Ion-modified nanoparticles induce different apatite formation in cervical dentine

Aim: To investigate if crystallinity and ultrastructure are modified when cervical dentine is treated with four different nanogels-based solutions for remineralizing purposes.

Methodology: Experimental nanogels based on polymeric nanoparticles (NPs) and zinc, calcium or doxycycline-loaded NPs were applied to citric acid etched dentine to facilitate the occlusion of tubules and the mineralization of the dentine surface. Dentine surfaces were studied by X-ray diffraction and transmission electron microscopy through selected area diffraction and bright-field imaging.

Results: Crystals at the dentine surface were identified as hydroxyapatite with the highest crystallographic maturity and crystallite size in dentine treated with Zn-NPs-based gel. Texture increased in all samples from 24 h to 7 days, except in dentine surfaces treated with Zn-NPs gel. Polyhedral, plate-like and drop-like shaped apatite crystals constituted the bulk of minerals in dentine treated with Zn-NPs gel, after 7 days. Polymorphic, cubic and needle-like shaped crystals distinguished minerals, with more amorphous characteristics in dentine treated with Ca-NPs gel after 7 days than that found when Zn-NPs were applied. Doxycycline-NPs produced the smallest crystallites with poor crystallinity, maturity and chemical stability.

Conclusions: Crystalline and amorphous phases of newly formed hydroxyapatite were described in both types of dentine treated with Zn-NPs as well as Ca-NPs gels with multiple shapes of crystallites. Crystal shapes ranged from rounded/drop-like or plate-like crystals to needle-like or polyhedral and cubic apatite appearance.