Regulation of reactionary dentin formation by odontoblasts in response to polymicrobial invasion of dentin matrix

Correlation between Matrix Metalloproteinase Presence and Caries Surface Appearance

INTRODUCTION

Cariogenic bacterial acids dissolve the inorganic elements in dentine, leaving the dentine matrix exposed. Host-derived matrix metalloproteinases (MMPs) play an essential role in caries progression as they are significant regulators of extracellular matrix turnover and can degrade exposed collagen. This paper investigates the expression of MMP2 and MMP9 across various stages of caries in primary human teeth and relate this with a diagnosis recorded by the International Caries Detection and Assessment System (ICDAS).

METHODS

Twenty-four sections (150 μm in thickness) from extracted teeth, clinically diagnosed using ICDAS, were immunohistochemically treated with monoclonal anti-MMP2 and anti-MMP9 antibodies. Positive staining was visualised by immunofluorescence using a VectorFluor Duet Double Labeling Kit. Images from triplicate samples for each ICDAS score were analysed using ImageJ software. Collagen degradation in caries lesions was detected using a hydroxyproline assay.

RESULTS

MMPs were weakly detected in caries with ICDAS 1-2 scores, and an insignificant increase was detected in ICDAS 3. However, a significant increase in MMP expression was seen in caries with an ICDAS score of 4-6. There was a strong positive correlation between the ICDAS score and MMP2 (r [6] = 0.86, p = 0.002) and between ICDAS and MMP9 (r [6] = 0.82, p = 0.004). Data were analysed using two-way ANOVA followed by Tukey multiple comparison test (*p < 0.05).

CONCLUSION

The use of ICDAS to assess the severity of caries lesions and how this correlates with the presence of MMP in these lesions validates the modern approach to caries management with a minimally invasive concept.

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).

The Role of Bacterial, Dentinal, Salivary, and Neutrophil Degradative Activity in Caries Pathogenesis

Until recently, it was widely accepted that bacteria participate in caries pathogenesis mainly through carbohydrate fermentation and acid production, which promote the dissolution of tooth components. Neutrophils, on the other hand, were considered white blood cells with no role in caries pathogenesis. Nevertheless, current literature suggests that both bacteria and neutrophils, among other factors, possess direct degradative activity towards both dentinal collagen type-1 and/or methacrylate resin-based restoratives and adhesives, the most common dental restoratives. Neutrophils are abundant leukocytes in the gingival sulcus, where they can readily reach adjacent tooth roots or gingival and cervical restorations and execute their degradative activity. In this review, we present the latest literature evidence for bacterial, dentinal, salivary, and neutrophil degradative action that may induce primary caries, secondary caries, and restoration failure.

Dentin Degradation: From Tissue Breakdown to Possibilities for Therapeutic Intervention

Purpose of the Review

Presently, dental materials science is driven by the search for new and improved materials that can trigger specific reactions from the affected tissue to stimulate repair or regeneration while interacting with the oral environment to promote or maintain oral health. In parallel, evidence from the past decades has challenged the exclusive role of bacteria in dentin tissue degradation in caries, questioning our understanding of caries etiopathogenesis. The goal of this review is to recapitulate the current evidence on the host and bacterial contributions to degradation, inflammation, and repair of the dentin-pulp complex in caries.

Recent Findings

Contrasting findings attribute dentin breakdown to the activity of endogenous enzymes, such as matrix metalloproteinases (MMPs) and cathepsins, while the role of bacteria and their by-products in the destruction of dentin organic matrix and pulp inflammation has been for decades supported as an incontestable paradigm. Aiming to better understand the mechanisms involved in collagen degradation by host enzymes in caries, studies have showed that these proteinases are expressed in the mature dentin (i.e., after dentin formation) and become activated by the low pH in the acidic environment resulted by bacterial metabolism in caries. However, different host sources other than dentin-bound proteinases seem to also contribute to caries progression, such as saliva and pulp. Interestingly, studies evaluating pulp responses to bacteria invasion and inflammation in caries report higher levels of MMPs and cathepsins in inflamed tissue, but also showed MMP potential to resolve inflammation and stimulate wound healing. Notably, as reported for other tissues, MMPs exert dual roles in the dentin-pulp complex in caries, participating or regulating both degradative and reparative mechanisms.

Summary

The specific roles of host and bacteria and their by-products in caries progression have yet to be clarified. The complex interactions between inflammation and repair in caries pose challenges to a clear understanding of the dentin-pulp complex responses and changes to bacteria invasion. However, it opens new venues for the development of novel therapies and dental biomaterials based on the modulation of specific mechanisms to favor tissue repair and healing.

Smart dental materials for antimicrobial applications

Smart biomaterials can sense and react to physiological or external environmental stimuli (e.g., mechanical, chemical, electrical, or magnetic signals). The last decades have seen exponential growth in the use and development of smart dental biomaterials for antimicrobial applications in dentistry. These biomaterial systems offer improved efficacy and controllable bio-functionalities to prevent infections and extend the longevity of dental devices. This review article presents the current state-of-the-art of design, evaluation, advantages, and limitations of bioactive and stimuli-responsive and autonomous dental materials for antimicrobial applications. First, the importance and classification of smart biomaterials are discussed. Second, the categories of bioresponsive antibacterial dental materials are systematically itemized based on different stimuli, including pH, enzymes, light, magnetic field, and vibrations. For each category, their antimicrobial mechanism, applications, and examples are discussed. Finally, we examined the limitations and obstacles required to develop clinically relevant applications of these appealing technologies.

25-Hydroxycholesterol induces odontoclastic differentiation through RANK-RANKL upregulation and NF-κB activation in odontoblast-like MDPC-23 cells: An in vitro study

AIM

The physiological effects and cellular mechanism of 25-hydroxycholesterol (25-HC), which is an oxysterol synthesized from cholesterol by cholesterol-25-hydroxylase (CH25H) expressed under inflammatory conditions, are still largely unknown during odontoclastogenesis. This study aimed to evaluate 25-HC-induced odontoclastogenesis and its cellular mechanisms in odontoblast-like MDPC-23 cells.

METHODOLOGY

To investigate 25-HC-induced odontoclastogenesis of MDPC-23 cells and its cellular mechanism, haemotoxylin and eosin staining, tartrate-resistant acid phosphatase (TRAP) staining, dentine resorption assay, zymography, reactive oxygen species (ROS) detection, immunocytochemistry, and nuclear translocation were performed. The experimental values are presented as mean ± standard deviation and were compared using analysis of variance, followed by post hoc multiple comparisons (Tukey's test) using SPSS software version 22 (IBM Corp.). A p-value <.05 was considered statistically significant.

RESULTS

Lipopolysaccharide or receptor activator of nuclear factor-κB ligand (RANKL) induced the synthesis of 25-HC via the expression of CH25H in MDPC-23 cells (p < .01). Multinucleated giant cells with morphological characteristics and TRAP activity of the odontoclast were increased by 25-HC in MDPC-23 cells (p < .01). Moreover, 25-HC increased dentine resorption through the expression and activity of matrix metalloproteinases in MDPC-23 cells. It not only increased the expression of odontoclastogenic biomarkers but also translocated cytosolic nuclear factor-κB (NF-κB) to the nucleus in MDPC-23 cells. Additionally, 25-HC not only increased the production of ROS (p < .01), expression of inflammatory mediators (p < .01), pro-inflammatory cytokines, receptor activator of NF-κB (RANK), and RANKL but also suppressed the expression of osteoprotegerin (OPG) in MDPC-23 cells. In contrast, CDDO-Me, a chemical NF-κB inhibitor, decreased TRAP activity (p < .01) and downregulated the expression of the odontoclastogenic biomarkers, including RANK and RANKL, in MDPC-23 cells.

