The pulp healing process: from generation to regeneration

Direct pulp capping procedures - Evidence and practice

The aim of direct pulp capping (DPC) is to promote pulp healing and mineralized tissue barrier formation by placing a dental biomaterial directly over the exposed pulp. Successful application of this approach avoids the need for further and more extensive treatment. In order to ensure a complete pulp healing with the placement of restorative materials, a mineralized tissue barrier must form to protect the pulp from microbial invasion. The formation of mineralized tissue barrier can only be induced when there is a significant reduction in pulp inflammation and infection. Consequently, promoting the healing of pulp inflammation may provide a favorable therapeutic opportunity to maintain the sustainability of DPC treatment. Mineralized tissue formation was observed as the favorable reaction of exposed pulp tissue against a variety of dental biomaterials utilized for DPC. This observation reveals an intrinsic capacity of pulp tissue for healing. Therefore, this review focuses on the DPC and its healing procedure as well as the materials used for DPC treatment and their mechanisms of action to promote pulpal healing. In addition, the factors that can affect the healing process of DPC, clinical considerations and future perspective has been described.

Nano eggshell-based slurry as a direct pulp-capping material: In vitro characterization and histopathological assessment in an experimental animal model

AIM

Pulp vitality is essential for tooth integrity. Following pulp exposure, choosing a suitable pulp-capping material is crucial to maintain pulp vitality. However, the reparative dentine bridge created by calcium hydroxide (Ca(OH)2 ) is generally porous and incomplete. The aim of the current study is to assess the in vitro and in vivo bioactivities of nano eggshell-based slurry (NES), using NES as a direct pulp-capping material, compared with Ca(OH)2 in rabbit animal model.

METHODOLOGY

Nano eggshell powder (NE) was characterized for particle morphology, chemical composition and ion release. In vitro bioactivity was tested by immersion in simulated body fluid (SBF) for 7 days. For histopathological evaluation, 36 adult New Zealand rabbits (72 pulp exposures) were divided into nine groups (n = 8) according to the pulp-capping material (NES, Ca(OH)2 and no capping as negative control group) and the animals were sacrificed after 7, 14 or 28 days. The pulps of the two lower central incisors were exposed and then directly capped by Ca(OH)2 or NES or left untreated. The cavities were then sealed with glass ionomer cement. Teeth were collected for histopathological evaluation using an optical microscope. Pulp haemorrhage, inflammation, fibrosis and calcific bridge formation were assessed. Results were statistically analysed using anova and Tukey's tests.

RESULTS

Nano eggshell particles were spherical with a 20 nm diameter and were composed mainly of calcite. Statistical analysis showed that there was a significant increase in the release of all investigated ions between days 1 and 28, except for copper. NES group showed a significantly higher release of all elements as compared to Ca(OH)2 . Environmental scanning electron microscope micrographs of NES incubated for 7 days in SBF showed the formation of HAp with a Ca/P ratio (1.686). For histopathological evaluation, the difference between groups was statistically significant. At day 28, 75% of the pulps of the Ca(OH)2 group showed mild calcific bridge in comparison with 100% moderate calcific bridge in the NES group. The NES group showed significantly less inflammation at days 7 and 28, and higher fibrosis at day 7 compared with Ca(OH)2 .

CONCLUSIONS

Nano eggshell-based slurry represents a promising novel direct pulp-capping material with favourable pulp tissue response.

Facilitating Reparative Dentin Formation Using Apigenin Local Delivery in the Exposed Pulp Cavity

