Biomimetic remineralization of dentin

Biomimetic Growth of Metal-Organic Frameworks for the Stabilization of the Dentin Matrix and Control of Collagenolysis

The dentin matrix is a collagenous scaffold structurally involved in anchoring resin-based materials to the tooth. Time-dependent degradation of this scaffold at the resin-dentin interface remains a core problem in adhesive dentistry, limiting the service life of dental fillings. This study explored the use of emergent materials termed metal-organic frameworks (MOFs)─formed by the self-assembly of metal ions and organic building blocks─to safeguard the collagen integrity in the functional dentin matrix. We demonstrate that collagen fibrils (from demineralized human dentin) can induce the biomimetic growth of MOF crystals as protective coatings to strengthen and stabilize the fibrils. Zeolitic imidazolate framework-8 (ZIF-8), a zinc-based microporous MOF, was used to fabricate the MOF composites via a "one-pot" reaction in water. The ZIF-modified dentin matrix presented superior mechanical strength and resistance to proteolysis, which can positively affect the longevity of collagen as an anchoring substrate. This work identifies a potential biomedical application of biomimetically synthesized MOFs in repairing dental tissues critical to restorative therapies.

Deep and compact dentinal tubule occlusion via biomimetic mineralization and mineral overgrowth

Dentinal tubule (DT) occlusion by desensitizing agents has been widely applied to inhibit the transmission of external stimuli that cause dentin hypersensitivity (DH). However, most desensitizing agents merely accomplish porous blocking or the formation of a superficial tubular occlusion layer, resulting in a lack of mechanical and acid resistance and long-term stability. Herein, combining biomimetic mineralization and mineral overgrowth of the dentinal matrix was shown to effectively occlude DTs, resulting in the formation of a compact and deep occluding mineral layer that is strongly bound to the organic matrix on tubule walls. This DT occlusion method could achieve both mechanical resistance and acid resistance, demonstrating the potential of an inexpensive, long-term, and efficient therapy for treating DH.

Anti-Acid Biomimetic Dentine Remineralization Using Inorganic Silica Stabilized Nanoparticles Distributed Electronspun Nanofibrous Mats

Background

To manage the sharp pain of dentine hypersensitivity, various materials are utilized to conduct dentine remineralization. However, many prior materials are limited with their single function and complicated operations. In this study, silica and calcium (strontium) carbonates mineralized nano cellulose fibrous (Si/Ca(Sr)-NCF) mat with the ability to release acid resistant and biomimetic mineralizational silica/calcium (strontium) carbonate co-precipitation nanoparticles (Si/Ca(Sr) NPs) were fabricated. The dentine occluding effects, antibacterial activity and cytocompatibility of the Si/Ca(Sr)-NCF mats were evaluated.

Methods

The Si/Ca(Sr)-NCF mats were fabricated by dipping the electrospun nano cellulose fiber (NCF) into silica and calcium (strontium) carbonate liquid. Physicochemical characterizations and ion release were confirmed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ion release assays and transmission electron microscopy (TEM). Sixty dentine discs were randomly divided into five groups: 1, blank NCF; 2, Si/Ca(Sr 0)-NCF; 3, Si/Ca(Sr 0.01)-NCF; 4, Si/Ca(Sr 0.05)-NCF; 5, Si/Ca(Sr 0.1)-NCF. Dentine discs were mineralized by the mats and observed with SEM immediately, after acid challenge and remineralized in artificial saliva. The releasing liquid was investigated by TEM and type I collagen model. Then, antibacterial property and cytocompatibility were evaluated.

Results

SEM and TEM results confirmed that the experiment mats continuously released amorphous Si/Ca(Sr) NPs and consequently realized anti-acid dentine biomimetic remineralization. Homogeneous surface coverage and collagen intrafibrillar mineralization in strontium adding groups illustrated the mineralization effect was not only by in site precipitation, but also collagen heterogeneous nucleation. Additionally, acceptable antibacterial and cytocompatibility properties were illustrated in low and middle Sr²⁺ containing mats.

Conclusion

In vitro studies on human dentine discs and type I collagen demonstrated that Si/Ca(Sr)–NCF system was a multifunction system inducing anti-acid, biomimetic, antibacterial and cytocompatible dentine remineralization. This multifunction mat would be a promising DH treatment candidate for complicated exposed dentine surfaces.

Enhancing resin-dentin bond durability using a novel mussel-inspired monomer

Numerous approaches have been developed to improve the resin-dentin bond performance, among which the bio-application of mussel-derived compounds have drawn great attention recently. To assess the performance of N-(3,4-dihydroxyphenethyl)methacrylamide (DMA), a mussel-derived compound, as a functional monomer in dental adhesive, its potential property to cross-link with dentin collagen and polymerize with adhesive will first be evaluated by transmission electron microscopy (TEM), attenuated total reflectance technique of Fourier transform infrared (ATR-FTIR), and atomic force microscopy (AFM) via Peakforce QNM mode. After validating the influence of DMA on collagen and adhesive separately, the overall performance of DMA/ethanol solution as a primer in dentin bonding was examined using micro-tensile bond strength (μTBS) testing, fracture pattern observation, and nanoleakage evaluation both immediately and after 10,000 times thermocycling aging. The inhibitory effect of DMA on endogenous metalloproteinases (MMPs) was evaluated by in situ zymography using confocal laser scanning microscopy (CLSM) and the cytotoxicity of DMA was evaluated using cell counting kit-8. Results demonstrated that DMA successfully cross-linked with dentin collagen via non-covalent bonds and had no influence on the polymerization and mechanical properties of the adhesive. Furthermore, even after 10,000 times thermocycling aging, the μTBS and nanoleakage expression of the DMA-treated groups showed no significant change compared with their immediate values. In situ zymography revealed reduced endogenous proteolytic activities after the application of DMA, and no cytotoxicity effect was observed for DMA concentration up to 25 ​μmol/L. Thus, DMA could be used as a novel, biocompatible functional monomer in dentin bonding.

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DMA acts as a functional monomer in dentin bonding system with high biocompatibility.

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DMA connects the adhesive and collagen network to resist various external attacks.

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DMA/ethanol inhibits the activity of MMPs and improve resin-dentin bond durability.

Advances in biomineralization-inspired materials for hard tissue repair

Biomineralization is the process by which organisms form mineralized tissues with hierarchical structures and excellent properties, including the bones and teeth in vertebrates. The underlying mechanisms and pathways of biomineralization provide inspiration for designing and constructing materials to repair hard tissues. In particular, the formation processes of minerals can be partly replicated by utilizing bioinspired artificial materials to mimic the functions of biomolecules or stabilize intermediate mineral phases involved in biomineralization. Here, we review recent advances in biomineralization-inspired materials developed for hard tissue repair. Biomineralization-inspired materials are categorized into different types based on their specific applications, which include bone repair, dentin remineralization, and enamel remineralization. Finally, the advantages and limitations of these materials are summarized, and several perspectives on future directions are discussed.