CONCLUSION

25-HC induced odontoclastogenesis by modulating the RANK-RANKL-OPG axis via NF-κB activation in MDPC-23 cells. Therefore, these findings provide that 25-HC derived from cholesterol metabolism may be involved in the pathophysiological etiological factors of internal tooth resorption.

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.

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 Mouse Model for Studying the Development of Apical Periodontitis with Age

Older age is associated with reduced immune function. Our aim was to study how age affects the development of apical periodontitis (AP). AP was induced in two age groups of mice (young vs. adult). Histological samples were stained by Hematoxylin Eosin, Brown and Brenn, and Tartrate-Resistant Acid Phosphatase. In addition, the samples were scanned by Micro-Computerized-Tomography (micro-CT) to evaluate apical constriction and periapical lesion size. Cell density in the periapical region was computationally assessed. Moreover, lesion immune cell populations were characterized by flow cytometry and immunofluorescence. The young group presented more canals with necrotic radicular pulp compared to the adults. There was no difference in bacteria location in the canals between the groups. Apical constriction size was larger in the young mice compared to the adults. The periapical cell density was higher in the young group, while the dominant immune cells in the lesions were neutrophils, which also exhibited the highest young/adult ratio. Immunofluorescence demonstrated neutrophils in the lesion. More osteoclasts were present in the lesions of the young mice, in correlation to the higher volume of bone resorption in this group. Overall, we conclude that the immune reaction to AP stimuli was attenuated in the adult mice compared to the young.

Expression of fibroblast growth factor receptor1, -2c, and -3c transcripts in mouse molars after tooth eruption

A previous study suggested that fibroblast growth factor (FGF) signaling plays an important role in dentin formation during tooth development. In this study, to examine dentin formation after tooth eruption involving secondary and tertiary dentin, we analyzed the expression patterns and expressing cells of Fgfr1, -2c, and -3c in mouse maxillary first molars (M₁). Since it is difficult to recover the mRNAs from mineralized tissues, we tested methods for extraction after fixation and decalcification of teeth. We successfully obtained consistent results with quantitative real-time PCR (qPCR) using β-actin transcripts for validation. qPCR for Dentin sialo phosphoprotein (Dspp), Fgfr1, -2c, and -3c transcripts was performed on mice at ages of 2-20 weeks. The results showed that the highest expression levels of Dspp and Fgfr2c occurred at 2 weeks old followed by lower expression levels after 4 weeks old. However, the expression levels of Fgfr1 and Fgfr3c were constant throughout the experimental period. By in situ hybridization, Dspp, Fgfr1, and Fgfr3c transcripts were detected in odontoblasts at ages of 2 and 4 weeks. In addition, Dspp and Fgfr1 transcripts were detected in odontoblasts facing reactionary dentin at 8 weeks old. These results suggest that FGF-FGFR signaling might be involved in the regulation of odontoblasts even after tooth eruption, including secondary and tertiary dentin formation. Moreover, our modified method for extracting mRNA from mineralized tissues after fixation and decalcification successfully produced consistent results.

Role of connexin 43 in odontoblastic differentiation and structural maintenance in pulp damage repair

Dental pulp can initiate its damage repair after an injury of the pulp–dentin complex by rearrangement of odontoblasts and formation of newly differentiated odontoblast-like cells. Connexin 43 (Cx43) is one of the gap junction proteins that participates in multiple tissue repair processes. However, the role of Cx43 in the repair of the dental pulp remains unclear. This study aimed to determine the function of Cx43 in the odontoblast arrangement patterns and odontoblastic differentiation. Human teeth for in vitro experiments were acquired, and a pulp injury model in Sprague-Dawley rats was used for in vivo analysis. The odontoblast arrangement pattern and the expression of Cx43 and dentin sialophosphoprotein (DSPP) were assessed. To investigate the function of Cx43 in odontoblastic differentiation, we overexpressed or inhibited Cx43. The results indicated that polarized odontoblasts were arranged along the pulp–dentin interface and had high levels of Cx43 expression in the healthy teeth; however, the odontoblast arrangement pattern was slightly changed concomitant to an increase in the Cx43 expression in the carious teeth. Regularly arranged odontoblast-like cells had high levels of the Cx43 expression during the formation of mature dentin, but the odontoblast-like cells were not regularly arranged beneath immature osteodentin in the pulp injury models. Subsequent in vitro experiments demonstrated that Cx43 is upregulated during odontoblastic differentiation of the dental pulp cells, and inhibition or overexpression of Cx43 influence the odontoblastic differentiation. Thus, Cx43 may be involved in the maintenance of odontoblast arrangement patterns, and influence the pulp repair outcomes by the regulation of odontoblastic differentiation.

Mineral trioxide aggregate-induced AMPK activation stimulates odontoblastic differentiation of human dental pulp cells

AIM

To investigate the role of autophagy in MTA-induced odontoblastic differentiation of human dental pulp cells (HDPCs).

METHODOLOGY

In MTA-treated HDPCs, odontoblastic differentiation was assessed based on expression levels of dentine sialophosphoprotein (DSPP) and dentine matrix protein 1 (DMP1), alkaline phosphatase activity (ALP) activity by ALP staining and the formation of mineralized nodule by Alizarin red S staining. Expression of microtubule-associated protein 1A/1B-light chain3 (LC3), adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signalling molecules and autophagy-related genes was analysed by Western blot analysis and Acridine orange staining was used to detect autophagic lysosome. For in vivo experiments, tooth cavity preparation models on rat molars were established and the expression of proteins-related odontogenesis and autophagy markers was observed by Immunohistochemistry and Western blot analysis. Kruskal-Wallis with Dunn's multiple comparison was used for statistical analysis.

RESULTS

Mineral trioxide aggregate (MTA) promoted odontoblastic differentiation of HDPCs, accompanied by autophagy induction, including formation of autophagic lysosome and cleavage of LC3 to LC3II (P < 0.05). Conversely, inhibition of autophagy through 3MA significantly attenuated the expression level of DSPP (P < 0.05) and DMP1 (P < 0.05) as well as formation of mineralized nodules (P < 0.05), indicating the functional significance of autophagy in MTA-induced odontoblastic differentiation. Also, MTA increased the activity of AMPK (P < 0.01), whereas inhibition of AMPK by compound C downregulated DSPP (P < 0.01) and DMP1 (P < 0.05), but increased the phosphorylation of mTOR (P < 0.05), p70S6 (P < 0.01) and Unc-51-like kinases 1 (ULK1) (ser757) (P < 0.01), explaining the involvement of AMPK pathway in MTA-induced odontoblast differentiation. In vivo study, MTA treatment after tooth cavity preparation on rat molars upregulated DMP-1 and DSPP as well as autophagy-related proteins LC3II and p62, and enhanced the phosphorylation of AMPK.

CONCLUSION

MTA induced odontoblastic differentiation and mineralization by modulating autophagy with AMPK activation in HDPCs. Autophagy regulation is a new insight on regenerative endodontic therapy using MTA treatment.

Endodontic regeneration: hard shell, soft core

A loss of organs or the destruction of tissue leaves wounds to which organisms and living things react differently. Their response depends on the extent of damage, the functional impairment and the biological potential of the organism. Some can completely regenerate lost body parts or tissues, whereas others react by forming scars in the sense of a tissue repair. Overall, the regenerative capacities of the human body are limited and only a few tissues are fully restored when injured. Dental tissues may suffer severe damage due to various influences such as caries or trauma; however, dental care aims at preserving unharmed structures and, thus, the functionality of the teeth. The dentin-pulp complex, a vital compound tissue that is enclosed by enamel, holds many important functions and is particularly worth protecting. It reacts physiologically to deleterious impacts with an interplay of regenerative and reparative processes to ensure its functionality and facilitate healing. While there were initially no biological treatment options available for the irreversible destruction of dentin or pulp, many promising approaches for endodontic regeneration based on the principles of tissue engineering have been developed in recent years. This review describes the regenerative and reparative processes of the dentin-pulp complex as well as the morphological criteria of possible healing results. Furthermore, it summarizes the current knowledge on tissue engineering of dentin and pulp, and potential future developments in this thriving field.

