A dentin-derived hydrogel bioink for 3D bioprinting of cell laden scaffolds for regenerative dentistry

Recent studies in tissue engineering have adopted extracellular matrix (ECM) derived scaffolds as natural and cytocompatible microenvironments for tissue regeneration. The dentin matrix, specifically, has been shown to be associated with a host of soluble and insoluble signaling molecules that can promote odontogenesis. Here, we have developed a novel bioink, blending printable alginate (3% w/v) hydrogels with the soluble and insoluble fractions of the dentin matrix. We have optimized the printing parameters and the concentrations of the individual components of the bioink for print accuracy, cell viability and odontogenic potential. We find that, while viscosity, and hence printability of the bioinks, was greater in the formulations containing higher concentrations of alginate, a higher proportion of insoluble dentin matrix proteins significantly improved cell viability; where a 1:1 ratio of alginate and dentin (1:1 Alg-Dent) was most suitable. We further demonstrate high retention of the soluble dentin molecules within the 1:1 Alg-Dent hydrogel blends, evidencing renewed interactions between these molecules and the dentin matrix post crosslinking. Moreover, at concentrations of 100 μg ml^-1, these soluble dentin molecules significantly enhanced odontogenic differentiation of stem cells from the apical papilla encapsulated in bioprinted hydrogels. In summary, the proposed novel bioinks have demonstrable cytocompatibility and natural odontogenic capacity, which can be a used to reproducibly fabricate scaffolds with complex three-dimensional microarchitectures for regenerative dentistry in the future.

Cracked teeth: a review of the literature

Although cracked teeth are a common problem for patients and dentists, there is a dearth of evidence-based guidelines on how to prevent, diagnose, and treat cracks in teeth. The purpose of this article is to review the literature to establish what evidence exists regarding the risk factors for cracked teeth and their prevention, diagnosis, and treatment.

The effect of different polishing systems on surface roughness and gloss of various resin composites

PURPOSE

The purpose of this in vitro study was to evaluate the surface finish and gloss of five direct resin composites polished with six polishing systems.

MATERIALS AND METHODS

One hundred and fifty disk-shaped composite specimens (D=10.0 mm, 2-mm-thick, N=30 per material) were made. One side of each specimen was finished with a 16-fluted carbide finishing bur and then polished. Five specimens of each resin composite were randomly assigned to one of the six polishing systems. The surface roughness and gloss were measured with a surface profilometer and a glossmeter. The results were analyzed by two-way analysis of variance and Tukey's t-test (p<or= 0.05).

RESULTS

There was no significant interaction between the composite and the polishing systems for surface roughness (p=0.059). The order of surface roughness ranked according to composite was: Durafill < Esthet-X < Supreme < Z250 < Z100; and the ranking for the polishing system was: Pogo < Sof-Lex < Diacomp/Enamelize < Diacomp < ComposiPro brush < Jiffy. There was interaction of gloss values between the composites and the polishing systems (p < 0.001). The highest gloss value was recorded for Supreme + Pogo; the lowest was recorded for Z100 + Jiffy. Pogo showed the highest gloss values for all composites.

CLINICAL SIGNIFICANCE

The nanofill (Supreme) and minifill (Esthet-X) composites presented a surface roughness comparable to a microfill (Durafill), independent of the polishing system used, and a gloss comparable to a microfill, when polished with a one-step system (Pogo). As compared with the multiple-step systems, the smoothest surfaces and the highest gloss values were achieved using the one-step system (Pogo) for all the evaluated composites.

RoBDEMAT: A risk of bias tool and guideline to support reporting of pre-clinical dental materials research and assessment of systematic reviews

OBJECTIVES

To develop a risk of bias tool for pre-clinical dental materials research studies that aims to support reporting of future investigations and improve assessment in systematic reviews.

METHODS

A four-stage process following EQUATOR network recommendations was followed, which included project launch, literature review, Delphi process and the tool finalization. With the support of the European Federation of Conservative Dentistry (EFCD) and the Dental Materials Group of the International Association for Dental Research (DMG-IADR), a total of 26 expert stakeholders were included in the development and Delphi vote of the initial proposal. The proposal was built using data gathered from the literature review stage. During this stage, recent systematic reviews featuring dental materials research, and risk of bias tools found in the literature were comprehensively scanned for bias sources. The experts thus reached a consensus for the items, domains and judgement related to the tool, allowing a detailed guide for each item and corresponding signalling questions.