Experimental Bioactive Glass-Containing Composites and Commercial Restorative Materials: Anti-Demineralizing Protection of Dentin

The purpose of this in vitro study was to investigate whether different types of experimental and commercial restorative dental materials can protect dentin against acid-induced softening. Experimental composites were prepared with a photocurable mixture of methacrylates and two types of bioactive glass (45S5 and a customized low-Na F-containing formulation). Human dentin samples were prepared from mid-coronal tooth slices and immersed in lactic acid solution (pH = 4.0) at 5 mm from set specimens of restorative material. After 4, 8, 12, 16, 20, 24, 28, and 32 days, surface microhardness of dentin samples and pH of the immersion solution were measured, followed by replenishing of the immersion medium. Microstructural analysis was performed using scanning electron microscopy. The protective effect of restorative materials was determined as dentin microhardness remaining statistically similar to initial values for a certain number of acid additions. Scanning electron microscopy showed a gradual widening of dentinal tubules and proved less discriminatory than microhardness measurements. To produce a protective effect on dentin, 20 wt% of low-Na F-containing bioactive glass was needed, whereas 10 wt% of bioactive glass 45S5 was sufficient to protect dentin against acid-induced demineralization. The anti-demineralizing protective effect of experimental and commercial restoratives on dentin was of shorter duration than measured for enamel in a previous study using the same experimental approach.

The Application of Chitosan Nanostructures in Stomatology

Chitosan (CS) is a natural polymer with a positive charge, a deacetylated derivative of chitin. Chitosan nanostructures (nano-CS) have received increasing interest due to their potential applications and remarkable properties. They offer advantages in stomatology due to their excellent biocompatibility, their antibacterial properties, and their biodegradability. Nano-CSs can be applied as drug carriers for soft tissue diseases, bone tissue engineering and dental hard tissue remineralization; furthermore, they have been used in endodontics due to their antibacterial properties; and, finally, nano-CS can improve the adhesion and mechanical properties of dental-restorative materials due to their physical blend and chemical combinations. In this review, recent developments in the application of nano-CS for stomatology are summarized, with an emphasis on nano-CS’s performance characteristics in different application fields. Moreover, the challenges posed by and the future trends in its application are assessed.

A laboratory study to assess the physical, mechanical, and 3-D structural properties of nano-apatite grafted glass fibre-based endodontic posts

AIM

To fabricate and characterize nano-hydroxyapatite (nHA) grafted and non-grafted glass fibre-based endodontic posts.

METHODOLOGY

Experimental glass fibre posts were fabricated using silanized nHA grafted (ex-HA) and non-grafted glass fibre (ex-P) reinforced resins. The structural analysis and morphological patterns were analysed with Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. EverStick^® glass fibre posts (eS) were used as a control group. The degree of conversion, flexural strength, and flexural modulus was investigated and the fractured structure was evaluated with a scanning electron microscope. Root canals were prepared in human extracted teeth restored with experimental and control posts. The push-out bond strength was evaluated with radicular dentine at days 7, 30, and 90, and the presence of voids at the interface were measured at day 1, 7, 30, and 90 with micro-computed tomography. The Shapiro-Wilk test and one-way ANOVA post-hoc Tukey's test were performed. The level of significance was set at 0.05.

RESULTS

The SEM and FTIR confirmed the presence of a silane-coupling agent on the glass fibres. The ex-HA post had a significantly lower degree of conversion compared to the ex-P post (p = .0008), but a significantly higher conversion than the eS post (p = .0014). The maximum flexural strength value was obtained with the ex-HA post with an insignificant difference (p = .366) compared to ex-P post and a significant difference (p = .029) compared to the eS post. The flexural modulus of ex-HA, ex-P, and eS posts were significantly different (p = .037). Similarly, the ex-HA post had a significantly higher push-out bond strength at days 7 and 30 (p = .037) compared to the ex-P and eS posts. The volume of voids had a nonlinear behaviour amongst the groups with no significant difference between the posts.

CONCLUSION

The fabrication of the experimental posts was successful and the ex-HA post had greater flexural strength and push-out bond strength compared to the ex-P post. The degree of conversion of the ex-HA post was lower than the ex-P and eS posts. The volume of voids of ex-HA and ex-P posts was lower than that of eS posts.

Inductive Materials for Regenerative Engineering

Regenerative engineering has pioneered several novel biomaterials to treat critical-sized bone injuries. However, despite significant improvement in synthetic materials research, some limitations still exist. The constraints correlated with the current grafting methods signify a treatment paradigm shift to osteoinductive regenerative engineering approaches. Because of their intrinsic potential, inductive biomaterials may represent alternative approaches to treating critical bone injuries. Osteoinductive scaffolds stimulate stem cell differentiation into the osteoblastic lineage, enhancing bone regeneration. Inductive biomaterials comprise polymers, calcium phosphate ceramics, metals, and graphene family materials. This review will assess the cellular behavior toward properties of inductive materials.

Manifestation and Mechanisms of Abnormal Mineralization in Teeth

Tooth biomineralization is a dynamic and complicated process influenced by local and systemic factors. Abnormal mineralization in teeth occurs when factors related to physiologic mineralization are altered during tooth formation and after tooth maturation, resulting in microscopic and macroscopic manifestations. The present Review provides timely information on the mechanisms and structural alterations of different forms of pathological tooth mineralization. A comprehensive study of these alterations benefits diagnosis and biomimetic treatment of abnormal mineralization in patients.

Dentin remineralization in acidic solution without initial calcium phosphate ions via poly(amido amine) and calcium phosphate nanocomposites after fluid challenges

OBJECTIVES

A previous study showed that the combination of poly(amido amine) (PAMAM) and rechargeable composites with nanoparticles of amorphous calcium phosphate (NACP) induced dentin remineralization in an acidic solution with no initial calcium (Ca) and phosphate (P) ions, mimicking the oral condition of individuals with dry mouths. However, the frequent fluid challenge in the oral cavity may decrease the remineralization capacity. Therefore, the objective of the present study was to investigate the remineralization efficacy on dentin in an acid solution via PAMAM + NACP after fluid challenges for the first time.

METHODS

The NACP nanocomposite was stored in a pH 4 solution for 77 days to exhaust its Ca and P ions and then recharged. Demineralized dentin samples were divided into four groups: (1) control dentin, (2) dentin coated with PAMAM, (3) dentin with recharged NACP composite, and (4) dentin with PAMAM + recharged NACP. PAMAM-coated dentin was shaken in phosphate-buffered saline for 77 days to desorb PAMAM from dentin. Samples were treated in pH 4 lactic acid with no initial Ca and P ions for 42 days.

RESULTS

After 77 days of fluid challenge, PAMAM failed to prevent dentin demineralization in lactic acid. The recharged NACP nanocomposite raised the pH to above 6.5 and re-released more than 6.0 and 4.0 mmol/L Ca and P ions daily, respectively, which inhibited further demineralization. In contrast, the PAMAM + NACP combined method induced great dentin remineralization and restored the dentin microhardness to 0.54 ± 0.04 GPa, which approached that of sound dentin (P = 0.426, P > 0.05).

CONCLUSIONS

The PAMAM + NACP combination achieved dentin remineralization in an acid solution with no initial Ca and P ions, even after severe fluid challenges.

CLINICAL RELEVANCE

The novel PAMAM + NACP has a strong and sustained remineralization capability to inhibit secondary caries, even for individuals with dry mouths.

Proanthocyanidin-functionalized hydroxyapatite nanoparticles as dentin biomodifier

OBJECTIVE

This study evaluated the potential combined effects of nanohydroxyapatite and proanthocyanidin on the remineralization and collagen stabilization of demineralized dentin.

METHODS

Seventy-five coronal dentin beams (6 × 1 × 1 mm³) were randomly allocated into five experimental groups (n = 15): Sound (no treatment), Control (pH-cycling), nHAp (nanohydroxyapatite), nHAp_PA (Proanthocyanidin-functionalized nanohydroxyapatite), and PA (proanthocyanidin) treatments. The sound group (negative control) were immersed in distilled water over the experimental period. The remaining groups were submitted to a pH-cycling process for 14 days. Following the de-re mineralization process, specimens corresponding to the control group (positive control) were immersed in distilled water whereas the test groups were immersed in 1 mL of respective solution treatment (nHAp, nHAp_PA, or PA) for 1 min. The dentin samples were analyzed to determine their chemical composition (ATR-FTIR and Thermogravimetric) and mineralogical (XRD) characteristics as well as their mechanical response, obtained by three-point bending test.