Autophagy-Related Protein MAP1LC3C Plays a Crucial Role in Odontogenic Differentiation of Human Dental Pulp Cells

BACKGROUND

Autophagy plays important roles in odontogenic differentiation of dental pulp cells (DPCs) in the developmental stage of tooth bud. Few studies have reported the role of autophagy during reparative dentin formation process. The objective of this study was to discover gene expression pattern correlated to autophagy and their role during odontogenic differentiation process in DPCs.

METHODS

After tooth cavities were prepared on the mesial surface of lower first molar crown of rats. Odontogenic differentiation and reparative dentin formation were assessed based on detection of morphology change with hematoxylin and eosin staining.

RESULTS

After tooth cavities were prepared on the mesial surface of lower first molar crown of rats, odontogenic differentiation and reparative dentin formation were assessed based on detection of morphology change with hematoxylin and eosin staining and dentin sialophosphoprotein (DSPP), whereas autophagy inhibitor 3-methyladenine (3MA) reversed. Results of quantitative polymerized chain reaction array of autophagosome formation related genes revealed that GABARAPL2 was prominently upregulated while expression of other ATG8 family members were moderately increased after tooth cavity preparation. In addition, human DPCs incubated in differentiation medium predominantly upregulated MAP1LC3C, which selectively decreased by 3MA but not by autophagy enhancer trehalose. Knock-down of MAP1LC3C using shRNA resulted in strong downregulation of dentin matrix protein 1 and DSPP as well-known odontogenic marker compared to knock-down of MAP1LC3B during odontogenic differentiation process of human DPCs.

CONCLUSION

Our results suggest that MAP1LC3C plays a crucial role in odontogenic differentiation of human DPCs via regulating autophagic flux.

A novel hypothesis based on clinical, radiological, and histological data to explain the dentinogenesis imperfecta type II phenotype

Purpose/Aim: The aim of this study was to explore whether dentinogenesis imperfecta (DGI)-related aberrations are detectable in odontogenic tissues. Materials and Methods: Morphological and histological analyses were carried out on 3 teeth (two maxillary 1^st molars, one maxillary central incisor) extracted from a patient with DGI Type II. A maxillary 2^nd molar teeth extracted from a healthy patient was used as control. A micro-computed tomographic (μCT) data-acquisition system was used to scan and reconstruct samples. Pentachrome and picrosirius red histologic stains were used to analyze odontogenic tissues and their collagenous matrices. Results: Our findings corroborate DGI effects on molar and incisor root elongation, and the hypo-mineralized state of DGI dentin. In addition to these findings, we discovered changes to the DGI pulp cavity: Reactionary dentin formation, which we theorize is exacerbated by the early loss of enamel, nearly obliterated an acellular but still-vascularized DGI pulp cavity. We also discovered an accumulation of lamellated cellular cementum at the root apices, which we hypothesize compensates for the severe and rapid attrition of the DGI tooth. Conclusions: Based on imaging and histological data, we propose a novel hypothesis to explain the complex dental phenotypes observed in patients with DGI Type II.

Melatonin antagonizes lipopolysaccharide-induced pulpal fibroblast responses

Background

Pulpal inflammation is known to be mediated by multiple signaling pathways. However, whether melatonin plays regulatory roles in pulpal inflammation remains unclear. This study aimed at elucidating an in situ expression of melatonin and its receptors in human pulpal tissues, and the contribution of melatonin on the antagonism of lipopolysaccharide (LPS)-infected pulpal fibroblasts.

Methods

Melatonin expression in pulpal tissues harvested from healthy teeth was investigated by immunohistochemical staining. Its receptors, melatonin receptor 1 (MT1) and melatonin receptor 2 (MT2), were also immunostained in pulpal tissues isolated from healthy teeth and inflamed teeth diagnosed with irreversible pulpitis. Morphometric analysis was subsequently performed. After LPS infection of cultured pulpal fibroblasts, cyclo-oxygenase (COX) and interleukin-1 β (IL-1 β) transcripts were examined by using reverse transcription-polymerase chain reaction (RT-PCR). Analysis of mRNA expression was performed to investigate an antagonism of LPS stimulation by melatonin via COX and IL-1 β induction. Mann-Whitney U test and One-way ANOVA were used for statistical analysis to determine a significance level.

Results

Melatonin was expressed in healthy pulpal tissue within the odontoblastic zone, cell-rich zone, and in the pulpal connective tissue. Furthermore, in health, strong MT1 and MT2 expression was distributed similarly in all 3 pulpal zones. In contrast, during disease, expression of MT2 was reduced in inflamed pulpal tissues (P-value< 0.001), but not MT1 (P-value = 0.559). Co-culturing of melatonin with LPS resulted in the reduction of COX-2 and IL-1 β expression in primary pulpal fibroblasts, indicating that melatonin may play an antagonistic role to LPS infection in pulpal fibroblasts.

Conclusions

Human dental pulp abundantly expressed melatonin and its receptors MT1 and MT2 in the odontoblastic layers and pulpal connective tissue layers. Melatonin exerted antagonistic activity against LPS-mediated COX-2 and IL-1 β induction in pulpal fibroblasts, suggesting its therapeutic potential for pulpal inflammation and a possible role of pulpal melatonin in an immunomodulation via functional melatonin receptors expressed in dental pulp.

Fisiopatología de los odontoblastos: una revisión

Los odontoblastos son células post-mitóticas de origen mesenquimal dispuestas en forma de palizada en la periferia de la pulpa dental y responsables de la formación de la dentina. Los odontoblastos derivan de la cresta neural y su diferenciación es la consecuencia de las interacciones epitelio-mesénquima entre las células de la papila dental y el epitelio dental interno. Este trabajo tiene como objetivo revisar los aspectos fisiológicos y patológicos de los odontoblastos, comprendiendo su origen, mecanismos de diferenciación y propiedades funcionales. Se realizó una búsqueda electrónica de literatura desde el año 2000 hasta Febrero de 2018, seleccionando 2889 artículos, de los cuales 52 artículos fueron analizados y discutidos. Los resultados exponen el origen, etapas y los factores relacionados con la diferenciación odontoblástica, junto con los aspectos principales de la organización estructural y funciones que desempeñan los odontoblastos. Esta revisión demuestra mediante la evidencia científica actual como los estudios concernientes a los odontoblastos se focalizan en comprender los mecanismos en la formación de la dentina reparativa, la respuesta inmunitaria y su rol en los procesos de inflamación y dolor. Trabajos futuros deberán esclarecer las diferentes señales involucradas en los procesos fisiopatológicos celulares y moleculares llevados a cabo por los odontoblastos. 

Metalloproteinase 14 (MMP-14) and hsa-miR-410-3p expression in human inflamed dental pulp and odontoblasts

The objective of this study is to evaluate MMP-14 expression in odontoblasts and in the bulk of dental pulp of teeth with pulpitis; to determine the expression of microRNA-410 (miR-410) in pulp tissue, since sequence analysis suggests that miR-410 has potential binding site on MMP-14’s 3′UTR, and hence, can regulate expression of the latter one. Tissue samples of dental pulp from teeth with pulpitis and healthy (control) were formalin fixed and paraffin embedded (FFPE). Samples were examined using immunohistochemical staining for MMP-14 and the expression of miR-410 was evaluated using qRT-PCR. In both, healthy and inflamed pulp odontoblasts stained more intensively than remaining pulp tissue, but this difference was not statistically significant. More positive staining was observed in inflamed pulps compared to healthy pulps. Expression of miR-410 was found significantly lower in inflamed pulps than in healthy ones. In the two examined zones, odontoblasts and remaining pulp, miR-410 was expressed on a similar level. No statistically significant correlation of miR-410 and MMP-14 expression was found. We showed that inflammation changes the MMP-14 expression in pulp tissue and odontoblasts. This study demonstrates for the first time miR-410 expression in human dental pulp and that expression of this microRNA was downregulated in inflamed dental pulp and odontoblasts.