RESULTS

The tool features nine items in total, spread between 4 domains, pertaining to the following types of bias: bias related to planning and allocation (D1), specimen preparation (D2), outcome assessment (D3) and data treatment and outcome reporting (D4). RoBDEMAT, as presented, features signalling questions and a guide that can be used for RoB judgement. Its use as a checklist is preferred over a final summary score.

CONCLUSION

RoBDEMAT is the first risk of bias tool for pre-clinical dental materials research, supported and developed by a broad group of expert stakeholders in the field, validating its future use.

CLINICAL SIGNIFICANCE

This new tool will contribute the study field by improving the scientific quality and rigour of dental materials research studies and their systematic reviews. Such studies are the foundation and support of future clinical research and evidence-based decisions.

Influence of the antagonist material on the wear of different composites using two different wear simulation methods

OBJECTIVES

The aim of the study was to evaluate two ceramic materials as possible substitutes for enamel using two wear simulation methods, and to compare both methods with regard to the wear results for different materials.

METHODS

Flat specimens (OHSU n=6, Ivoclar n=8) of one compomer and three composite materials (Dyract AP, Tetric Ceram, Z250, experimental composite) were fabricated and subjected to wear using two different wear testing methods and two pressable ceramic materials as stylus (Empress, experimental ceramic). For the OHSU method, enamel styli of the same dimensions as the ceramic stylus were fabricated additionally. Both wear testing methods differ with regard to loading force, lateral movement of stylus, stylus dimension, number of cycles, thermocycling and abrasive medium. In the OHSU method, the wear facets (mean vertical loss) were measured using a contact profilometer, while in the Ivoclar method (maximal vertical loss) a laser scanner was used for this purpose. Additionally, the vertical loss of the ceramic stylus was quantified for the Ivoclar method. The results obtained from each method were compared by ANOVA and Tukey's test (p<0.05). To compare both wear methods, the log-transformed data were used to establish relative ranks between material/stylus combinations and assessed by applying the Pearson correlation coefficient.

RESULTS

The experimental ceramic material generated significantly less wear in Tetric Ceram and Z250 specimens compared to the Empress stylus in the Ivoclar method, whereas with the OHSU method, no difference between the two ceramic antagonists was found with regard to abrasion or attrition. The wear generated by the enamel stylus was not statistically different from that generated by the other two ceramic materials in the OHSU method. With the Ivoclar method, wear of the ceramic stylus was only statistically different when in contact with Tetric Ceram. There was a close correlation between the attrition wear of the OHSU and the wear of the Ivoclar method (Pearson coefficient 0.83, p=0.01).

SIGNIFICANCE

Pressable ceramic materials can be used as a substitute for enamel in wear testing machines. However, material ranking may be affected by the type of ceramic material chosen. The attrition wear of the OHSU method was comparable with the wear generated with the Ivoclar method.

Effect of shrinkage strain, modulus, and instrument compliance on polymerization shrinkage stress of light-cured composites during the initial curing stage

OBJECTIVES

The aim of this study was to investigate the influence of shrinkage strain, modulus, and instrument compliance on the polymerization shrinkage stress measurement of light-cured composites, and to determine whether the silorane-based low-shrinkage composite shows a low-polymerization shrinkage stress.

METHODS

A universal hybrid; Z250 (Z2), a flowable; Z350 (Z3), and a silorane-based; P90 (P9) composite was examined. A modified "bonded disc method" was used to measure the axial shrinkage strain of the composite. For the measurement of the initial modulus development of composites during light curing, a dynamic oscillatory shear test was undertaken using a custom-made oscillation rheometer. A frequency of 6 Hz and strain amplitude of 0.0091 rad for 20 s was employed and the complex shear modulus (G(*)) was determined. A newly designed stress-strain analyzer was made to measure the shrinkage stress of the composites with two modes: (1) high compliance, or (2) low compliance. The shift between the two modes was controlled by an On-Off switch of a negative feedback circuit. Theoretical shrinkage stress was calculated from the shrinkage strain and modulus measured above, and compared with experimentally measured stress. Data were analyzed with one-way ANOVA and Tukey's post hoc test (alpha=0.05), and correlation analysis was done to investigate the relationship between measured stress and shrinkage strain, modulus, and theoretical stress.

