Demineralized dentin 3D porosity and pore size distribution using mercury porosimetry

Reinforced dentin remineralization via a novel dual-affinity peptide

OBJECTIVES

In light of the constantly flowing saliva, anti-caries remineralization agents are inclined to be taken away. Owing to their limited residence time, the remineralization effect is not as desirable as expected. Hence, our study aimed to synthesize a novel peptide (DGP) with high affinity to both collagen fibrils and hydroxyapatite, and investigated its dentin remineralization efficacy in vitro and anti-caries capability in vivo.

METHODS

DGP was synthesized through Fmoc solid-phase reaction. The binding ability and interaction mechanism of DGP to demineralized dentin were investigated. Dentin specimens were demineralized, then treated with DGP and deionized water respectively. The specimens were incubated in artificial saliva and in-vitro remineralization effectiveness was analyzed after 14 days. The rat caries model was established to further scrutinize the in-vivo efficacy of caries prevention.

RESULTS

DGP possesses an enhanced adhesion force of 12.29 ± 1.12 nN to demineralized dentin. The favorable adsorption capacity is ascribed to the stable hydrogen bonds between S2P-101 and ASP-100 of DGP and GLY33 and PRO-16 of collagen fibers. Abundant mineral deposits and remarkable tubule occlusion were observed in the DGP group. DGP-treated dentin obtained notable microhardness recovery and higher mineral content after a 14-day remineralization regimen. DGP also demonstrated potent caries prevention in vivo, with substantially fewer carious lesions and significantly lower Keyes scoring.

SIGNIFICANCE

DGP proves to possess a high affinity to demineralized dentin regardless of saliva flowing, thus enhancing remineralization potency significantly in vitro and in vivo, potential for dental caries prevention and combatting initial dentin caries clinically.

The role of lateral branches on effective stiffness and local overstresses in dentin

The 3D microstructure of dentinal tissue, the main tissue of the tooth, is the subject of an increasingly comprehensive body of knowledge. The relationship between this microstructure and the mechanical behaviour of dentinal tissue remains, nonetheless, under question. This article proposes an original SEM analysis of dentin microstructure, accounting for lateral branches, and a mechanical model based on these findings. An interesting observation is that lateral branches have a dense collar, as do tubules. The diameter of these branches as well as a percentage area are quantified all along the depth of a dentin sample. We use these unprecedented data to build an orthotropic homogenized model of dentin. The heterogeneities of microstructure are taken into account using level-set functions. The results reveal that the lateral branches slightly influence the global homogenized elastic behavior of the dentin tissue, albeit creating stress concentration areas that are highly influenced by the inclination of the traction with respect to the tubule and branches.

Postulated release profile of recombinant human bone morphogenetic protein-2 (rhBMP-2) from demineralized dentin matrix

Demineralized dentin matrix (DDM) has been used as a recombinant human bone morphogenetic protein-2 (rhBMP-2) carrier in many clinical trials. To optimize the clinical safety and efficacy of rhBMP-2 with DDM, efforts have been made to improve the delivery of rhBMP-2 by 1) lowering the administered dose, 2) localizing the protein, and 3) prolonging its retention time at the action site as well as the bone forming capacity of the carrier itself. The release profile of rhBMP-2 that is associated with endogenous BMP in dentin has been postulated according to the type of incorporation, which is attributed to the loosened interfibrillar space and nanoporous dentinal tubule pores. Physically adsorbed and modified, physically entrapped rhBMP-2 is sequentially released from the DDM surface during the early stage of implantation. As DDM degradation progresses, the loosened interfibrillar space and enlarged dentinal tubules release the entrapped rhBMP-2. Finally, the endogenous BMP in dentin is released with osteoclastic dentin resorption. According to the postulated release profile, DDM can therefore be used in a controlled manner as a sequential delivery scaffold for rhBMP-2, thus sustaining the rhBMP-2 concentration for a prolonged period due to localization. In addition, we attempted to determine how to lower the rhBMP-2 concentration to 0.2 mg/mL, which is lower than the approved 1.5 mg/mL.

