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.

Role of matrix metalloproteinases in radicular cysts and periapical granulomas

AIM

The aim of the present study was to evaluate the expression and distribution of different classes of matrix metalloproteinases (MMPs) in radicular cysts and periapical granulomas.

METHODS

Twenty consecutive specimens of radicular cysts and 20 of periapical granulomas were selected. Expression of MMP-2, -9, -8, -13, -3 was immunohistochemically evaluated. The intensity of expression of the MMPs was evaluated using a semi-quantitative analysis: low = +; intermediate = ++; high = +++.

RESULTS

Positive expression of MMPs was present with different distribution. MMP-9 expressed differently in the lesions. Indeed, in periapical granulomas low expression was found in endothelial cells and fibroblasts, whilst high intensities were only detected in inflammatory cells. On the contrary, in radicular cysts the high intensities were mainly present in keratinocytes and fibroblasts. MMP-8 was mainly expressed in inflammatory cells of periapical granulomas. MMP-2 and -3 presented a low intensity of expression in both groups. MMP-13 showed a variable pattern of distribution in the different cell types of the two different lesions.

CONCLUSION

The present investigation supports the role of MMPs in the inflammatory process leading to the development of radicular cysts and periapical granulomas. The results of the present study suggested that the increased enlargement of radicular cysts, compared to periapical granulomas, might be related to a higher expression of MMP-9. On the other hands, the higher intensity of expression of MMP-8 in periapical granulomas could be related to an active inflammatory process. MMP-8 could play an important role in the inflammation processes during the development of periapical lesions.

[Histopathology and etiopathogenesis of chronic apical periodontitis--periapical granuloma]

Periapical lesions are among the most frequently diagnosed apical odontogenic pathologies in human teeth. The condition is generally described as apical periodontitis. Apical periodontitis is a sequel to endodontic infection and manifests itself as the host defense response to microbial challenge emanating from the root canal system to the periapical tissue. It is viewed as a dynamic encounter between microbial factors and host defenses at the interface between infected radicular pulp and periodontal ligament that results in local inflammation, resorption of hard tissues, destruction of other periapical tissues, and eventual formation of various histopathological categories of apical periodontitis, commonly referred to as periapical lesions. There are also factors located within the inflamed periapical tissue that can interfere with post-treatment healing of the lesion. The purpose of this article is to provide a comprehensive overview of the etiopathogenesis of apical periodontitis and causes of failed endodontic treatment. This study presents a histopathological analysis through optical microscopy of periapical lesions, commonly referred to as solid dental or periapical granuloma.

Gamma interferon (IFN-gamma) and IFN-gamma-inducing cytokines interleukin-12 (IL-12) and IL-18 do not augment infection-stimulated bone resorption in vivo

Periapical granulomas are induced by bacterial infection of the dental pulp and result in destruction of the surrounding alveolar bone. In previous studies we have reported that the bone resorption in this model is primarily mediated by macrophage-expressed interleukin-1 (IL-1). The expression and activity of IL-1 is in turn modulated by a network of Th1 and Th2 regulatory cytokines. In the present study, the functional roles of the Th1 cytokine gamma interferon (IFN-gamma) and IFN-gamma-inducing cytokines IL-12 and IL-18 were determined in a murine model of periapical bone destruction. IL-12-/-, IL-18-/-, and IFN-gamma-/- mice were subjected to surgical pulp exposure and infection with a mixture of four endodontic pathogens, and bone destruction was determined by microcomputed tomography on day 21. The results indicated that all IL-12-/-, IL-18-/-, and IFN-gamma-/- mice had similar infection-stimulated bone resorption in vivo as wild-type control mice. Mice infused with recombinant IL-12 also had resorption similar to controls. IFN-gamma-/- mice exhibited significant elevations in IL-6, IL-10, IL-12, and tumor necrosis factor alpha in lesions compared to wild-type mice, but these modulations had no net effect on IL-1alpha levels. Recombinant IL-12, IL-18, and IFN-gamma individually failed to consistently modulate macrophage IL-1alpha production in vitro. We conclude that, at least individually, endogenous IL-12, IL-18, and IFN-gamma do not have a significant effect on the pathogenesis of infection-stimulated bone resorption in vivo, suggesting possible functional redundancy in proinflammatory pathways.

