanolayering is unlikely to contribute to the overall resin-dentin bond durability. The durability of resin-dentin bonds in 10-MDP containing self-etching adhesives has been anecdotally attributed to the presence of nanolayering of 10-MDP-calcium salts in the resin-dentin interface. Results of the present work indicate that such a claim cannot be justified. Complete elution of the phosphoric acid ester monomer from mineralized dentin powder in the column chromatography experiments using ethanol-water mobile phase to simulate the solvent mixture employed in most 10-MDP-containing dentin adhesives further challenges the previously proposed adhesion-decalcification concept that utilizes chemical bonding of phosphoric acid ester monomers to apatite as a bonding mechanism in 10-MDP containing dentin adhesives.