Inflammatory Response Mechanisms of the Dentine-Pulp Complex and the Periapical Tissues.

The macroscopic and microscopic anatomy of the oral cavity is complex and unique in the human body. Soft-tissue structures are in close interaction with mineralized bone, but also dentine, cementum and enamel of our teeth. These are exposed to intense mechanical and chemical stress as well as to dense microbiologic colonization. Teeth are susceptible to damage, most commonly to caries, where microorganisms from the oral cavity degrade the mineralized tissues of enamel and dentine and invade the soft connective tissue at the core, the dental pulp. However, the pulp is well-equipped to sense and fend off bacteria and their products and mounts various and intricate defense mechanisms. The front rank is formed by a layer of odontoblasts, which line the pulp chamber towards the dentine. These highly specialized cells not only form mineralized tissue but exert important functions as barrier cells. They recognize pathogens early in the process, secrete antibacterial compounds and neutralize bacterial toxins, initiate the immune response and alert other key players of the host defense. As bacteria get closer to the pulp, additional cell types of the pulp, including fibroblasts, stem and immune cells, but also vascular and neuronal networks, contribute with a variety of distinct defense mechanisms, and inflammatory response mechanisms are critical for tissue homeostasis. Still, without therapeutic intervention, a deep carious lesion may lead to tissue necrosis, which allows bacteria to populate the root canal system and invade the periradicular bone via the apical foramen at the root tip. The periodontal tissues and alveolar bone react to the insult with an inflammatory response, most commonly by the formation of an apical granuloma. Healing can occur after pathogen removal, which is achieved by disinfection and obturation of the pulp space by root canal treatment. This review highlights the various mechanisms of pathogen recognition and defense of dental pulp cells and periradicular tissues, explains the different cell types involved in the immune response and discusses the mechanisms of healing and repair, pointing out the close links between inflammation and regeneration as well as between inflammation and potential malignant transformation.

Evaluation of antibacterial activity of propolis on regenerative potential of necrotic immature permanent teeth in dogs.

BACKGROUND: This study evaluated the antibacterial efficiency and ability of propolis to promote regeneration of immature permanent non-vital dogs' teeth. METHODS: Ninety six immature permanent premolars teeth in 6 mongrel dogs were divided randomly into: experimental teeth (N = 72) and control teeth (N = 24). Periapical pathosis was induced in all experimental and positive control teeth. Experimental teeth were classified according to the used intra-canal medication into: group I (N = 36), propolis paste was used and group II (N = 36), triple antibiotic paste (TAP) was used. Bacteriologic samplings were collected before and after exposure to intra-canal medicaments. After the disinfection period (3 weeks), revascularization was induced in all experimental teeth. Each group was subdivided according to the root canal orifice plug into: subgroup A (N = 18), propolis paste was used and subgroup B (N = 18), mineral trioxide aggregates (MTA) was used. Each subgroup was further subdivided according to the evaluation period into 3 subdivisions (6 teeth each): subdivision 1; after 2 weeks, subdivision 2; after one month and subdivision 3; after 2 months. Positive control group had 12 teeth with induced untreated periapical pathosis. Negative control group had 12 untouched sound teeth. All teeth were evaluated with radiography and histology. The bacteriologic and radiographic data were analyzed using repeated measures ANOVA and post-hoc Tukey tests. The histologic data were analyzed using Kruskal-Wallis test, Mann-Whitney U test with Bonferroni's adjustment and Chi-square test. The significance level was set at P ≤ .05. RESULTS: There was no significant difference in the antibacterial effectiveness between TAP and propolis groups (P > .05). In all subdivisions, there was no significant difference between the experimental groups in terms of increase in root length and dentin thickness, decrease in apical closure, new hard tissue formation, vital tissue formation inside the pulp canal and apical closure scores (P > .05). CONCLUSION: Propolis can be comparable with TAP as a disinfection treatment option in regenerative endodontic. As a root canal orifice plug after revascularization of necrotic immature permanent teeth in dogs, propolis induces a progressive increase in root length and dentin thickness and a decrease in apical diameter similar to those of MTA.

