The anti-caries effects of copper tetraamine fluoride on enamel: An in vitro study

Objective: To investigate the antibacterial, remineralising, and discolouring effects of copper tetraamine fluoride (CTF) on artificial enamel caries.

Method: Human enamel blocks with artificial caries were treated with CTF, silver diamine fluoride (SDF, positive control) and water (negative control) before being challenged with Streptococcus mutans. The morphology, viability, and growth kinetics of biofilm were evaluated using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and colony-forming unit (CFU) counting. The lesion depths, mineral loss, micro-hardness, and crystal characteristics were assessed using micro-computed tomography, Knoop Hardness Tester, and X-ray diffraction (XRD), respectively. The discolouring property was assessed by spectrophotometry.

Results: SEM showed that bacteria completely covered the enamel surface treated with water, but not the enamel surface treated with CTF and SDF. CLSM showed dead-to-live ratio of biofilm treated with CTF, SDF and water were 0.8 ± 0.1, 0.9 ± 0.2 and 0.5 ± 0.1 (p < 0.001, CTF, SDF>Water). Log₁₀ CFU values of biofilm treated with CTF, SDF and water were 7.7 ± 0.2, 7.7 ± 0.1 and 8.1 ± 0.1 (p < 0.001, CTF, SDF<Water). Lesion-depths (μm) of the CTF, SDF and water groups were 93 ± 6, 92 ± 7 and 152 ± 29 (p < 0.001, CTF, SDF<Water). Mineral loss (gHApcm^-3) of the CTF, SDF and water groups were 0.4 ± 0.1, 0.4 ± 0.2 and 1.0 ± 0.2 (p < 0.001, CTF, SDF<Water). Knoop hardness of the CTF, SDF and water groups were 70 ± 23, 68 ± 16 and 21 ± 10 (p < 0.05, CTF, SDF>Water). XRD revealed well-crystallised hydroxyapatite in enamel treated with CTF and SDF, but not water. Spectrophotometry showed ΔE values of the CTF, SDF and water groups were 5 ± 3, 54 ± 6 and 6 ± 2 (p < 0.001, CTF, water<SDF).

Conclusion: CTF inhibited Streptococcus mutans biofilm and remineralised artificial enamel caries without discolouration.

Clinical significance: If CTF is successfully translated into clinical use, it can be a simple agent for clinicians to arrest enamel caries.