title: Effect of nanolayering of calcium salts of phosphoric acid ester monomers on the durability of resin-dentin bonds.
abstract: 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, (31)P 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.
authors.affiliation: Department of Cariology and Endodontology, School and Hospital of Stomatology, Peking University, Beijing, PR China.
authors.forename: Fu-Cong
authors.initials: FC
authors.lastname: Tian
authors.affiliation: Department of Cariology and Endodontology, School and Hospital of Stomatology, Peking University, Beijing, PR China.
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Wang
authors.affiliation: Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Huang
authors.affiliation: State Key Laboratory of Military Stomatology & National Clinical Research Center for Oral Diseases & Shaanxi Key Laboratory of Oral Diseases, Department of Prosthodontics, School of Stomatology, The Fourth Military Medical University, Xi'an, China. Electronic address: niulina831013@126.com.
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Niu
authors.affiliation: The Dental College of Georgia, Augusta University, Augusta, GA, USA.
authors.forename: Jan
authors.initials: J
authors.lastname: Mitchell
authors.affiliation: Department of Prosthodontics, School & Hospital of Stomatology, Zhejiang University, Hangzhou, Zhejiang, China.
authors.forename: Zheng-Yi
authors.initials: ZY
authors.lastname: Zhang
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO, USA.
authors.forename: Chandrani
authors.initials: C
authors.lastname: Prananik
authors.affiliation: Department of Cariology and Endodontology, School and Hospital of Stomatology, Peking University, Beijing, PR China.
authors.forename: Lu
authors.initials: L
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Military Stomatology & National Clinical Research Center for Oral Diseases & Shaanxi Key Laboratory of Oral Diseases, Department of Prosthodontics, School of Stomatology, The Fourth Military Medical University, Xi'an, China.
authors.forename: Ji-Hua
authors.initials: JH
authors.lastname: Chen
authors.affiliation: Department of Biomedical and Neuromotor Sciences, DIBINEM, University of Bologna, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Breschi
authors.affiliation: The Dental College of Georgia, Augusta University, Augusta, GA, USA.
authors.forename: David H
authors.initials: DH
authors.lastname: Pashley
authors.affiliation: The Dental College of Georgia, Augusta University, Augusta, GA, USA. Electronic address: ftay@gru.edu.
authors.forename: Franklin R
authors.initials: FR
authors.lastname: Tay
mesh_terms: D003804:Dentin / Q000737:chemistry*; D017886:Durapatite / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D008689:Methacrylates / Q000737:chemistry / Q000494:pharmacology; D008963:Molar / Q000737:chemistry*; D012117:Resins, Synthetic / Q000737:chemistry / Q000494:pharmacology; D045162:Thiazolidinediones / Q000737:chemistry / Q000494:pharmacology
chemical_list: C575035:(Z)2-(5-(4-methoxybenzylidene)-2,4-dioxothiazolidin-3-yl)acetic acid; D008689:Methacrylates; D012117:Resins, Synthetic; D045162:Thiazolidinediones; C069749:methacryloyloxydecyl dihydrogen phosphate; D017886:Durapatite
keywords: 10-MDP; Analog; Bond durability; Nanolayering; Organic-inorganic hybrid calcium salt; Phosphoric acid ester resin monomer