Autologous Platelet Concentrates for Pulp and Dentin Regeneration: A Literature Review of Animal Studies.

INTRODUCTION: The purpose of this study was to evaluate the effectiveness of autologous platelet concentrates (APCs) in promoting pulp and dentin regeneration in animal models. METHODS: An electronic search was performed on MEDLINE, Embase, Scopus, SciELO, LILACS, and CENTRAL. Animal studies using APC as a root filling material after pulpectomy in mature or immature teeth were included. Articles underwent risk of bias assessment. Histologic evaluation of intracanal neoformed tissue was the primary outcome; root development, root wall thickening, apical closure, and periapical healing in apical periodontitis were the secondary outcomes. RESULTS: Seven articles were included. Platelet-rich plasma (PRP) was used as root filling material during regenerative procedures in the experimental group in either mature or immature teeth. After revascularization with PRP alone or in conjunction with stem cells of a different source, the histologic analyses revealed that, in addition to an odontoblastic cell layer or dentinlike structure, the neoformed intracanal tissues were mainly cementumlike, bonelike, and connective tissues. CONCLUSIONS: True regeneration of necrotic pulp may not be achieved with current techniques using PRP, all of which stimulated tissue repair. Benefits of PRP adjunct for pulp tissue regeneration in preclinical studies remain unclear. Further studies with standardized protocols are necessary to assess the actual contribution of PRP in endodontic regenerative therapies.

Regenerative potential of immature permanent non-vital teeth following different dentin surface treatments.

This study evaluates the regenerative potential of immature permanent non-vital teeth following different dentin surface treatments in dogs. Periapical lesions and necrotic pulps were induced in 288 roots of 144 teeth in twelve dogs. Teeth were randomly divided into 3 equal groups according to the evaluation period. Each group was subdivided into 8 subgroups according to the treatment modalities including; blood clot, blood clot and collagen, blood clot and Ethylenediaminetetraacetic acid (EDTA), blood clot, collagen and EDTA, blood clot and Mixture Tetracycline Citric Acid and Detergent (MTAD), blood clot, collagen and MTAD, positive control and negative control. Apart from control subgroups, all infected root canals were cleaned with sodium hypochlorite solution and triple antibiotics paste before different treatment protocols. After different treatments, the root length, thickness and apical diameter were evaluated by radiographic examination. Histopathological examination was carried out to evaluate the inflammation, bone/root resorption, tissue in-growth in pulp space, new hard tissue formation and apical closure. Using EDTA solution as a surface modifier showed significantly higher levels of tissue in-growth in the pulp space after 6 weeks and 3 months. Addition of collagen as a scaffold caused significantly more bone/root resorption than the other subgroups while EDTA caused significantly lower inflammatory cell counts only after 2 weeks. Final rinse with 17% EDTA solution before blood clot induction has positive impact on tissue interaction along dentinal walls without modification of the cell type. Moreover, the use of collagen as a scaffold material and MTAD as a surface modifier did not improve the quality of the regenerative process.

Survival of rat functional dental pulp cells in vascularized tissue engineering chambers.

Regenerative endodontics aims to preserve, repair or regenerate the dental pulp tissue. Dental pulp stem cells, have a potential use in dental tissue generation. However, specific requirements to drive the dental tissue generation are still obscured. We established an in vivo model for studying the survival of dental pulp cells (DPC) and their potential to generate dental pulp tissue. DPC were mixed with collagen scaffold with or without slow release bone morphogenic protein 4 (BMP-4) and fibroblast growth factor 2 (FGF2). The cell suspension was transplanted into a vascularized tissue engineering chamber in the rat groin. Tissue constructs were harvested after 2, 4, 6, and 8 weeks and processed for histomorphological and immunohistochemical analysis. After 2 weeks newly formed tissue with new blood vessel formation were observed inside the chamber. DPC were found around dentin, particularly around the vascular pedicle and also close to the gelatin microspheres. Cell survival, was confirmed up to 8 weeks after transplantation. Dentin Sialophosphoprotein (DSPP) positive matrix production was detected in the chamber, indicating functionality of dental pulp progenitor cells. This study demonstrates the potential of our tissue engineering model to study rat dental pulp cells and their behavior in dental pulp regeneration, for future development of an alternative treatment using these techniques.

