Ex vivo investigations on bioinspired electrospun membranes as potential biomaterials for bone regeneration.

OBJECTIVES: To assess the surface characteristics and composition that may enhance osteoblasts viability on novel electrospun composite membranes (organic polymer/silicon dioxide nanoparticles). METHODS: Membranes are composed by a novel polymer blend, the mixture of two hydrophilic copolymers 2-hydroxyethylmethacrylate-co-methylmethacrylate and 2-hydroxyethylacrylate-co-methylacrylate, and they are doped with silicon dioxide nanoparticles. Then the membranes were functionalized with zinc or doxycycline. The membranes were morphologically characterized by atomic force and scanning electron microscopy (FESEM), and mechanically probed using a nanoindenter. Biomimetic calcium phosphate precipitation on polymeric tissues was assessed. Cell viability tests were performed using human osteosarcoma cells. Cells morphology was also studied by FESEM. Data were analyzed by ANOVA, Student-Newman-Keuls and Student t tests (p < 0.05). RESULTS: Silica doping of membranes enhanced bioactivity and increased mechanical properties. Membranes morphology and mechanical properties were similar to those of trabecular bone. Zinc and doxycycline doping did not exert changes but it increased novel membranes bioactivity. Membranes were found to permit osteoblasts proliferation. Silica-doping favored cells proliferation and spreading. As soon as 24 h after the seeding, cells in silica-doped membranes were firmly attached to experimental tissues trough filopodia, connected to each other. The cells produced collagen and minerals onto the surfaces. CONCLUSIONS: Silica nanoparticles enhanced surface properties and osteoblasts viability on electrospun membranes. CLINICAL SIGNIFICANCE: The ability of silica-doped matrices to promote precipitation of calcium phosphate, together with their mechanical properties, observed non-toxicity, stimulating effect on osteoblasts and its surface chemistry allowing covalent binding of proteins, offer a potential strategy for bone regeneration applications.

Silver improves collagen structure and stability at demineralized dentin: A dynamic-mechanical and Raman analysis.

OBJECTIVE: This study aimed to evaluate the effect of silver loaded nanoparticles (NPs) application on dentin remineralization. METHODS: Polymethylmetacrylate-based NPs and silver loaded NPs (Ag-NPs) were applied on demineralized dentin surfaces. Dentin was characterized morphologically by scanning electron microscopy, mechanically probed by a nanoindenter to test nanohardness and Young modulus, and chemically analyzed by Raman spectroscopy after 24 h and 7 d of storage. Untreated surfaces were used as control. Data were submitted to ANOVA and Student-Newman-Keuls multiple comparisons tests (P < 0.05). RESULTS: After Raman analysis, dentin treated with Ag-NPs obtained the lowest mineralization and intensity of stoichiometric hydroxyapatite when compared with specimens treated with undoped-NPs. The lowest relative mineral concentration, expressed as the ratio phosphate or carbonate/phenyl group, and crystallinity was attained by dentin treated with Ag-NPs, after 7 d. Ag-NPs application generated the highest values of collagen crosslinking (intensity at 1032 cm-1 band). The molecular conformation of the collagen's polypeptide chains, amide-I and CH2 also attained the highest peaks in dentin treated with Ag-NPs. Staggered and demineralized collagen fibrils were observed covering the dentin surfaces treated with Ag-NPs, at both 24 h and 7 d. Samples treated with Ag-NPs attained the lowest values of nanohardness and Young's modulus at 7 d of storage. CONCLUSIONS: Peritubular and intertubular dentin were remineralized when using undoped-NPs. After 7 d, collagen treated with NPs was remineralized but dentin treated with Ag-NPs attained an improved collagen matrix structure and stability but the lowest mineralization and crystallinity. CLINICAL SIGNIFICANCE: Preservation of the demineralized organic matrix is fundamental in operative dentistry. Silver contributed to improve crosslinking, nature and secondary structure of demineralized dentin collagen, for further long-term intrafibrillar mineralization.

Bleaching agents increase metalloproteinases-mediated collagen degradation in dentin.

