Pathologic study of periapical lesions 1. Periapical granulomas: clinical, histopathologic and immunohistopathologic studies

The Limitations of Periapical X-ray Assessment in Endodontic Diagnosis-A Systematic Review

Diagnosis is a key aspect in endodontic treatment, in a decade where invasive interventions are misapprehended as social tendency instead of medical necessity. All diagnostic facets should be considered before intending the operative phase. Intraoral endodontic radiology-based diagnosis has been shown to be limited. Periapical X-ray is the most used endodontic imaging, yet it does not provide high accuracy. Traditionally, dentists have been trained to diagnose a cyst by certain aspects (size, shape and appearance); hence, an assumption that teeth are affected by "periapical cyst" were subjected to unnecessary extraction or apicoectomy. The aim of this systematic review is to critically appraise the publications that relate the histological diagnosis of a periapical lesion (considered the gold standard) to intraoral X-ray investigation. Ovid Medline, PubMed, ScienceDirect, Mendeley and Scopus were searched for English-language studies comparing periapical diagnosis obtained by using two techniques (histopathology and X-ray). Sixteen articles were included for the final analysis (qualitative and quantitative evaluation) out of which only two supported the statement that periapical diagnosis can be coherently assessed through periapical imaging. Although there is not enough evidence to deliver a definitive conclusion, there are many publications that refute the diagnosis of a cyst via periapical X-ray.

Definition and management of odontogenic maxillary sinusitis

Background

Maxillary sinusitis of odontogenic origin, also known as maxillary sinusitis of dental origin or odontogenic maxillary sinusitis (OMS), is a common disease in dental, otorhinolaryngologic, allergic, general, and maxillofacial contexts. Despite being a well-known disease entity, many cases are referred to otorhinolaryngologists by both doctors and dentists. Thus, early detection and initial diagnosis often fail to detect its odontogenic origin.

Main body

We searched recent databases including MEDLINE (PubMed), Embase, and the Cochrane Library using keyword combinations of "odontogenic," "odontogenic infection," "dental origin," "tooth origin," "sinusitis," "maxillary sinus," "maxillary sinusitis," "odontogenic maxillary sinusitis," "Caldwell Luc Procedure (CLP)," "rhinosinusitis," "functional endoscopic sinus surgery (FESS)," "modified endoscopy-assisted maxillary sinus surgery (MESS)," and "paranasal sinus." Aside from the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) trial, there have been very few randomized controlled trials examining OMS. We summarized the resulting data based on our diverse clinical experiences.

Conclusion

To promote the most efficient and accurate management of OMS, this article summarizes the clinical features of rhinosinusitis compared with OMS and the pathogenesis, microbiology, diagnosis, and results of prompt consolidated management of OMS that prevent anticipated complications. The true origin of odontogenic infections is also reviewed.

Role of mast cells in inflammatory and reactive pathologies of pulp, periapical area and periodontium

Mast cells (MCs) have been discovered over 130 years ago; their function was almost exclusively linked to allergic affections. At the time being, it is well known that MCs possess a great variety of roles, in both physiologic and pathologic conditions. In the oral tissues, MCs release different pro-inflammatory cytokines and tumor necrosis factor-alpha that promote leukocyte infiltration in various inflammatory states of the oral cavity. These cells play a key role in the inflammatory process and, as a consequence, their number changes in different pathologic conditions of the oral cavity, such as gingivitis and periodontitis. By understanding the role of MCs in the pathogenesis of different inflammatory diseases of the oral cavity, these cells may become therapeutic targets that could possibly improve the prognosis. Therefore, this review summarizes the current understanding of the role of MCs in various inflammatory pulpal, periapical and periodontal pathophysiological conditions.

Nonsurgical endodontic treatment of teeth associated with large periapical lesion using triple antibiotic paste and mineral trioxide aggregate apical plug: A case series

Periapical diseases are induced as a result of the direct or indirect involvement of oral bacteria. The etiologic factor being the degenerating pulp tissue. A periapical lesion is formed within an area of apical periodontitis which cannot form by itself and is inflammatory in origin. If the microbial etiology of periapical lesions and in the root canal is removed by nonsurgical root canal therapy the lesions regress. Mere surgical removal of the periapical lesions without proper root canal disinfection and obturation will not result in the healing of periapical tissues. Nonsurgical treatment with triple antibiotic paste offers a high success rate in the healing of large periapical lesions. The present clinical cases show the nonsurgical endodontic management of large periapical pathosis using triple antibiotic paste and mineral trioxide aggregate.

