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Acta Biomater. 2016 Jul 1;38:190-200. doi: 10.1016/j.actbio.2016.04.034. Epub 2016 Apr 27.

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

Author information

1
Department of Cariology and Endodontology, School and Hospital of Stomatology, Peking University, Beijing, PR China.
2
Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China.
3
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.
4
The Dental College of Georgia, Augusta University, Augusta, GA, USA.
5
Department of Prosthodontics, School & Hospital of Stomatology, Zhejiang University, Hangzhou, Zhejiang, China.
6
Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO, USA.
7
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.
8
Department of Biomedical and Neuromotor Sciences, DIBINEM, University of Bologna, Italy.
9
The Dental College of Georgia, Augusta University, Augusta, GA, USA. Electronic address: ftay@gru.edu.

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.

STATEMENT OF SIGNIFICANCE:

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.

KEYWORDS:

10-MDP; Analog; Bond durability; Nanolayering; Organic-inorganic hybrid calcium salt; Phosphoric acid ester resin monomer

PMID:
27130275
DOI:
10.1016/j.actbio.2016.04.034
[Indexed for MEDLINE]

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