Immunohistochemical localization of four and a half LIM domains 2 in the odontoblasts of mature human teeth.

Four and a half LIM domains 2 (FHL2) participates in cell differentiation and cancer development of various tissues, possessing dual functions either as an activator or as a repressor depending on the protein partners involved. Recent studies show that FHL2 plays an important role in osteoblast differentiation and bone formation. The present study was to investigate the expression and localization of FHL2 in human pulp-dentin complex by immunohistochemistry. Our results showed that in sound mature human teeth, FHL2 was expressed in odontoblasts and some endothelial cells of blood vessels. Moreover, in carious teeth FHL2 immunoreactivity was detected in odontoblasts, odontoblast-like cells and endothelial cells of blood vessels. FHL2 was mainly distributed in cytosol of the odontoblast cell bodies and partly located in nuclei of odontoblasts, but not in the odontoblast processes. Our data suggest a role of FHL2 in odontoblast differentiation and dentin formation both in normal and in carious teeth.

Pulp and dentin tissue engineering and regeneration: current progress.

Dental pulp tissue is vulnerable to infection. Entire pulp amputation followed by pulp-space disinfection and filling with an artificial rubber-like material is employed to treat the infection - commonly known as root-canal therapy. Regeneration of pulp tissue has been difficult as the tissue is encased in dentin without collateral blood supply except from the root apical end. However, with the advent of the concept of modern tissue engineering and the discovery of dental stem cells, regeneration of pulp and dentin has been tested. This article will review the early attempts to regenerate pulp tissue and the current endeavor of pulp and dentin tissue engineering, and regeneration. The prospective outcome of the current advancement in this line of research will be discussed.

Eph/ephrinB mediate dental pulp stem cell mobilization and function.

Damage to the dentin matrix investigates the proliferation and mobilization of dental progenitor cells to the injury site, the mechanisms of which are not defined. EphB receptors and ephrin-B ligands expressed within the perivascular niche of dental pulp have been implicated following tooth injury. We propose that elevated levels of ephrin-B1 following injury may prevent the proliferation and migration of dental pulp stem cell (DPSC), while EphB/ephrin-B interaction facilitates odontoblastic differentiation. The migration, proliferation, and differentiation of DPSC in response to Eph/ephrin-B molecules was assessed in an established ex vivo tooth injury model and by in vitro assays for the assessment of colony formation and differentiation. Analysis of our data demonstrated that EphB forward signaling promoted DPSC proliferation, while inhibiting migration. Conversely, reverse signaling enhanced DPSC mineral production. These observations suggest that EphB/ephrin-B molecules are important for perivascular DPSC migration toward the dentin surfaces and differentiation into functional odontoblasts, following damage to the dentin matrix.

Effect of simulated pulpal microcirculation on intrachamber temperature changes following application of various curing units on tooth surface.