Assessment of root caries under wet and dry conditions using swept-source optical coherence tomography (SS-OCT)

The purpose of this study was to compare optical properties of root caries under two observing conditions using swept-source optical coherence tomography (SS-OCT). In vitro and natural root caries were observed by SS-OCT under wet and dry conditions, followed by confocal laser scanning microscope (CLSM) and transverse microradiography (TMR). Signal intensity (SI), distance between SI peaks (SI-distance) and optical lesion depth were obtained from OCT. Lesion depth was measured from CLSM; lesion depth (LD_TMR) and mineral loss (ML) were obtained from TMR. In vitro root caries under wet and dry conditions showed different OCT images and SI patterns. Lesion depth of OCT and that of CLSM, SI-distance and LD_TMR, LD_TMR and ML significantly correlated. Under dry conditions, half natural root caries showed similar OCT images and SI patterns as in vitro root caries. The base of demineralized dentin could be detected more clearly under dry conditions than under wet conditions.

Collagen-Based Medical Device as a Stem Cell Carrier for Regenerative Medicine

Maintenance of mesenchymal stem cells (MSCs) requires a tissue-specific microenvironment (i.e., niche), which is poorly represented by the typical plastic substrate used for two-dimensional growth of MSCs in a tissue culture flask. The objective of this study was to address the potential use of collagen-based medical devices (HEMOCOLLAGENE^®, Saint-Maur-des-Fossés, France) as mimetic niche for MSCs with the ability to preserve human MSC stemness in vitro. With a chemical composition similar to type I collagen, HEMOCOLLAGENE^® foam presented a porous and interconnected structure (>90%) and a relative low elastic modulus of around 60 kPa. Biological studies revealed an apparently inert microenvironment of HEMOCOLLAGENE^® foam, where 80% of cultured human MSCs remained viable, adopted a flattened morphology, and maintained their undifferentiated state with basal secretory activity. Thus, three-dimensional HEMOCOLLAGENE^® foams present an in vitro model that mimics the MSC niche with the capacity to support viable and quiescent MSCs within a low stiffness collagen I scaffold simulating Wharton's jelly. These results suggest that haemostatic foam may be a useful and versatile carrier for MSC transplantation for regenerative medicine applications.

The peritubular reinforcement effect of porous dentine microstructure

In the current study, we evaluate the equivalent stiffness of peritubular reinforcement effect (PRE) of porous dentine optimized by the thickness of peritubular dentine (PTD). Few studies to date have evaluated or quantitated the effect of PRE on composite dentine. The miscrostructure of porous dentine is captured by scanning electron microscope images, and then finite element modeling is used to quantitate the deformation and stiffness of the porous dentine structure. By optimizing the radius of PTD and dentine tubule (DT), the proposed FE model is able to demonstrate the effect of peritubular reinforcement on porous dentine stiffness. It is concluded that the dentinal equivalent stiffness is reduced and degraded with the increase of the radius of DT (i.e., porosity) in the certain ratio value of E_p/E_i and certain radius of PTD, where E_p is the PTD modulus and E_i is the intertubular dentine modulus. So in order to ensure the whole dentinal equivalent stiffness is not loss, the porosity should get some value while the E_p/E_i is certain. Thus, PTD prevents the stress concentration around DTs and reduces the risk of DTs failure. Mechanically, the overall role of PTD appears to enhance the stiffness of the dentine composite structure. These results provide some new and significant insights into the biological evolution of the optimal design for the porous dentine microstructure. These findings on the biological microstructure design of dentine materials are applicable to other engineering structural designs aimed at increasing the overall structural strength.

Evaluate the effect of different mmps inhibitors on adhesive physical properties of dental adhesives, bond strength and mmp substarte activity

We have evaluated and compare the effect of different exogenous MMP inhibitors on adhesive physical properties of dental adhesives, bond strength, micro permeability and MMP substrate activity. 180-grit Sic paper was used to obtain the superficial dentin surface from each and every tooth after the wet grinding procedure. Dentin was exposed to four different MMP inhibitors to evaluate the effect on resin adhesive dentin interface. The four groups used in study were: 2% chlorhexidine digluconate, 2% doxycycline solution, 5% Proanthocyanidin (PR), Control Group. We evaluated and compared the four groups at each and every step of etching, bonding and resin application. Then, the immunolabeling was done with the help of the secondary antibodies with the pH of 7 and the dilution of 1:20. Amongst all the etching pretreatment groups, CHE group (Chlorhexidine etching group) revealed highest exposure to collagen fibrils than the other groups of etching. Then after the CHE group, the next group which has the second highest exposure DOE group. MMP inhibitor application for time duration of 1 minute after the etching procedures significantly improves the bond strength, exposure to collagen fibres and uniforms the dense form of dentin hybrid layer.