Apigenin, a natural product belonging to the flavone class, affects various cell physiologies, such as cell signaling, inflammation, proliferation, migration, and protease production. In this study, apigenin was applied to mouse molar pulp after mechanically pulpal exposure to examine the detailed function of apigenin in regulating pulpal inflammation and tertiary dentin formation. In vitro cell cultivation using human dental pulp stem cells (hDPSCs) and in vivo mice model experiments were employed to examine the effect of apigenin in the pulp and dentin regeneration. In vitro cultivation of hDPSCs with apigenin treatment upregulated bone morphogenetic protein (BMP)- and osteogenesis-related signaling molecules such as BMP2, BMP4, BMP7, bone sialoprotein (BSP), runt-related transcription factor 2 (RUNX2), and osteocalcin (OCN) after 14 days. After apigenin local delivery in the mice pulpal cavity, histology and cellular physiology, such as the modulation of inflammation and differentiation, were examined using histology and immunostainings. Apigenin-treated specimens showed period-altered immunolocalization patterns of tumor necrosis factor (TNF)-α, myeloperoxidase (MPO), NESTIN, and transforming growth factor (TGF)-β1 at 3 and 5 days. Moreover, the apigenin-treated group showed a facilitated dentin-bridge formation with few irregular tubules after 42 days from pulpal cavity preparation. Micro-CT images confirmed obvious dentin-bridge structures in the apigenin-treated specimens compared with the control. Apigenin facilitated the reparative dentin formation through the modulation of inflammation and the activation of signaling regulations. Therefore, apigenin would be a potential therapeutic agent for regenerating dentin in exposed pulp caused by dental caries and traumatic injury.

Local Drug Delivery Systems for Vital Pulp Therapy: A New Hope

Vital pulp therapy (VPT) is deliberated as an ultraconservative/minimally invasive approach for the conservation of vital pulpal tissues, preservation of dental structure, and maintenance of tooth function in the oral cavity. In VPT, following the exposure of the dental pulp, the environment is prepared for the possible healing and probable refunctionalisation of pulpal connective tissue. However, to succeed in VPT, specific biomaterials are used to cover and/or dress the exposed pulp, lower the inflammation, heal the dental pulp, provoke the remaining odontoblastic cells, and induce the formation of a hard tissue, i.e., the dentinal bridge. It can be assumed that if the employed biomaterial is transferred to the target site using a specially designed micro-/nanosized local drug delivery system (LDDS), the biomaterial would be placed in closer proximity to the connective tissue, may be released in a controlled and sustained pattern, could properly conserve the remaining dental pulp and might appropriately enhance hard-tissue formation. Furthermore, the loaded LDDS could help VPT modalities to be more ultraconservative and may minimise the manipulation of the tooth structure as well as pulpal tissue, which could, in turn, result in better VPT outcomes.

Minimal Intervention in Dentistry: A Literature Review on Biodentine as a Bioactive Pulp Capping Material

Root canal treatment has been the treatment of choice for carious pulp exposures. In the perspective of minimally invasive dentistry and preventive endodontics, a direct pulp capping procedure with a reliable bioactive material may be considered an alternative approach provided that the pulp status is favorable. However, the treatment of pulp exposure by pulp capping is still a controversial issue with no clear literature available on this topic, leaving the concerned practitioner more confused than satisfied. Biodentine is a relatively new bioactive material explored for vital pulp therapy procedures. This article discusses its role in direct pulp capping procedures. A thorough literature search of the database was done using PubMed, Google Scholar, and Scopus using the keywords preventive endodontics, calcium silicate cement, direct pulp capping, Biodentine, and vital pulp therapy. Reference mining of the articles that were identified was used to locate other papers and enrich the findings. No limits were imposed on the year of publication, but only articles in English were considered. This paper is aimed at reviewing the current literature on Biodentine as a direct pulp capping material. The review will provide a better understanding of Biodentine's properties and can aid in the decision-making process for maintaining the vitality of exposed dental pulp with minimal intervention.

Comparative assessment of titanium-prepared platelet-rich fibrin, EndoSequence root repair material, and calcium hydroxide as pulpotomy agents in permanent teeth with irreversible pulpitis: A randomized controlled trial

Context:

Pulpotomy is a procedure in which part of an exposed vital pulp is removed, usually as a means of preserving the vitality and function of the remaining part.

Aim:

The aim is to compare the effectiveness of Dycal (CH), EndoSequence, and Titanium-prepared platelet-rich fibrin with EndoSequence (T-PRF) as pulpotomy agents in mature permanent molars with irreversible pulpitis.