The periapical space--a dynamic interface

The ultimate aim of endodontic treatment is to encourage the healing of apical periodontitis, or to prevent it from occurring if it was not present prior to treatment. Apical periodontitis is a general term used to describe an inflammatory response to irritation caused by the contents of a root canal system and it has several distinct forms. The most common is a granuloma but this can develop into other disease entities such as an abscess, a periapical pocket cyst or a true cyst, all of which present as radiolucencies. However, periapical radiolucencies may also be caused by extra-radicular infections, foreign body reactions and periapical scars, or they may be due to other tumours and cysts that have not originated from pulp disease. Practitioners must recognise and understand the different pathological entities and the dynamic interactions that occur in the periapical tissues in order to correctly diagnose and treat these conditions.

Exarticulation and reimplantation utilizing guided tissue regeneration: a case report

The extraction and reimplantation of teeth is a technique that has been practiced for many years, resulting in successful retention of teeth for up to 30 years. Although evidence confirming the advantages of this technique is limited, clinical observations and histologic examinations have revealed some important factors that are prerequisites for success: limitation of the time the tooth is exposed to the extraoral environment and preservation of vital periodontal tissue attachments on root surfaces. The latter goal can be achieved by gentle, atraumatic removal of the tooth from its socket, and hence the term exarticulation and reimplantation is more representative of the technique. In the present case report, a maxillary lateral incisor with a developmental defect was treated by exarticulation and reimplantation and application of calcium sulfate. Exarticulation and reimplantation seems to be a useful clinical procedure, but controlled studies are required to confirm its efficacy.

Effect of interleukin-6 deficiency on the formation of periapical lesions after pulp exposure in mice

OBJECTIVE

The multifunctional cytokine interleukin-6 (IL-6) has actions on multiple cell types, including promotion of the development of immune cells and osteoclasts. Periapical inflammation as the result of root canal infection is characterized by the accumulation of inflammatory cells and bone resorption. The effect of IL-6 on periapical lesion formation after pulpal infection is unknown. We sought to determine whether deletion of IL-6 affects periapical lesion formation after pulp exposure.

METHODS

Molar pulps of homozygous IL-6 knock-out mice (IL-6(-/-), strain B6, 129-Il6tm1Koe ) and wild-type mice (IL-6(+/+)) were exposed, and the mice were killed at 1, 2, 3, 5, and 8 weeks after the exposure. Mouse jaws were decalcified and prepared for histologic examination of periapical lesions.

RESULTS

The IL-6(-/-) mice developed larger periapical lesions more rapidly than did the IL-6(+/+) mice.

CONCLUSIONS

IL-6 deletion promoted periapical lesion development.

Tuberculous osteomyelitis of the mandible: a case report

Osteomyelitis of jaws caused by infection with Mycobacterium tuberculosis is uncommon, especially in children. We present a case of tuberculous osteomyelitis in a young child. Its clinical presentation, with features similar to a dento-alveolar abscess, underline the importance of considering it in the differential diagnosis of jaw lesions. We discuss of the diagnostic techniques, management and preventive measures, and stress the importance of history taking during clinical examination.

Development and treatment of retrograde peri-implantitis involving a site with a history of failed endodontic and apicoectomy procedures: a series of reports

Osseointegrated implants provide predictable restorative support for crowns, restorations, prosthesis abutments, and removable dentures. Their widespread use in recent years has produced different types of complications. Retrograde peri-implantitis, a lesion occurring at the periapical area of an osseointegrated implant, has recently been described. This paper presents a series of reports describing the occurrence and management of retrograde peri-implantitis involving implants replacing teeth with histories of failed endodontic and apicoectomy procedures.