RESULTS

Higher phosphate content (v₄ PO₄: ATR-FTIR) and amount of mineral (XRD) was observed in the nHAp_PA group. Furthermore, a larger induction of collagen cross-links (ATR-FTIR) and %Organic Matter (TGA) would indicate the PA incorporation and the achievement of dentin matrix stability. These effects on dentin properties were related to increasing flexural strength (MPa), demonstrating that 15% w/v nHAp_PA treatment improved the mechanical properties of the samples.

SIGNIFICANCE

nHAp_PA shows significant potential for promoting remineralization while improving collagen stability into demineralized dentin in a clinically feasible period of 1 min.

Experimental Dental Composites Containing a Novel Methacrylate-Functionalized Calcium Phosphate Component: Evaluation of Bioactivity and Physical Properties

The aim of this study was to synthesize and characterize a novel methacrylate-functionalized calcium phosphate (MCP) to be used as a bioactive compound for innovative dental composites. The characterization was accomplished by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The incorporation of MCP as a bioactive filler in esthetic dental composite formulations and the ability of MCP containing dental composites to promote the precipitation of hydroxyapatite (HAp) on the surfaces of those dental composites was explored. The translucency parameter, depth of cure, degree of conversion, ion release profile, and other physical properties of the composites were studied with respect to the amount of MCP added to the composites. Composite with 3 wt.% MCP showed the highest flexural strength and translucency compared to the control composite and composites with 6 wt.% and 20 wt.% MCP. The progress of the surface precipitation of hydroxyapatite on the MCP containing dental composites was studied by systematically increasing the MCP content in the composite and the time of specimen storage in Dulbecco's phosphate-buffered solution with calcium and magnesium. The results suggested that good bioactivity properties are exhibited by MCP containing composites. A direct correlation between the percentage of MCP in a composite formulation, the amount of time the specimen was stored in PBS, and the deposition of hydroxyapatite on the composite's surface was observed.

Molecular Dynamics Exploration of the Growth Mechanism of Hydroxyapatite Nanoparticles Regulated by Glutamic Acid

Morphological control can enhance the performance of materials like hydroxyapatite (HAP), a well-known bioceramic with various morphologies, including spheres, rods, whiskers, needles, and plates. To obtain certain HAP morphologies, the crystal growth mechanisms at different planes should be investigated. Here, molecular dynamics was employed to understand the mechanism of HAP nanoparticle growth regulated by glutamic acid (Glu). Long-time dynamics simulations and free energy calculations were performed to explore the effect of Glu on calcium and phosphate ion precipitation on the HAP (100) and (001) faces. Without Glu, PO₄^3- prefers binding to the HAP (100) surface, whereas with Glu, the (001) surface is preferred. This could partially explain why HAP changes from needle-like to plate-like with Glu addition in experiments. Our theoretical results indicate that Glu inhibits calcium and phosphate ion deposition on the crystal surfaces by occupying the calcium sites on the outermost layers. In addition, Glu has a strong concentration gradient effect on HAP deposition. At Glu concentrations of >80 mM, ion deposition was inhibited more on the (100) than on the (001) surface. Our results agree with experimental observations and afford insights into complicated HAP crystal growth mechanisms with foreign additives, which will aid in HAP synthesis with morphological control.

Synergistic effect of graphene oxide/calcium phosphate nanofiller in a dentin adhesive on its dentin bond integrity and degree of conversion. A scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared, micro-Raman, and bond strength study

The objective was to formulate and analyze a dentin adhesive incorporated with graphene oxide (GO) nanoparticle and calcium phosphate (CaP) composite. Methods comprising of scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX), micro-Raman spectroscopy, shear bond strength (SBS), and Fourier transform infrared (FTIR) spectroscopy were used to characterize nanoparticle composite, dentin bond toughness, degree of conversion (DC), and adhesive-dentin interaction. Postsynthesis of GO nanoparticles, they were functionalized with CaP using standard process. The GO-CaP composite was not added to experimental adhesive (negative control group, GO-CaP-0%), and added at 2.5 and 5 wt% to yield GO-CaP-2.5% and GO-CaP 5% groups, respectively. Teeth were set to form bonded samples utilizing adhesives in three groups for SBS testing, with and without thermocycling. The homogenous diffusion of GO-CaP composite was verified in the adhesive. Resin tags having standard penetrations were observed on SEM micrographs. The EDX analysis confirmed the occurrence of calcium, phosphorus, and carbon ions in the composite containing adhesives. The SBS test revealed highest mean values for GO-CaP-5% followed by GO-CaP-2.5%. The FTIR spectra verified the presence of apatite peaks and the micro-Raman spectra showed characteristic D and G bands for GO nanoparticles. GO-CaP composite in dentin adhesive may improve its bond strength. The addition of 5 wt% resulted in a bond strength that was superior to all other groups. GO-CaP-5% group demonstrated lower DC (to control), uniform distribution of GO and CaP composite within adhesive, appropriate dentin interaction, and resin tag formation.

The Stability of Dentin Surface Biobarrier Consisting of Mesoporous Delivery System on Dentinal Tubule Occlusion and Streptococcus Mutans Biofilm Inhibition

Background

The dentin exposure always leads to dentin hypersensitivity and/or caries. Given the dentin’s tubular structure and low mineralization degree, reestablishing an effective biobarrier to stably protect dentin remains significantly challenging. This study reports a versatile dentin surface biobarrier consisting of a mesoporous silica-based epigallocatechin-3-gallate (EGCG)/nanohydroxyapatite delivery system and evaluates its stability on the dentinal tubule occlusion and the Streptococcus mutans (S. mutans) biofilm inhibition.

Materials and Methods

The mesoporous delivery system was fabricated and characterized. Sensitive dentin discs were prepared and randomly allocated to three groups: 1, control group; 2, casein phosphopeptide–amorphous calcium phosphate (CPP–ACP) group; and 3, the mesoporous delivery system group. The dentin permeability, dentinal tubule occlusion, acid and abrasion resistance, and S. mutans biofilm inhibition were determined for 1 week and 1 month. The in vitro release profiles of EGCG, Ca, and P were also monitored.

Results

The mesoporous delivery system held the ability to sustainably release EGCG, Ca, and P and could persistently occlude dentinal tubules with acid and abrasion resistance, reduce the dentin permeability, and inhibit the S. mutans biofilm formation for up to 1 month compared with the two other groups. The system provided prolonged stability to combat oral adverse challenges and served as an effective surface biobarrier to protect the exposed dentin.

Conclusion

The establishment of the dentin surface biobarrier consisting of a mesoporous delivery system indicates a promising strategy for the prevention and the management of dentin hypersensitivity and caries after enamel loss.

[Application of biomimetic restoration in oral-maxillofacial hard tissue repair]

Oral-maxillofacial hard tissue is the support of maxillofacial structure and appearance, and lays the foundation for functions of oral and maxillofacial system. Once the defect occurs, it will not only affect the physiological functions such as chewing and pronunciation, but also have a significant impact on the psychological and social life of patients. However, the self-repairing capability of the oral-maxillofacial hard tissue is pretty limited, in which case, substitute materials are required for tissue repair. A huge gap exists between the physical, chemical, structural characteristics of conventional substitute materials and those of human hard tissues, resulting in poor repair effect. Based on this, scholars simulated the process of biomineralization in the development of hard tissues, to improve the structure and function of materials through biomimetic mineralization technology and enhance the repair performance of materials. The current understanding of biomineralization theory and the construction of biomimetic repair technology is still in the stage of rapid development. In recent years, a mass of innovative studies are keeping emerging. In this review, the representative advances in the repair of oral-maxillofacial hard tissues of the past five years are reviewed.

