Fatigue resistance of human carious dentin treated with ammonia- and water-based silver fluoride

To evaluate the flexural strength and fatigue resistance of carious dentin treated with ammonia- or water-based silver fluoride using an in vitro microcosm biofilm model, under quasi-static and cyclic load conditions.

Dentin beams (0.4 ×1.4 ×6 mm) were prepared and exposed to microcosm biofilm model (Saliva+McBain Medium+0.2% Sucrose) for two days. Microcosm biofilm efficacy was assessed using colony-forming unit counts, dentin microhardness (surface and cross-section), lactic acid production and MTT metabolic activity. Carious beams were treated with either ammonia- (Silver Diamine Fluoride, SDFa and SDFa+KI, Riva Star, SDI) or water-based (Silver Fluoride, SFw and SFw+KI, Riva Star Aqua, SDI) silver fluoride for 60 s. Untreated carious dentin (CD) and sound dentin (SD) beams served as negative and positive controls, respectively. Dentin beams were incubated in artificial saliva for three days and tested under 4-point flexure at quasi-static loads (n = 15) and then under cyclic loads (n = 25). The stress-life fatigue behavior was evaluated using the staircase method (4 Hz) and apparent endurance limits were calculated at 10⁷ cycles. Tension sides of fractured beams were examined under SEM. Quasi-static data (one-way ANOVA, Tukey) and cyclic-load data (Kruskal-Wallis) were analyzed (α=0.05).

Quasi-static flexural strength was highest in SD (p < 0.05). Among carious groups, no significant differences were observed in flexural strength values (p > 0.05). SFw treatment revealed lower fatigue resistance than SD, however, significantly exceeding SDFa, SDFa+KI, SFw+KI and CD (p < 0.05). Fatigue resistance of SDFa was higher than CD (p < 0.05). SEM confirmed denser silver-particle deposition in SFw group, correlating with higher fatigue resistance.

Ammonia- and water-based silver fluoride treatments could enhance the structural integrity and mechanical strength of carious dentin. However, the use of potassium iodide may impair potential improvements in fatigue resistance of SFw-treated carious dentin.