Structural analysis of reactionary dentin formed in response to polymicrobial invasion

Presence of host and bacterial-derived collagenolytic proteases in carious dentin: a systematic review of ex vivo studies

Introduction and aim

The presence of host collagenases in the degradation of the protein matrix at later stages of carious dentin lesions development, as well as the potential involvement of bacterial collagenases, have been suggested but lack conclusive evidence. This study aims to conduct a systematic review to comprehensively assess the profile of host and bacterial-derived collagenolytic proteases in both root and coronal dentin carious lesions.

Methods

The search was performed in eight databases and the grey literature. Studies evaluating ex vivo dentin, extracted teeth, or biofilms from natural caries lesions were included. The methodological quality of studies was assessed using the Joanna Briggs Institute tool. Synthesis of the results and the certainty of evidence were performed following the Synthesis without Meta-analysis (SWiM) checklist and GRADE approach for narrative synthesis, respectively.

Results

From 935 recovered articles, 18 were included. Although the evidence was very uncertain, it was possible to suggest that 1) MMP-2, MMP-9, MMP-13, and CT-B may be increased in carious dentin when compared to sound dentin; 2) there is no difference in MMP-2 presence, while MMP-13 may be increased in root when compared to coronal carious dentin; 3) there is no difference of MMP-2 and MMP-9 expression/activity before and after cavity sealing; 4) MMP-8 may be increased in the dentin before cavity sealing compared to dentin after cavity sealing; 5) there is no difference of MMP-20 in irradiated vs. non-irradiated carious dentin. MMP-20 probably reduces in carious outer dentin when compared to carious inner dentin (moderate certainty). Genes encoding bacterial collagenolytic proteases and protein-degrading bacteria were detected in coronal and root carious lesions.

Conclusion

Trends in the direction of the effect were observed for some collagenolytic proteases in carious dentin, which may represent a potential target for the development of new treatments. (Protocol register-PROSPERO: CRD42020213141).

Equine odontoclastic tooth resorption and hypercementosis (EOTRH): microspatial distribution of trace elements in hypercementosis-affected and unaffected hard dental tissues

Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) is a common, painful and poorly understood disease. Enamel, dentin and cementum accumulate both essential and toxic trace elements during mineralization. Characterization of the spatial accumulation pattern of trace elements may provide insight into the role that toxic elements play and inform biological processes affecting these hard dental tissues for future research. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to map the distribution of multiple trace elements and heavy metals across equine healthy and diseased (hypercementosis-affected) hard dental tissues among four teeth extracted from horses with EOTRH. Results showed banding patterns of some trace elements (lead, strontium, barium), reflecting the temporal component of accumulation of trace elements during dentin mineralization. Essential elements zinc and magnesium did not show banding patterns. Comparison to the unaffected cementum and dentin adjacent to the hypercementosis region showed that there is an underlying incremental pattern in the uptake of some metals with spatial irregularities. This supports a possible metabolic change involved in hypercementosis lesion development. This represents the first use of LA-ICP-MS to study the microspatial distribution of trace elements in equine teeth, establishing a baseline for elemental distribution in normal and EOTRH impacted dental hard tissue.

Dentin Matrix Metalloproteinases: A Futuristic Approach Toward Dentin Repair and Regeneration

Matrix metalloproteinases (MMPs) have been linked to modulating healing during the production of tertiary dentin, as well as the liberation of physiologically active molecules and the control of developmental processes. Although efforts to protect dentin have mostly centered on preventing these proteases from doing their jobs, their role is actually much more intricate and crucial for dentin healing than anticipated. The role of MMPs as bioactive dentin matrix components involved in dentin production, repair, and regeneration is examined in the current review. The mechanical characteristics of dentin, especially those of reparative and reactionary dentin, and the established functions of MMPs in dentin production are given particular attention. Because they are essential parts of the dentin matrix, MMPs should be regarded as leading applicants for dentin regeneration.

