Anticaries Properties of Dental Materials Containing Silver and Calcium-phosphate Nanoparticles

Dental materials with anticaries properties could help inhibit the development of lesions. Objectives: To investigate the antibacterial effects in vitro of incorporating nanoparticles of silver (NAg) and nanoparticles of amorphous calcium phosphate (NACP) into a bonding agent, and to assess the effects of NACP-filled nanocomposite on enamel mineral loss in an in situ model. Methods: For the in vitro study, commercial adhesive and primer were used as control.  NAg were incorporated into the primer and adhesive at 0.1% by mass. NACP were mixed into adhesive at 10%, 20%, 30% and 40%. Dentin bond strength and oral microcosm biofilm response were measured. For the in situ study, caries-like lesions were produced in which 25 volunteers wore palatal devices with enamel slabs restored using NACP nanocomposite or control composite. Ca and P ion concentrations were measured in biofilms on the slabs. Enamel demineralization was assessed by transverse microradiography. Results: Bonding agents containing NAg and NACP showed bond strengths ranged from 26 to 34 MPa, with no significant difference (p>0.1).  Substantial reductions in bacterial viability were obtained (p<0.05), including metabolic activity (reduced by 60%), CFU for total microorganisms, total streptococci, and mutans streptococci (50-85%), and lactic acid production (65-85%). SEM examination showed NACP infiltration into dentinal tubules. In the in situ study, NACP nanocomposite significantly increased Ca and P ion concentrations in biofilms and substantially reduced mineral loss in enamel (p<0.05). Conclusions:  Incorporation of NACP and NAg imparted a great anticaries effect by inhibiting the cariogenic biofilm viability and lactic acid production, as well as promoting remineralization in tooth enamel. The method of combining an antibacterial agent and a remineralizing agent in the adhesive or the composite is promising to inhibit secondary caries, and may have potential for use in a wide range of materials including adhesives, composites, cements, and sealants.