Growth Factors and Cell Homing in Dental Tissue Regeneration

Purpose of Review

To summarize current views on the role and therapeutic potential of growth factors (GFs) within endodontic cell homing.

Recent Findings

Cell homing/revitalization techniques aim to regenerate dentin and pulp using endogenous cells. Clinically, revitalization has successfully created new vital tissue in necrotic permanent teeth with an open apex; however, there is no evidence of new odontoblasts, pulp tissue, or predictable extension in root length. Although the response is reparative rather than regenerative, exciting opportunities to improve these biologically-based strategies remain by (1) efficiently sequestering dentin-matrix-components (DMCs) using irrigants and dental materials (2) designing next-generation GF-releasing scaffold materials and (3) utilizing other sources of GF such as cells and plasma-rich plasma and plasma-rich fibrin.

Summary

GFs can promote reparative-dentinogenesis and pulp-like tissue formation. The future development and clinical approval of GF-functionalized-scaffolds is a priority; however, current focus should be to harness DMCs and target the interaction of stem cells and GFs.

The Effect of Chemically Modified Tetracycline-3 on the Progression of Dental Caries in Rats

OBJECTIVE

Matrix metalloproteinases (MMPs) exist in human saliva and dentin and play an important role in the degradation of organic matrix in teeth. Chemically modified tetracycline-3 (CMT-3) is an inhibitor of MMPs. CMT-3 has been used experimentally to treat caries since 1999, but no distinction between dental caries prevalence and dentin caries prevalence has been described.

METHODS

A total of 65 Sprague-Dawley rats were randomly divided into three groups. The positive control group (25 rats) was inoculated with Streptococcus mutans (ATCC700610) and fed the cariogenic feed of improved Keyes Diet 2000. The CMT-3 group (25 rats) was also inoculated with S. mutans and fed the cariogenic feed of improved Keyes Diet 2000; the surfaces of rats' molars were daily treated with 0.02% CMT-3. The negative control group (15 rats) was only fed the standard rodent chow. At the end of the 10th week, the dental caries prevalence and dentin caries prevalence of each group were calculated, and the regions of caries were assessed.

RESULTS

No caries was found in the negative control group. The dental caries prevalence of the CMT-3 and the positive control group was 75.0 and 83.3%, respectively (p > 0.05, Table 2). The dentin caries prevalence of the CMT-3 and the positive control group was 33.3 and 70.8%, respectively (p < 0.05, Table 2). The Keyes scoring of dentin caries in the CMT-3 group was significantly lower than that in the positive control group (p < 0.05, Table 3).

CONCLUSIONS

CMT-3 had no effect on the prevalence of dental caries, but could lower the prevalence and slow down the progression of dentin caries.

Microcomputed Tomography Evaluation of Dentine Mineral Concentration in Primary Molars Managed by Three Treatment Protocols

The objectives of the study were to quantify the dentine mineral concentration (DMC) in teeth restored conventionally, according to the atraumatic restorative treatment (ART) and ultraconservative (UCT) protocols (open cavities and small ART restorations), and the DMC underneath the open cavities of teeth managed by UCT versus nontreated, open cavities. We studied 50 teeth with restorations/open cavities, 39 restored teeth (9 by conventional restorative treatment [CRT], 17 by ART, and 13 by UCT) and 16 teeth with open cavities. Each restoration/open cavity was scanned using microcomputed tomography, with 3 hydroxyapatite disks with respective densities of 1.24, 1.33, and 1.57 g/cm3 as a reference. Images were reconstructed and the greyscale images were converted into DMC values. For each restoration/open cavity, 15 measurements of dentine immediately underneath and from the corresponding area in sound dentine were taken. DMC was expressed as a percentage of the DMC of sound dentine. ANOVA and the Student t test were used for statistical analysis. The mean DMC underneath restorations of the ART protocol group (98.93%) was statistically significantly higher than that of the UCT protocol group (91.98%), but not of the CRT protocol group (91.33%). On multiple surfaces, mean DMC in the axial area (94.32%) was statistically significantly higher than in the gingival area (92.80%). The mean DMC of open cavities managed by UCT protocol (89.05%) was statistically significantly higher than in nontreated open cavities (83.90%). In conclusion, a dentine-hypermineralized area underneath ART restorations was observed. Managing open cavities with a toothbrush and fluoride toothpaste (the UCT protocol) resulted in higher mineralized dentine underneath the cavity than in nontreated open cavities.

In situ analysis of gelatinolytic activity in human dentin

Matrix metalloproteinases (MMPs) such as gelatinases are differentially expressed in human tissues. These enzymes cleave specific substrates involved in cell signaling, tissue development and remodeling and tissue breakdown. Recent evidences show that gelatinases are crucial for normal dentin development and their activity is maintained throughout the entire tooth function in the oral cavity. Due to the lack of information about the exact location and activity of gelatinases in mature human dentin, the present study was designed to examine gelatinolytic levels in sound dentin. In situ zymography using confocal microscopy was performed on both mineralized and demineralized dentin samples. Sites presenting gelatinase activity were identified throughout the entire biological tissue pursuing different gelatinolytic levels for distinct areas: predentin and dentinal tubule regions presented higher gelatinolytic activity compared to intertubular dentin. Dentin regions with higher gelatinolytic activity immunohistochemically were partially correlated with MMP-2 expression. The maintenance of gelatinolytic activity in mature dentin may have biological implications related to biomineralization of predentin and tubular/peritubular dentinal regions, as well as regulation of defensive mechanisms of the dentin-pulp complex.

Regulation of Reactionary Dentine Formation

During the treatment of dental caries that has not penetrated the tooth pulp, maintenance of as much unaffected dentine as possible is a major goal during the physical removal of decayed mineral. Damage to dentine leads to release of fossilized factors (transforming growth factor-β [TGF-β] and bone morphogenic protein [BMP]) in the dentine that are believed to stimulate odontoblasts to secrete new "tertiary" dentine (reactionary dentine). This is formed on the pulpal surface of existing dentine and rethickens the dentine. We have previously shown that activation of Wnt/β-catenin signaling is pivotal for tooth repair in exposed pulp injury, and the pathway can be activated by small-molecule GSK-3 antagonists, resulting in enhanced reparative dentine formation. Here, we use a nonexposed pulp injury model to investigate the mechanisms of reactionary dentine formation in vivo, using small molecules to modulate the Wnt/β-catenin, TGF-β, and BMP pathways. We found that a local increase of Wnt activation at the injury site enhances reactionary dentine secretion. In addition, inhibition of TGF-β, BMP, or Wnt pathways does not impede reactionary dentine formation, although inhibition of TGF-β and/or BMP signaling does result in more disorganized, nontubular reactionary dentine. This suggests that Wnt/β-catenin signaling plays no major role in the formation of reactionary dentine, but in common with reparative dentine formation, exogenous elevation of Wnt/β-catenin signaling can enhance tertiary dentine formation. Release of latent TGF-β or BMPs from dentine is not required for the deposition of mineral to form reactionary dentine but does play a role in its organization.

