Effect of Silver Nitrate and Sodium Fluoride with Tri-calcium Phosphate on Streptococcus mutans and Demineralised Dentine

Objectives: To investigate the adjunctive effect of 25% silver nitrate (AgNO₃) solution and 5% sodium fluoride (NaF) varnish with functionalized tri-calcium phosphate (fTCP) on demineralised dentine and cariogenic biofilm.
Methods: 120 human dentine specimens were demineralised and allocated to four groups - Group 1: 25% AgNO₃ and 5% NaF + fTCP varnish (Clinpro, 3M); Group 2: 25% AgNO₃ (Silver nitrate, Gordon Lab) and 5% NaF (Duraphat, Colgate); Group 3: 25% AgNO₃; Group 4: water. After Streptococcus mutans (S. mutans) biofilm challenge for 7 days, the biofilm and dentine surface morphology were studied by scanning electron microscopy (SEM). Lesion depth, crystal characteristics and collagen degradation of specimens were assessed by micro-computed tomography (Micro-CT), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. Confocal laser scanning microscopy (CLSM) and colony forming units (CFU) were used to study the viability of the biofilms.
Results: SEM images revealed severe surface damage in Group 4 and modest surface destruction in Group 3. The mean lesion depths (± standard deviation) from Group 1 to Group 4 were 212.6±20.1µm, 280.8±51.6µm, 402.5±61.7µm and 497.4±67.2µm, respectively (Groups 1<2<3<4, p<0.001). XRD results demonstrated precipitation of silver chloride in Groups 1, 2 and 3. FTIR showed the amide I:HPO₄^2- ratio of the 4 groups were 0.22±0.05, 0.25±0.05, 0.41±0.12 and 0.64±0.14, respectively (Groups 1, 2<3<4; p<0.001). The SEM and CLSM images showed suppression of biofilm growth in Groups 1, 2 and 3. The mean log CFU values of S. mutans (±standard deviation) from Groups 1 to 4 were 4.5±0.7, 4.4±0.9, 4.4±0.9 and 6.7±1.0 (Groups 1,2,3<4, p<0.001).
Conclusions: Addition of NaF with/without fTCP to AgNO₃ can reduce the damage of dentine caused by cariogenic biofilm. Besides, the addition does not affect the antibacterial effect of AgNO₃.