The roles of 10-methacryloyloxydecyl dihydrogen phosphate and its calcium salt in preserving the adhesive-dentin hybrid layer

OBJECTIVES

10-Methacryloyloxydecyl dihydrogen phosphate (MDP) has been regarded as the most effective dentin-bonding monomer for more than 20 years. Although the dentin-bonding promoting effect of MDP has been well demonstrated, the mechanisms by which it benefits the stably of collagen within the adhesive-dentin hybrid layer are not currently fully understood. The objective of this study was to investigate the roles of MDP and its calcium salt in preserving the adhesive-dentin hybrid layer.

METHODS

MDP-conditioned collagen was investigated by Fourier-transform infrared spectroscopy, Ultraviolet-visible spectroscopy, and molecular docking. The structural changes to the dentin surface upon acid-etching and MDP-conditioning were observed by SEM. X-ray diffraction and nuclear magnetic resonance were used to investigate the chemical interactions between MDP and HAp. The collagen-protecting effects of MDP and its Ca salt were investigated using in-situ zymography, rhMMP-9 colorimetric assay, hydroxyproline assay, and molecular docking.

RESULTS

MDP forms a stable collagen-phosphate complex through hydrogen bonding with the collagen in dentin. Furthermore, it generates MDP-Ca salts that are deposited on the dentin collagen scaffold, protecting it from degradation. Moreover, both free MDP and the MDP-Ca salt inhibit matrix metallopeptidase and exogenous proteases, with the inhibitory effect of the calcium salt being significantly stronger than that of the free form.

SIGNIFICANCE

MDP-based adhesives preserve the collagen within the hybrid layer by simultaneously improving collagen's resistance to exogenous enzymes and inhibiting MMP activity, both of which contribute to the longevity of dentin-resin bonding.

Interactions of two phosphate ester monomers with hydroxyapatite and collagen fibers and their contributions to dentine bond performance

OBJECTIVES

To evaluate the interactions of two phosphate ester monomers [10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) and dipentaerythritol penta-acrylate phosphate (PENTA)] with hydroxyapatite and collagen and understand their influence on dentine bonding.

METHODS

Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, nuclear magnetic resonance, ultraviolet-visible, and molecular docking were applied for separately evaluating the interactions of two monomers with hydroxyapatite and collagen. Hydrophilicity tests and morphological observation were employed to characterize pretreated dentine. Microtensile bond strength (μTBS) and nanoleakage were investigated to evaluate the bonding performance. Hydroxyproline assay, in situ zymography, and matrix metalloproteinase-9 (MMP-9) activity assay were used to confirm the MMP inhibition.

RESULTS

Chemoanalytic characterization confirmed the interactions of 10-MDP and PENTA with hydroxyapatite and collagen. The interactions of PENTA were weaker than 10-MDP. PENTA possessed better dentine tubule sealing after etching than 10-MDP. Dentine treated with PENTA was more hydrophilic than 10-MDP. 10-MDP and PENTA treating significantly increased the initial μTBS than the control group without primer conditioning. μTBS decreased significantly during aging, and the decrease was more severe in the PENTA group than 10-MDP. The 10-MDP and PENTA groups exhibited relatively less fluorescence than the control. The relative inhibition percentages of MMP-9 decreased in the order of 10-MDP-Ca salt, 10-MDP and PENTA. The 10-MDP, PENTA, and 10-MDP-Ca salt groups showed significantly lower hydroxyproline contents than the control.

CONCLUSIONS

Although PENTA adsorbed on hydroxyapatite, it did not form a stable calcium salt. The interactions of 10-MDP with hydroxyapatite and collagen are different than those of PENTA.

CLINICAL SIGNIFICANCE

The sealing of dentinal tubules by PENTA and the inhibition of MMP by 10-MDP and its calcium salts contribute to improving the dentine bonding durability.

Erosive Effect of Acidic Beverages and Dietary Preservatives on Extracted Human Teeth—An In Vitro Analysis

Objectives Frequent consumption of acidic beverages and dietary preservatives in younger generation, diet-conscious (celebrities), and obese individuals have a rapid impact on demineralization of the teeth. An attempt was made to analyze the erosive potential of various acidic beverages.

Materials and Methods One hundred and ninety extracted human permanent teeth were sectioned longitudinally, pre-weighed, randomly grouped, and placed in nine acidic beverages (200 mL) with predetermined pH, i.e., three commercially available fruit juices, three carbonated drinks, and three dietary preservatives.