The Histone-Deacetylase-Inhibitor Suberoylanilide Hydroxamic Acid Promotes Dental Pulp Repair Mechanisms Through Modulation of Matrix Metalloproteinase-13 Activity

Direct application of histone-deacetylase-inhibitors (HDACis) to dental pulp cells (DPCs) induces chromatin changes, promoting gene expression and cellular-reparative events. We have previously demonstrated that HDACis (valproic acid, trichostatin A) increase mineralization in dental papillae-derived cell-lines and primary DPCs by stimulation of dentinogenic gene expression. Here, we investigated novel genes regulated by the HDACi, suberoylanilide hydroxamic acid (SAHA), to identify new pathways contributing to DPC differentiation. SAHA significantly compromised DPC viability only at relatively high concentrations (5 μM); while low concentrations (1 μM) SAHA did not increase apoptosis. HDACi-exposure for 24 h induced mineralization-per-cell dose-dependently after 2 weeks; however, constant 14d SAHA-exposure inhibited mineralization. Microarray analysis (24 h and 14 days) of SAHA exposed cultures highlighted that 764 transcripts showed a significant >2.0-fold change at 24 h, which reduced to 36 genes at 14 days. 59% of genes were down-regulated at 24 h and 36% at 14 days, respectively. Pathway analysis indicated SAHA increased expression of members of the matrix metalloproteinase (MMP) family. Furthermore, SAHA-supplementation increased MMP-13 protein expression (7 d, 14 days) and enzyme activity (48 h, 14 days). Selective MMP-13-inhibition (MMP-13i) dose-dependently accelerated mineralization in both SAHA-treated and non-treated cultures. MMP-13i-supplementation promoted expression of several mineralization-associated markers, however, HDACi-induced cell migration and wound healing were impaired. Data demonstrate that short-term low-dose SAHA-exposure promotes mineralization in DPCs by modulating gene pathways and tissue proteases. MMP-13i further increased mineralization-associated events, but decreased HDACi cell migration indicating a specific role for MMP-13 in pulpal repair processes. Pharmacological inhibition of HDAC and MMP may provide novel insights into pulpal repair processes with significant translational benefit. J. Cell. Physiol. 231: 798-816, 2016. © 2015 Wiley Periodicals, Inc.

Distribution of Cathepsin K in Late Stage of Tooth Germ Development and Its Function in Degrading Enamel Matrix Proteins in Mouse

Cathepsin K (CTSK) is a member of cysteine proteinase family, and is predominantly expressed in osteoclastsfor degradationof bone matrix proteins. Given the similarity in physical properties of bone and dental mineralized tissues, including enamel, dentin and cementum, CTSK is likely to take part in mineralization process during odontogenesis. On the other hand, patients with pycnodysostosis caused by mutations of the CTSK gene displayedmultipledental abnormalities, such as hypoplasia of the enamel, obliterated pulp chambers, hypercementosis and periodontal disease. Thereforeitis necessary to study the metabolic role of CTSK in tooth matrix proteins. In this study, BALB/c mice at embryonic day 18 (E18), post-natal day 1 (P1), P5, P10 and P20 were used (5 mice at each time point)for systematic analyses of CTSK expression in the late stage of tooth germ development. We found that CTSK was abundantly expressed in the ameloblasts during secretory and maturation stages (P5 and P10) by immunohistochemistry stainings.During dentinogenesis, the staining was also intense in the mineralization stage (P5 and P10),but not detectable in the early stage of dentin formation (P1) and after tooth eruption (P20).Furthermore, through zymography and digestion test in vitro, CTSK was proved to be capable of hydrolyzing Emdogain and also cleaving Amelogenininto multiple products. Our resultsshed lights on revealing new functions of CTSK and pathogenesis of pycnodysostosis in oral tissues.

Transforming growth factor beta 1 increases collagen content, and stimulates procollagen I and tissue inhibitor of metalloproteinase-1 production of dental pulp cells: Role of MEK/ERK and activin receptor-like kinase-5/Smad signaling

BACKGROUND/PURPOSE

In order to clarify the role of transforming growth factor beta 1 (TGF-β1) in pulp repair/regeneration responses, we investigated the differential signaling pathways responsible for the effects of TGF-β1 on collagen turnover, matrix metalloproteinase-3 (MMP-3), and tissue inhibitor of metalloproteinase-1 (TIMP-1) production in human dental pulp cells.

METHODS

Pulp cells were exposed to TGF-β1 with/without pretreatment and coincubation by 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenyl mercapto)butadiene (U0126; a mitogen-activated protein kinase kinase [MEK]/extracellular signal-regulated kinase [ERK] inhibitor) and 4-(5-benzol[1,3]dioxol-5-yl-4-pyrldin-2-yl-1H- imidazol-2-yl)-benzamide hydrate (SB431542; an activin receptor-like kinase-5/Smad signaling inhibitor). Sircol collagen assay was used to measure cellular collagen content. Culture medium procollagen I, TIMP-1, and MMP-3 levels were determined by enzyme-linked immunosorbent assay.

RESULTS

TGF-β1 increased the collagen content, procollagen I, and TIMP-1 production, but slightly decreased MMP-3 production of pulp cells. SB431542 and U0126 prevented the TGF-β1-induced increase of collagen content and TIMP-1 production of dental pulp cells.

CONCLUSION

These results indicate that TGF-β1 may be involved in the healing/regeneration processes of dental pulp in response to injury by stimulation of collagen and TIMP-1 production. These events are associated with activin receptor-like kinase-5/Smad2/3 and MEK/ERK signaling.

High pH-Sensitive TRPA1 Activation in Odontoblasts Regulates Mineralization

Calcium hydroxide and mineral trioxide aggregate are widely used for indirect and direct pulp capping and root canal filling. Their dissociation into Ca(2+) and OH(-) in dental pulp creates an alkaline environment, which activates reparative/reactionary dentinogenesis. However, the mechanisms by which odontoblasts detect the pH of the extracellular environment remain unclear. We examined the alkali-sensitive intracellular Ca(2+) signaling pathway in rat odontoblasts. In the presence or absence of extracellular Ca(2+), application of alkaline solution increased intracellular Ca(2+) concentration, or [Ca(2+)]i Alkaline solution-induced [Ca(2+)]i increases depended on extracellular pH (8.5 to 10.5) in both the absence and the presence of extracellular Ca(2+) The amplitude was smaller in the absence than in the presence of extracellular Ca(2+) Each increase in [Ca(2+)]i, activated by pH 7.5, 8.5, or 9.5, depended on extracellular Ca(2+) concentration; the equilibrium binding constant for extracellular Ca(2+) concentration decreased as extracellular pH increased (1.04 mM at pH 7.5 to 0.11 mM at pH 9.5). Repeated applications of alkaline solution did not have a desensitizing effect on alkali-induced [Ca(2+)]i increases and inward currents. In the presence of extracellular Ca(2+), alkaline solution-induced [Ca(2+)]i increases were suppressed by application of an antagonist of transient receptor potential ankyrin subfamily member 1 (TRPA1) channels. Ca(2+) exclusion efficiency during alkaline solution-induced [Ca(2+)]i increases was reduced by a Na(+)-Ca(2+) exchanger antagonist. Alizarin red and von Kossa staining revealed increased mineralization levels under repeated high pH stimulation, whereas the TRPA1 antagonist strongly reduced this effect. These findings indicate that alkaline stimuli-such as the alkaline environment inside dental pulp treated with calcium hydroxide or mineral trioxide aggregate-activate Ca(2+) mobilization via Ca(2+) influx mediated by TRPA1 channels and intracellular Ca(2+) release in odontoblasts. High pH-sensing mechanisms in odontoblasts are important for activating dentinogenesis induced by an alkaline environment.

Effect of sealing infected dentin with glass ionomer cement on the abundance and localization of MMP-2, MMP-8, and MMP-9 in young permanent molars in vivo

BACKGROUND

The study of MMPs' behavior in carious lesions contributes to the understanding of the mechanisms involved in dentin reorganization after restoration.