Scanning electron microscopy reveals severe external root resorption in the large periapical lesion

The present study was designed to investigate the relationships between clinicopathological findings and the resorptive conditions of root apices of teeth with periodontitis. The samples included 21 root apices with large periapical radiolucent lesions. The preoperative computed tomography (CT) and intraoperative findings were correlated with the presence, extension, and the progression pattern of periapical resorption using a scanning electron microscope. The subjects' age, gender, chief complaint, type of tooth, percussion test results, size of periapical lesion using CT, and intraoperative findings were recorded. All apicoectomies were performed under an operative microscope for endodontic microsurgery. A significant large size was observed in cystic lesions compared with granulomatous lesions. The cementum surface at the periphery of the lesion was covered with globular structures (2-3 μm in diameter). Cementum resorption started as small defect formations at the surface. As the defect formation progressed, a lamellar structure appeared at the resorption area, and the size of globular structures became smaller than that of globules at the surface. Further resorption produced typical lacuna formation, which was particularly observed in fracture cases. The most morphologically severe destructive pattern of dentin resorption was observed in large cystic lesions. This study is the first report to elucidate the relationships between three clinical types of undesirable periapical lesions: (1) undertreatment, (2) periapical fracture, (3) macro-level resorption, and the microstructure of external root resorption including from small defects at the cementum surface to a significant destructive pattern inside the dentin. Microsc. Res. Tech. 79:495-500, 2016. © 2016 Wiley Periodicals, Inc.

High levels of CXC ligand 12/stromal cell-derived factor 1 in apical lesions of endodontic origin associated with mast cell infiltration

INTRODUCTION

CXC ligand 12/stromal-derived factor-1 (CXCL12/SDF-1) is a pleiotropic chemokine that regulates the influx of a wide range of leukocytes. The aim of this study was to characterize CXCL12/SDF-1 in apical lesions (ALs) of endodontic origin, with special emphasis in associated immune cell populations.

METHODS

In this case-control study, 29 individuals with chronic apical periodontitis and 21 healthy volunteers were enrolled. ALs and healthy periodontal ligament samples were obtained for tissue homogenization, immune Western blotting, and enzyme-linked immunosorbent assay to determine CXCL12/SDF-1 forms and levels. Anatomopathologic diagnosis, immunostaining for CXCL12/SDF-1, CD117-CXCL12/SDF-1, and toluidine blue were also performed to identify tissue and cell localization. Finally, a set of tissue samples were digested and analyzed by flow cytometry to identify CXCL12/SDF-1 in different immune cell populations. Data were analyzed with Stata v11 and WinDi 2.9 software, and significance was considered if P < .05.

RESULTS

CXCL12/SDF-1 was predominantly identified as monomers; levels of CXCL12/SDF-1 were significantly higher in ALs compared with controls, and it was primarily localized to inflammatory infiltrates. Expression of CXCL12/SDF-1 was colocalized to mast cells in tissue sections. Furthermore, CD117(+) mast cells were the second most frequent infiltrating cells and the main CXCL12/SDF-1 expressing cells, followed by CD4(+) lymphocytes, monocytes/macrophages, neutrophils, and dendritic cells.

CONCLUSIONS

ALs of endodontic origin demonstrated higher levels of CXCL12/SDF-1 compared with controls. CXCL12/SDF-1 was identified in immune cell populations, whereas mast cells represented the major CXCL12/SDF-1 expressing cells, suggesting that this chemokine might play a central role in apical tissue destruction, most probably inducing persistent recruitment of immune cells, particularly of mast cells.

Immunophenotypic characterization and distribution of dendritic cells in odontogenic cystic lesions

OBJECTIVE

To analyze the expression and distribution patterns of mature dendritic cells (mDCs) and immature DCs (imDCs) in radicular cysts (RCs), dentigerous cysts (DtCs), and keratocystic odontogenic tumors (KCOTs).

MATERIALS AND METHODS

Forty-nine odontogenic cystic lesions (OCLs) (RCs, n = 20; DtCs, n = 15; KCOTs, n = 14) were assessed using the following markers: S100, CD1a and CD207 for imDCs; and CD83 for mDCs.

RESULTS

Almost all cases were S100, CD1a, and CD207 positive, whereas 63% were CD83 positive. RCs presented greater number of immunostained cells, followed by DtCs, and KCOTs. The number of S100+ cells was greater than both CD1a+ and CD207+ cells (P < 0.001), which showed approximately similar amounts, followed by lower number of CD83+ cells (P < 0.001) in each OCL type. Different from S100+ cells, both CD1a+ and CD207+ cells on the epithelium (P < 0.05) and CD83+ cells on the capsule (P < 0.05) were preferentially observed. In RCs, significant correlation was found between the thickness epithelium with S100+ and CD1a+ cells, and between the degree of inflammation with CD83+ cells.

CONCLUSIONS

Dendritic cell populations in OCLs can be phenotypically heterogeneous, and it could represent distinct lineages and/or functional stages. It is suggested that besides DC-mediated immune cell interactions, DC-mediated tissue differentiation and maintenance in OCLs should also be considered.

Mast cells in human odontogenic cysts

Mast cells are granule-containing cells in mucosal and connective tissues that are known to play a central role in allergic and inflammatory responses owing to pro-inflammatory mediators. Cysts in jaws are among the most common expansive, benign and destructive bone lesions; at some stage they are associated with chronic inflammation. Earlier studies have identified mast cells in odontogenic cysts (OC). We investigated the presence and distribution of mast cells and compared their number in different types of radicular cysts (RC), dentigerous cysts (DC) and odontogenic keratocysts (OKC). Ten cases each of RC, DC and OKC diagnosed clinically and histopathologically were selected and stained with 1% toluidine blue. The greatest number of mast cells/mm(2) was found in RC. The fewest mast cells/mm(2) were found in OKC. The subepithelial zones of all cysts contained more mast cells than the deeper zones.