Statistical Analysis The sectioned specimens (n = 10) were analyzed at time intervals of 12, 24, 48, and 96 days. Mean weight loss was calculated, and surface changes were assessed under a stereomicroscope. The demineralization pattern and microscopic changes were observed under a compound and polarizing microscope. One-way analysis of variance test followed by Tukey's post-hoc analysis was employed.

Results Overall the maximum demineralizing effect was caused by vinegar and apple cider. In the fruit juices category, lemon juice induced significant changes, while in the carbonated drinks category Coca-Cola induced the maximum changes and in the category of food preservatives vinegar induced the maximum changes. Severe discoloration was seen with respect to Coca-Cola followed by Mountain Dew (carbonated drink).

Conclusion The present study is unique as three different types of microscopes have been employed and both dentin and enamel of permanent teeth have been analyzed. In addition, the effect of dietary preservatives on hard tissues was evaluated. Oral health educators can reinforce important practices such as decreasing the frequency of consumption and time duration of beverage contact with the teeth. Also, the use of mouth rinses and buffering agents after the consumption of dietary beverages can be advocated along with regular fluoride application for those who are regular consumers.

Applications of scanning electron microscopy and focused ion beam milling in dental research

The abilities of scanning electron microscopy (SEM) and focused ion beam (FIB) milling for obtaining high-resolution images from top surfaces, cross-sectional surfaces, and even in three dimensions, are becoming increasingly important for imaging and analyzing tooth structures such as enamel and dentin. FIB was originally developed for material research in the semiconductor industry. However, use of SEM/FIB has been growing recently in dental research due to the versatility of dual platform instruments that can be used as a milling device to obtain low-artifact cross-sections of samples combined with high-resolution images. The advent of the SEM/FIB system and accessories may offer access to previously inaccessible length scales for characterizing tooth structures for dental research, opening exciting opportunities to address many central questions in dental research. New discoveries and fundamental breakthroughs in understanding are likely to follow. This review covers the applications, key findings, and future direction of SEM/FIB in dental research in morphology imaging, specimen preparation for transmission electron microscopy (TEM) analysis, and three-dimensional volume imaging using SEM/FIB tomography.

Leukotriene B4 loaded in microspheres regulate the expression of genes related to odontoblastic differentiation and biomineralization by dental pulp stem cells

Background

Leukotriene B₄ (LTB₄) is a potent lipid mediator that stimulate the immune response. Because dental pulp inflammation and dentin repair are intrinsically related responses, the aim of this research was to investigate the potential of LTB₄ in inducing differentiation of dental pulp stem cells.

Methods

Microspheres (MS) loaded with LTB₄ were prepared using an oil emulsion solvent extraction evaporation process and sterility, characterization, efficiency of LTB₄ encapsulation and in vitro LTB₄ release assay were investigated. Mouse dental pulp stem cells (OD-21) were stimulated with soluble LTB₄ or MS loaded with LTB₄ (0.01 and 0.1 μM). Cytotoxicity and cell viability was determined by lactate dehydrogenase and methylthiazol tetrazolium assays. Gene expression were measured by quantitative reverse transcription polymerase chain reaction after 3, 6, 24, 48 and 72 h. Mineralized nodule formation was assessed after 28 days of OD-21 cell stimulation with LTB₄ in mineralized media or not. Groups were compared using one-way ANOVA test followed by Dunnett’s post-test (α = 0.05).

Results

Treatment with LTB₄ or MS loaded with LTB₄ (0.01 and 0.1 µm-μM) were not cytotoxic to OD-21 cells. Treatment with LTB₄ modulated the expression of the Ibsp (integrin binding sialoprotein) and Runx2 (runt-related transcription factor 2) genes differently depending on the experimental period analyzed. Interestingly LTB₄ loaded in microspheres (0.1 μM) allowed long term dental pulp cell differentiation and biomineralization.

Conclusion

LTB₄, soluble or loaded in MS, were not cytotoxic and modulated the expression of the Ibsp and Runx2 genes in cultured OD-21 cells. When LTB₄ was incorporated into MS, odontoblast differentiation and mineralization was induced in long term culture.