RESULTS

The shrinkage strain of Z3 (4.12%) at 10 min was the highest, followed by Z2 (2.31%) and P9 (0.77%). At 10 s after light curing, Z2 showed the highest modulus (466.2 MPa), Z3 (154.1 MPa), and P9 the lowest (130.7 MPa). The measured stresses with low compliance were much higher than those with high compliance. With high compliance, the contraction stress of Z3 was the highest (2.75 MPa), followed by Z2 (1.54 MPa) and P9 (0.48 MPa). In low-compliance mode, the stresses of Z3 (7.93 MPa) and Z2 (7.48 MPa) were similar (p=0.323) while the stress of P9 (3.23 MPa) was much lower. A strong correlation was observed between the theoretical stress and the measured stress with low compliance (R=0.996). In high-compliance mode, the shrinkage strain also showed a near-linear relationship with the stress measured (R=0.937), but the modulus showed a low correlation with the measured stress (R=0.398).

SIGNIFICANCE

Depending on the instrument compliance, polymerization shrinkage stress showed significant differences for each material. In high-compliance shrinkage strain played a greater role, while in low-compliance shrinkage strain and elastic modulus contributed comparably in determining the shrinkage stress. The low-shrinkage silorane-based composite demonstrated considerable reduction in shrinkage strain and stress.

Influence of instrument compliance and specimen thickness on the polymerization shrinkage stress measurement of light-cured composites

OBJECTIVES

The aim of our study was to investigate the effects of instrument compliance and specimen geometry on the polymerization shrinkage stress measurements of composites.

METHODS

A custom designed stress-strain analyzer was made using a linear variable differential transformer probe and a cantilever load cell. A sandblasted glass rod was fixed at the free end of the load cell, and another glass rod was located on a base plate. A composite was placed between the two rods and light cured. The end displacement of the load cell during polymerization was recorded for 10 min. A flowable (Filtek Flow), a universal hybrid (Z100), and a packable (P60) composite were studied. To investigate the effect of specimen geometry and instrument compliance, specimen thickness was varied between 0.5, 1.0, and 2.0 mm, and three load cells with maximum capacities of 20, 100, and 500kgf were used. Ten maxillary premolars were prepared with two sizes of MOD cavities; the bucco-lingual widths and depths of the cavities were 1.5 mm x 2 mm and 3 mm x 2 mm, and the cusp compliance and deflection were measured before and during composite polymerization.

RESULTS

The measured polymerization stress decreased in the order of Filtek Flow, Z100, and P60 for all measurement conditions. As the specimen thickness was increased, the shrinkage stress per unit thickness (mm) decreased. The measured stress decreased with increasing instrument compliance. The cusp compliance (3.32 microm/N) of the 3 mm x 2 mm cavities was similar to that of instrument with a 20 kgf load cell (3.34 microm/N).

SIGNIFICANCE

For determining the most clinically relevant values for shrinkage stress of dental composites, the instrument compliance should closely match that of the tooth walls in the cavity geometry to be tested.

Dissolution of mercury from amalgam into saline solution

Dissolution of mercury from amalgams and some intermetallic compounds found in the amalgam structure, such as gamma 1, gamma 2, and beta 1, was examined during one week of aging in 0.9% NaCl solution at 37 degrees C. The amount of mercury released from gamma 1 (30.2 micrograms/cm2) was at least 13 times that released from amalgam (0.5-2.2 micrograms/cm2) and five times that released from beta 1(5.7 micrograms/cm2). Gamma 2 released the least amount of mercury (0.46 micrograms/cm2). The study revealed that as high as 55% of the mercury ions liberated from the amalgams and the amalgam phases was adsorbed onto the walls of the vials in which the specimens were aged.