Identification of bacteria associated with spreading odontogenic infections by 16S rRNA gene sequencing

OBJECTIVE

To determine the bacterial species associated with spreading odontogenic infections (SOIs).

STUDY DESIGN

Pus samples from 4 cases of SOI were analyzed by microbiological culture methods for the presence of bacteria, and by polymerase chain reaction (PCR) amplification, cloning, and sequencing of bacterial 16S rRNA genes.

RESULTS

Culture methods identified species from the genera Prevotella, Streptococcus, and Fusobacterium, as well as anaerobic streptococci. Molecular detection methods identified a far more diverse microflora. The predominant genus detected was Prevotella, representing 102 (50.2%) of 203 clones analyzed. Prevotella oris was the most abundant species identified, representing 45 (22.2%) of 203 clones analyzed. Twelve clones (5.9%) represented uncultivable species, namely Prevotella PUS9.180, an uncultured Peptostreptococcus species, and an uncultured bacterium belonging to the Bacteroidetes phylum.

CONCLUSIONS

Prevotella species may play an important role in SOIs, and further work to examine in more detail the pathogenicity determinants of these organisms and associated host responses is warranted.

Importance of Mast Cells in Human Periapical Inflammatory Lesions

The role of mast cells (MCs) in periapical inflammatory lesions is not well understood. The objective of this work was to quantify MC numbers in human periapical lesions with the aim to clarify their role in the pathogenesis of these lesions. We analyzed the slides of 64 human periapical inflammatory lesions stained with pH 8.0 toluidine blue technique, quantified the number of MCs, and evaluated any correlation with age, gender, size, and location. The results of this study suggest that MCs were more numerous in females (p < 0.01); MC numbers were higher in biopsies from granulomas with proliferating epithelium and lower in biopsies from chronic apical abscesses; MC counts did not correlate with patients' age or size. MCs were observed more commonly in areas containing inflammatory infiltrate and degranulation was a frequent finding in these zones. Our results suggest that MCs play an active role in the pathogenesis of the periapical inflammatory lesions. The potential role of MCs related with the initiation, development, and persistence of the periapical inflammatory process are discussed.

Pathogenesis of apical periodontitis and the causes of endodontic failures

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. 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. The treatment of apical periodontitis, as a disease of root canal infection, consists of eradicating microbes or substantially reducing the microbial load from the root canal and preventing re-infection by orthograde root filling. The treatment has a remarkably high degree of success. Nevertheless, endodontic treatment can fail. Most failures occur when treatment procedures, mostly of a technical nature, have not reached a satisfactory standard for the control and elimination of infection. Even when the highest standards and the most careful procedures are followed, failures still occur. This is because there are root canal regions that cannot be cleaned and obturated with existing equipments, materials, and techniques, and thus, infection can persist. In very rare cases, there are also factors located within the inflamed periapical tissue that can interfere with post-treatment healing of the lesion. The data on the biological causes of endodontic failures are recent and scattered in various journals. This communication is meant to provide a comprehensive overview of the etio-pathogenesis of apical periodontitis and the causes of failed endodontic treatments that can be visualized in radiographs as asymptomatic post-treatment periapical radiolucencies.

Interleukin-6 and granulocyte-macrophage colony-stimulating factor in apical periodontitis: correlation with clinical and histologic findings of the involved teeth

Apical periodontitis is characterized by the presence of immunocompetent cells producing a wide variety of inflammatory mediators. Releasing cytokines with long-range action, such as interleukin-6 (IL-6) and granulocyte-macrophage colony-stimulating factor (GM-CSF), apical periodontitis may induce changes in remote organs of the host. This study quantified the levels of IL-6 and GM-CSF in symptomatic and asymptomatic human periradicular lesions. Lesions were also characterized by size and histologic findings. Tissue samples were homogenized and supernatants were assayed using an enzyme-linked immunosorbent assay (ELISA). Correlations between cytokine levels and characteristic features (as single variables) of the lesions were analysed. There was a trend for higher levels of IL-6 and GM-CSF in symptomatic than in asymptomatic lesions, but the difference was not significant. Levels also tended to be higher in large than in small lesions, in polymorphonuclear (PMN) cell-rich than in PMN cell-poor samples, and in epithelialized than in non-epithelialized lesions. Significantly higher levels of IL-6 (778.1 +/- 220.5 pg/microg) and GM-CSF (363.3 +/- 98.4 pg/microg) were found in samples coincidentally possessing symptomatic and epithelialized features than in asymptomatic, small, PMN cell-poor, non-epithelialized lesions (IL-6: 45.2 +/- 13.1 pg/microg and GM-CSF: 135.1 +/- 26.4 pg/microg). These results suggest that symptomatic lesions containing epithelial cells represent an immunologically active stage of apical periodontitis, whereas asymptomatic, small, PMN cell-poor, non-epithelialized lesions represent healing apical lesions.

Immunohistochemical localization of cyclooxygenase-2 in radicular cysts

AIM

The purpose of this study was to investigate the expression of cyclooxygenase-2 (COX-2) in radicular cysts.