Assessment of Demineralization Inhibition Effects of Dentin Desensitizers Using Swept-Source Optical Coherence Tomography

The purpose of this study was to evaluate the mechanism of action and the inhibiting effects of two types of desensitizers against dentin demineralization using pre-demineralized hypersensitivity tooth model in vitro. In this study, we confirmed that a hypersensitivity tooth model from our preliminary experiment could be prepared by immersing dentin discs in an acetic acid-based solution with pH 5.0 for three days. Dentin discs with three days of demineralization were prepared and applied by one of the desensitizers containing calcium fluoro-alumino-silicate glass (Nanoseal, NS) or fluoro-zinc-silicate glass (Caredyne Shield, CS), followed by an additional three days of demineralization. Dentin discs for three days of demineralization (de3) and six days of demineralization (de6) without the desensitizers were also prepared. The dentin discs after the experimental protocol were scanned using swept-source optical coherence tomography (SS-OCT) to image the cross-sectional (2D) view of the samples and evaluate the SS-OCT signal. The signal intensity profiles of SS-OCT from the region of interest of 300, 500, and 700 µm in depth were obtained to calculate the integrated signal intensity and signal attenuation coefficient. The morphological differences and remaining chemical elements of the dentin discs were also analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. SS-OCT images of CS and NS groups showed no obvious differences between the groups. However, SS-OCT signal profiles for both the CS and NS groups showed smaller attenuation coefficients and larger integrated signal intensities than those of the de6 group. Reactional deposits of the desensitizers even after the additional three days of demineralization were observed on the dentin surface in NS group, whereas remnants containing Zn were detected within the dentinal tubules in CS group. Consequently, both CS and NS groups showed inhibition effects against the additional three days of demineralization in this study. Our findings demonstrate that SS-OCT signal analysis can be used to monitor the dentin demineralization and inhibition effects of desensitizers against dentin demineralization in vitro.

Polymer-Induced Liquid Precursor (PILP) remineralization of artificial and natural dentin carious lesions evaluated by nanoindentation and microcomputed tomography

OBJECTIVES

The study evaluates the efficacy to remineralize artificial and natural dentin lesions through restorative dental procedures that include the Polymer-Induced Liquid Precursor (PILP) method comprising polyaspartic acid (pAsp).

METHODS

Novel ionomeric cement compositions based on bioglass 45S5 and pAsp mixtures, as well as conditioning solutions (conditioner) containing 5 mg/mL pAsp, were developed and tested on demineralized dentin blocks (3-4 mm thick) on shallow and deep lesions with the thickness of 140 μm ± 50 and 700 μm ± 50, respectively. In the first treatment group, 20 μL of conditioner was applied to demineralized shallow (n = 3) and deep (n = 3) lesion specimens for 20 s before restoration with glass ionomer cement (RMGIC). For the PILP cement treatment group, cement was applied onto the wet surface of the demineralized specimen for both shallow (n = 3) and deep (n = 3) artificial lesions after the application of the conditioner and before the final restoration. Sample groups were compared to RMGIC restoration, for both shallow and deep lesions (n = 3 each) and treatments in PILP-solution (n = 3 for deep lesions) without restoration for 4 weeks. All of the restored specimens were immersed in simulated body fluid (SBF) solution for 2 weeks and 4 weeks for shallow and deep lesions respectively to allow for remineralization. The artificial lesion specimens were evaluated for changes in the nanomechanical profile (E-modulus and hardness) using nanoindentation. Shallow lesions were analyzed by SEM under vacuum for changes in morphology caused by PILP treatments. Also, a pilot study on human third molars with moderate lesions in dentin (n = 3) was initiated to test the efficacy of treatments in natural lesions based on mineral densities using microcomputed tomography (μCT) at 0, 1, and 3 months.

RESULTS

This study showed that functional remineralization of artificial lesions using PILP-releasing restoratives occurred, indicated by an increase of the elastic modulus in shallow lesions and in the middle zone of deep artificial lesions. The mechanical improvement was significant when compared to RMGIC restoration without pAsp (P < 0.05). Nonetheless, recovery across artificial lesions was most significant when specimens were immersed into PILP-solution with restorative (P < 0.01). Furthermore, natural lesions increased in mineral volume content to a higher degree when the restorative treatment included the PILP-method (P < 0.05). However, none of the natural lesions recovered to full mineral degree regardless of the treatments.

CLINICAL SIGNIFICANCE/CONCLUSION

These findings indicate the benefit of PILP applications in the functional repair of dentin caries and illustrate the challenge to integrate the PILP-method into a restorative approach in minimally invasive dental procedures.

A novel dentin bonding scheme based on extrafibrillar demineralization combined with covalent adhesion using a dry-bonding technique

Dentin bonding is a dynamic process that involves the penetration of adhesive resin monomers into the extrafibrillar and intrafibrillar demineralized collagen matrix using a wet-bonding technique. However, adhesive resin monomers lack the capacity to infiltrate the intrafibrillar space, and the excess water that is introduced by the wet-bonding technique remains at the bonding interface. This imperfectly bonded interface is inclined to hydrolytic degradation, severely jeopardizing the longevity of bonded clinical restorations. The present study introduces a dentin bonding scheme based on a dry-bonding technique, combined with the use of extrafibrillar demineralization and a collagen-reactive monomer (CRM)-based adhesive (CBA). Selective extrafibrillar demineralization was achieved using 1-wt% high-molecular weight (MW) carboxymethyl chitosan (CMCS) within a clinically acceptable timeframe to create a less aggressive bonding substance for dentin bonding due to its selectively extrafibrillar demineralization capacity. CMCS demineralization decreased the activation of in situ collagenase, improved the shrinking resistance of demineralized collagen, and thus provided stronger and more durable bonding than traditional phosphoric acid etching. The new dentin bonding scheme that contained CMCS and CBA and used a dry-bonding technique achieved an encouraging dentin bonding strength and durability with low technical sensitivity. This bonding scheme can be used to improve the stability of the resin-dentin interface and foster the longevity of bonded clinical restorations.

Surface-Directed Mineralization of Fibrous Collagen Scaffolds in Simulated Body Fluid for Tissue Engineering Applications

The use of polymer additives that stabilize fluidic amorphous calcium phosphate is key to obtaining intrafibrillar mineralization of collagen in vitro. On the other hand, this biomimetic approach inhibits the nucleation of mineral crystals in unconfined extrafibrillar spaces, that is, extrafibrillar mineralization. The extrafibrillar mineral content is a significant feature to replicate from hard connective tissues such as bone and dentin as it contributes to the final microarchitecture and mechanical stiffness of the biomineral composite. Herein, we report a straightforward route to produce densely mineralized collagenous composites via a surface-directed process devoid of the aid of polymer additives. Simulated body fluid (1×) is employed as a biomimetic crystallizing medium, following a preloading procedure on the collagen surface to quickly generate the amorphous precursor species required to initiate matrix mineralization. This approach consistently leads to the formation of extrafibrillar bioactive minerals in bulk collagen scaffolds, which may offer an advantage in the production of osteoconductive collagen-apatite materials for tissue engineering and repair purposes.