AIM

To compare the abundance and localization of MMPs 2, 8, and 9 in infected dentin before and after restoration.

DESIGN

The sample consisted of 23 young permanent molars with active deep carious lesions. Infected carious dentin samples were collected from the same tooth at baseline and 60 days after cavity lining with GIC and composite resin restoration and processed for immunohistochemistry assays. After digital images were obtained, two calibrated operators analyzed the samples according to the immunostaining intensity and the MMPs' localization. Chi-square test was used for statistical analysis.

RESULTS

The intensity of immunostaining for MMP-8 was reduced after 60 days (P = 0.02), and no difference was observed for MMP-2 (P = 0.32) and MMP-9 (P = 0.14). The MMPs' distribution was generalized in the intertubular dentin and absent or located in the intratubular dentin, regardless of the period.

CONCLUSION

The sealing of infected carious dentin in young permanent molars reduced the expression of MMP-8, which is consistent with the initial remodeling process of the dentin matrix.

Changes in dermal matrix in the absence of Rac1 in keratinocytes

Keratinocytes, in response to irritants, secrete pro-inflammatory mediators which recruit and activate immune and mesenchymal cells, including fibroblasts, to repair the skin. Fibroblasts respond by synthesising collagen and promoting the crosslinking extracellular matrix (ECM). We recently showed that the deletion of Rac1 in keratinocytes causes heightened inflammation due to aberrant crosstalk with immune cells. Indeed, the skin of these mice shows a higher inflammatory response to the induction of irritant contact dermatitis (ICD), and also even to treatment with a vehicle alone, compared with controls. As inflammation is intimately linked with fibrotic disease in the skin, this raised the question as to whether this deletion may also affect the deposition and arrangement of the dermal ECM. This study assessed the effects of Rac1 deletion in keratinocytes and of the heightened inflammatory status by induction of ICD on the tissue localisation and arrangements of dermal collagen. Qualitative analysis did not reveal evidence for the formation of pathologies in the dermis. However, quantitative analysis did reveal some perturbations in the dermal matrix, namely that only the combination of the lack of Rac1 and ICD affects the architectural organisation of the dermal collagen, and that a higher inflammatory state in the tissue (i.e. when Rac1 is deleted in the keratinocytes or ICD is induced in the skin, or a combination of both) influences the diameter of the collagen fibrils. It is proposed that this increase in the diameter of collagen fibrils due to inflammation may serve as pre-fibrotic marker enabling earlier determination of fibrosis and earlier treatment. This study has revealed previously unknown effects on the ECM due to the deletion of Rac1 in keratinocytes.

Clinical, mineral and ultrastructural changes in carious dentin of primary molars after restoration

INTRODUCTION

Partial caries removal has been shown to be an effective method to treat deep carious lesions in deciduous teeth. Nevertheless, the possibility of keeping infected dentin in the cavity still requires additional investigation. The objective of this research was to describe changes in primary infected dentin after restoration with glass ionomer cement.

METHODS

Dentin from 45 primary molars with deep and active carious lesions was evaluated using clinical and laboratory criteria, before and 60 days after restoration. The clinical analysis evaluated dentin colour (CO), dentin consistency (COS) and laser fluorescence (LF). The laboratory procedures assessed bacterial contamination and mineral content (MC), and evaluated the dentin ultrastructure and collagen content. Data on CO, COS, LF and colony forming units were analysed using the Wilcoxon signed-rank test; MC, bacterial counts and collagen evaluations were evaluated using the Student's t-test.

RESULTS

After 60 days, lower values of LF were observed, together with a lower bacterial count, and a higher COS was found, with an increase in calcium, phosphorus and collagen contents. Differences were not detected for CO or for fluorine content. Baseline samples showed enlarged tubules with bacterial invasion; 60-day samples showed better organised tissue, with a more compact intertubular dentin and narrower tubules.

CONCLUSION

It is concluded that appropriate cavity sealing can promote beneficial changes in deep carious lesions of primary teeth, even in the presence of infected dentin.

Bonding Strategies of Resin Cement to Er, Cr:YSGG Lased Dentin: Micro-CT Evaluation and Microshear Bond Strength Testing

Aims

Pretreatment of the tooth surface is essential for establishing effective micromechanical retention between it and the restoration. The purpose of this study was to evaluate the bond strength between the resin and the Er, Cr:YSGG laser irradiated dentin and to examine morphologic characterization of the dentin-resin interface. In addition, the study evaluated the quantity of opened and closed dentinal tubules.

Subjects and Methods

Thirty extracted human molars were sectioned into samples of 1 mm thickness. The samples were randomly assigned to two groups containing 15 specimens each. Surface treatments were not applied to the samples in the control group and the samples in the experimental group were irradiated with an Er,Cr:YSGG laser. Two resin cement samples were polymerized on the surface of each sliced dentin. The micro-shear bond strength (μSBS) between dentin and cement (n = 30 for each group) was measured with a universal testing machine. The topography and morphology of the resin-dentin interface were evaluated by micro-CT (n = 20 for each group). The areas of closed tubular space, closed porosity, area of open tubular space, open porosity, total area of tubular space and fractal dimension were investigated by micro-CT. Statistical analysis used: The data for each parameter were analyzed by Shapiro-Wilk and Student's t test (p<0.05).

Results

μSBS values for control group were higher than experimental group. Dentin surfaces in the control group revealed less closed and more opened dentin tubules compared to the experimental group. Total area of tubular space was found to have decreased due to the laser ablation. There was no significant difference between the fractal dimensions of the control and experimental groups.

Conclusions

The lased dentin surface was not favorable for the bonding mechanism due to alterations in the dentinal structure.

Release of bio-active dentine extracellular matrix components by histone deacetylase inhibitors (HDACi)

AIM

To characterize dentine matrix component (DMC) release and smear layer removal by histone deacetylase inhibitors (HDACis).

METHODOLOGY

DMCs were extracted from powdered human dentine over 14 days using three HDACis, valproic acid (VPA), trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA) and compared with a control extractant, 10% (w/v) EDTA. Protein compositions of the resultant extracts were analysed by 1D-polyacrylamide gel electrophoresis (1D-PAGE), TGF-β-1 and MMP-9 ELISAs and a high-throughput growth factor antibody array. Dentine discs with a standardized smear layer were prepared from human molars and treated with EDTA (17% w/v), polyacrylic acid (PA) (20% v/v) and the experimental HDACis prior to analysis by scanning electron microscopy. Parametric ELISA data were analysed using one-way anova and Tukey's post hoc test, whilst nonparametric smear layer data were analysed by Kruskal-Wallis test and Mann-Whitney U-test (P < 0.05).

RESULTS

HDACis did not remove smear layer in the presence or absence of PA pre-treatment (P ≥ 0.478). 1D-PAGE analysis demonstrated different protein profiles for EDTA and HDACi extracts. All HDACi solutions released TGF-β-1 although less effectively than EDTA (P < 0.001), whilst MMP-9 was extracted in significantly higher concentration by EDTA and VPA compared with TSA (P < 0.012). Antibody array analysis demonstrated the ability of HDACis to extract a complex cocktail of established/novel growth factors from dentine, albeit significantly less efficiently than EDTA for certain cytokines (TGF-β-1, PDGF-AA, VEGF-A) and significantly more effectively for others (GDF-15, IGF-1, EGRF-1, NGFR, BDNF, SCF-R).

CONCLUSIONS

HDACi release a range of bioactive DMCs that could promote dentine repair processes in vivo; however, they are ineffective at removing smear layer.