Mesoscale porosity at the dentin-enamel junction could affect the biomechanical properties of teeth

In this paper, the 3D-morphology of the porosity in dentin is investigated within the first 350μm from the dentin-enamel junction (DEJ) by fluorescence confocal laser scanning microscopy (CLSM). We found that the porous microstructure exhibits a much more complex geometry than classically described, which may impact our fundamental understanding of the mechanical behavior of teeth and could have practical consequences for dental surgery. Our 3D observations reveal numerous fine branches stemming from the tubules which may play a role in cellular communication or mechanosensing during the early stages of dentinogenesis. The effect of this highly branched microstructure on the local mechanical properties is investigated by means of numerical simulations. Under simplified assumptions on the surrounding tissue characteristics, we find that the presence of fine branches negatively affects the mechanical properties by creating local stress concentrations. However, this effect is reduced by the presence of peritubular dentin surrounding the tubules. The porosity was also quantified using the CSLM data and compared to this derived from SEM imaging. A bimodal distribution of channel diameters was found near the DEJ with a mean value of 1.5-2μm for the tubules and 0.3-0.5μm for the fine branches which contribute to 30% of the total porosity (∼1.2%). A gradient in the branching density was observed from the DEJ towards the pulp, independently of the anatomical location. Our work constitutes an incentive towards more elaborate multiscale studies of dentin microstructure to better assess the effect of aging and for the design of biomaterials used in dentistry, e.g. to ensure more efficient bonding to dentin. Finally, our analysis of the tubular network structure provides valuable data to improve current numerical models.

Different methods of dentin processing for application in bone tissue engineering: A systematic review

Dentin has become an interesting potential biomaterial for tissue engineering of oral hard tissues. It can be used as a scaffold or as a source of growth factors in bone tissue engineering. Different forms of dentin have been studied for their potential use as bone substitutes. Here, we systematically review different methods of dentin preparation and the efficacy of processed dentin in bone tissue engineering. An electronic search was carried out in PubMed and Scopus databases for articles published from 2000 to 2016. Studies on dentin preparation for application in bone tissue engineering were selected. The initial search yielded a total of 1045 articles, of which 37 were finally selected. Review of studies showed that demineralization was the most commonly used dentin preparation process for use in tissue engineering. Dentin extract, dentin particles (tooth ash), freeze-dried dentin, and denatured dentin are others method of dentin preparation. Based on our literature review, we can conclude that preparation procedure and the size and shape of dentin particles play an important role in its osteoinductive and osteoconductive properties. Standardization of these methods is important to draw a conclusion in this regard. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2616-2627, 2016.

Understanding nature's residual strain engineering at the human dentine-enamel junction interface

Human dental tissue is a hydrated biological mineral composite. In terms of volume and mass, a human tooth mainly consists of dentine and enamel. Human dental tissues have a hierarchical structure and versatile mechanical properties. The dentine enamel junction (DEJ) is an important biological interface that provides a durable bond between enamel and dentine that is a life-long success story: while intact and free from disease, this interface does not fail despite the harsh thermo-mechanical loading in the oral cavity. The underlying reasons for such remarkable strength and durability are still not fully clear from the structural and mechanical perspectives. One possibility is that, in an example of residual stress engineering, evolution has led to the formation of a layer of inelastic strain adjacent to the DEJ during odontogenesis (tooth formation). However, due to significant experimental and interpretational challenges, no meaningful quantification of residual stress in the vicinity of the DEJ at the appropriate spatial resolution has been reported to date. In this study, we applied a recently developed flexible and versatile method for measuring the residual elastic strain at (sub)micron-scale utilising focused ion beam (FIB) milling with digital image correlation (DIC). We report the results that span the transition from human dentine to enamel, and incorporate the material lying at and in the vicinity of the DEJ. The capability of observing the association between internal architecture and the residual elastic strain state at the micrometre scale is useful for understanding the remarkable performance of the DEJ and may help the creation of improved biomimetic materials for clinical and engineering applications.

