We formulated a pH-sensitive chlorhexidine-loaded mesoporous silica nanoparticles (MSN) modified with poly-(lactic-co-glycolic acid) (CHX-loaded/MSN-PLGA) and incorporated into experimental resin-based dentin adhesives at 5 and 10 wt%. Nanocarriers were characterized in terms of morphology, physicochemical features, spectral analyses, drug-release kinetics at varying pH and its effect on dentin-bound proteases was investigated. The modified dentin adhesives were characterized for cytotoxicity, antimicrobial activity, degree of conversion (DC) along with CHX release, micro-tensile bond strength (μTBS) and nano-leakage expression were studied at different pH values and storage time. CHX-loaded/MSN-PLGA nanocarriers exhibited a significant pH-dependent drug release behavior than CHX-loaded/MSN nanocarriers without PLGA modification. The highest percentage of CHX release was seen with 10 wt% CHX-loaded/MSN-PLGA doped adhesive at a pH of 5.0. CHX-loaded/MSN-PLGA modified adhesives exhibited more profound antibiofilm characteristics against S. mutans and more sustained CHX-release which was pH dependent. After 6 months in artificial saliva at varying pH, the 5 wt% CHX-loaded/MSN-PLGA doped adhesive showed excellent bonding under SEM/TEM, higher μTBS, and least nano-leakage expression. The pH-sensitive CHX-loaded/MSN-PLGA could be of crucial advantage for resin-dentin bonding applications especially in reduced pH microenvironment resulting from biofilm formation; and the activation of dentin-bound proteases as a consequence of acid etching and acidic content of bonding resin monomers.
The aim of this study was to characterize multiscale interactions between high intensity focused ultrasound (HIFU) and dentin collagen and associated matrix-metalloproteinases, in addition to the analysis of the effect of HIFU on bacterial biofilms and biological properties. Dentin specimens were subjected to 5, 10 or 20 s HIFU. XPS spectra were acquired and TEM was performed on dentin slabs. Collagen orientation was performed using Raman spectroscopy. Calcium measurements in human dental pulpal cells (hDPCs) were carried out after 7 and 14 days. For macrophages, CD36+ and CD163+ were analysed. Biofilms were analyzed using CLSM. Tandem mass spectroscopy was performed for the detection of hydroxyproline sequences along with human MMP-2 quantification. Phosphorus, calcium, and nitrogen were detected in HIFU specimens. TEM images demonstrated the collagen network appearing to be fused together in the HIFU 10 and 20 s specimens. The band associated with 960 cm-1 corresponds to the stretching ν1 PO43-. The control specimens showed intensive calcium staining followed by HIFU 20 s > HIFU 10 s > HIFU 5 s specimens. Macrophages in the HIFU specimens co-expressed CD80+ and CD163+ cells. CLSM images showed the HIFU treatment inhibiting bacterial growth. SiteScore propensity determined the effect of HIFU on the binding site with a higher DScore representing better site exposure on MMPs. Multiscale mapping of dentin collagen after HIFU treatment showed no deleterious alterations on the organic structure of dentin.