Settings and Design:

Sixty permanent mandibular molars with carious exposure and symptoms of irreversible pulpitis were randomly allocated to three groups.

Subjects and Methods:

Full pulpotomy was performed using Dycal, EndoSequence, and T-PRF with EndoSequence as pulpotomy agents. Pain intensity was analyzed using a Numeric Rating Scale score at baseline 24 h, 7 days, 6 months, and 1 year. The clinical and radiographic evaluations were done at 6 months and 1 year.

Statistical Analysis:

Nonparametric tests (Kruskal–Wallis, Chi-square) were applied to analyze the data as the normality test does not follow a normal distribution.

Results:

T-PRF and EndoSequence showed effective results when compared clinically, and there was no significant difference between radiographic success rates among the three groups at (P = 0.325 at 6 months, 0.466 at 12 months) follow-up.

Conclusion:

T-PRF and EndoSequence showed higher success rates among Dycal, EndoSequence as pulpotomy agents in teeth with irreversible pulpitis.

Macrophage modulation of dental pulp stem cell activity during tertiary dentinogenesis

The interaction between immune cells and stem cells is important during tissue repair. Macrophages have been described as being crucial for limb regeneration and in certain circumstances have been shown to affect stem cell differentiation in vivo. Dentine is susceptible to damage as a result of caries, pulp infection and inflammation all of which are major problems in tooth restoration. Characterising the interplay between immune cells and stem cells is crucial to understand how to improve natural repair mechanisms. In this study, we used an in vivo damage model, associated with a macrophage and neutrophil depletion model to investigate the role of immune cells in reparative dentine formation. In addition, we investigated the effect of elevating the Wnt/β-catenin pathway to understand how this might regulate macrophages and impact upon Wnt receiving pulp stem cells during repair. Our results show that macrophages are required for dental pulp stem cell activation and appropriate reparative dentine formation. In addition, pharmacological stimulation of the Wnt/β-catenin pathway via GSK-3β inhibitor small molecules polarises macrophages to an anti-inflammatory state faster than inert calcium silicate-based materials thereby accelerating stem cell activation and repair. Wnt/β-catenin signalling thus has a dual role in promoting reparative dentine formation by activating pulp stem cells and promoting an anti-inflammatory macrophage response.

Bio-Inductive Materials in Direct and Indirect Pulp Capping-A Review Article

The article is aimed at analyzing the available research and comparing the properties of bio-inductive materials in direct and indirect pulp capping procedures. The properties and clinical performances of four calcium-silicate cements (ProRoot MTA, MTA Angelus, RetroMTA, Biodentine), a light-cured calcium silicate-based material (TheraCal LC) and an enhanced resin-modified glass-ionomer (ACTIVA BioACTIVE) are widely discussed. A correlation of in vitro and in vivo data revealed that, currently, the most validated material for pulp capping procedures is still MTA. Despite Biodentine’s superiority in relatively easier manipulation, competitive pricing and predictable clinical outcome, more long-term clinical studies on Biodentine as a pulp capping agent are needed. According to available research, there is also insufficient evidence to support the use of TheraCal LC or ACTIVA BioACTIVE BASE/LINER in vital pulp therapy.

Bioactive tri/dicalcium silicate cements for treatment of pulpal and periapical tissues

Over 2500 articles and 200 reviews have been published on the bioactive tri/dicalcium silicate dental materials. The indications have expanded since their introduction in the 1990s from endodontic restorative and pulpal treatments to endodontic sealing and obturation. Bioactive ceramics, based on tri/dicalcium silicate cements, are now an indispensable part of the contemporary dental armamentarium for specialists including endodontists, pediatric dentists, oral surgeons andfor general dentists. This review emphasizes research on how these materials have conformed to international standards for dental materials ranging from biocompatibility (ISO 7405) to conformance as root canal sealers (ISO 6876). Potential future developments of alternative hydraulic materials were included. This review provides accurate materials science information on these important materials. STATEMENT OF SIGNIFICANCE: The broadening indications and the proliferation of tri/dicalcium silicate-based products make this relatively new dental material important for all dentists and biomaterials scientists. Presenting the variations in compositions, properties, indications and clinical performance enable clinicians to choose the material most suitable for their cases. Researchers may expand their bioactive investigations to further validate and improve materials and outcomes.