Bioactivity—Symphony or Cacophony? A Personal View of a Tangled Field

In the pursuit of better treatments, the concept of a chemically-active material, responding to local conditions by causing reactions, or reacting to produce substances that are deemed beneficial, seems laudable. Ultimately, the goal appears to be to recruit natural biological processes such that a natural ‘repair’ is effected. This goal seems to be the reason for prefixing “bio-” to many terms with a view to advertising the desire, yet without presenting evidence that it has occurred, or indeed that it is capable of occurring, relying instead on non-biological processes to justify the claims. The dogma is such that all work where local ‘responsive’ chemistry is involved must receive the label “bioactive” to legitimize and promote. Nevertheless, the primary evidence adduced is flawed, and the claim must fail. A rethink to restore scientific sense and confidence in the endeavour is essential if real progress is to be made.

Impact of biomineralization on resin/biomineralized dentin bond longevity in a minimally invasive approach: An "in vitro" 18-month follow-up

OBJECTIVES

To determine the impact of treating caries-affected dentin (CAD) with: 0.2% sodium fluoride (NaF), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP/MI Paste™) or peptide P₁₁-4 (Curodont™ Repair) on the longevity of resin/CAD interface at storage times of 24 -h, 6- and 18-month.

METHODS

255 caries-free third molars were used, and CAD was produced by a biological method. The teeth were randomly distributed into: G1- Sound dentin (SD); G2- CAD; G3- CAD + 0.2% NaF (CAD/NaF); G4- CAD + CPP-ACP (CAD/ACP); G5- CAD + Curodont™ Repair (CAD/P₁₁-4). The Filtek Z350 composite resin block was bonded to dentin using Adper™ Single 2 (4 mm/height). Resin/dentin blocks were stored in a solution of Simulated Body Fluid at 37 °C, pressures were modified to simulate natural pulpal pressures. Specimens were investigated by microtensile bond strength (μTBS) (n = 8), Scanning Electron Microscopy (to assess the failure mode) (n = 8), nanoinfiltration (to assess the interface sealing) (n = 3), in situ zymography (to assess the gelatinolytic activity) (n = 3) and micro-computed microtomography (μ-CT) (to assess the mineralization) (n = 3). Data from μTBS, μ-CT and, nanoinfiltration and hybrid layer formation/degradation were submitted to two-way ANOVA and Tukey tests, and failure patterns and in situ zymography to Kruskal-Wallis and Dunn tests (α = 5%).

RESULTS

The highest mineral density change by μ-CT, smallest silver nitrate infiltration and proteolytic activity in the adhesive layer were obtained significantly for the groups SD, CAD/ACP and CAD/P₁₁-4, with most mixed fractures at 18-month (p < 0.001). CAD/NaF showed significantly similar values to CAD, CAD and CAD/NaF which presented a high percentage of adhesive fracture (p < 0.001) at all time periods.

SIGNIFICANCE

Treating caries-affected dentin with remineralizing agents CPP-ACP and Curodont™ Repair, has the potential to be a clinically relevant treatment protocol to increase the longevity of adhesive restorations.

Biomimetic fabrication and application of fibrous-like nanotubes

AIMS

To investigate the biomimetic fabrication of fibrous-like organic-inorganic hybrid structures via a simple bottom-up approach, viz. self-assembly of simple molecules, and apply fibrous-like composites as a novel primer to improve dentin bond strengths of self-etch adhesives.

MATERIALS AND METHODS

The resultants of commercial amorphous calcium phosphate (ACP) nanoparticles and 10-methacryloyloxydecyl dihydrogen phosphate (MDP) ethanol-aqueous solution were analyzed by TEM, SEM, XRD, DLS and AFM. The acid and alkali resistance of abovementioned self-assembled composites were analyzed with TEM. Micro-tensile bond strengths (MTBS) tests were performed after polished dentin surfaces were pretreated with self-assembled composites. The pretreated dentin surfaces and dentin-resin interfaces were characterized by SEM/TEM.

KEY FINDINGS

ACP nanoparticles in MDP solution could self-assemble into fibrous-like nanotube structures in 8 nm diameter. Self-assembly and self-proliferation process went from ACP nanoparticles, dissolved ACP nanoparticles (less than 50 nm), twig-like structures and fibrous-like nanotubes to cellular networks. The fibrous-like nanotubes were only detected when the amount of ACP in reaction system were more than 0.01 g. The more ACP interacted with MDP, the more fibrous-like nanotubes were formed. After the dentin surfaces were treated with fibrous-like nanotube composites, MTBS could be significantly improved. Moreover, the fibrous-like nanotube structures could be resistant to acidic challenge, and were stable at least for 3 months.

SIGNIFICANCE

The fibrous-like nanotube structures could be self-assembled via a bottom-up approach at certain ratio of MDP and commercial ACP nanoparticles. The application of fibrous-like nanotube composites as a novel primer prior to self-etch adhesives greatly improved dentin bond strengths.

Rechargeable adhesive with calcium phosphate nanoparticles inhibited long-term dentin demineralization in a biofilm-challenged environment

OBJECTIVES

This study aims to investigate the long-term demineralization-inhibition capability of a rechargeable adhesive with nanoparticles of amorphous calcium phosphate (NACP) on dentin in a biofilm-challenged environment.

METHODS

The NACP adhesive was immersed in a pH 4 solution to exhaust calcium (Ca) and phosphate (P) ions and then recharged with Ca and P ions. Dentin samples were demineralized underStreptococcus mutans biofilms for 24 h and randomly divided into two groups: (1) dentin control, (2) dentin with recharged NACP adhesives. Each day, all the samples were immersed in brain heart infusion broth with 1% sucrose (BHIS) for 4 h, and then in artificial saliva (AS) for 20 h. This cycle was repeated for 10 days. The pH of BHIS, the Ca and P ions content of the BHIS and AS were measured daily. After 10 days, the lactic acid production and colony-forming units of the biofilms were tested. The changes of remineralization/demineralization were also analyzed.

RESULTS

Dentin in the control group showed further demineralization. The recharged NACP adhesive neutralized acids, increasing the pH to above 5, and released large amounts of Ca and P ions each day. The recharged NACP adhesive decreased the production of lactic acid (P < 0.05), inhibited dentin demineralization and sustained the dentin hardness in the biofilm-challenged environment, showing an excellent long-term demineralization-inhibition capability.

CONCLUSIONS

The NACP adhesive could continuously inhibit dentin demineralization in a biofilm-challenged environment by recharging with Ca and P ions.

SIGNIFICANCE

The rechargeable NACP adhesive could provide long-term dentin bond protection.

[Effect of bioactive glass pretreatment on the durability of dentin bonding interface]

OBJECTIVE

To study the effect of bioactive glass (BG) on the dentin bond strength and the microleakage of hybrid layer.

METHODS

In the study, 30 dentin planes were prepared from the third molars with no caries and equally assigned to the control group, BG group, and sodium trimetaphosphate (STMP)-polyacrylic acid (PAA)-BG group (S-P-BG group), randomly. After etched with 35% phosphoric acid, the dentin planes of BG group were pretreated with 0.5 g/L BG, and the dentin planes of S-P-BG group were pretreated with 5% STMP, 5% PAA and 0.5 g/L BG. No additional pretreatment was done to the dentin planes of control group. Then the dentin planes were bonded using 3M Single Bond 2 adhesive to 3M Z350XT composite resin, and cut into 0.9 mm×0.9 mm column samples, which were stored at 37 ℃ artificial saliva (AS). After 24 hours, 1 month, and 3 months, the microtensile bond strength test was performed. The data were analyzed using one-way ANOVA and LSD method. The morphology of the bond fracture interface was observed with scanning electron microscope. Other 27 teeth were collected and the enamel layer and roots cut off, with the pulp chamber exposed. 0.1% rhodamine B was added to the 3M Single Bond 2 adhesive, and then the adhesive was applied to complete the bonding procedures as above. The teeth were stored in 37 ℃ AS for 24 hours, 1 month, 3 months, and then 0.1% sodium fluorescein solution was placed in the chambers and stained for 1 hour. Confocal laser scanning microscopy was used to observe the interface morphology and microleakage of the hybrid layer.

