Polymeric nanoparticles protect the resin-dentin bonded interface from cariogenic biofilm degradation

Abstract

The objective was to assess doxycycline (Dox) and zinc (Zn) doped nanoparticles' (NPs) potential to protect the resin-dentin interface from cariogenic biofilm. Three groups ofpolymeric NPs were tested: unloaded, loaded with zinc and with doxycycline. NPs were appliedafter dentin etching. The disks were exposed to a cariogenic biofilm challenge in a Drip-FlowReactor during 72 h and 7 d. Half of the specimens were not subjected to biofilm formation butstored 72 h and 7 d. LIVE/DEAD® viability assay, nano-dynamic mechanicalassessment, Raman spectroscopy and field emission electron microscopy (FESEM) analysiswere performed. The measured bacterial death rates, at 7 d were 46% for the control group, 51%for the undoped-NPs, 32% for Dox-NPs, and 87% for Zn-NPs; being total detected bacteriareduced five times in the Dox-NPs group. Zn-NPs treated samples reached, in general, thehighest complex modulus values at the resin-dentin interface over time. Regarding the mineralcontent, Zn-NPs-treated dentin interfaces showed the highest mineralization degree associatedto the phosphate peak and the relative mineral concentration. FESEM images after Zn-NPsapplication permitted to observe remineralization of the etched and non-resin infiltratedcollagen layer, and bacteria were scarcely encountered. The combined antibacterial andremineralizing effects, when Zn-NPs were applied, reduced biofilm formation. Dox-NPs exertedan antibacterial role but did not remineralize the bonded interface. Undoped-NPs did notimprove the properties of the interfaces. Application of Zn-doped NPs during the bondingprocedure is encouraged.