Effects of a New Nano-Silver Fluoride-Containing Dentifrice on Demineralization of Enamel and Streptococcus mutans Adhesion and Acidogenicity

Received Jan 18, 2018; Revised Mar 13, 2018; Accepted Apr 1, 2018

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1. Introduction

Mutans streptococci produce short-chain acids which dissolve the hard tissue of teeth. They are highly acidogenic and metabolize sucrose to synthesize insoluble extracellular polysaccharides which enhance their adherence to the tooth. For this reason, Streptococcus mutans is considered to be the most cariogenic bacteria [1].

S. mutans and S. sobrinus are the main microorganisms involved in the caries process. However, S. mutans is more cariogenic because it produces cell-surface proteins that help it to adhere to the dental surface [2]. In addition, S. mutans is able to metabolize sucrose, glucose, fructose, and maltose in cellular glucogen-like polysaccharides [3], as well as acids that lead to demineralization of the enamel surface that leads to the induction of caries lesions [2].

The evidence supporting the efficacy of fluoride in preventing caries in children and adolescents is indisputable, and since tooth brushing with fluoridated dentifrices is the easiest way to deliver fluoride into the mouth, it is widely used by all ages. The declining prevalence of caries in the last 30 years in Western countries has been attributed to the widespread use of fluoride products [4]. Fluoride inhibits the demineralization of enamel by changing the critical pH for dissolution of Ca²⁺ and PO₄³⁻ in bacterial biofilm and adsorbing the apatite crystal surfaces, where it replaces Ca²⁺ to form acid-resistant mineral fluorapatite with low solubility [5]. Moreover, fluoride causes inhibition of bacterial activity [6] and acid production of S. mutans [7].

The antibacterial activity of silver on a wide range of microorganisms has been well known since ancient times and, at low concentrations, is not toxic to human cells [8]. Silver has a high chemical affinity for compounds containing nitrogen, sulfur, and phosphorus, so it has been suggested that the inhibitory power of silver ions is due to its interaction with the thiol groups of proteins and the phospholipid portion of the bacterial membrane [9]. When formed into nanoparticles, silver interacts more intensely with other organic and inorganic molecules due to...