METHODOLOGY

Thirty biopsy specimens of radicular cysts were examined using immunohistochemistry. A peroxidase-labelled streptavidin-biotin technique was used for identification of the COX-2. Fisher's exact test (two-tail) was used for statistical analysis of the results.

RESULTS

The result demonstrated that COX-2 expression was significantly higher in radicular cysts with higher levels of inflammatory infiltrates. COX-2 stain was detected in the lining epithelium, subepithelial fibroblasts, macrophages and endothelial cells in all specimens.

CONCLUSIONS

COX-2 expression is significantly higher in radicular cysts. COX-2 may play an important role in the pathogenesis of radicular cysts.

Prevalence of different periapical lesions associated with human teeth and their correlation with the presence and extension of apical external root resorption

AIM

The aim of this study was to determine the prevalence of various periapical pathologies and their association with the presence and extent of apical external inflammatory root resorption in human teeth.

METHODOLOGY

One hundred and four root apices from extracted teeth with periapical lesions were examined. Semi-serial sections of soft tissue lesions were stained with HE. The lesions were classified as noncystic or cystic, each with different degrees of acute inflammation: 0, 1, 2 and 3, increasing in severity. The root apices were analysed by SEM. External root resorption was classified according to site, as periforaminal or foraminal, and the extension of the resorbed area graded in increasing area as 0, 1, 2 or 3.

RESULTS

Cysts accounted for 24.5% of the samples, 84% of which were associated with marked inflammation. The most prevalent diagnosis was noncystic periapical abscess with varying degrees of severity (63.7%). Periapical granuloma was not a frequent finding. SEM analysis showed that 42.2% of the root apices had periforaminal resorption extending over 50% of their circumference. When the foraminal resorption was evaluated, 28.7% had resorption affecting >50% of the periphery. Only 8.9% of the samples showed no periforaminal or foraminal resorption.

CONCLUSIONS

In the sample of extracted teeth investigated, 24.5% of the periapical lesions were cysts. Most periapical lesions (84.3%) displayed acute inflammation, whether cystic or not. Periforaminal resorption was present in 87.3% of the cases, and foraminal resorption in 83.2%. Periforaminal and foraminal resorptions were independent entities. There was no association between external root resorption and the nature of the periapical lesions.

Immunohistochemical analysis of CD1a-labeled Langerhans cells in human dental periapical inflammatory lesions--correlation with inflammatory cells and epithelial cells

OBJECTIVE

Distribution and density of CD1a-labeled Langerhans cells (LCs) were examined in human dental periapical inflammatory lesions, and compared with inflammatory cell infiltration or epithelial cell proliferation.

MATERIALS AND METHODS

Eighty three periapical lesions (26 apical granulomas (AGs), 8 epitheliated granulomas (EGs), 34 radicular cysts (RCs), 15 residual radicular cysts (RRCs)) were collected. As control, specimens of periodontal ligaments including Malassez epithelial rests were curetted from 21 teeth. LC densities were measured and various degrees of inflammatory cell infiltration were examined immunohistochemically. Labeling indices for the cellular proliferation markers Ki-67 antigen and DNA topoisomerase II alpha were calculated in the epithelial components.

RESULTS

LCs were found in all periapical lesions but not in Malassez epithelial rests. LCs were more abundant in epithelial components than in subepithelial layers. Intraepithelial LCs were more frequent in RCs than in RRCs, whereas subepithelial LCs were less frequent in RRCs than in AGs and EGs. T lymphocytes consistently outnumbered macrophages, plasma cells and B lymphocytes. The range of the CD4/CD8-positive cell ratio differed according to the lesions. Increased LC density was associated with the severity of CD3-positive cell infiltration. Ki-67- and Topo II-LI showed various degrees of epithelial immunoreactivity. There was a significant correlation between LC density and proliferative potential of the epithelium in periapical lesions.

CONCLUSION

These findings suggested that LCs appeared to be associated with T lymphocyte infiltration and proliferative potential of the epithelial tissue in periapical lesions.

Protective and destructive immune reactions in apical periodontitis

Apical periodontitis is initiated primarily by the mixed microflora of infected root canals. Continuous flow of bacteria and their products through the apical foramen induces influx, activation and coordinated interaction of immune-inflammatory cells within the periapical area. Successful mobilization of host defense mechanisms prevents abundant extraradicular bacterial invasion. However, anti-infective effector mechanisms are not restricted to killing the invading microorganisms but also destroy normal tissue components and induce bone absorption, resulting ultimately in the loss of the affected teeth. Moreover, autocrine and paracrine loops of stimulation may lead to the perpetuation of the local inflammatory lesion and may also alter the function of remote tissues and organs. This review attempts to summarize current knowledge about the pathogenic mechanism of apical periodontitis, focusing on the formation of a special granulation tissue that effectively fights bacteria originated from the infected pulp chamber and, by exerting this protective function, also contributes to harmful local and distant events. The dynamic equilibrium between defensive and destructive mechanisms may provide a pathobiological basis for better understanding of clinical signs and symptoms of various forms of apical periodontitis lesions and influence treatment strategy and practice.

