Novel dental adhesives containing nanoparticles of silver and amorphous calcium phosphate

Abstract

Objectives: Secondary caries is the main reason for restoration failure, and replacement of the failed restorations accounts for 50-70% of all restorations. Antibacterial adhesives could inhibit residual bacteria in tooth cavity and invading bacteria along the margins. Calcium (Ca) and phosphate (P) ion release could remineralize the lesions. The objectives of this study were to incorporate nanoparticles of silver (NAg) and nanoparticles of amorphous calcium phosphate (NACP) into adhesive for the first time, and to investigate the effects on dentin bond strength and plaque microcosm biofilms.

Methods: Scotchbond multi-purpose adhesive was used as control. NAg were added into primer and adhesive at 0.1% by mass. NACP were mixed into adhesive at 10%, 20%, 30% and 40%. Microcosm biofilms were grown on disks with primer covering the adhesive on a composite. Biofilm metabolic activity, colony-forming units (CFU) and lactic acid were measured.

Results: Human dentin shear bond strengths (n=10) ranged from 26 to 34 MPa; adding NAg and NACP into adhesive did not decrease the bond strength (p>0.1). SEM examination revealed resin tags from well-filled dentinal tubules. Numerous NACP infiltrated into the dentinal tubules. While NACP had little antibacterial effect, NAg in bonding agents greatly reduced the biofilm viability and metabolic activity, compared to the control (p<0.05). CFU for total microorganisms, total streptococci, and mutans streptococci on bonding agents with NAg were an order of magnitude less than those of the control. Lactic acid production by biofilms for groups containing NAg was 1/4 of that of the control.

Significance: Dental plaque microcosm biofilm viability and acid production were greatly reduced on bonding agents containing NAg and NACP, without compromising dentin bond strength. The novel method of incorporating dual agents (remineralizing agent NACP and antibacterial agent NAg) may have wide applicability to other dental bonding systems.

Copyright © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Figures

Fig 1

Dentin shear bond testing. (A) Schematic of specimen preparation, (B) schematic of testing, (C) human dentin shear bond strengths. Each value is mean ± sd (n = 10). Horizontal line indicates values that are not significantly different from each other (p > 0.1).

Fig 2

Representative SEM micrographs of dentin-adhesive interfaces. (A) SBMP control, (B) P+NAg, A+NAg+20NACP, (C) P+NAg, A+NAg+40NACP. (D) P+NAg, A+NAg+20NACP at a higher magnification, and (E, F) at even higher magnifications. Adhesives filled the dentinal tubules and formed resin tags “T” for all six groups. “HL” indicates the hybrid layer between the adhesive and the underlying mineralized dentin. High magnification SEM in (D–F) revealed numerous NACP nanoparticles in the adhesive layer, in the hybrid zone, and inside the dentinal tubules. Arrows in (D–F) indicate NACP in the dentinal tubules. NACP were not only able to infiltrate with the adhesive into straight tubules (E), but also into bent and irregularly-shaped tubules (F).

Fig 3

Representative SEM images of adhesive/hybrid layers at a higher magnification: (A) 20%, (B) 30% and (C) 40% of NACP. NACP in the adhesive and hybrid layers were more readily visible at 20% NACP than at 30% and 40% NACP. However, the NACP were present in the adhesive and hybrid layers at 30% and 40% NACP, as indicated by the arrows. (D) The flow of the adhesive pastes (mean ± sd; n = 6). Flow is inversely related to the viscosity, with a larger adhesive area after flow indicating a lower viscosity. Values with dissimilar letters are significantly different from each other (p

Fig 4

Dental plaque microcosm biofilm testing and live/dead assay. (A) Schematic of biofilm on the layered specimen, (B–G) live/dead images for the six groups. Live bacteria were stained green, and dead bacteria were stained red. Live and dead bacteria in the proximity of each other produced yellow/orange colors. SBMP control disks were covered with live biofilms. A&P+NAg, with or without NACP, had mostly dead bacteria on the specimens. Therefore, the modified bonding agents with NAg and NACP possessed a potent antibacterial effect.

Fig 5

(A) Live bacteria area fraction, and (B) MTT assay of metabolic activity. Each value is mean ± sd (n = 6). In each plot, the same letters indicates values that are not significantly different (p > 0.1).

Fig 6

Biofilm CFU per disk for: (A) Total microorganisms, (B) total streptococci, and (C) mutans streptococci (mean ± sd; n = 6). In each plot, values with dissimilar letters are significantly different (p

Fig 7

Lactic acid production by biofilms (mean ± sd; n = 6). Values with dissimilar letters are significantly different (p