Site specific properties of carious dentin matrices biomodified with collagen cross-linkers.

PURPOSE: To assess in non-cavitated carious teeth the mechanical properties of dentin matrix by measuring its reduced modulus of elasticity and the effect of dentin biomodification strategies on three dentin matrix zones: caries-affected, apparently normal dentin below caries-affected zone and sound dentin far from carious site. METHODS: Nano-indentations were performed on dentin matrices of carious molars before and after surface modification using known cross-linking agents (glutaraldehyde, proanthocyanidins from grape seed extract and carbodiimide). RESULTS: Statistically significant differences were observed between dentin zones of demineralized dentin prior to surface biomodification (P < 0.05). Following surface modification, there were no statistically significant differences between dentin zones (P < 0.05). An average increase of 30-fold, 2-fold and 2.2-fold of the reduced modulus of elasticity was observed following treatments of the three dentin zones with proanthocyanidin, carbodiimide and glutaraldehyde, respectively.

Biomimetic extracellular matrix-incorporated scaffold induces osteogenic gene expression in human marrow stromal cells.

Engineering biomaterials mimicking the biofunctionality of the extracellular matrix (ECM) is important in instructing and eliciting cell response. The native ECM is highly dynamic and has been shown to support cellular attachment, migration, and differentiation. The advantage of synthesizing an ECM-based biomaterial is that it mimics the native cellular environment. However, the ECM has tissue-specific composition and patterned arrangement. In this study, we have employed biomimetic strategies to develop a novel collagen/chitosan template that is embedded with the native ECM of differentiating human marrow stromal cells (HMSCs) to facilitate osteoblast differentiation. The scaffold was characterized for substrate stiffness by magnetic resonance imaging and nanoindentation and by immunohistochemical analysis for the presence of key ECM proteins. Gene expression analysis showed that the ECM scaffold supported osteogenic differentiation of undifferentiated HMSCs as significant changes were observed in the expression levels of growth factors, transcription factors, proteases, receptors, and ECM proteins. Finally, we demonstrate that the scaffold had the ability to nucleate calcium phosphate polymorphs to form a mineralized matrix. The results from this study suggest that the three-dimensional native ECM scaffold directly controls cell behavior and supports the osteogenic differentiation of mesenchymal stem cells.

Long-term stability of dentin matrix following treatment with various natural collagen cross-linkers.

OBJECTIVES: Collagen disorganization is one of the main degradation patterns found in unsuccessful adhesive restorations. The hypothesis of this study was that pretreatment using natural collagen cross-linking agents rich in proanthocyanidin (PA) would improve mechanical properties and stability over time of the dentin collagen and, thus, confer a more resistant and lasting substrate for adhesive restorations. METHODS: PA-based extracts, from grape seed (GSE), cocoa seed (CSE), cranberry (CRE), cinnamon (CNE) and açaí berry (ACE) were applied over the demineralized dentin. The apparent elastic modulus (E) of the treated dentin collagen was analyzed over a 12 month period. Specimens were immersed in the respective solution and E values were obtained by a micro-flexural test at baseline, 10, 30, 60, 120 and 240 min. Samples were stored in artificial saliva and re-tested after 3, 6 and 12 months. Data was analyzed using ANOVA and Tukey test. RESULTS: GSE and CSE extracts showed a time-dependent effect and were able to improve [240 min (MPa): GSE = 108.96 ± 56.08;CSE = 59.21 ± 24.87] and stabilize the E of the organic matrix [12 months (MPa): GSE = 40.91 ± 19.69;CSE = 42.11 ± 13.46]. CRE and CNE extracts were able to maintain the E of collagen matrices constant over 12 months [CRE = 11.17 ± 7.22;CNE = 9,96 ± 6.11;MPa]. ACE (2.64 ± 1.22 MPa) and control groups immersed in neat distilled water (1.37 ± 0.69 MPa) and ethanol-water (0.95 ± 0.33 MPa) showed no effect over dentin organic matrix and enable their degradation and reduction of mechanical properties. SIGNIFICANCE: Some PA-based extracts were capable of improving and stabilizing collagen matrices through exogenous cross-links induction.

Long-term nano-mechanical properties of biomodified dentin-resin interface components.

Failures of dental composite restorative procedures are largely attributed to the degradation of dentin-resin interface components. Biomodification of dentin using bioactive agents may improve the quality and durability of the dentin-resin bonds. The aim of this study was to nanomechanically assess the reduced modulus of elasticity (Er) and nano-hardness (H) of major components of the dentin-resin interface (hybrid layer, adhesive layer and underlying dentin) biomodified by collagen cross-linkers at 24h, 3 and 6 months following restorative procedure. Demineralized dentin surfaces were biomodified with 5% glutaraldehyde (GD) or 6.5% grape seed extract (GSE) prior to placement of adhesive systems and composite resin. Nano-measurements of the interface components in a fluid cell showed that both agents increased the Er and H of underlying dentin after 3 and 6 months when compared to a control. The mechanical properties of the adhesive and hybrid layers decreased over time. Biomodification of the dentin-resin interface structures using GD and GSE can increase the mechanical properties of the interface over time and may contribute to the long-term quality of adhesive restorations.