Differential in situ distribution of interleukin-8, monocyte chemoattractant protein-1 and Rantes in human chronic periapical granuloma

In situ distribution of three prototype chemokines interleukin (IL)-8, monocyte chemoattractant protein (MCP)-1 and Rantes was determined in chronic human periapical granulomas by immunohistochemistry using monoclonal antibodies. IL-8 was found primarily in the cytoplasm of the Malassez epithelial cells. MCP-1 immunoreactivity was confined to the endothelial cells that lined small venules. Each of the three investigated chemokines, including Rantes, exhibited a characteristic binding pattern to the extracellular matrix of the lesion. The observed chemokines may play a role in establishing the cellular composition of chronic apical periodontitis, thus augmenting the intensity of local inflammation and tissue damage.

Cell synthesis, proliferation and apoptosis in human dental periapical lesions analysed by in situ hybridisation and immunohistochemistry

OBJECTIVE

The role of structural and host defensive cells in periapical lesions has been assessed previously by morphometric and immunohistochemical studies. The aim of this study was to investigate the function of peri- apical cells by employing molecular techniques to estimate the cell synthetic activity, proliferation and apoptosis in these lesions. We specifically sought answers to the following questions. Which cells of the periapical lesions are quiescent or actively synthesising proteins? Do immune cells proliferate in this region in the same way as epithelial cells proliferate? Furthermore do cells in peri- apical lesions undergo apoptosis, and if so which cells exhibit this programmed cell death?

MATERIALS

Twenty-five periapical tissue samples (15 granulomas and 10 radicular cysts) were assessed. Poly-adenosine (poly (A)) RNA and ribosomal RNA (rRNA) bearing cells in formalin-fixed/paraffin-embedded peri- apical tissues were analysed by in situ hybridization (ISH) using digoxigenin-labelled oligo d (T) and 28S rRNA probes respectively in order to estimate cell synthetic activity. Furthermore, S-phase proliferating and cycling cells were examined by ISH using a histone probe and Ki-67 immunostaining so as to assess cellular proliferation. Mononuclear cells were further differentiated by immunohistochemistry (IHC) as T cells, B cells and macrophages. Apoptotic cells were determined by in situ end-labelling methodology for detecting fragmented DNA.

RESULTS

Poly (A) RNA (mostly messenger RNA) and 28S rRNA-expressing cells were detected in all samples. Plasma cells exhibited strongest staining for the two probes, with slight to moderate staining found in the epithelium, fibroblasts, macrophages, endothelial cells and lymphocytes, whereas almost all polymorphonuclear leucocytes (PMN) were negative for these probes. A few histone mRNA-expressing cells were detected in basal and suprabasal epithelial cells and mononuclear cells in 15/25 cases but their reactivity was weak. Ki-67 positive cells were found in all samples and their numbers were generally higher than histone mRNA positive cells. Apo- ptotic cells were detected in 23/25 cases and the majority of apoptotic cells were PMN which were engulfed by large cytophagocytic macrophages.

CONCLUSION

This study indicates that in dental periapical lesions, apoptosis occurs predominantly in PMN. It is evident that most cells apart from PMN are exhibiting synthetic activity but only epithelial cells undergo proliferation which implies that immune cells must proliferate at distant lymph nodes and travel to the periapical lesion rather than proliferating within the lesion. These results suggest considerable advantages in estimating gene expression within cells in addition to the immunohistochemical detection of cells to determine cell activity at inflamed sites. Clearly, functional cell synthetic activity, resolution and clearance systems operate in peri- apical cystic and granuloma lesions.

Periapical inflammatory responses and their modulation

Periapical inflammatory responses occur as a consequence of bacterial infection of the dental pulp, as a result of caries, trauma, or iatrogenic insult. Periapical inflammation stimulates the formation of granulomas and cysts, with the destruction of bone. These inflammatory responses are complex and consist of diverse elements. Immediate-type responses--including vasodilatation, increased vascular permeability, and leukocyte extravasation--are mediated by endogenous mediators, including prostanoids, kinins, and neuropeptides. Non-specific immune responses--including polymorphonuclear leukocyte and monocyte migration and activation, and cytokine production--are elicited in response to bacteria and their products. Interleukin-1 and prostaglandins in particular have been implicated as central mediators of periapical bone resorption. Chronic periapical inflammation further involves specific T- and B-cell-mediated anti-bacterial responses, and activates a network of regulatory cytokines which are produced by Th1- and Th2-type T-lymphocytes. Various naturally occurring and genetically engineered models of immunodeficiency are beginning to help elucidate those components of the immune system which protect the pulpal/periapical complex. Both specific and non-specific responses interface with and are regulated by the neural system. The modulation of these responses by immune response modifies, cytokine antagonists, and other novel therapeutic agents is discussed. As an experimental model, periapical inflammation has many advantages which permit it to be used in studies of microbial ecology and pathogenesis, host response, neuroimmunology, and bone resorption and regeneration.

