Effect of parathyroid hormone doped nanoparticles on multiscale modeling and hydroxyapatite formation at the resin-dentin interface

Abstract

Objectives: To determine the effects of dentin infiltration with polymeric nanoparticles (NPs) doped with parathyroid hormone (PTH) (PTH-NPs) on hydroxyapatite formation, crystallinity, energy dissipation and viscoelasticity of resin-dentin interfaces. Methods: Etched dentin surfaces were infiltrated with NPs or PTH-NPs. Bonded interfaces were obtained, 24 h stored and submitted to thermal or mechanical challenging. Resin dentin interfaces were evaluated through nano-DMA/complex-loss-storage moduli-tan delta assessment, atomic force microscopy (AFM)/topographical mapping-collagen fibril diameter, X-ray diffraction (XRD)/refined XRD2 profile-Debye-Scherrer rings and transmission electron microscopy (TEM)/Bright field-selected area electron diffraction Fast Fourier Transforms. Results: Load cycling of specimens infiltrated with PTH-NPs achieved the highest complex modulus and the lowest tan (δ), at the hybrid layer, promoting intratubular mineral precipitation, total occlusion of the dentinal tubules and thick platforms of mineral in dentin. Bridges of slipped mineralized dentin appeared close to peritubular structures, and the collagen fibrils width significantly augmented. PTH-NPS facilitated the highest crystallinity, crystallite size and microstrain in the longitudinal and perpendicular directions of the c-axis, with a right defined lineation. Undoped NPs and load cycling did not totally occlude the dentin tubules, and provoked microcracking and breakdown of the unfilled tubules. New crystals, with a low calcium and phosphorous percentage, were amorphous in absence of PTH. Significance: PTH-NPs dentin infiltration ensured intrafibrillar mineralization and advanced crystallinity, that resulted associated to high mechanical performance. The new crystals were hydroxyapatite in nature and showed the strongest chemical stability of the created nano-rods. Thermocycling of samples treated with PTH-NPs showed lower resistance to deformation and limited dentin mineralization. The mineral precipitates obtained with undoped NPs had scarce crystallinity, high grade of impurities and elevated biodegradability.