OBJECTIVE: The purpose of this study was to evaluate ex vivo the rise in intrachamber temperature induced by the application of various curing units on tooth surface, under conditions of continuous water flow inside the pulp chamber simulating pulp microcirculation. METHODS: Fifteen extracted intact human teeth were selected. Intrachamber temperature increases were induced by applying the following curing units to the buccal aspect of the tested teeth: a conventional halogen lamp, two high-intensity halogen lamps, a plasma arc curing light, a mercury/metal-halide lamp, and a diode laser. Temperature changes on the tooth surfaces were recorded using thermocouples connected to a data logger. The Greenhouse-Geisser and Bonferroni tests in the SPSS software package were used for analysis of the data. The level of significance was set at 0.05. RESULTS: Under conditions of water flow the average intrachamber temperature rise was less than 6 degrees C, for all curing units. Without water flow, the increase in pulp temperature exceeded 6 degrees C for all units except the conventional halogen lamp. The diode laser produced a significantly greater temperature increase than any other curing unit. Application of the diode laser and the two high-intensity halogen lamps to lateral incisor specimens produced significantly greater temperature increases than other teeth. CONCLUSIONS: When the simulated pulp microcirculation was absent, the temperature increases produced by all curing units except the conventional halogen lamp were large enough to be potentially harmful to the pulp. On the contrary, with the cooling effect of water flow inside the pulp chamber, all units proved to be safe for use.

Effect of simulated pulpal microcirculation on intrapulpal temperature changes following application of heat on tooth surfaces.

AIM: To evaluate ex vivo whether a simulated pulpal microcirculation inside a pulp chamber influenced intrapulpal temperature rise following application of heat on tooth surfaces. METHODOLOGY: An ex vivo model that allowed the circulation of 37 degrees C warm water inside the pulp chamber of an extracted human tooth was designed. The experimental model resembled pulpal microcirculation. After application of specific thermal stimuli for 30 s to the external surface of 15 maxillary central incisors, lateral incisors and canines, temperature changes were measured in the pulp chamber. The Greenhouse-Geisser and Bonferroni tests were used for analysis of the data. The level of significance was set at 0.05. RESULTS: Significant differences were found in all three groups of teeth between temperature measurements with or without intrapulpal water flow. Additionally, temperature changes resulting from the application of different stimuli to the group of lateral incisors were significantly greater compared with the other groups of teeth (P < 0.05). CONCLUSIONS: The importance of the cooling effect of simulated pulp microcirculation in the thermal behaviour of the dentine was established. Thickness of tooth tissue influenced significantly pulp temperature rise ex vivo.

Morphological variations in a tooth family through ontogeny in Pleurodeles waltl (Lissamphibia, Caudata).

Most nonmammalian species replace their teeth continuously (so-called polyphyodonty), which allows morphological and structural modifications to occur during ontogeny. We have chosen Pleurodeles waltl, a salamander easy to rear in the laboratory, as a model species to establish the morphological foundations necessary for future molecular approaches aiming to understand not only molecular processes involved in tooth development and replacement, but also their changes, notably during metamorphosis, that might usefully inform studies of modifications of tooth morphology during evolution. In order to determine when (in which developmental stage) and how (progressively or suddenly) tooth modifications take place during ontogeny, we concentrated our observations on a single tooth family, located at position I, closest to the symphysis on the left lower jaw. We monitored the development and replacement of the six first teeth in a large growth series ranging from 10-day-old embryos (tooth I1) to adult specimens (tooth I6), using light (LM), scanning (SEM), and transmission electron (TEM) microscopy. A timetable of the developmental and functional period is provided for the six teeth, and tooth development is compared in larvae and young adults. In P. waltl the first functional tooth is not replaced when the second generation tooth forms, in contrast to what occurs for the later generation teeth, leading to the presence of two functional teeth in a single position during the first 2 months of life. Larval tooth I1 shows dramatically different features when compared to adult tooth I6: a dividing zone has appeared between the dentin cone and the pedicel; the pulp cavity has enlarged, allowing accommodation of large blood vessels; the odontoblasts are well organized along the dentin surface; tubules have appeared in the dentin; and teeth have become bicuspidate. Most of these modifications take place progressively from one tooth generation to the next, but the change from monocuspid to bicuspid tooth occurs during the tooth I3 to tooth I4 transition at metamorphosis.

Pulp-dentin biology in restorative dentistry. Part 2: initial reactions to preparation of teeth for restorative procedures.

Pulpal complications involving inflammation, degradation, and necrosis are the result of a series of traumatic injuries. The restorative dentist must minimize the trauma to dentin and pulp inflicted during clinical procedures, including that inflicted during tooth preparation. Part 11 of this series discusses the structural and physiologic changes in the pulp-dentin complex that result from crown and cavity preparation and the clinical implication of these changes.