RESULTS

At the end of 24 hours and 1 month, there was no significant difference in the microtensile bond strength among the three groups (P>0.05). After 3 months of soaking, the S-P-BG group [(36.91±7.07) MPa] had significantly higher microtensile bond strength than the control group [(32.73±8.06) MPa] (P=0.026); For the control group and the BG group, the microtensile bond strength significantly decreased at the end of 3 months compared with 24 hours (control group: P=0.017, BG group: P=0.01); The microtensile bond strength of S-P-BG group af the end of 3 months had no significant difference in compared with 24 hours [(37.99±7.98) MPa] (P>0.05). Observation of the fracture surface at the 24 hours showed no obvious mineralization in all the three groups. After 1 and 3 months, mineral formation was observed in BG group and S-P-BG group, and no obvious collagen exposure was observed in S-P-BG group. Confocal laser scanning microscopy revealed no obvious differences in the morphology and quantity of the resin tag in the control group, BG group and S-P-BG group. At the end of 24 hours, leakage was found in all the three groups. The microleakage of the control group increased at the end of 3 months, while the microleakage of the BG and S-P-BG groups decreased.

CONCLUSION

BG pretreatment of dentin bonding interface can induce mineralization at the bonding interface and reduce the microleakage of the hybrid layer; pretreating the dentin bonding interface with STMP, PAA and BG may enhance the maintaining of the dentin bonding durability.

[Effect of bioactive glass pretreatment on the durability of dentin bonding interface]

OBJECTIVE

To study the effect of bioactive glass (BG) on the dentin bond strength and the microleakage of hybrid layer.

METHODS

In the study, 30 dentin planes were prepared from the third molars with no caries and equally assigned to the control group, BG group, and sodium trimetaphosphate (STMP)-polyacrylic acid (PAA)-BG group (S-P-BG group), randomly. After etched with 35% phosphoric acid, the dentin planes of BG group were pretreated with 0.5 g/L BG, and the dentin planes of S-P-BG group were pretreated with 5% STMP, 5% PAA and 0.5 g/L BG. No additional pretreatment was done to the dentin planes of control group. Then the dentin planes were bonded using 3M Single Bond 2 adhesive to 3M Z350XT composite resin, and cut into 0.9 mm×0.9 mm column samples, which were stored at 37 ℃ artificial saliva (AS). After 24 hours, 1 month, and 3 months, the microtensile bond strength test was performed. The data were analyzed using one-way ANOVA and LSD method. The morphology of the bond fracture interface was observed with scanning electron microscope. Other 27 teeth were collected and the enamel layer and roots cut off, with the pulp chamber exposed. 0.1% rhodamine B was added to the 3M Single Bond 2 adhesive, and then the adhesive was applied to complete the bonding procedures as above. The teeth were stored in 37 ℃ AS for 24 hours, 1 month, 3 months, and then 0.1% sodium fluorescein solution was placed in the chambers and stained for 1 hour. Confocal laser scanning microscopy was used to observe the interface morphology and microleakage of the hybrid layer.

RESULTS

At the end of 24 hours and 1 month, there was no significant difference in the microtensile bond strength among the three groups (P>0.05). After 3 months of soaking, the S-P-BG group [(36.91±7.07) MPa] had significantly higher microtensile bond strength than the control group [(32.73±8.06) MPa] (P=0.026); For the control group and the BG group, the microtensile bond strength significantly decreased at the end of 3 months compared with 24 hours (control group: P=0.017, BG group: P=0.01); The microtensile bond strength of S-P-BG group af the end of 3 months had no significant difference in compared with 24 hours [(37.99±7.98) MPa] (P>0.05). Observation of the fracture surface at the 24 hours showed no obvious mineralization in all the three groups. After 1 and 3 months, mineral formation was observed in BG group and S-P-BG group, and no obvious collagen exposure was observed in S-P-BG group. Confocal laser scanning microscopy revealed no obvious differences in the morphology and quantity of the resin tag in the control group, BG group and S-P-BG group. At the end of 24 hours, leakage was found in all the three groups. The microleakage of the control group increased at the end of 3 months, while the microleakage of the BG and S-P-BG groups decreased.

CONCLUSION

BG pretreatment of dentin bonding interface can induce mineralization at the bonding interface and reduce the microleakage of the hybrid layer; pretreating the dentin bonding interface with STMP, PAA and BG may enhance the maintaining of the dentin bonding durability.

Harnessing biomolecules for bioinspired dental biomaterials

Dental clinicians have relied for centuries on traditional dental materials (polymers, ceramics, metals, and composites) to restore oral health and function to patients. Clinical outcomes for many crucial dental therapies remain poor despite many decades of intense research on these materials. Recent attention has been paid to biomolecules as a chassis for engineered preventive, restorative, and regenerative approaches in dentistry. Indeed, biomolecules represent a uniquely versatile and precise tool to enable the design and development of bioinspired multifunctional dental materials to spur advancements in dentistry. In this review, we survey the range of biomolecules that have been used across dental biomaterials. Our particular focus is on the key biological activity imparted by each biomolecule toward prevention of dental and oral diseases as well as restoration of oral health. Additional emphasis is placed on the structure-function relationships between biomolecules and their biological activity, the unique challenges of each clinical condition, limitations of conventional therapies, and the advantages of each class of biomolecule for said challenge. Biomaterials for bone regeneration are not reviewed as numerous existing reviews on the topic have been recently published. We conclude our narrative review with an outlook on the future of biomolecules in dental biomaterials and potential avenues of innovation for biomaterial-based patient oral care.

Biomimetic Aspects of Oral and Dentofacial Regeneration

Biomimetic materials for hard and soft tissues have advanced in the fields of tissue engineering and regenerative medicine in dentistry. To examine these recent advances, we searched Medline (OVID) with the key terms “biomimetics”, “biomaterials”, and “biomimicry” combined with MeSH terms for “dentistry” and limited the date of publication between 2010–2020. Over 500 articles were obtained under clinical trials, randomized clinical trials, metanalysis, and systematic reviews developed in the past 10 years in three major areas of dentistry: restorative, orofacial surgery, and periodontics. Clinical studies and systematic reviews along with hand-searched preclinical studies as potential therapies have been included. They support the proof-of-concept that novel treatments are in the pipeline towards ground-breaking clinical therapies for orofacial bone regeneration, tooth regeneration, repair of the oral mucosa, periodontal tissue engineering, and dental implants. Biomimicry enhances the clinical outcomes and calls for an interdisciplinary approach integrating medicine, bioengineering, biotechnology, and computational sciences to advance the current research to clinics. We conclude that dentistry has come a long way apropos of regenerative medicine; still, there are vast avenues to endeavour, seeking inspiration from other facets in biomedical research.