Super high-quality SEM/FIB imaging of dentine structures without collagen fiber loss through a metal staining process

Scanning Electron Microscope/Focused Ion Beam (SEM/FIB) system has become valuable and popular tool for the analysis of biological materials such as dentine structures. According to physiological and anatomical studies, dentine structures are a complicated system containing collagen fibers, nanocrystalline hydroxyapatite, and numerous networks of tubular pores. During a routine FIB milling process, collagen fibers and other organic structures are vaporized, which increases the number of pores on the milled surface of the dentine. This causes the final cross-section to be more porous than the pristine sample. Unfortunately, little attention has been paid to the collagen fiber loss and how to preserve them during a FIB milling process. In this work, we present a novel and simple approach to preserve the organic portions of the dentine structure through metal staining. By using this method, the porosity of the dentine structure after the FIB milling process is significantly reduced similar to the pristine sample. This indicates that the organic portion of the dentine structure is well protected by the metal staining. This approach enables the SEM/FIB system to generate super-high quality SEM images with less ion beam damage; and the SEM images can better reflect the original condition of the dentine structure. Further, serial energy-dispersive X-ray spectroscopy (EDS) mapping of the stained dentine structure is achieved without an additional metal coating; and three-dimensional (3-D) elemental mapping of an occluded dentine is achieved with a significantly reduced data acquisition time.

Dentine matrix metalloproteinases as potential mediators of dentine regeneration

Matrix metalloproteinases (MMPs) have been implicated not only in the regulation of developmental processes but also in the release of biologically active molecules and in the modulation of repair during tertiary dentine formation. Although efforts to preserve dentine have focused on inhibiting the activity of these proteases, their function is much more complex and necessary for dentine repair than expected. The present review explores the role of MMPs as bioactive components of the dentine matrix involved in dentine formation, repair and regeneration. Special consideration is given to the mechanical properties of dentine, including those of reactionary and reparative dentine, and the known roles of MMPs in their formation. MMPs are critical components of the dentine matrix and should be considered as important candidates in dentine regeneration.

A software approach for identifying the effect of dental caries on dentin-enamel junction

Dental decay is the most prevalent oral disease worldwide since more than 2.4 billion people suffer from caries of permanent teeth. Therefore, any details about its progression into the hard-dental tissues could contribute to unravelling the mechanisms underlying this process. We have analyzed dental tissue sections with and without caries in order to detect structure differences corelating them with clinical aspects observable from the tooth surface. Our working hypothesis was based on finding a link between the process of tertiary dentin laying (as a response to coronal caries) and the subsequent obliteration of dentin tubules. We have selected N=10 extracted teeth with/without coronal caries, resin-embedded and sectioned them. A specific software was used to digitally quantify the density of unobliterated dentin tubules reaching the dentin-enamel junction (DEJ), considering as positive threshold criteria the presence of the odontoblast process inside the analyzed tubule. This study showed the differences between the healthy and carious-affected hard-dental coronal tissues. More odontoblast processes reached the DEJ in unaffected teeth. Using specific software, we have quantified their density decrease near a lesion. We have studied the dynamics of the carious study and measured the consequent structural modifications of the dentin. In conclusion, there is a significant difference between the number of dentin tubules containing odontoblast processes that reach the DEJ in healthy∕altered tissues. The tooth reacts not only by production of tertiary dentin to protect the pulp chamber, but also by obliteration of dentin tubules, thus reducing the number of odontoblast processes reaching the DEJ. This pilot study could serve as the starting point in developing a dedicated software that could deliver a personalized pattern for decay progression by analyzing one single tooth and extrapolate the result to all the patient's remaining ones.