Pulp response in primary teeth with deep residual caries treated with silver fluoride and glass ionomer cement ('atraumatic' technique)

Histological assessment of the dental pulps of 55 carious primary teeth was carried out 3 to 58 months after treatment by the 'atraumatic' technique involving application of 40 per cent silver fluoride to residual caries followed by restoration with glass ionomer cement. Fifty of the 55 teeth examined showed a favourable pulpal response, inducing presence of abundant reparative dentine and a wide odontoblast layer. Histological comparisons were made between these teeth and others not treated with silver fluoride but restored with glass ionomer cement, amalgam or zinc oxide and eugenol. Possible mechanisms of the action of silver fluoride in arresting residual caries are discussed. The question of whether or not treatment of carious dentine with silver fluoride represents a biologically acceptable clinical procedure cannot be answered on the basis of pulpal histology alone. The very high concentration of fluoride in commercial preparations of silver fluoride raises several questions concerning its clinical safety.

Dynamics of the pulpo-dentin complex.

Dentin has a relatively high water content due to its tubular structure. Once dentin is exposed, this intratubular water is free to move in response to thermal, osmotic, evaporative, or tactile stimuli. Fluid shifts across dentin are thought to cause sufficient shear forces on odontoblasts, nerve endings, nearby fibroblasts, and blood vessels to cause significant mechanical irritation, disruption, or damage, depending on the magnitude of the fluid shift. Even in the absence of fluid shifts, the water-filled tubules provide diffusion channels for noxious (i.e., bacterial products) substances which diffuse inward toward the pulp, where they can activate the immune system, provide chemotactic stimuli, cytokine production, and produce pain and pulpal inflammation. Viewed from this perspective, dentin is a poor barrier to external irritants. However, pulpal tissues react to these challenges by increasing the activity of nerves, blood vessels, the immune system, and interstitial fluid turnover, to make the exposed dentin less permeable either physiologically, via increased outward fluid flow, or microscopically, by lining tubules with proteins, mineral deposits, or tertiary dentin, thereby enhancing the barrier properties of dentin, and providing additional protection to pulpal tissues. These reactions involve dentin and pulp, both in the initiation of the processes and in their resolution. These responses of the dental pulp to irritation of dentin demonstrate the dynamic nature of the pulpo-dentin complex.

Collagen fibrils in the odontoblast layer of the rat incisor by scanning electron microscopy using the maceration method.

BACKGROUND: There is not universal agreement on the existence of the extracellular pathway from the pulp along the odontoblast layer to the predentin. METHOD: To confirm this pathway, the architecture of collagen fibrils in the rat incisor dentin and pulp, especially in the odontoblast layer of the lateral (periodontal ligament) sides of the tooth, was demonstrated in the present investigation using scanning electron microscopy of the maceration method for collagen networks. RESULTS: Numerous collagen bundles were observed in the odontoblast layer in the mature odontoblast region which, except for the young odontoblast region, comprises the major portion of the incisor. The collagen bundles went from the pulp, through the odontoblast layer, and were woven into the collagen network of the predentin. The meshwork structure was composed of fine secondary fibrils among these collagen bundles. The surface of the predentin contained many oval-shaped holes which were surrounded by collagen fibrils. Fracturing the dentin longitudinally relative to the dentinal tubules revealed that the arrangement of the collagen fibrils at the surface of the tubules was either circular or oblique. In the young odontoblast region, i.e., the thin portion from the apical end of the incisor where the mineralization of the dentin does not occur and where the height of the odontoblasts was less than 30 microns, many thick bundles composed of thick collagen fibrils ran straight from the pulp to the predentin through the odontoblast layer and fanned out in the collagen network of the predentin. These thick bundles might correspond to the so-called "von Korff fibers." The distribution of collagen fibrils in the pulp was random except on the surface of the blood vessels where the fibrils comprised two sheets of collagen: the inner sheet which coursed longitudinally to the long axis of the vessel, and the outer sheet which ran transversely. CONCLUSION: It was considered that the fluid in the pulp could flow to the predentin along the collagen fibrils through the tight junction between the odontoblasts.