Spotlight on bond strength testing--unraveling the complexities

The variability in methods and outcomes of bond strength testing reports is well documented in the dental literature. Many studies lack important information, which impairs the ability to reproduce them as well as to compare them to other studies in the literature. In order to critically discuss the important issues around bond strength testing methods, and to move closer to at least standardizing the reporting of such studies, the Academy of Dental Materials held a conference in 2009 entitled Adhesion in Dentistry-Analyzing Bond Strength Testing Methods, Variables, and Outcomes. Short synopses of the presentations are presented in this article. This article also provides a list of the variables that should be reported in bond strength studies, regardless of testing methods, to be used by authors conducting future studies, as well as journal reviewers and editors. The goal is to provide guidance and a rationale for what should be included in a study so that reporting might be more standardized and to enhance the possibility that more meaningful comparisons and conclusions may be drawn across studies. The table lists detailed descriptions covering all aspects of testing procedures, including variables related to tooth substrate, restorative material, specimen preparation, pre-testing conditions, testing methods, data reporting and analysis.

Carbon-Based Solid-State Calcium Ion-Selective Microelectrode and Scanning Electrochemical Microscopy: A Quantitative Study of pH-Dependent Release of Calcium Ions from Bioactive Glass

Solid-state ion-selective electrodes are used as scanning electrochemical microscope (SECM) probes because of their inherent fast response time and ease of miniaturization. In this study, we report the development of a solid-state, low-poly(vinyl chloride), carbon-based calcium ion-selective microelectrode (Ca(2+)-ISME), 25 μm in diameter, capable of performing an amperometric approach curve and serving as a potentiometric sensor. The Ca(2+)-ISME has a broad linear response range of 5 μM to 200 mM with a near Nernstian slope of 28 mV/log[a(Ca(2+))]. The calculated detection limit for Ca(2+)-ISME is 1 μM. The selectivity coefficients of this Ca(2+)-ISME are log K(Ca(2+),A) = -5.88, -5.54, and -6.31 for Mg(2+), Na(+), and K(+), respectively. We used this new type of Ca(2+)-ISME as an SECM probe to quantitatively map the chemical microenvironment produced by a model substrate, bioactive glass (BAG). In acidic conditions (pH 4.5), BAG was found to increase the calcium ion concentration from 0.7 mM ([Ca(2+)] in artificial saliva) to 1.4 mM at 20 μm above the surface. In addition, a solid-state dual SECM pH probe was used to correlate the release of calcium ions with the change in local pH. Three-dimensional pH and calcium ion distribution mapping were also obtained by using these solid-state probes. The quantitative mapping of pH and Ca(2+) above the BAG elucidates the effectiveness of BAG in neutralizing and releasing calcium ions in acidic conditions.

Slumping resistance and viscoelasticity prior to setting of dental composites

OBJECTIVES

The aim of this study was to develop a method for measuring the slumping resistance of resin composites and to evaluate the efficacy using rheological methodology.

METHODS

Two commercial hybrid composites (Z100 and Z250) and a nanofill composite (Z350) were used to make disc-shaped specimens of 2mm thickness. Three kinds of aluminum molds with triangular, circular, and square shaped cutting surfaces were pressed onto the resin discs to make standardized imprints. The imprints were light-cured either immediately (non-slumped) or after waiting for 2min at 25 degrees C (slumped). White stone replicas were made and then scanned for topography using a laser 3-D profilometer. Slumping resistance index (SRI) was defined as the ratio of the groove depth of the slumped specimen to that of the non-slumped specimen. The pre-cure viscoelasticity of each composite was evaluated by an oscillatory shear test and normal stress was measured by a squeeze test using a rheometer. Correlation analysis was performed to investigate the relationship between the viscoelastic properties and SRI.

RESULTS

SRI varied between the three materials (Z100<Z250<Z350) and the imprint shapes did not affect the slumping tendency. The SRI was strongly correlated with the loss shear modulus G'' but not with the loss tangent. Also, slumping resistance was more closely related to the resistance to shear flow than to the normal stress.