Increased susceptibility of RAG-2 SCID mice to dissemination of endodontic infections

Specific immunity has been implicated in the pathogenesis of periapical lesions, although the extent to which these mechanisms are actually involved in either protection or destruction of the pulp-periapex complex is yet to be established. To investigate this question we compared periapical-lesion pathogenesis in RAG-2 severe combined immunodeficient (SCID) mice with immunocompetent control mice following surgical pulp exposure. In order to equalize the bacterial challenge, an infection protocol using Prevotella intermedia, Fusobacterium nucleatum, Peptostreptococcus micros, and Streptococcus intermedius was devised. The results demonstrated that after infection, the proportion of the root canal flora represented by the four pathogens was almost identical in both groups (39.9 and 42.2% for RAG-2 and immunocompetent control mice, respectively). The effects of abrogation of T- and B-cell mechanisms on periapical pathogenesis were then assessed. Approximately one-third of the RAG-2 mice developed endodontic abscesses, while no immunocompetent controls had abscesses, results which indicated regional dissemination of the infection. A similar incidence of abscesses was found in two additional experiments. Abscessed RAG-2 teeth had significantly larger periapical lesions than did nonabscessed RAG-2 teeth (P < or = 0.05) and exposed immunocompetent controls (P < or = 0.01), whereas nonabscessed RAG-2 teeth were not significantly different from those of exposed immunocompetent controls in periapical-lesion size. We conclude that B- and T-cell-mediated immunity protects the host from the dissemination of endodontic infections and that RAG-2 mice are more susceptible to infection-induced pulp-periapex destruction.

Mast cell-derived tryptase in odontogenic cysts

Inflammatory and developmental cysts of the jaws are relatively common bone destructive lesions in the human maxillofacial skeleton but their pathogenesis is still poorly understood. In this study the role of mast cells (MC), and mast cell tryptase in particular, was evaluated in the pathophysiology of bone resorption and jaw cyst formation in different types of cysts. The distribution of MC and the amount of tryptase in histological tissue sections were determined by immunohistochemistry using monoclonal antihuman tryptase antibodies and the results were quantitated by using an image analyzing system. The amount of tryptase was further studied by Western-blotting and measurement of trypsin-like activity from the neutral salt extracts obtained from different types of jaw cysts. In contrast to control tissue, high trypsin-like activities and abundant immunoreactive tryptase were observed in the extracts of all types of cysts studied (radicular, dentigerous and keratocyst). In tissue sections the highest amount of tryptase-positive staining was observed in radicular cysts (mean 6.2% of reference area) and the lowest amount in keratocysts (mean 2.1% of reference area, P < 0.01). MC were found to be located in inflammatory cell-rich tissue areas and just beneath the cyst epithelium. Importantly, MC located at the border of bone were observed to be degranulated, indicating high activity of MC and release of tryptase at the regions of early bone destruction. Based on previous findings addressing the role of mast cell tryptase in proteolytic cascades, and the known association of MC with osteoporosis, we suggest that mast cells and mast cell tryptase may contribute significantly to jaw cyst tissue remodelling during growth of a cyst, and to the destruction of the surrounding bone, resulting in jaw cyst expansion.

Types and incidence of human periapical lesions obtained with extracted teeth

OBJECTIVES

To determine (1) the frequency of the incidence of abscess, granuloma, and radicular cyst among human periapical lesions obtained with extracted teeth; and (2) whether periapical cysts occur in two categories when histologically analyzed in relation to the root canals.

STUDY DESIGN

A total of 256 lesions were analyzed. The specimens were decalcified and embedded in plastic. Serial sections or step-serial sections were prepared, and the sections were evaluated on the basis of predefined histopathologic criteria.

RESULTS

The 256 specimens consisted of 35% periapical abscess, 50% granuloma, and 15% cysts. The latter occurred in two categories, the apical true cysts and the apical pocket cysts.

CONCLUSIONS

These results show (1) the low incidence of radicular cysts among periapical lesions as against the widely held view that almost half of all periapical lesions are cysts; and (2) the occurrence of two classes of radicular cysts. We are of opinion that the pocket cysts may heal after root canal therapy but the true cysts are less likely to be resolved by conventional root canal treatment.

Immunohistochemical examination on the localization of macrophages and plasma cells in induced rat periapical lesions

To investigate the role of plasma cells and macrophages in the development of periapical lesions, we immunohistochemically examined the distribution of these inflammatory cells in experimental induced rat periapical lesions after pulpectomy. The number of ED1-positive mononuclear cells increased rapidly, reached a plateau which remained stable between days 10 and 60, and subsequently decreased. Immunoglobulin (Ig)-bearing plasma cells appeared after 60 days, and, of these, IgG-bearing plasma cells were predominant after 90 days. The radiographic and histopathological findings indicated the development of bone destruction at 10 days which continued until 60 days; tissue repair began to take place after 90 days. The results suggested that macrophages had a close relation to bone destruction and that plasma cells might participate in tissue repair rather than the development of periapical lesions.

The role of reactive oxygen intermediates in the pathogenesis of chronic apical periodontitis

The level of malondialdehyde, a stable end product of lipid peroxidation induced by reactive oxygen intermediates and the activity of two potent antioxidant enzymes, superoxide dismutase and glutathione peroxidase, was investigated in tissue homogenates of 22 surgical periapical granuloma specimens. Malondialdehyde levels were significantly higher and glutathione peroxidase activity was significantly lower in periapical granuloma samples than in healthy gingival tissue homogenates, which were used as controls. The activity of superoxide dismutase was similar in periapical granuloma and in control samples. Our results indicate an altered balance between the production and the elimination of toxic oxygen metabolites in chronic apical periodontitis. We hypothesize that reactive oxygen intermediates, which are being produced by activated phagocytic cells abundantly present in periapical granulomas, can contribute to periapical tissue injury and bone loss in this disease.