Contemporary restorative ion-releasing materials: current status, interfacial properties and operative approaches

Minimally invasive (MI) concepts in restorative dentistry in the year 2020 request from the practitioner not only a scientifically supported rationale for carious tissue removal/excavation and defect-oriented, biological cavity preparation, but also a deep understanding of how to ensure a biomechanically stable and durable restoration in different clinical situations by applying different restorative options. Bio-interactive materials play an increasingly relevant role, as they not only replace diseased or lost tissue, but also optimise tissue mineral recovery (among other properties) when used in restorative and preventive dentistry. Indeed, this is of certain interest in MI restorative dentistry, especially in those cases where gap formation jeopardises the integrity of the margins along resin composite restorations, causing penetration of bacteria and eventually promoting the formation of secondary caries. Recently, the interest in whether ion-releasing materials may reduce such biofilm penetration into margin gaps and reduce such a risk for development and propagation of secondary caries is growing significantly among clinicians and scientists. The aim of this article was to explore mechanisms involved in the process that allow mineral deposition at the interface between such materials and dentine, and to describe how conventional 'bioactive' restorative materials currently available on the market may benefit treatments in MI dentistry.

Effects of a biomimetic analog-based experimental bonding system on caries-affected and sound dentin

This study compared the ultrastructure, chemical composition, and proteases activity (PA) of sound (SD) and caries-affected dentin (CAD) in the dentin hybrid layer after using an experimental bonding system containing pyromellitic dianhydride glycerol methacrylate and biomimetic analogs. The bonding system used a three step and a total-etch procedure. Polyacrylic acid (5%) and sodium trimetaphosphate (5%) were added to the primer and monocalcium phosphate monohydrate (9%), beta-tricalcium phosphate (10.5%), and calcium hydroxide (0.5%) were added to the adhesive. Transmission electron microscopy (TEM) was used to evaluate the resultant structure, particularly the adhesive-dentin and the demineralized-SD interfaces. The chemical composition was evaluated through energy-dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED). The PA was measured with the Coomassie Blue-G250 coloring test, and the PA data were analyzed by ANOVA. EDS identified the presence of isolated calcium phosphate nanoparticles in the demineralized region; however, the SAED analysis did not show any evidences of hydroxyapatite (HA) neoformation in SD and CAD. The biomimetic analog-based adhesive system inhibited the activities of dentin proteases immediately after treatment. Additionally, the proteolytic activity on the affected dentin resembled that of the SD. In conclusion, no HA formed in the demineralized SD and CAD although there were calcium and phosphate deposits. The experimental adhesive system inhibited dentin proteases. The present study uses a new approach to investigate the hybrid layer behavior in dentin. The experimental adhesive system was synthesized and used on sound and affected-caries dentin as the substrate to reproduce real clinical conditions.

Antibacterial tooth surface created by laser-assisted pseudo-biomineralization in a supersaturated solution

A technique for implementing biocompatible and antibacterial functions to a targeted region on tooth surfaces has potential in dental treatments. We have recently demonstrated pseudo-biomineralization, i.e., the growth of an apatite layer on a human dentin substrate by a laser-assisted biomimetic (LAB) process, based on pulsed laser irradiation in a supersaturated CaP solution. In this study, pseudo-biomineralization was induced in the presence of fluoride ions using the LAB process in order to fabricate an antibacterial fluoride-incorporated apatite (FAp) layer on the dentin surface. After processing for 30 min, a micron-thick FAp layer was formed heterogeneously at the laser-irradiated solid-liquid interface via pseudo-biomineralization. A time-course study revealed that the LAB process first eliminated the pre-existing organic layer, while allowing fluoride incorporation into the dentin surface within 1 min. Within 5 min, FAp nanocrystals precipitated on the dentin surface. Within 30 min, these nanocrystals acquired a pillar-like structure that was weakly oriented in the direction normal to the substrate surface to form a dense micron-thick layer. This layer was integrated seamlessly with the underlying dentin without any apparent gaps. The FAp layer exhibited antibacterial activity against a major oral bacterium, Streptococcus mutans. The proposed LAB process is expected to be a useful new tool for tooth surface functionalization via facile and area-specific pseudo-biomineralization.

Thermal and bioactive optimization of a unidose 3-step etch-and-rinse dentin adhesive

STATEMENT OF PROBLEM

The limited durability of resin-dentin bonds is considered a major disadvantage of adhesive restorations. Therefore, clinical strategies have been developed to improve hybrid layer stability over time. These strategies require testing.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of preheating and the inclusion of a bioactive glass in a unidose 3-step etch-and-rinse adhesive system on the adhesion of direct composite resin restorations.

MATERIAL AND METHODS

Dentin disks from 80 molars were assigned to 8 groups (n=10): CG-T1/CG-T2: control group; PG-T1/PG-T2: adhesive preheated to 68 °C; BG-T1/BG-T2: 0.05 mg of Bioglass 45S5 (BAG) (particle size: 3 μm) added to primer; PBG-T1/PBG-T2: adhesive and BAG-modified primer preheated to 68 °C. Sticks were fabricated for microtensile bond strength (μTBS) testing and were tested at 1 week (T1) and after 6 months (T2) of storage. μTBS data were analyzed by using 2-way ANOVA and the Tukey-Kramer post hoc test (α=.05). Scanning electron microscopy was used to analyze the failure mode. Attenuated total reflection Fourier transform infrared spectroscopy was used to quantitatively analyze the modifications to the chemical structure of the adhesive system from preheating and BAG inclusion.

RESULTS

The mean bond strength values at 1 week were statistically different, with PG-T1 (69.8 ±7.8 MPa) superior to all other groups. CG-T1 (58.2 ±6.7 MPa), BG-T1 (60.7 ±4.4 MPa), and PBG-T1 (61.0 ±4.6 MPa) were not statistically different (P>.05). PG-T2 maintained the highest bond strength at 6 months (68.3 ±3.7 MPa), with no decrease in μTBS observed over time. Failure modes were mostly adhesive. Attenuated total reflection Fourier transform infrared spectroscopy analysis reported that primer preheating caused solvent evaporation and revealed that preheating the bonding agent promoted the condensation reaction between the silane and adhesive fillers.

CONCLUSIONS

No decrease in μTBS was observed for any group after 6 months. Preheating the adhesive system (primer and bonding resin) significantly increased the 1-week and 6-month μTBS. Inclusion of BAG did not affect the bond strength.

Inhibition of matrix metalloproteinases: a troubleshooting for dentin adhesion

Matrix metalloproteinases (MMPs) are enzymes that can degrade collagen in hybrid layer and reduce the longevity of adhesive restorations. As scientific understanding of the MMPs has advanced, useful strategies focusing on preventing these enzymes' actions by MMP inhibitors have quickly developed in many medical fields. However, in restorative dentistry, it is still not well established. This paper is an overview of the strategies to inhibit MMPs that can achieve a long-lasting material-tooth adhesion. Literature search was performed comprehensively using the electronic databases: PubMed, ScienceDirect and Scopus including articles from May 2007 to December 2019 and the main search terms were “matrix metalloproteinases”, “collagen”, and “dentin” and “hybrid layer”. MMPs typical structure consists of several distinct domains. MMP inhibitors can be divided into 2 main groups: synthetic (synthetic-peptides, non-peptide molecules and compounds, tetracyclines, metallic ions, and others) and natural bioactive inhibitors mainly flavonoids. Selective inhibitors of MMPs promise to be the future for specific targeting of preventing dentin proteolysis. The knowledge about MMPs functionality should be considered to synthesize drugs capable to efficiently and selectively block MMPs chemical routes targeting their inactivation in order to overcome the current limitations of the therapeutic use of MMPs inhibitors, i.e., easy clinical application and long-lasting effect.

Remineralization of dentin slices using casein phosphopeptide-amorphous calcium phosphate combined with sodium tripolyphosphate

Background

The remineralization approach mechanically occludes the exposed dentinal tubules mechanically, reduces the permeability of dentinal tubules and eliminates the symptoms of dentin hypersensitivity. The aim of the present study was to investigate the remineralization of demineralized dentin slices using CPP–ACP combined with TPP, and the research hypothesis was that CPP–ACP combined with TPP could result in extrafibrillar and intrafibrillar remineralization of dentin.