SIGNIFICANCE

Slumping tendency could be quantified using the imprint method and SRI. The index may be applicable to evaluate the clinical handling characteristics of composites.

Dentin matrix components extracted with phosphoric acid enhance cell proliferation and mineralization

OBJECTIVE

Acids, such as those used in adhesive dentistry, have been shown to solubilize bioactive molecules from dentin. These dentin matrix components (DMC) may promote cell proliferation and differentiation, and ultimately contribute to dentin regeneration. The objective of this study was to evaluate the potential for varying concentrations of DMC extracted from human dentin by phosphoric acid of a range of pHs to stimulate proliferation and mineralization of two different cultured pulp cell populations.

METHODS

DMC were solubilized from powdered human dentin (7 days - 4°C) by phosphoric acid of pH 1, 3, and 5 and also, EDTA. Extracts were dialyzed for 7 days against distilled water and lyophilized. Undifferentiated mouse dental pulp cells (OD-21) and cells of the odontoblast-like cell line (MDPC-23) were seeded in six-well plates (1×10(5)) and cultured for 24h in DMEM (Dulbecco's modified Eagle's medium) containing 10% (v/v) FBS (fetal bovine serum). The cells were washed with serum-free medium and then treated with different concentrations of DMC (0.01, 0.1, 1.0 and 10.0μg/ml) daily in serum free medium for 7 days. After 3, 5 (MDPC-23 only), and 7 days of treatment, cell proliferation was measured using 10vol% Alamar blue solution, which was added to each well for 1h. Cell numbers were first measured by cell counting (Trypan blue; n=5) and Alamar blue fluorescence to validate the assay, which was then used for the subsequent assessments of proliferation. Mineralization was assessed by Alizarin Red S assay after 12 days exposure to DMC (n=5). Controls were media-only (DMEM) and dexamethasone (DEX; positive control). Results were analysed by ANOVA/Tukey's (p≤0.05).

RESULTS

There was a linear correlation between cell counts and Alamar blue fluorescence (R(2)>0.96 for both cell types) , verifying the validity of the Alamar blue assay for these cell types. In general, there was a dose-dependent trend for enhanced cell proliferation with higher concentration of DMC for both cell lines, especially at 10.0μg/ml. DEX exposure resulted in significantly higher mineralization, but did not affect cell proliferation. DMC exposure demonstrated significantly greater mineralization than media-only control for 10μg/ml for all extracts, and at lower concentrations for EDTA and pH 5 extracts.

SIGNIFICANCE

Human dentin matrix components solubilized by acids at pH levels found in commercial dentin adhesives enhanced cell proliferation and mineralization of mouse and rat undifferentiated dental pulp cells when presented in adequate concentration.

Real-time measurement of dentinal fluid flow during amalgam and composite restoration

OBJECTIVES

This study examined changes in the dentinal fluid flow (DFF) during restorative procedures and compared permeability after restoration among restorative materials and adhesives.

METHODS

A class 1 cavity was prepared and restored with either amalgam (Bestaloy), or composite (Z-250) with one of two etch-and-rinse adhesives (Scotchbond MultiPurpose: MP and Single Bond 2: SB) or one of two self-etch adhesives (Clearfil SE Bond: CE and Easy Bond: EB) on an extracted human third molar which was connected to a sub-nanoliter fluid flow measuring device (NFMD) under 20 cm water pressure. DFF was measured from the intact tooth state through the restoration procedures to 30 min after restoration, and re-measured at 3 and 7 days post-restoration.

RESULTS

Inward flow during cavity preparation was followed by outward flow after preparation. In amalgam restoration, the outward flow changed into an inward flow during amalgam filling, which was followed by a slight outward flow after finishing. In composite restoration, MP and SB showed an inward flow and outward flow for the rinsing and drying steps, respectively. Application of a hydrophobic bonding resin in the MP and CE systems caused a decrease in the flow rate. Air-drying of solvent for the CE and EB systems caused a sudden outward flow, whereas light-curing of the adhesive and composite caused an abrupt inward flow.

CONCLUSIONS

Each restorative step clearly changed the direction and the rate of the DFF during restoration, which could be well identified with NFMD.