Langerhans cells: structure, function and role in oral pathological conditions

Langerhans cells (LCs) are dendritic bone marrow derived cells situated suprabasally in most stratified squamous epithelia, such as the epidermis and the epithelium of oral mucosa, including the gingiva. Langerhans cells are thought to act as antigen-presenting cells (APC) during induction of immune responses. The exact role of Langerhans cells in the oral mucosa is not fully understood although several investigations suggest that these cells are involved in reactions to antigen challenge under both normal and pathological situations. In this paper the structure, phenotypic markers and derivation of Langerhans cells are reviewed. In view of recent findings, the immunological characteristics and the implications of Langerhans cells in pathologic oral reactions are discussed.

Characterization of inflammatory cell infiltrate in dental periapical lesions

Sixty-three dental periapical lesions were investigated in order to study the involvement of inflammatory and immunologic reactions in the pathogenesis and maintenance of chronic apical periodontitis. Of 61 well-preserved specimens, 38 were classified as granulomatous, 3 as exudative periapical granulomas and 20 as periapical scars. The quantitative composition of T-lymphocyte subpopulation and macrophages, the proportion of IgE-producing cells compared with other immunoglobulin producing plasma cells, and the tissue distribution of IgE-producing plasma cells compared with that of mast cells were determined in the granulomatous types of granulomas using immunofluorescent, immunohistochemical and enzymehistochemical methods. The results indicated a decreased ratio of helper/inducer versus cytotoxic/suppressor T-lymphocytes, a remarkably high proportion of macrophages, a low frequency of IgE-producing plasma cells with different localization when compared with that of mast cells. These observations suggest that T-lymphocytes and macrophages may play an important role in the complex events of tissue destruction and repair taking place in the periapical region.

Quantitative significance of IgE-producing plasma cells and tissue distribution of mast cells in apical periodontitis

A total of 30 dental periapical lesions were used for estimating the frequency of IgE-producing plasma cells by the unlabelled antibody peroxidase antiperoxidase method. Mast cells were detected in adjacent sections by the naphthol-AS-D-chloroacetate esterase technique. IgE-producing plasma cells were present in the central granulation tissue in 26 of the 30 specimens. The average ratio of IgE-containing plasma cells was 0.22% as related to all plasma cells. The central granulation tissue was devoid of mast cells, but numerous mast cells were found in the fibrous capsule of periapical lesions.

Mast cells in human odontogenic cysts

Mast cells have been shown to be present in substantial numbers in both nonkeratinizing and keratinizing odontogenic cysts and could be seen in the connective tissue capsule and the epithelial lining. Within the cyst capsule, mast cells were more prevalent just beneath the epithelium than in deeper areas. This distribution pattern for mast cells is in accord with the histochemical picture for heparin staining in odontogenic cysts. In the non-keratinizing cysts, there appeared to be some trend towards mast cells being associated with increasing inflammation but not in the odontogenic keratocyst. No evidence could be found for distinct mast cell subpopulations in odontogenic cysts. The presence of mast cells in odontogenic cyst could contribute to their pathogenesis in several ways.

The effect of indomethacin on experimental dental periapical lesions in rats

The role of prostaglandins in the pathogenesis of dental granulomas and associated bone loss was studied by testing the ability of indomethacin, a potent inhibitor of prostaglandin synthesis, to influence bone resorption in experimentally induced dental granulomas. The cusps of maxillary first molar teeth of Sprague-Dawley rats were ground away, exposing the dental pulps to the oral environment. Daily i.p. injections of 0.1 to 0.2 ml of indomethacin (10 mg per kg) dissolved in 95% ethyl alcohol were administered to one group of the rats while the other group received i.p. injections of 0.1 to 0.2 ml of 95% ethyl alcohol. The rats were killed after 6 wk and specimens of the molar teeth and surrounding jaw bone were taken for routine histopathological processing. The specimens from indomethacin-treated rats demonstrated milder inflammatory changes and a significantly lower degree of periapical alveolar bone resorption. These results support the suggestion that prostaglandins are involved in the events leading to bone resorption in dental periapical lesions.

Human T-lymphocyte subpopulations in periapical lesions

Both B-lymphocyte-and T-lymphocyte-mediated immunologic reactions have been implicated in the pathogenesis of human periapical lesions. The purpose of this study was to identify various subpopulations of T-lymphocytes in these lesions. Fifteen periapical lesions were obtained during periapical surgery. Each specimen was quick-frozen and stored in liquid nitrogen. Immunoperoxidase staining for the presence of T-lymphocyte subpopulation, was done with the use of the monoclonal antibody and Vecta-stain ABC/peroxidase kit. Cryostat tissue sections were incubated with 3% normal horse serum. Specific monoclonal antibody (Coulter T4, T8, T11) was placed on the section, washed, and then covered with biotinylated antibody to mouse IgG. After TRIS HC1 washing, the ABC/peroxidase solution was placed on the section and 3,3-diaminobenzidine was applied; the section was washed and then counterstained with 2% methyl green. After dehydration, sections were mounted and examined under the light microscope. The presence of lymphocytes was confirmed by the appearance of brown rings around cells with lymphocyte morphology. Fourteen lesions were diagnosed as granuloma and stained positively for pan T-lymphocytes (T11), T helper cells (T4), and T cytotoxic cells (T8). The remaining specimen, diagnosed as an apical scar, contained no T-lymphocytes. The presence of T-cells in periapical lesions indicates that cell-mediated reactions participate in the pathogenesis of these lesions.