Neovascularization of surface demineralized dentin.

Uneventful healing of the wound site created by periodontal reconstructive surgery is crucial for the long term survival of the dentition. Wound healing has been shown to be initiated and mediated by matrix components and polypeptide growth factors. Neovascularization (or angiogenesis) is one of the most important events in the healing process of a wound site. Any increase in the degree and/or rate of neovascularization could result in more rapid or complete healing. Previously, we have shown that basic fibroblast growth factor (bFGF) selectively enhances periodontal ligament cell migration and proliferation. In addition, we have shown that FGF stimulates human umbilical vein endothelial cell migration and proliferation. In this study we examined whether human umbilical vein endothelial cells could be influenced to form capillary-like structures in a type I collagen stroma and on dentin surfaces in response to fibroblast growth factor (FGF). We observed tubule-like structures formed from a monolayer of endothelial cells within a type I collagen sponge in response to a gradient of FGF. Furthermore, we observed tubule-like structures formed from self-association of individual endothelial cells on partially demineralized dentin surfaces in response to FGF. Proliferation of human endothelial cells on dentin was dose dependent and maximally stimulated at a concentration of 10 ng/ml FGF. These data indicate that FGF can induce endothelial cell migration, proliferation and tubule formation on dentin.

Scanning electron microscopic study of giant tubule content in bovine dentin.

Incisal segments of unerupted permanent incisors from 1/2-1 1/2-yr-old calves were fractured along an axiomesiodistal plane exposing the organic components within the giant tubule lumina situated in this plane. Along the lining wall of the pulpal vascularized giant tubule portion, large flattened cells and a few odontoblasts were situated in shallow depressions. Just incisal to the vascular loop numerous cells were seen, both along the giant tubule wall and enclosed within a loosely textured collagenous matrix. Further incisally, the number and size of the cells decreased, and they were embedded in a compact unmineralized collagenous matrix that completely filled out the giant tubule lumina. This matrix consisted of fibrils regularly arranged in separate bundles whose orientation was mainly longitudinal. The incisal origins of the giant tubules were filled with coarse fibrils being about three times thicker than those of the luminal matrix and those of the circumpulpal dentin proper.

Light microscopic study of giant tubules in bovine dentin.

Demineralized, H-E stained longitudinal and transversal sections of unerupted permanent incisors from 1/2-3-yr-old calves were studied by light microscopy. The most incisal dentin in all teeth was characterized by a regular pattern of straight axially oriented giant tubules situated in the axiomesiodistal plane with interglobular dentin between them. In younger teeth, the pulpal part of every giant tubule contained an afferent and an efferent blood vessel, forming a hairpin loop and being surrounded by basophil cells. Incisal to the blood vessel loops, cells enbedded in an eosinophil matrix were present in the giant tubule lumina, showing increasing degenerative changes incisally. In older teeth there was a mesiodistally extended eosinophil dentin band near the pulp, with few, irregularly arranged, tortuous dentinal and giant tubules, the latter containing single blood vessels accompanied by pulpal cells. Isolated degenerating odontoblasts in lacunar cavities were seen in the transition area of the normal circumpulpal dentin and the eosinophil dentin band. A hypothesis on the initiation and subsequent development of giant tubules is presented.

Osteodentin formation in continuously erupting teeth of guinea pigs.

Osteodentin formation in guinea pig teeth was studied using in vivo microscopic and histologic techniques. The coronal half of both incisors and molars contained varying amounts of osteodentin. Within the osteodentin, narrow canals that contained pulp tissue were observed. Serial histologic sections demonstrated that these canals opened to the occlusal surface thereby exposing the pulp to the oral cavity.