Mineral trioxide aggregate (MTA) as a root end filling material in apical surgery--a case report

Many root end filling materials for apical surgeries have been identified either for scientific evaluation or clinical usage but none meets the requirements of an ideal root end filling material. Recently a new cement, Mineral Trioxide Aggregate (MTA) was researched as a potential root end filling material and showed promising results. This paper reports the significant findings of research done on MTA as a root end filling material and presents a clinical case where apical surgery was performed using MTA as retrograde filling.

The periapical space--a dynamic interface

The ultimate aim of endodontic treatment is to encourage the healing of apical periodontitis, or to prevent it from occurring if it was not present prior to treatment. Apical periodontitis is a general term used to describe an inflammatory response to irritation caused by the contents of a root canal system and it has several distinct forms. The most common is a granuloma but this can develop into other disease entities such as an abscess, a periapical pocket cyst or a true cyst, all of which present as radiolucencies. However, periapical radiolucencies may also be caused by extra-radicular infections, foreign body reactions and periapical scars, or they may be due to other tumours and cysts that have not originated from pulp disease. Practitioners must recognize and understand the different pathological entities and the dynamic interactions that occur in the periapical tissues in order to correctly diagnose and treat these conditions.

Replacement of a mandibular subperiosteal implant

This case report describes the replacement of a failed subperiosteal implant with a tripodal design in a 60-year-old woman. The patient had been given the option of an augmentation using an autogenous iliac crest graft with subsequent insertion of endosteal implants or of replacing the failed implant with another of more sophisticated design. The latter, a more conservative approach, was selected for both economic and quality-of-life issues.

Peripheral giant cell granuloma--a case report

Peripheral giant cell granuloma is a lesion arising mainly from the connective tissue of gingiva or periosteum of alveolar ridge. A case of peripheral giant cell granuloma involving a deciduous molar and the succedaneous tooth is reported. The lesion was large and interfered with occlusion. Surgical excision of the lesion along with the deciduous first molar was done. The underlying permanent first premolar was also involved, and had to be removed. The importance of an adequate salivary flow and maintenance of oral hygiene in the prevention of such lesions is stressed.

[The role of cell adhesion molecules in the formation of periapical granulomas]

Cell adhesion molecules (CAMs) are cell surface proteins involved in the binding of cells, usually leukocytes, to each other, to endothelial cells, or to extracellular matrix. Specific signals produced in response to wounding and infection control the expression and activation of certain of these adhesion molecules. The interactions and responses then initiated by binding of these CAMs to their receptors/ligands play important roles in the mediation of the inflammatory and immune reactions that consult one line of the body's defense against these insults. Most of the CAMs characterized so far fall into three general families of proteins: the immunoglobulin (Ig) superfamily, the integrin family, or the selectine family. Recent studies have indicated that selectins (E,L,P) are implicated in cell trafficking, an important aspect of inflammation-related process. Regulation of white blood cell trafficking from the blood vascular compartment to regions of pathogenic exposure is one of the most important functions of the immune system. The distinct phases of leukocyte migration include: rolling, activation, firm adhesion, transendothelial migration and subendothelial migration. The selectins have been implicated in the first step of this cascade. An inflammatory response is first evoked in the pulpal tissue in an attempt to neutralize the injurious agent and to dispose of damaged tissue and cells. The pulpal vessels dilate and blood flow to the tooth increases. At the same time, permeability of the vessels increases allowing leakage of fluid and leukocytes into the tissue.

Chlorhexidine as a root canal medicament for treating inflammatory lesions in the periodontal space

The purpose of the present study was to investigate the therapeutic effect of intra-canal application of chlorhexidine on inflammatory root resorption. Dental pulps from monkey incisors were infected and resealed prior to extraction of the teeth. Root dentin was mechanically exposed and the teeth were replanted under aseptic conditions. After 4 weeks, the experimental teeth were dressed with chlorhexidine gel and resealed. Animals were sacrificed 4 weeks later, and their jaws prepared for histologic examination. Results showed that both marginal and apical periodontal inflammation and resorption were reduced in the chlorhexidine-treated teeth. It was concluded that the use of intra-canal chlorhexidine may be a useful adjunct in the treatment of inflammatory root resorption, but further human trials need to be undertaken before its clinical use can be recommended.