Immunocytochemical examination of immune cells in periapical granulomata and odontogenic cysts

Monoclonal antibodies (mAbs) were used to determine the presence and distribution of immune cells including lymphocytes, macrophages and Langerhans cells, in normal periodontal ligament, periapical granulomata, periapical cysts and dental developmental cysts. Isolated T-lymphocytes, but not B-lymphocytes, were detected in specimens of non-inflamed periodontal ligament. Increased numbers of T and B lymphocytes were found in all of the lesions examined. Monocytes/macrophages were associated with most periapical granulomata, dental developmental cysts and all periapical cysts. Langerhans cells, intraepithelial lymphocytes, and monocytes/macrophages were not detected in the rests of Malassez but were found in some epithelia within periapical granulomata and in most epithelial linings of odontogenic cysts. Increased numbers of immune cells were seen around proliferative epithelia and adjacent to the epithelial linings of cysts. Epithelium, particularly that of odontogenic cysts, showed positive reactions for HLA-Dr, lysozyme and for alpha-1 antitrypsin. The presence of immune cells in periapical granulomata and odontogenic cysts, suggests that cell-mediated and humoral immunoreactions occur in these lesions and may be associated with the epithelial proliferation within the periapical lesions.

Histochemical studies on glycosaminoglycans of odontogenic cysts

Histochemical examination of odontogenic cyst connective tissue has demonstrated that hyaluronic acid is the predominant glycosaminoglycan present with lesser amounts of the sulphated glycosaminoglycans. Mast cells were frequently observed in the connective tissue, particularly just beneath the epithelium and may be responsible for the enhanced staining for heparin observed in this area. Local tissue metabolism and inflammation will contribute to the release of glycosaminoglycans from connective tissue into the lumenal fluid. Staining of glycosaminoglycans was generally minimal in the epithelium, although hyaluronic acid and chondroitin sulphate were detected in goblet cells. Glycosaminoglycans previously demonstrated in cyst fluids are probably derived from several sources in the cyst and will be important in its expansile growth.

Quantification and analysis of the glycosaminoglycans in human odontogenic cyst linings

Glycosaminoglycans (GAG) were extracted from the connective tissue of 15 dental cysts, 2 dentigerous cysts and 7 keratocysts, and separated electrophoretically and chromatographically. Hyaluronic acid (dental, 2.38; dentigerous, 3.98; keratocyst, 3.19 micrograms uronic acid/mg lyophilized tissue) was the major GAG detected, with lesser amounts of heparin (dental, 1.70; dentigerous, 1.95; keratocyst, 1.80 micrograms uronic acid/mg lyophilized tissue) and chrondroitin-4-sulphate (dental, 1.33; dentigerous, 2.85; keratocyst, 1.37 micrograms uronic acid/mg lyophilized tissue). It is suggested that enzymic release of these GAGs allows their diffusion into the luminal fluid where they may contribute to expansile cyst growth.

In situ characterization of cells in periapical granuloma by monoclonal antibodies

Monoclonal antibodies were used in histopathologic and immunohistologic studies of periapical granulomas. In cellular zones, plasma cells and lymphocytes predominated, with variable numbers of fibroblasts, macrophages, and polymorphonuclear leukocytes. Labeling with monoclonal antibodies disclosed relatively infrequent, usually scattered macrophages. Plasma cells were numerous and frequently clumped. The vast majority of lymphocytes were T cells, scattered individually or in small groups of three or four cells and dispersed throughout the granulomas without any topographic predilection, with prevalence of T-suppressor/cytotoxic cells over T-helper/inducer cells. Our findings of numerous plasma cells, which were in agreement with descriptions of numerous immunoglobulin-producing cells by other authors, imply the participation of antibody-mediated immune reactions in periapical granulomas. The presence of cell-mediated immunity, in spite of numerous T cells, could not be confirmed.

An apical granuloma with epithelial integument

A chronic periapicalesion--apical granuloma--of the first left maxillary molar, which had rarefied the bony plate and grown into the maxillary sinus, was observed in a 64-year-old white male patient. Light microscopic study of the epon-embedded specimen showed a lesion that had been infiltrated predominantly by mononuclear cells and that had isolated neutrophil-dominated foci. The lesion contained extensive networks and arcades of proliferating epithelium. Unlike the classic granulomas of the periapex, which are generally delimited by a well-developed connective tissue capsule, this particular lesion was lined with epithelial tissue consisting of ciliated columnar and stratified squamous components. While the former seemed to be an extension of the sinus epithelium, the latter appeared to be an outgrowth of the proliferating epithelium encountered within the lesion.