INTRODUCTION: Tooth bleaching is based on hydrogen peroxide application. The Objective of this study was to determine whether dental bleaching agents affect metalloproteinases-mediated dentin collagen degradation. METHODS: Human dentin specimens were subjected to different treatments: (1) untreated dentin; (2) demineralization by 37% phosphoric acid (PA); (3) demineralization by 37% PA, followed by application of Single Bond (SB); (4) 2 immersions of 7 days each in a nonvital bleaching agent, followed by PA; (5) 2 immersions of 7 days each in nonvital bleaching, followed by PA and SB application; (6) 3 immersions by using in-office bleaching gel for 20 minutes; (7) 3 immersions by using in-office bleaching gel for 20 minutes plus activation with a light source; and (8) immersion in home bleaching gel for 8 hours per day during 3 weeks. Specimens were stored in artificial saliva. C-terminal telopeptide determinations (radioimmunoassay) were performed after 24 hours, 1 week, and 4 weeks. RESULTS: Bleaching agents increased collagen degradation, but C-terminal telopeptide of type I collagen (ICTP) values were higher when dentin was PA-demineralized. Nonvital bleaching plus PA promoted the highest collagenolytic activity, which was reduced after SB infiltration. Halogen light application did not influence ICTP values. At 24 hours, home bleaching exhibited high collagenolytic activity, which decreased up to 4 weeks. After 4 weeks of storage, all bleaching procedures showed similar values of collagen degradation, which were not different from those of PA-demineralized and resin-infiltrated dentin. CONCLUSIONS: All tested bleaching agents increase matrix metalloproteinases-mediated collagen degradation in dentin. This effect was not completely reverted after 4 weeks. Home bleaching induced the highest collagen degradation.

Zinc-doped dentin adhesive for collagen protection at the hybrid layer.

The aim of the study was to ascertain whether the addition of zinc to adhesives may decrease metalloproteinase-mediated collagen degradation without affecting bonding efficacy. Human dentin beams were treated with phosphoric acid, with Clearfil SE Bond Primer or with Clearfil SE Bond Primer plus ZnCl(2) (2 wt%). Acid-etched dentin was infiltrated with Single Bond, Single Bond plus ZnCl(2) (2 wt%), or Single Bond plus ZnO nanoparticles (10 wt%), and Clearfil SE Bond-primed dentin was infiltrated with Clearfil SE Bonding resin, Clearfil SE-Bonding resin with ZnCl(2) (2 wt%), or Clearfil SE-Bonding resin with ZnO nanoparticles (10 wt%). The C-terminal telopeptide concentrations were determined 24 h, and 1 and 4 wk after treatment. Microtensile bond strength to dentin was determined for the tested adhesives. Matrix metalloproteinases-mediated collagen degradation occurred in acid-etched and SE-primed dentin. Resin infiltration decreased collagen degradation. Lower collagen degradation was found for SE Bond than for Single Bond. Zinc-doped Single Bond resin always reduced collagen degradation, the ZnO particles being more effective than ZnCl(2) . Zinc-doped SE Bond reduced the liberation of C-terminal telopeptide only at 24 h. Bond strength to dentin was not decreased when Zn-doped resins were employed, except when ZnCl(2) was added to SE Primer. Zinc-doped resin reduced collagen degradation in Single Bond hybrid layers, but did not affect bond strength. The addition of zinc to SE Bond had no beneficial effects.

Effect of dentin etching and chlorhexidine application on metalloproteinase-mediated collagen degradation.

Dentin matrix metalloproteinases (MMPs) are involved in the degradation of collagen in resin-dentin interfaces. This study evaluated whether collagen degradation can be prevented by chlorhexidine digluconate (CHX) after different dentin demineralization procedures. The demineralization of human dentin was performed with phosphoric acid (PA), EDTA or acidic monomers (Clearfil SE Bond and Xeno V). Specimens were stored (for 24 h, or for 1 or 3 wk) in the presence or absence of CHX. In half of the groups, active MMP-2 was incorporated into the storage solution. At the end of each storage period, the C-terminal telopeptide (ICTP) concentration (which indicates the amount of collagen degradation) was measured in the storage solution. Collagen degradation was higher in PA- and EDTA-demineralized dentin. Chlorhexidine digluconate reduced collagen degradation in these groups only for 24 h. When dentin was demineralized with Clearfil SE Bond or Xeno V, collagen degradation was reduced by up to 30%, but the addition of exogenous MMP-2 significantly increased collagen degradation. In self-etchant-treated dentin, the inhibitory effect of CHX on MMPs lasted for up to 3 wk. Treating dentin with EDTA, PA or self-etching agents produces enough demineralization to permit cleavage of the exposed collagen. Monomer infiltration may exert protection on demineralized collagen, probably through immobilization of MMPs. The partial inhibitory action of CHX on MMP activity produced by self-etching adhesives was prolonged compared with the short-acting PA- or EDTA-treated dentin.