Toward dental caries: Exploring nanoparticle-based platforms and calcium phosphate compounds for dental restorative materials

Abstract

Millions of people worldwide suffer from a toothache due to tooth cavity, and often permanent tooth loss. Dental caries, also known as tooth decay, is a biofilm-dependent infectious disease that damages teeth by minerals loss and presents a high incidence of clinical restorative polymeric fillings (tooth colored fillings). Until now, restorative polymeric fillings present no bioactivity. The complexity of oral biofilms contributes to the difficulty in developing effective novel dental materials. Nanotechnology has been explored in the development of bioactive dental materials to reduce or modulate the activities of caries-related bacteria. Nano-structured platforms based on calcium phosphate and metallic particles have advanced to impart an anti-caries potential to restorative materials. The bioactivity of these platforms induces prevention of mineral loss of the hard tooth structure and antibacterial activities against carries-related pathogens. It has been suggested that this bioactivity could minimize the incidence of caries around restorations (CARS) and increase the longevity of such filling materials. The last few years witnessed growing numbers of studies on the preparation evaluations of these novel materials. Herein, the caries disease process and the role of pathogenic caries-related biofilm, the increasing incidence of CARS, and the recent efforts employed for incorporation of bioactive nanoparticles in restorative polymer materials as useful strategies for prevention and management of caries-related-bacteria are discussed. We highlight the status of the most advanced and widely explored interaction of nanoparticle-based platforms and calcium phosphate compounds with an eye toward translating the potential of these approaches to the dental clinical reality.

Keywords: Bioactive; Dental caries; Dental materials; Nanoparticles.

Graphical abstract

Fig. 1

Schematic drawing illustrating the cariogenic biofilm formation. 1A) Cariogenic dental plaque biofilm, where mainly Mutans streptococci (MS), lactobacilli and non-MS acid-producer bacteria are responsible for the acidic attack; 1B) The cariogenic biofilm is found in dental plaque that grows over the tooth and esthetic tooth-colored restorative materials; 1C) The acidic attack is responsible for the continuous net mineral loss; and 1D) For enamel and dentin, the net mineral loss is present when the pH is lower than 5.5 and 6.5, respectively.

Fig. 2

A) Clinical aspect of secondary caries lesions (CARS) and demineralized areas around multiple composite resin restorations in a young adult; B) Black and white version of the same figure illustrating the location of esthetic tooth-colored restorative materials, CARS, and demineralized areas.

Fig. 3

Schematics is indicating the pathways of bioactivity toward dental caries prevention via dental restorative materials. A) Control of tooth mineral loss via nanosized particles of CaP, highlighting NACP and bioactive glass and B) Reduction and modulation of biofilm formation via antibacterial metallic nanoparticles.

Fig. 4

Calcium (Ca) and phosphate (P) ion release from dental resin composite containing 40% NACP, and the resin composite containing 40% NACP and 20% TTCP and the timeline of their Calcium (Ca) and phosphate (P) ion release. (A) Ca and (B) P ion releases (mean ± SD; n = 3). Low pH is associated with the higher amount of ion release. The greater release in lower pH is promising to respond to the acid attack and low pH environment, which then might neutralize the pH and prevent demineralization around tooth-colored restorative materials. Adapted from Ref. [42], with permission from ^© 2017 Elsevier.

Fig. 5

Microradiographs of dentin lesions before and after the cyclic demineralization/remineralization regimen. The left column: the initial dentin demineralization created in the acidic solution. The middle column: four weeks of the cyclic demineralization/remineralization regimen. The right column: after eight weeks of the cyclic demineralization/remineralization regimen. Adapted from Ref. [42], with permission from ^© 2017 Elsevier.

Fig. 6

Remineralization (mean ± SD; n = 15) of human dentin lesions in the cyclic demineralization/remineralization regimen in vitro. Remineralization with NACP and NACP-TTCP resin composites had the highest values compared to lesions with no resin composite or lesions restored with commercial resin composites (TPH, Caulk/Dentsply), values indicated by different letters are significantly different from each other (p < 0.05). Adapted from Ref. [42], with permission from ^© 2017 Elsevier.

Fig. 7

Transverse microradiography analysis for subsurface enamel lesions around (A) controls resin composite, and (B) NACP resin composite. (D) Exposed enamel (no varnish cover) under biofilms in situ had much less lesion around NACP resin composite compared to control in (C). Adapted from Ref. [46], with permission from ^© 2013 Elsevier.

Fig. 8

Live/dead staining assay for different composition resin composite disks. (A) Schematic of biofilm on cured disk with three layers: Primer, adhesive, and composite. (B–F) Illustrate live/dead images as live bacteria were stained green, and dead bacteria were stained red. Orange/yellow colors are an illustration of live and dead bacteria when they come close to each other. Control disks were associated with alive biofilms, while disks incorporated with nanoparticles of silver (Nag) and nanoparticles of silver-quaternary ammonium dimethacrylate (Nag-QADM) had large amounts of dead bacteria. Adapted from Ref. [60], with permission from ^© 2012 WILEY PERIODICALS, INC.

Fig. 9

Colony-forming unit (CFU) counts for biofilms on resin composite disks (mean six sd; n 1⁄4 6). (A) Total microorganisms, (B) total streptococci, (C) mutans streptococci, and (D) lactobacilli. The CFU counts for biofilms on the experimental bonding agents were reduced to about 20%–30% compared to control, values indicated by different letters are statistically different from each other (p < 0.05). Adapted from Ref. [60], with permission from ^© 2012 WILEY PERIODICALS, INC.