Epulis granulomatosa: extraction sequellae

Epulis granulomatosa is a post-surgical lesion emanating from an extraction socket. It can be misdiagnosed with lesions of similar appearance, for example, foreign body or pyogenic granulomas, or as a herniation of the maxillary sinus. Based on clinical appearance and microscopic description, granulomas all appear to represent essentially the same lesion. However, pathonomonically, the epulis granulomatosa emanates only from an extraction socket; the other granulomas can be found anywhere in the body.

GTR treatment of degree III furcation defects with 2 different resorbable barriers. An experimental study in dogs

The aim of the present study was to describe the periodontal tissue that formed after GTR when different resorbable barriers were applied to degree III furcation defects. The study was performed in 5 foxhound dogs. The 2nd and 4th premolars in both sides of the mandible were extracted. Degree III furcation defects were produced in the 3rd mandibular premolars. 5 weeks later, GTR therapy using a barrier composed by a polylactide-glycolide copolymer was performed on one quadrant (group A). In the contralateral quadrant, a barrier made of polylactide and citric acid ester (group B) was used. The dogs were sacrificed 6 months after reconstructive therapy. Tissue blocks containing the experimental teeth were excised, demineralised in EDTA and embedded in paraffin. Serial sections were cut in the mesio-distal plane and parallel with the long axis of the roots. The microtome was set at 7 microm. The sections were stained in hematoxyline and eosin. From each biopsy, 3 sections representing the central part of the furcation were selected for light microscopic examination. In the healed furcation sites, descriptive histological analysis and histomorphometric measurements of the newly formed tissues were performed. In both groups the root surface of the healed furcation defects was covered by a cellular, extrinsic-intrinsic fibers type cementum. The composition of the newly formed periodontal ligament was similar in both groups. The proportions of bone, bone marrow and periodontal ligament, however, were substantially larger in group A than in group B. In Group B, an area in the previous furcation defect was consistently occupied by a granuloma. It is suggested that the presence of the granuloma in the healed furcation defect prevented bone regrowth.

Microorganisms in closed periapical lesions

The purpose of this study was to investigate the microorganisms of strictly selected closed periapical lesions associated with both refractory endodontic therapy and pulpal calcification. Definitive criteria were established that assured complete clinical isolation of the periapical lesion from the oral and periodontal environment. A total of 13 criteria-referenced lesions were selected from 70 patients with endodontic surgical indications. A well controlled culturing method was used in all cases and samples were taken by one clinician at three separate sites during each surgery. Samples taken at the surgical window and within the body of the lesion served as controls, whilst a third sample was taken at the apex. In all 13 cases, samples taken from the apex yielded microorganisms comprising 63.6% obligate anaerobes and 36.4% facultative anaerobes. Prevalence of the isolated species was 31.8% for Actinomyces sp., 22.7% Propionibacterium sp., 18.2% Streptococcus sp., 13.6% Staphlyococcus sp., 4.6% Porphyromonas gingivalis, 4.6% Peptostreptococcus micros and 4.6% Gram-negative enterics. The results of this investigation indicate that closed periapical lesions associated with calcified teeth or those resistant to root canal treatment harbour bacteria. The inability to eradicate all root canal microorganisms during root canal treatment, along with anatomical factors, may allow further bacterial colonization of the root apex and surrounding periapical tissues, and consequently prevent healing.

