Silver ions distribution and caries hardness after silver fluoride application

Objectives: To describe the distribution of silver ions in and the micro-hardness of dentine caries lesion treated by topical application of silver diamine fluoride (SDF) solution.

Methods: Primary incisors that were going to exfoliate in children who participated in a 30-month clinical trial of SDF treatment were extracted after obtaining parental consent. Eight collected teeth, four had arrested caries and the other four had soft caries, were sectioned longitudinally along the midline of the carious lesion. On one half, the hardness of the carious lesions was measured by Knoop indenter on a micro-hardness tester using 5-gram force for 10 seconds. Distribution of silver ions in the SDF treated lesion was observed using backscattered electron (BSE) imaging on the other half.

Results: The median Knoop Hardness (KH) in clinically diagnosed arrested caries was found to be more than 40 in the outer 50 μm of the lesion. It then lay mostly in the range of 20 to 30 at points deeper than 50 μm from the surface. The KH of soft dentine caries was below 10 in the outer 50 μm of the lesion and was less than 15 in the outer 100 μm. It then gradually increased to 20 at 200 μm from the surface. BSE image found a continuous layer of silver ions deposited on the surface of the caries lesion treated with SDF. Most silver ions were located in the outer 200 μm and only a trace of silver ions was found beyond 500 μm from the surface of the lesion.

Conclusion: The Knoop Hardness in clinically diagnosed arrested dentine caries was higher than that of soft caries in the outer 100 μm of the surface. The silver ions were found mainly deposited on the outer 200 μm from the surface.