Reactionary Versus Reparative Dentine in Deep Caries

The dentine-pulp complex response in deep caries is histological characterized by tertiary formation and mild chronic pulp inflammation. The quiescent primary odontoblasts are reactivated, laying down reactionary tertiary dentine. In more severe carious damage the primary odontoblasts die and reparative tertiary dentine is secreted by odontoblast-like cells, which are differentiated in adult teeth mainly from dental pulp stem cells DPSC. Though associated with reversible pulpitis DPSC still preserve in deep caries the capability of migration, proliferation and differentiation. Some common mechanisms of molecular signals involved in tertiary dentine formation might also explain the balance between inflammation and regeneration of dentine-pulp complex.

Epigenetic regulation in dental pulp inflammation

Dental caries, trauma, and other possible factors could lead to injury of the dental pulp. Dental infection could result in immune and inflammatory responses mediated by molecular and cellular events and tissue breakdown. The inflammatory response of dental pulp could be regulated by genetic and epigenetic events. Epigenetic modifications play a fundamental role in gene expression. The epigenetic events might play critical roles in the inflammatory process of dental pulp injury. Major epigenetic events include methylation and acetylation of histones and regulatory factors, DNA methylation, and small non-coding RNAs. Infections and other environmental factors have profound effects on epigenetic modifications and trigger diseases. Despite growing evidences of literatures addressing the role of epigenetics in the field of medicine and biology, very little is known about the epigenetic pathways involved in dental pulp inflammation. This review summarized the current knowledge about epigenetic mechanisms during dental pulp inflammation. Progress in studies of epigenetic alterations during inflammatory response would provide opportunities for the development of efficient medications of epigenetic therapy for pulpitis.

Is hard tissue formation in the dental pulp after the death of the primary odontoblasts a regenerative or a reparative process?

OBJECTIVES

Conceptually, two types of tertiary dentine may be produced in response to caries and environmental irritations: "reactionary dentine" that is secreted by existing primary odontoblasts and "reparative dentine", formed after the death of the odontoblasts by proliferation and differentiation of progenitor cells into odontoblast-like cells. Because histologic evidence for tubular dentine generated by newly differentiated odontoblast-like cells is lacking in human teeth, the present study examined pulpal cellular changes associated with caries/restorations, in the presence or absence of pulpal exposures.

METHODS

Ninety-six extracted human teeth were histologically processed and serial sectioned for light microscopy: 65 contained untreated enamel/dentine caries; 20 were heavily restored and 11 had carious exposures managed by direct pulp-capping.

RESULTS

Sparsely distributed, irregularly arranged dentinal tubules were identified from the tertiary dentine formed in teeth with unexposed medium/deep caries and in restored teeth; those tubules were continuous with the tubules of secondary dentine; in some cases, tubules were absent. The palisade odontoblast layer was reduced to a single layer of flattened cells. In direct pulp-capping of pulp exposures, the defects were repaired by the deposition of an amorphous dystrophic calcified tissue that resembled pulp stones more than dentine, sometimes entrapping pulpal remnants. This atubular hard tissue was lined by fibroblasts and collagen fibrils.

CONCLUSIONS

Histological evidence from the present study indicates that reparative dentinogenesis cannot be considered as a regenerative process since the so-formed hard tissue lacks tubular features characteristic of genuine dentine. Rather, this process represents a repair response that produces calcified scar tissues by pulpal fibroblasts.

CLINICAL SIGNIFICANCE

Formation of hard tissue in the dental pulp after the death of the primary odontoblasts has often been regarded by clinicians as regeneration of dentine. If the objective of the clinical procedures involved is to induce healing, reduce dentine hypersensitivity, or minimise future bacteria exposure, such procedures may be regarded as clinical success. However, current clinical treatment procedures are not adept at regenerating physiological dentne because the tissues formed in the dental pulp are more likely the result of repair responses via the formation of calcified scar tissues.