STATEMENT OF SIGNIFICANCE

We studied the micron-scale residual stresses that exist within human teeth, between enamel (outer tooth shell, hardest substance in the human body) and dentine (soft bone-like vascularised tooth core). The dentine-enamel junction (DEJ) is an extremely interesting example of nature's design in terms of hierarchical structuring and residual stress management. Key developments reported are systematic focused ion beam (FIB) milling and digital image correlation (DIC) micrometre scale residual strain evaluation, and the determination of principal strain direction near DEJ, correlated with internal architecture responsible for remarkable strength. This work helps understanding DEJ performance and improving biomimetic materials design for clinical and engineering applications.

Improved adsorption properties of granulated copper hexacyanoferrate with multi-scale porous networks

Designed porous copper hexacyanoferrate micro-capsule beads (CuHCF-MCB) were prepared using freeze-drying (FD).

On some features of the shape effect in human dentin under compression

Contribution of inorganic and organic phases of human dentin in the shape effect under uniaxial compression is discussed. Comparison of the deformation behavior under compression of the samples with the different ratios between the diagonal of the compression surface and the height of quartz glass, aluminum oxide and PMMA with dentin samples having similar aspect ratios is carried out. In addition, the comparison of the deformation behavior of these materials under tensile stress is carried out. It has been shown that the shape effect of human dentin under compression is caused by the inorganic phase. The organic phase of dentin is responsible for the lowering of the Young's modulus and the compression strength and the increasing of its plasticity. Plasticity of the dentin can be additionally provided by its porosity, when the d/h ratio of the samples exceeds 1.5.

Stress-strain analysis for evaluating the effect of the orientation of dentin tubules on their mechanical properties and deformation behavior

A model whose porosity does not vary with compression depth is developed for evaluating the mechanical properties of dentin tubules with various orientation angles from micro-pillar nanocompression tests. Experimental results for a range of loading rates indicate that the yielding parameters and the elastic modulus are little affected by the creep behavior. For a given compression depth, the hardness, elastic modulus, and yielding strength decrease with increasing orientation angle of dentin. The mechanical properties obtained using the proposed model are consistent with the reported data, and are actually more precise since they consider the orientation angle. The proposed testing method can be applied to materials that yield a negative value of the elastic modulus due to creep behavior.

Biomimetic remineralization as a progressive dehydration mechanism of collagen matrices--implications in the aging of resin-dentin bonds

Biomineralization is a dehydration process in which water from the intrafibrillar compartments of collagen fibrils are progressively replaced by apatites. As water is an important element that induces a lack of durability of resin-dentin bonds, this study has examined the use of a biomimetic remineralization strategy as a progressive dehydration mechanism to preserve joint integrity and maintain adhesive strength after ageing. Human dentin surfaces were bonded with dentin adhesives, restored with resin composites and sectioned into sticks containing the adhesive joint. Experimental specimens were aged in a biomimetic analog-containing remineralizing medium and control specimens in simulated body fluid for up to 12 months. Specimens retrieved after the designated periods were examined by transmission electron microscopy for the presence of water-rich regions using a silver tracer and for collagen degradation within the adhesive joints. Tensile testing was performed to determine the potential loss of bond integrity after ageing. Control specimens exhibited severe collagen degradation within the adhesive joint after ageing. Remineralized specimens exhibited progressive dehydration, as manifested by silver tracer reduction and partial remineralization of water-filled microchannels within the adhesive joint, as well as intrafibrillar remineralization of collagen fibrils that were demineralized initially as part of the bonding procedure. Biomimetic remineralization as a progressive dehydration mechanism of water-rich, resin-sparse collagen matrices enables these adhesive joints to resist degradation over a 12-month ageing period, as verified by the conservation of their tensile bond strength. The ability of the proof of concept biomimetic remineralization strategy to prevent bond degradation warrants further development of clinically relevant delivery systems.