Matrix metalloproteinase 14 modulates signal transduction and angiogenesis in the cornea

The cornea is transparent and avascular, and retention of these characteristics is critical to maintaining vision clarity. Under normal conditions, wound healing in response to corneal injury occurs without the formation of new blood vessels; however, neovascularization may be induced during corneal wound healing when the balance between proangiogenic and antiangiogenic mediators is disrupted to favor angiogenesis. Matrix metalloproteinases (MMPs), which are key factors in extracellular matrix remodeling and angiogenesis, contribute to the maintenance of this balance, and in pathologic instances, can contribute to its disruption. Here, we elaborate on the facilitative role of MMPs, specifically MMP-14, in corneal neovascularization. MMP-14 is a transmembrane MMP that is critically involved in extracellular matrix proteolysis, exosome transport, and cellular migration and invasion, processes that are critical for angiogenesis. To aid in developing efficacious therapies that promote healing without neovascularization, it is important to understand and further investigate the complex pathways related to MMP-14 signaling, which can also involve vascular endothelial growth factor, basic fibroblast growth factor, Wnt/β-catenin, transforming growth factor, platelet-derived growth factor, hepatocyte growth factor or chemokines, epidermal growth factor, prostaglandin E2, thrombin, integrins, Notch, Toll-like receptors, PI3k/Akt, Src, RhoA/RhoA kinase, and extracellular signal-related kinase. The involvement and potential contribution of these signaling molecules or proteins in neovascularization are the focus of the present review.

Matrix metalloproteinases and other matrix proteinases in relation to cariology: the era of 'dentin degradomics'

Dentin organic matrix, with type I collagen as the main component, is exposed after demineralization in dentinal caries, erosion or acidic conditioning during adhesive composite restorative treatment. This exposed matrix is prone to slow hydrolytic degradation by host collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins. Here we review the recent findings demonstrating that inhibition of salivary or dentin endogenous collagenolytic enzymes may provide preventive means against progression of caries or erosion, just as they have been shown to retain the integrity and improve the longevity of resin composite filling bonding to dentin. This paper also presents the case that the organic matrix in caries-affected dentin may not be preserved as intact as previously considered. In partially demineralized dentin, MMPs and cysteine cathepsins with the ability to cleave off the terminal non-helical ends of collagen molecules (telopeptides) may lead to the gradual loss of intramolecular gap areas. This would seriously compromise the matrix ability for intrafibrillar remineralization, which is considered essential in restoring the dentin's mechanical properties. More detailed data of the enzymes responsible and their detailed function in dentin-destructive conditions may not only help to find new and better preventive means, but better preservation of demineralized dentin collagenous matrix may also facilitate true biological remineralization for the better restoration of tooth structural and mechanical integrity and mechanical properties.

Dentin bonding: can we make it last?

In dentin bonding, contemporary dental adhesive systems rely on formation of the hybrid layer, a biocomposite containing dentin collagen and polymerized resin adhesive. They are usually able to create at least reasonable integrity of the hybrid layer with high immediate bond strength. However, loss of dentin-bonded interface integrity and bond strength is commonly seen after aging both in vitro and in vivo. This is due to endogenous collagenolytic enzymes, matrix metalloproteinases, and cysteine cathepsins, responsible for the time-dependent loss of hybrid layer collagen. In addition, the hydrophilic nature of adhesive systems creates problems that lead to suboptimal hybrid layers. These problems include, for example, insufficient resin impregnation of dentin, phase separation, and a low rate of polymerization, all of which may reduce the longevity of the bonded interface. Preservation of the collagen matrix integrity by inhibition of endogenous dentin proteases is key to improving dentin bonding durability. Several approaches to retain the integrity of the hybrid layer and to improve the long-term dentin bond strength have been tested. These include the use of enzyme inhibitors, either separately or as incorporated into the adhesive resins; increase of collagen resistance to enzymatic degradation; and elimination of water from the interface to slow down or eliminate hydrolytic loss of the hybrid layer components. This review looks at the principles, current status, and future of the different techniques designed to prevent the loss of hybrid layer and bond strength.

Role of dentin MMPs in caries progression and bond stability

Dentin can be described as a biological composite with collagen matrix embedded with nanosized hydroxyapatite mineral crystallites. Matrix metalloproteinases (MMPs) and cysteine cathepsins are families of endopeptidases. Enzymes of both families are present in dentin and collectively capable of degrading virtually all extracellular matrix components. This review describes these enzymes and their presence in dentin, mainly focusing on their role in dentin caries pathogenesis and loss of collagen in the adhesive hybrid layer under composite restorations. MMPs and cysteine cathepsins present in saliva, mineralized dentin, and/or dentinal fluid may affect the dentin caries process at the early phases of demineralization. Changes in collagen and noncollagenous protein structure may participate in observed decreases in mechanical properties of caries-affected dentin and reduce the ability of caries-affected dentin to remineralize. These endogenous enzymes also remain entrapped within the hybrid layer during the resin infiltration process, and the acidic bonding agents themselves (irrespective of whether they are etch-and-rinse or self-etch) can activate these endogenous protease proforms. Since resin impregnation is frequently incomplete, denuded collagen matrices associated with free water (which serves as a collagen cleavage reagent for these endogenous hydrolase enzymes) can be enzymatically disrupted, finally contributing to the degradation of the hybrid layer. There are multiple in vitro and in vivo reports showing that the longevity of the adhesive interface is increased when nonspecific enzyme-inhibiting strategies are used. Different chemicals (i.e., chlorhexidine, galardin, and benzalkonium chloride) or collagen cross-linker agents have been successfully employed as therapeutic primers in the bonding procedure. In addition, the incorporation of enzyme inhibitors (i.e., quaternary ammonium methacrylates) into the resin blends has been recently promoted. This review will describe MMP functions in caries and hybrid layer degradation and explore the potential therapeutic role of MMP inhibitors for the development of improved intervention strategies for MMP-related oral diseases.

Soluble toll like receptor 2 (TLR-2) is increased in saliva of children with dental caries

Background

Dental caries is the most common microbial disease affecting mankind. Caries risk assessment methods, identification of biomarkers and vaccine development strategies are being emphasized to control the incidence of the largely preventable disease. Pattern recognition receptors such as the toll like receptors (TLR) have been implicated as modulators of host-microbial interactions. Soluble TLR-2 and its co-receptor, CD14 identified in saliva can bind the cell wall components of cariogenic bacteria and modulate the disease process. The objective of this study is to determine the potential of salivary sTLR-2 and sCD14 as biomarkers of caries activity and indirect measures of the cariogenic bacterial burden.

Methods

Unstimulated whole saliva was collected from twenty caries free and twenty caries active children between the ages of 5 and 13 years. The concentration of sCD14 and sTLR-2 together with that of the cytokine IL-8 reported to be increased in dental caries was assessed by the enzyme linked immunosorbent assay.

Results

While the level of sCD14 and that of IL-8 was equivocal between the two groups, the sTLR-2 concentration in caries active saliva was significantly higher than that in caries free saliva.

Conclusions

The sTLR-2 in saliva could serve as a potential biomarker for caries activity.

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.

Reactionary Dentinogenesis and Neuroimmune Response in Dental Caries

Reactionary dentin formation is an adaptive secretory response mediated by odontoblasts to moderate dentin injury. The implications of this process for neuroimmune interactions operating to contain pathogens have not been fully appreciated. The purpose of the present study was to describe the relationship between reactionary dentinogenesis, the neurogenic changes of dental pulp innervation, and dendritic cell recruitment to caries progression, using a comparative immunohistochemical approach in human teeth from young adult individuals. Reactionary dentin formation during dentin caries progression is associated with changes in the integrity of junctional complexes within the odontoblast layer. Diminished coexpression of Cx43 and zonula occludens 1 implies a reduced level of intercellular connectivity between odontoblasts. Dentin caries also causes overexpression of growth-associated protein 43, a modulator of neural plasticity that promotes extensive sprouting of nerve endings into the reactionary dentin matrix. At the same time, an elevated number of HLA-DR-positive dendritic cells infiltrate the odontoblast layer and subsequently invade reactionary dentin formed underneath the early caries-affected regions. Simultaneous odontoblast layer remodeling, nerve fiber sprouting, and activation of dendritic cells during caries progression suggest a coordinated neuroimmune response to fight caries pathogen invasion and to promote dentin-pulp healing. We propose that reactionary dentin formation hinders pathogen invasion and supports defensive neuroimmune interactions against infection. The eventual understanding of this complex scenario may contribute to the development of novel approaches to dental caries treatment.