Biomineralization of Dental Tissues Treated with Silver Diamine Fluoride

Silver diamine fluoride (SDF) is a dental biomaterial used to arrest dental caries. To better understand SDF's mechanism of action, we examined the localization of silver within the tissues of SDF-treated teeth. Carious primary teeth fixed within 2 min of SDF application (SDF-minutes, n = 3), at 3 wk after SDF application in vivo (SDF-weeks, n = 4), and at 2 y after multiple SDF applications in vivo (SDF-multiple, n = 1) were investigated in this study. Carious primary teeth without SDF application (no-SDF, n = 3) served as controls. Mineral density and structural analyses were performed via micro-X-ray computed tomography and scanning electron microscopy. Elemental analyses were performed through X-ray fluorescence microprobe and energy-dispersive X-ray spectroscopic techniques. SDF-treated teeth revealed higher X-ray-attenuated surface and subsurface regions within carious lesions, and similar regions were not present in no-SDF teeth. Regions of higher mineral density correlated with regions of silver abundance in SDF-treated teeth. The SDF penetration depth was approximated to 0.5 ± 0.02 mm and 0.6 ± 0.05 mm (mean ± SD) for SDF-minutes and SDF-weeks specimens, respectively. A higher percentage of dentin tubular occlusion by silver or calcium phosphate particles was observed in primary teeth treated with SDF-weeks as compared with SDF-minutes. Elemental analysis also revealed zinc abundance in carious lesions and around the pulp chamber. SDF-weeks teeth had significantly increased tertiary dentin than SDF-minutes and no-SDF teeth. These results suggest that SDF treatment on primary teeth affected by caries promotes pathologic biomineralization by altering their physicochemical properties, occluding dentin tubules, and increasing tertiary dentin volume. These seemingly serendipitous effects collectively contribute to the cariostatic activity of SDF.

Structure-Function Correlative Microscopy of Peritubular and Intertubular Dentine

Peritubular dentine (PTD) and intertubular dentine (ITD) were investigated by 3D correlative Focused Ion Beam (FIB)-Scanning Electron Microscopy (SEM)-Energy Dispersive Spectroscopy (EDS) tomography, tapping mode Atomic Force Microscopy (AFM) and scattering-type Scanning Near-Field Optical Microscopy (s-SNOM) mapping. The brighter appearance of PTD in 3D SEM-Backscattered-Electron (BSE) imaging mode and the corresponding higher grey value indicate a greater mineral concentration in PTD (~160) compared to ITD (~152). However, the 3D FIB-SEM-EDS reconstruction and high resolution, quantitative 2D map of the Ca/P ratio (~1.8) fail to distinguish between PTD and ITD. This has been further confirmed using nanoscale 2D AFM map, which clearly visualised biopolymers and hydroxyapatite (HAp) crystallites with larger mean crystallite size in ITD (32 ± 8 nm) than that in PTD (22 ± 3 nm). Correlative microscopy reveals that the principal difference between PTD and ITD arises primarily from the nanoscale packing density of the crystallites bonded together by thin biopolymer, with moderate contribution from the chemical composition difference. The structural difference results in the mechanical properties variation that is described by the parabolic stiffness-volume fraction correlation function introduced here. The obtained results benefit a microstructure-based mechano-chemical model to simulate the chemical etching process that can occur in human dental caries and some of its treatments.

Scaffolds of hydroxyl apatite nanoparticles disseminated in 1, 6-diisocyanatohexane-extended poly(1, 4-butylene succinate)/poly(methyl methacrylate) for bone tissue engineering

Poly(1, 4-butyl succinate) extended 1, 6-diisocyanatohexane (PBSu-DCH) polymers and Polymethylmethacrylate (PMMA) scaffolds decorated with nano hydroxyl apatite have been prepared and characterized for regeneration of bone in cranio-maxillofacial region. Synthesized scaffolds revealed good response in bone regeneration and excellent cell viability in comparison to commercial available glass plate, which lead to better proliferation of MG-63 cell lines. Additionally, they demonstrate high porosity and excellent water retention ability. Moreover, controlled degradation (in pH=7.4) and sustained drug release in pH (4.5 and 7.4) are advantages of these scaffolds to serve as delivery vehicles for therapeutic drugs. Samples also provide the protection against Escherichia coli and Methicillin Resistant Staphylococcus aureus microorganisms which can be helpful for quick recovery of the patient. In-vitro inflammatory response has been assessed via adsorption of human plasma/serum proteins on the surface of the scaffolds. Results suggest that prepared scaffolds have good bone regeneration ability and provide friendly environment for the cell growth with the additional advantage of protection of the surrounding tissues from microbial infection. With all these features, it is speculated that these scaffolds will have wide utility in the area of tissue engineering and regenerative medicine.