In-vitro models of biocompatibility testing for restorative dental materials: From 2D cultures to organs on-a-chip

Dental caries is a biofilm-mediated, diet-modulated, multifactorial and dynamic disease that affects more than 90% of adults in Western countries. The current treatment for decayed tissue is based on using materials to replace the lost enamel or dentin. More than 500 million dental restorations are placed annually worldwide, and materials used for these purposes either directly or indirectly interact with dentin and pulp tissues. The development and understanding of the effects of restorative dental materials are based on different in-vitro and in-vivo tests, which have been evolving with time. In this review, we first discuss the characteristics of the tooth and the dentin-pulp interface that are unique for materials testing. Subsequently, we discuss frequently used in-vitro tests to evaluate the biocompatibility of dental materials commonly used for restorative procedures. Finally, we present our perspective on the future directions for biological research on dental materials using tissue engineering and organs on-a-chip approaches. STATEMENT OF SIGNIFICANCE: Dental caries is still the most prevalent infectious disease globally, requiring more than 500 million restorations to be placed every year. Regrettably, the failure rates of such restorations are still high. Those rates are partially based on the fact that current platforms to test dental materials are somewhat inaccurate in reproducing critical components of the complex oral microenvironment. Thus, there is a collective effort to develop new materials while evolving the platforms to test them. In this context, the present review critically discusses in-vitro models used to evaluate the biocompatibility of restorative dental materials and brings a perspective on future directions for tissue-engineered and organs-on-a-chip platforms for testing new dental materials.

A Chemical Approach to Optimizing Bioactive Glass Dental Composites

The chemical microenvironment surrounding dental composites plays a crucial role in controlling the bacteria grown on these specialized surfaces. In this study, we report a scanning electrochemical microscopy (SECM)-based analytic technique to design and optimize metal ion-releasing bioactive glass (BAG) composites, which showed a significant reduction in biofilm growth. SECM allows positioning of the probe without touching the substrate while mapping the chemical parameters in 3-dimensional space above the substrate. Using SECM and a solid-state H⁺ and Ca²⁺ ion-selective microprobe, we determined that the local Ca²⁺ concentration released by different composites was 10 to 224 µM for a BAG particle size of <5 to 150 µm in the presence of artificial saliva at pH 4.5. The local pH was constant above the composites in the same saliva solution. The released amount of Ca²⁺ was determined to be maximal for particles <38 µm and a BAG volume fraction of 0.32. This optimized BAG-resin composite also showed significant inhibition of biofilm growth (24 ± 5 µm) in comparison with resin-only composites (53 ± 6 µm) after Streptococcus mutans bacteria were grown for 3 d in a basal medium mucin solution. Biofilm morphology and its subsequent volume, as determined by the SECM imaging technique, was (0.59 ± 0.38) × 10⁷ µm³ for BAG-resin composites and (1.29 ± 0.53) × 10⁷ µm³ for resin-only composites. This study thus lays the foundation for a new analytic technique for designing dental composites that are based on the chemical microenvironment created by biomaterials to which bacteria have been exposed.

Comparison of efficacy of an in-office whitening system used with and without a whitening priming agent

PURPOSE

The purpose of this study was to compare the whitening efficacy of an in-office whitening system with and without the whitening primer application and evaluate tooth and soft tissue sensitivity.

MATERIALS AND METHODS

This was a randomized, split-mouth design, single-blinded, clinical study. Twenty-five patients received a whitening priming agent (Power Swabs, Power Swabs Corporation, Beaverton, OR, USA) on right or left maxillary incisors prior to in-office tooth whitening with Opalescence Boost (38% hydrogen peroxide; Ultradent Products, Inc., South Jordan, UT, USA). Color was evaluated with the Bleachedguide 3D Master (Vita Zahnfabrik, Bad Sackingen, Germany) and Vita Easyshade spectrophotometer (Vident, Brea, CA, USA), after 30 minutes, 1 day, and 15 days postwhitening. After each tooth color measurement, the subjects were asked to rate their tooth and soft tissue sensitivity experience using a visual analog scale (1-10 categories). Results were analyzed by two-way repeated measurements analysis of variance/Tukey's (p<0.05); Mann-Whitney rank sum test and Kruskal-Wallis.