Mature human odontoblasts express virus-recognizing toll-like receptors

AIM

To study the expression of toll-like receptors (TLR) -3, -7, -8 and -9 as well as interferon receptors alpha and gamma (IFNAR1/IFNAR2 and IFNGR1/IFNGR2), which play important roles in the defence against viruses.

METHODOLOGY

DNA microarray and quantitative PCR analyses of TLR3, -7, -8 and -9 as well as IFNAR1/IFNAR2 and IFNGR1/IFNGR2 genes in mature native human odontoblasts and pulp were performed. Immunohistochemistry was used to confirm TLR8 protein in odontoblasts of healthy and carious human teeth.

RESULTS

TLR3, -7, -8 and -9 mRNAs were detected both in odontoblasts and in pulp, but TLR8 expression level was higher in the odontoblasts. IFNAR and IFNGR expression was observed in both tissues. Immunohistochemical analysis of healthy teeth revealed positive TLR8 staining in the pre-dentine and the dentine but varying staining patterns in the different portions of tooth. Lighter TLR8 staining was observed in dentine of mildly carious teeth. In teeth with carious lesions extending into the mid-dentine, only very weak staining was detected.

CONCLUSIONS

The finding of these virus-recognition-related genes in odontoblasts strengthens the view that odontoblasts participate in the immune response of the dentine-pulp complex.

Abundance of MMPs and Cysteine Cathepsins in Caries-affected Dentin

Degradation of dentin matrix components within caries dentin has been correlated with the activity of host-derived proteases, such as matrix metalloproteases (MMPs) and cysteine cathepsins (CTs). Since this relationship has not been fully established, we hypothesized that the abundance of MMPs and CTs in caries-affected dentin must be higher than in intact dentin. To test this premise, we obtained 5 slices (200 µm) from 5 intact teeth and from 5 caries-affected teeth (1 slice/tooth) and individually incubated them with primary antibodies for CT-B, CT-K, MMP-2, or MMP-9. Negative controls were incubated with pre-immune serum. Specimens were washed and re-incubated with the respective fluorescent secondary antibody. Collagen identification, attained by the autofluorescence capture technique, and protease localization were evaluated by multi-photon confocal microscopy. The images were analyzed with ZEN software, which also quantitatively measured the percentages of collagen and protease distribution in dentin compartments. The abundance of the test enzymes was markedly higher in caries-affected than in intact dentin. CT-B exhibited the highest percentage of co-localization with collagen, followed by MMP-9, MMP-2, and CT-K. The high expression of CTs and MMPs in caries-affected teeth indicates that those host-derived enzymes are intensely involved with caries progression.

Effects of industrial noise on circumpulpar dentin--a field emission scanning electron microscopy and energy dispersive spectroscopy analysis

Chronic exposure to Industrial Noise (IN), rich in Low Frequency Noise (LFN), causes systemic fibrotic transformation and sustained stress. Dental wear, significantly increased with exposure to LFN, affects the teeth particularly through the circumpulpar dentin. Our goal is to understand the consequences of IN exposure on the circumpulpar dentin of Wistar rats. 10 Wistar rats were exposed to IN for 4 months, according to an occupationally simulated time schedule and 10 animals were used as age-matched controls. The first and the second upper and lower molars of each animal were processed for observation by Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Spectroscopy (EDS) analysis was performed. In exposed animals FESEM showed a 2.0 to 6.0 μm-dense mineral band between dentin and the pulp with no regular continuity with the tubules. This structure had a few tubules where the odontoblasts processes could be observed embedded within the band and collagen fibers were trapped inside. EDS analysis revealed that it was hydroxyapatite similar to dentin, with a higher carbon content. FESEM results show that the band may be tertiary reparative dentin formed by odontoblast-like cells, but the increased amount of carbon (EDS) could mean that it is sclerotic dentin. IN should be acknowledge as a strong stimulus, able to cause an injury to odontoblasts and to the formation of reparative tertiary dentin, in a process that may accelerate the aging of the teeth, either by direct impact of acoustic pressure pulsations or by increased stress and dental wear.

Dentin matrix degradation by host matrix metalloproteinases: inhibition and clinical perspectives toward regeneration

Bacterial enzymes have long been considered solely accountable for the degradation of the dentin matrix during the carious process. However, the emerging literature suggests that host-derived enzymes, and in particular the matrix metalloproteinases (MMPs) contained in dentin and saliva can play a major role in this process by their ability to degrade the dentin matrix from within. These findings are important since they open new therapeutic options for caries prevention and treatment. The possibility of using MMP inhibitors to interfere with dentin caries progression is discussed. Furthermore, the potential release of bioactive peptides by the enzymatic cleavage of dentin matrix proteins by MMPs during the carious process is discussed. These peptides, once identified, may constitute promising therapeutical tools for tooth and bone regeneration.

Structural analysis of reactionary dentin formed in response to polymicrobial invasion

In response to microbial invasion of dentin odontoblasts secrete an altered calcified matrix termed reactionary dentin (Rd). 3D reconstruction of focused-ion-beam scanning electron microscopy (FIB-SEM) image slices revealed helical tubular structures in Rd that contrasted with regular cylindrical tubules characteristic of dentin from healthy teeth and affected so-called physiological dentin (Pd) lying exterior to Rd. This helical structure in Rd provided effective constriction of tubule lumen diameter that formed a barrier to bacterial advance towards the dental pulp. SEM of resin cast preparations revealed altered extension of odontoblast processes through Rd. The distribution of key mineral elements was studied by combination of 3D reconstruction of focused-ion-beam based X-ray microanalysis (FIB-EDS), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). There was a marked redistribution of calcium and phosphorous in Rd together with an increase of diffusely deposited magnesium compatible with the mineral deposition phase of synthesis of this altered matrix. Changes in tubule structure and mineral content characteristic of Rd are consistent with reduced hardness and lower elastic modulus reported for this matrix. Findings provide insight into the unique structure of Rd synthesised as a primary response to infection.

Optimizing dentin bond durability: control of collagen degradation by matrix metalloproteinases and cysteine cathepsins

OBJECTIVES

Contemporary adhesives lose their bond strength to dentin regardless of the bonding system used. This loss relates to the hydrolysis of collagen matrix of the hybrid layers. The preservation of the collagen matrix integrity is a key issue in the attempts to improve the dentin bonding durability.

METHODS

Dentin contains collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins, which are responsible for the hydrolytic degradation of collagen matrix in the bonded interface.

RESULTS

The identities, roles and function of collagenolytic enzymes in mineralized dentin has been gathered only within last 15 years, but they have already been demonstrated to have an important role in dental hard tissue pathologies, including the degradation of the hybrid layer. Identifying responsible enzymes facilitates the development of new, more efficient methods to improve the stability of dentin-adhesive bond and durability of bond strength.

SIGNIFICANCE

Understanding the nature and role of proteolytic degradation of dentin-adhesive interfaces has improved immensely and has practically grown to a scientific field of its own within only 10 years, holding excellent promise that stable resin-dentin bonds will be routinely available in a daily clinical setting already in a near future.