Effect of nanolayering of calcium salts of phosphoric acid ester monomers on the durability of resin-dentin bonds

To investigate the contribution of nanolayering on resin-dentin bond durability, two phosphoric acid ester resin monomers, 10-methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) or its analog, methacryloyloxy-penta-propyleneglycol-dihydrogen-phosphate (MDA), were examined for their affinity for mineralized dentin powder in a column chromatography setup. Hydroxyapatite (HA) powder was dispersed in experimental primers consisting of 10-MDP or MDA solvated in ethanol/water and examined with FTIR, (31)P MAS-NMR and XPS. Light-curable 10-MDP or MDA primers were used for bonding to dentin, and examined after 24h or one-year of water-aging by TEM for evidence of nanolayering, and for microtensile bond strength evaluation. Primer-bonded dentin was examined by thin-film XRD to identify short-range order peaks characteristic of nanolayering of resin monomer-Ca salts. Although 10-MDP had better affinity for mineralized dentin than MDA, both monomers completely eluted from the mineralized dentin powder column using ethanol-water as mobile phase, indicating that the adsorption processes were reversible. This finding was supported by chemoanalytic data. XRD of 10-MDP-bonded dentin showed three diffraction peaks hat were absent from MDA-bonded dentin. Nanolayering was identified by TEM in 10-MDP-bonded dentin, but not in MDA-bonded dentin. Significant drop in bond strength (in MPa) was observed for both groups after one-year of water-aging compared with 24-h: 10-MDP group from 48.3±6.3 to 37.4±4.6; MDA group from 50.7±5.0 to 35.7±3.8 (P<0.05), with no significant difference between the two groups at the same time-point. Because both functional monomer-primed, resin-bonded dentin exhibited similar bond strength decline after water-aging, presence of nanolayering is unlikely to contribute to the overall resin-dentin bond durability.

STATEMENT OF SIGNIFICANCE

The durability of resin-dentin bonds in 10-MDP containing self-etching adhesives has been anecdotally attributed to the presence of nanolayering of 10-MDP-calcium salts in the resin-dentin interface. Results of the present work indicate that such a claim cannot be justified. Complete elution of the phosphoric acid ester monomer from mineralized dentin powder in the column chromatography experiments using ethanol-water mobile phase to simulate the solvent mixture employed in most 10-MDP-containing dentin adhesives further challenges the previously proposed adhesion-decalcification concept that utilizes chemical bonding of phosphoric acid ester monomers to apatite as a bonding mechanism in 10-MDP containing dentin adhesives.

Glial network responses to polymicrobial invasion of dentin

This study investigated the distribution patterns of glial networks disclosed by reactivity for glial fibrillary acidic protein (GFAP) and S100B in healthy and carious human teeth. The objective was to determine the assembly and collapse of glial networks in response to encroaching infection. 15 healthy and 37 carious posterior teeth from adults were studied. Immediately after extraction, teeth were cleaned and vertically split and the half with pulp fixed and prepared for resin or frozen sections. Sections were stained with toluidine blue and for immunofluorescence, with observation by confocal laser microscopy and analysis by ImageJ software. Carious teeth were subdivided into three groups according to degree of carious involvement: microbial penetration through enamel (stage A), extension into dentin (stage B) and advanced penetration into dentin but without invasion of underlying pulp tissue (stage C). In stage A lesions there was marked increase in glial networks in dental pulp tissue that extended beyond the zone of microbial invasion. This response was maintained in stage B lesions. In advanced stage C lesions these networks were degraded in the zone of invasion in association with failure to contain infection. Cells expressing the glial markers GFAP and S100B showed a response to initial microbial invasion of dentin by increase in number and altered anatomical arrangement. The late stage of dentinal caries was marked by collapse of these networks in the region adjacent to advancing bacteria. This behaviour is important for understanding and explaining the defensive response of the neurosensory peripheral dental pulp apparatus to infection.