RESULTS

The teeth that were treated with the primer prior to tooth whitening did not show significant difference in ΔL*, Δa*, Δb*, ΔE* and delta shade guide from the teeth that were not treated with the primer, at the three time points evaluated (baseline versus 30 minutes after in-office treatment, baseline versus 1 day, and baseline versus 15 days). None of the subjects experienced soft tissue sensitivity, and those who experienced tooth sensitivity said it was not noticeable after 15 days postwhitening.

CLINICAL SIGNIFICANCE

The primer neither enhanced the whitening effect nor decreased tooth sensitivity when used before vital bleaching with Opalescence Boost (Ultradent Products, Inc., South Jordan, UT, USA). None of the subjects experienced soft tissue sensitivity, and some experienced transient tooth sensitivity.

A dual-ink 3D printing strategy to engineer pre-vascularized bone scaffolds in-vitro

A functional vascular supply is a key component of any large-scale tissue, providing support for the metabolic needs of tissue-remodeling cells. Although well-studied strategies exist to fabricate biomimetic scaffolds for bone regeneration, success rates for regeneration in larger defects can be improved by engineering microvascular capillaries within the scaffolds to enhance oxygen and nutrient supply to the core of the engineered tissue as it grows. Even though the role of calcium and phosphate has been well understood to enhance osteogenesis, it remains unclear whether calcium and phosphate may have a detrimental effect on the vasculogenic and angiogenic potential of endothelial cells cultured on 3D printed bone scaffolds. In this study, we presented a novel dual-ink bioprinting method to create vasculature interwoven inside CaP bone constructs. In this method, strands of a CaP ink and a sacrificial template material was used to form scaffolds containing CaP fibers and microchannels seeded with vascular endothelial and mesenchymal stem cells (MSCs) within a photo-crosslinkable gelatin methacryloyl (GelMA) hydrogel material. Our results show similar morphology of growing vessels in the presence of CaP bioink, and no significant difference in endothelial cell sprouting was found. Furthermore, our initial results showed the differentiation of hMSCs into pericytes in the presence of CaP ink. These results indicate the feasibility of creating vascularized bone scaffolds, which can be used for enhancing vascular formation in the core of bone scaffolds.

3D-printed microgels supplemented with dentin matrix molecules as a novel biomaterial for direct pulp capping

OBJECTIVES

To develop a 3D-printed, microparticulate hydrogel supplemented with dentin matrix molecules (DMM) as a novel regenerative strategy for dental pulp capping.

MATERIALS AND METHODS

Gelatin methacryloyl microgels (7% w/v) mixed with varying concentrations of DMM were printed using a digital light projection 3D printer and lyophilized for 2 days. The release profile of the DMM-loaded microgels was measured using a bicinchoninic acid assay. Next, dental pulp exposure defects were created in maxillary first molars of Wistar rats. The exposures were randomly capped with (1) inert material - negative control, (2) microgels, (3) microgels + DMM 500 µg/ml, (4) microgels + DMM 1000 µg/ml, (5) microgels + platelet-derived growth factor (PDGF 10 ng/ml), or (6) MTA (n = 15/group). After 4 weeks, animals were euthanized, and treated molars were harvested and then processed to evaluate hard tissue deposition, pulp tissue organization, and blood vessel density.

RESULTS

All the specimens from groups treated with microgel + 500 µg/ml, microgel + 1000 µg/ml, microgel + PDGF, and MTA showed the formation of organized pulp tissue, tertiary dentin, newly formed tubular and atubular dentin, and new blood vessel formation. Dentin bridge formation was greater and pulp necrosis was less in the microgel + DMM groups compared to MTA.

CONCLUSIONS

The 3D-printed photocurable microgels doped with DMM exhibited favorable cellular and inflammatory pulp responses, and significantly more tertiary dentin deposition.

CLINICAL RELEVANCE

3D-printed microgel with DMM is a promising biomaterial for dentin and dental pulp regeneration in pulp capping procedures.