Methods

Demineralized dentin slices were prepared and randomly divided into the following groups: A (the CPP–ACP group), B (the CPP–ACP + TPP combination group), C (the artificial saliva group), D (the negative control group), and E (the positive control group). Dentin slice samples from groups A, B and C were remineralized and the remineralization effect was evaluated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR) and X-ray diffraction (XRD).

Results

Treatment with CPP–ACP combined with TPP occluded the dentinal tubules and resulted in remineralization of collagen fibrils. The hydroxyapatite crystals formed via remineralization were found to closely resemble the natural dentin components.

Conclusion

CPP–ACP combined with TPP has a good remineralization effect on demineralized dentin slices.

In Situ Precipitation of Cluster and Acicular Hydroxyapatite onto Porous Poly(γ-benzyl-l-glutamate) Microcarriers for Bone Tissue Engineering

Bone tissue engineering scaffold based on microcarriers provides an effective approach for the repair of irregular bone defects. The implantation of microcarriers by injection can reduce surgical trauma and fill various irregular shaped bone defects. Microcarriers with porous structure and osteogenic properties have shown great potential in promoting the repair of bone defects. In this study, two kinds of hydroxyapatite/poly-(γ-benzyl-l-glutamate) (HA/PBLG) microcarriers were constructed by emulsion/in situ precipitation method and their structures and properties were studied. First, PBLG porous microcarriers were prepared by an emulsion method. Surface carboxylation of PBLG microcarriers was performed to promote the deposition of HA on PBLG microcarriers. Next, the modified porous PBLG microcarriers were used as the matrix, combined with the in situ precipitation method; the cluster HA and acicular HA were precipitated onto the surface of porous microcarriers in the presence of ammonia water and tri(hydroxymethyl)aminomethane (Tris) solution, respectively. The micromorphology, composition, and element distribution of the two kinds of microcarriers were characterized by TEM, SEM, and AFM. Adipose stem cells (ADSCs) were cultured on the cluster HA/PBLG and acicular HA/PBLG microcarriers, respectively. ADSCs could grow and proliferate normally on both kinds of microcarriers wherein the acicular HA/PBLG microcarriers were more favorable for early cell adhesion and showed a beneficial effect on mineralization and osteogenic differentiation of ADSCs. Successful healing of a rabbit femur defect verified the bone regeneration ability of acicular HA/PBLG microcarriers.

Three-dimensional observation and analysis of remineralization in dentinal caries lesions

The remineralization mechanism in dental caries lesions is not completely understood. This study reports on ultrastructural and chemical changes observed within arrested caries lesions. Carious human teeth were observed using scanning electron microscopy (SEM) and focused-ion-beam (FIB)-SEM. The crystals detected in the caries lesions were characterized by transmission electron microscopy (TEM), along with chemical element mapping using energy-dispersive spectroscopy (EDS)-STEM. FIB-SEM 3D reconstructions revealed a severely damaged dentin surface abundantly covered by bacteria. Although the dentin tubules were clogged up to a depth of 100 μm, bacterial invasion into dentin tubules was not observed. TEM crystal analysis and EDS-STEM revealed the presence of Ca and P, as well as of Mg within the HAp crystals deposited inside the dentin tubules. It was concluded that extensive remineralization with deposition of Mg-HAp crystals had occurred in dentin tubules of caries-arrested dentin. Understanding the natural remineralization process is thought to be helpful for developing clinical biomimetic remineralization protocols.

Enhancing Collagen Mineralization with Amelogenin Peptide: Towards the Restoration of Dentin

Mammalian teeth primarily consist of two distinct calcified tissues, enamel and dentin, that are intricately integrated by a complex and critical structure, the dentin-enamel junction (DEJ). Loss of enamel exposes the underlying dentin, increasing the risk of several irreversible dental diseases. This paper highlights the significance of utilizing the functional domains of a major enamel matrix protein, amelogenin, intrinsic to tooth enamel and the DEJ interface, to rationally design smaller bioinspired peptides for regeneration of tooth microstructures. Using this strategy, we designed a synthetic peptide, P26, that demonstrates a remarkable dual mineralization potential to restore incipient enamel decay and mineralization defects localized in peripheral dentin below the DEJ. As a proof of principle, we demonstrate that interaction between P26 and collagen prompts peptide self-assembly, followed by mineralization of collagen fibrils in vitro. P26-mediated nucleation of hydroxyapatite (HAP) crystals on demineralized dentin in situ significantly facilitates the recovery of mineral density and effectively restores the biomechanical properties of dentin to near-native levels, suggesting that P26-based therapy has promising applications for treating diverse mineralized tissue defects in the tooth.

Organic-Mineral Interaction between Biomimetic Materials and Hard Dental Tissues

The aim of the investigation was to study the integration between native human dental tissue and new-generation biomimetic materials replicating the mineral-organic complex of dentin and enamel using IR microspectroscopy for multidimensional visualization and analysis.

[Effect of genipin pretreatment on type Ⅰ collagen mineralization]

OBJECTIVE

To investigate the effects of bio-crosslinker genipin pretreatment on type Ⅰ collagen mineralization.

METHODS

Type Ⅰ collagen gels were prepared and pretreated with 0.5wt%genipin (experimental group) and deionized water (control group) for 2 h, respectively. The pretreated products were subjected to Fourier transform infrared spectroscopy (FT-IR). Reconstituted collagen fibrils were pretreated with genipin or deionized water for 2 h and were mineralized for 4 h. The collagen density and mineralization degree were examined with transmission electron microscopy (TEM) and analyzed with ImageJ software. Then scanning electron microscopy (SEM) and TEM were used to observe the mineralization of cross-linked demineralized dentin collagen.

RESULTS

FT-IR spectrum showed that the genipin was crosslinked with collagen. TEM observation and ImageJ results showed that after 4 h mineralization, the mineralization effect of 0.5wt% genipin group was significantly better than that of the control group[(73.3±5.3)%vs.(7.4±3.5)%,P<0.01]. TEM and SEM observation showed that the mineralization rate of type Ⅰ collagen and demineralized dentin pretreated with genipin were significantly faster than that of the control group.

CONCLUSIONS

The study demonstrates that 0.5 wt% concentration of genipin can significantly promote the mineralization of type Ⅰ collagen.

Effects of oligopeptide simulating DMP-1/mineral trioxide aggregate/agarose hydrogel biomimetic mineralisation model for the treatment of dentine hypersensitivity

Dentine hypersensitivity (DH) occurs when dentine is exposed to stimuli from the oral environment due to a lack of enamel or cementum. The use of biomimetic mineralisation in occluding exposed dentinal tubules and regenerating enamel-like tissues on dentine surfaces is preferred for a long-lasting treatment. In this study, we established a biomimetic mineralisation model composed of oligopeptide stimulating dentine matrix protein 1 (DMP-1), mineral trioxide aggregate (MTA) and an agarose hydrogel biomimetic mineralisation model (AHBMM); the proposed model is thus referred to as DMP-1@MTA@AHBMM. The effectiveness of DMP-1@MTA@AHBMM for the management of DH was analysed with scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and a microhardness test. The use of DMP-1@MTA@AHBMM on a demineralised dentine surface occluded the dentinal tubules and regenerated an enamel-like tissue containing well-defined fluoridated hydroxyapatite crystals on the dentine surface. The microhardness of the regenerated enamel-like tissue was greater than that of the demineralised dentine. Therefore, DMP-1@MTA@AHBMM can be a promising method for the management of DH.