Surgical treatment of a lateroradicular lesion on an invaginated lateral incisor (dens in dente)

The complex anatomy of invaginated teeth makes their endodontic treatment difficult. The case described here reports the successful management of an invaginated tooth presenting with a lateroradicular lesion. After the root was surgically exposed and the radicular defect was cleaned, gutta percha was sealed with a zinc oxide eugenol cement, heat-compacted under 5 degrees, and then cold-burnished. The osseous cavity was filled with Biocorail. Radiographs at 1 month and 5 years show periapical healing with osseous formation. This procedure, resulting in minimal loss of hard tissues, permitted retention of the tooth.

Bone-resorptive cytokine gene expression in periapical lesions in the rat

Periapical bone destruction is an important pathogenic sequela of pulpal infection. Recent findings from this laboratory have demonstrated that most bone-resorbing activity in extracts of rat periapical lesions can be neutralized by an anti-interleukin (IL)-1 alpha antiserum. To further clarify pathogenic mechanisms, bone-resorptive cytokine messenger RNA (mRNA) expression was analyzed in developing rat periapical lesions. The molar teeth of 20 Sprague-Dawley rats were surgically exposed and left open to permit infection from the oral environment. Total cell RNA was isolated from periapical granuloma tissue obtained on days 3, 7, 15 and 30 after exposure. mRNA for IL-1 alpha, IL-1 beta and tumor necrosis factor alpha (TNF-alpha) was amplified by reverse transcription polymerase chain reaction, and levels were approximated by comparison to the parallel amplification of the housekeeping gene glyceraldehyde phosphate dehydrogenase. IL-1 alpha and TNF-alpha mRNA were both highly expressed beginning on day 7, increased on day 15, and declined somewhat on day 30. In contrast, IL-1 beta mRNA was expressed at much lower levels, but with similar kinetics. The kinetics of steady state IL-1 alpha and TNF-alpha mRNA levels were confirmed using the quantitative RNase protection assay, whereas IL-1 beta mRNA could not be detected by this technique. IL-1 alpha mRNA-expressing cells were identified using in situ hybridization and included infiltrating macrophages, as well as resident fibroblasts, endothelial cells and osteoclasts. These results demonstrate that the IL-1 alpha and TNF-alpha genes are highly expressed in developing periapical lesions in the rat and confirm previous studies at the protein level in this model.

Histological findings of human leprosy periapical granulomas

Histological analysis of human leprosy periapical granulomas was conducted to study the histological responses to Mycobacterium leprae. Many Langhans-type giant cells and epithelioid cell tubercles were observed, although M. leprae were not detected in leprosy periapical granulomas. Although numerous T- and B-cells were infiltrated in leprosy periapical granuloma, the T-/B-cell ratio of leprosy is not changed to that of periapical granulomas isolated from normal patients. These findings suggested that human leprosy periapical granulomas develop as a result of immunological responses to M. leprae.

Endodontic cements induce alterations in the cell cycle of in vitro cultured osteoblasts

The effects of endodontic cements on the cell cycle of MG63 osteoblasts cultured in vitro have been examined. Three groups of compounds were tested. Group I encompassed zinc oxide- and eugenol-based cements (Tubliseal, Argoseal, N2), group II consisted of cements with a phenol group other than eugenol (AH26, Forfenan, Methode R/R), and group III included CaOH-based cements (Biocalex, Endocalex). The cell cycle of MG63 cells was analyzed by flow cytometry; the DNA content was evaluated by means of the propidium iodide uptake method, whereas the proportion of cells in the S phase was defined by the incorporation of bromodeoxyuridine later revealed by a specific antibody. The results showed that some root canal sealers could hamper the periapex healing processes by inhibiting the cell proliferation through a selective action on different phases of the cell cycle.

Dens invaginatus of a mandibular central incisor: surgical endodontic treatment

Dens invaginatus is a developmental malformation that mostly affects maxillary lateral teeth and mandibular teeth are rarely affected. In this paper a mandibular central incisor with a dens invaginatus is identified as requiring both endodontic and surgical treatment is presented. At one year recall appointment satisfactory clinical and radiographic healing was evident. This case demonstrates that also periapical surgery should be performed in some cases with dens invaginatus for resolution of periapical tissues.