Antibacterial and mineralising properties of copper tetraamine fluoride on dentine caries: A laboratory study

Objective: To investigate the antibacterial, mineralising, and discolouring properties of copper tetraamine fluoride (CTF) on artificial dentine caries.

Method: Demineralised human dentine blocks were treated with CTF, silver diamine fluoride (SDF, positive control) and water (negative control) before they were subjected to cariogenic challenge with Streptococcus mutans biofilm. The morphology, viability, and growth kinetics of the biofilm were assessed by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and colony-forming unit (CFU) counting. The lesion depths, mineral loss, chemical structure, and crystal characteristics were measured using micro-computed tomography, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The discolouring property on demineralised dentine was assessed by spectrophotometry. One-way analysis of variance with the Bonferroni post hoc test was performed to assess and compare the data.

Results: SEM revealed confluent bacterial growth covering the surface of dentine treated with Water but not CTF and SDF. CLSM showed the dead-to-live ratio of the biofilm treated with CTF, SDF and Water were 0.7 ± 0.1, 0.8 ± 0.1 and 0.5 ± 0.1 (p < 0.001, CTF, SDF>Water). The Log₁₀ CFU values of the biofilm treated with CTF, SDF and Water were 7.8 ± 0.1, 7.8 ± 0.1 and 8.1 ± 0.2 (p < 0.001, CTF, SDF<Water). Micro-computed tomography showed the Δlesion-depth (μm) of dentine treated with CTF, SDF and water were 33 ± 5, 40 ± 7 and 169 ± 17 (p < 0.001, CTF, SDF<Water). The Δmineral loss (gHApcm^-3) of dentine treated with CTF, SDF and Water were 0.19 ± 0.04, 0.18 ± 0.04 and 0.30 ± 0.04 (p < 0.001, CTF, SDF<Water). FTIR showed the amide I-to-hydrogen phosphate ratios of dentine treated with CTF, SDF and Water were 0.23 ± 0.02, 0.24 ± 0.05, and 0.44 ± 0.06 (p < 0.001, CTF, SDF<Water). XRD revealed well-crystallised hydroxyapatite in the CTF and SDF groups. Spectrophotometry showed the ΔE values of the CTF, SDF and Water groups were 6 ± 4, 49 ± 3 and 10 ± 3 (p < 0.001, CTF, water<SDF).

Conclusion: CTF inhibited Streptococcus mutans. It mineralised but not discoloured artificial dentine caries.

Clinical significance: If CTF is successfully translated into clinical application, it may be a non-discolouring anti-caries agent for clinicians to arrest dentine caries.