Calcium and silver nanoparticles in dentine held the bond for 12 months, so far in vitro
By treating demineralised dentine successively with calcium chloride and silver fluoride, researchers precipitated hybrid nanoparticles in it. After 12 months, microtensile bond strength was better than in the control, with less nanoleakage and biofilm halted.
A hybrid layer that degrades more slowly
The weak point of a composite restoration is not the composite but the hybrid layer, the zone where the adhesive interweaves with the demineralised collagen of dentine. That bond degrades over time, mostly because water remains within it. The team around Zhang, writing in Clinical Oral Investigations, describes an attempt to strengthen that zone by precipitating nanoparticles in situ.
The procedure is simple. Demineralised dentine is treated first with a calcium chloride solution and then with silver fluoride, which forms hybrid calcium and silver nanoparticles within the matrix. Surface potential, water sorption and thermogravimetric analysis showed less residual water at the interface: mass loss below 200 °C was lower than in the control.
The nanoparticles also acted on microbes. Confocal and electron microscopy showed that the treated surface inhibits biofilm formation and breaks down biofilm already formed, both for Streptococcus mutans and for saliva-derived biofilm. Within an hour, mineral deposition with a crystalline structure was visible on treated dentine, while the control remained unmineralised. The adhesive penetrated better, nanoleakage was lower, and microtensile bond strength after twelve months was better than in the control group.
Limitations
Everything was measured in vitro, on laboratory specimens and biofilms, and the authors themselves call for further testing before any clinical use. Silver compounds additionally carry a known risk of staining hard dental tissues, which this work did not measure.
For the practice
- It does not change the adhesion protocol yet: there is neither a commercial product nor a clinical study behind the procedure.
- The message that is usable today: moisture in the hybrid layer is the main enemy of bond durability, so moisture control during cementation pays off as much as the choice of adhesive.
- If you follow silver preparations such as SDF, this is one more direction in which silver moves from arresting caries into adhesive chemistry.