Immunohistochemical Detection of Factors Related to Cellular Proliferation and Apoptosis in Radicular and Dentigerous Cysts

CD34 and Ki-67 Immunoexpression in Periapical Granulomas: Implications for Angiogenesis and Cellular Proliferation

BACKGROUND/OBJECTIVES

The main mechanism of the formation of granulation tissue is the progression of an infection from the tooth to the periapical bone. At this level, the immune system tries to localize and annihilate the microorganism's injury. Ki-67 is a protein directly associated with the cell proliferation rate, while CD34 is a biomarker involved in angiogenesis, and studies suggest that they both have a positive correlation with the intensity of the local inflammatory infiltrate. This study will determine the immunoexpression of CD34 and Ki-67 in periapical granulomas and assess their impact on the growth and development of this tissue, as well as consider their roles in the proliferative process and aggressiveness of evolution.

METHODS

In the present study, 35 periapical granulomas obtained after a tooth extraction were included. The specimens were analyzed via histopathology and immunohistochemistry.

RESULTS

A positive reaction for the Ki-67 antibody was observed in 32 (86.5%) of the 35 periapical granuloma cases included in our study. We identified the overexpression of Ki-67 and CD34 and further calculated the Ki-67 index to evaluate and correlate the proliferation potential and angiogenesis with regard to the presence of an inflammatory infiltrate.

CONCLUSIONS

These findings suggest that the persistence of an inflammatory environment directly influences Ki-67 and CD34 expression, sustaining the proliferative capacity of cells and abnormal angiogenesis. This study is the first to evaluate the presence of the CD34+ and Ki-67+ proliferating vessels in periapical granulomas.

Primary cilia and hypoxia-associated signaling in developmental odontogenic cysts in relation to autosomal dominant polycystic kidney disease - A novel insight

Developmental cysts are pathological epithelial-lined cavities arising in various organs as a result of systemic or hereditary diseases. Molecular mechanisms involved in the formation of developmental odontogenic cysts (OCs) are not fully understood yet; the cystogenesis of renal cysts originating from the autosomal dominant polycystic kidney disease (ADPKD) has been, however, explored in much greater detail. This narrative review aimed i) to summarize molecular and cellular processes involved in the formation and growth of developmental OCs, especially dentigerous cysts (DCs) and odontogenic keratocysts (OKCs), ii) to find if there are any similarities in their cystogenesis to ADPKD cysts, and, based on that, iii) to suggest potential factors, candidate molecules, and mechanisms that could be involved in the DC formation, thus proposing further research directions. Here we suggest a possible association of developmental OCs with primary cilia disruption and with hypoxia, which have been previously linked with cyst formation in ADPKD patients. This is illustrated on the imagery of tissues from an ADPKD patient (renal cyst) and from developmental OCs, supporting the similarities in cell proliferation, apoptosis, and primary cilia distribution in DC/OKC/ADPKD tissues. Based on all that, we propose a novel hypothesis of OCs formation suggesting a crucial role of mutations associated with the signaling pathways of primary cilia (in particular, Sonic Hedgehog). These can lead to excessive proliferation and formation of cell agglomerates, which is followed by hypoxia-driven apoptosis in the centers of such agglomerates (controlled by molecules such as Hypoxia-inducible factor-1 alpha), leading to cavity formation and, finally, the OCs development. Based on this, we propose future perspectives in the investigation of OC pathogenesis.

Expression pattern of hypoxia-related genes in odontogenic cysts

OBJECTIVE

The aim of the present study was to reveal the effects of hypoxia-associated signaling in odontogenic cysts.

DESIGN

The expression levels of genes involved in the hypoxia-associated signaling pathway were determined by quantitative Polymerase Chain Reaction (PCR) method.

RESULTS

As a result, it was found that phosphatase and tensin homolog (PTEN) expression was low (p = 0.037), and the expression levels of phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) (p = 0.0127), hypoxia inducible factor 1 alpha (HIF1A) (p < 0.001), and HIF1A antisense RNA 1 (HIF1A-AS1) (p = 0.0218) were higher in cyst tissue compared to normal tissue. HIF1A gene expression was found to be significantly altered according to the pathologic subtypes of odontogenic keratocyst, dentigerous cyst, and radicular cyst.

CONCLUSIONS

Odontogenic cysts were found to have higher expression of HIF1A and HIF1A-AS1, which may be related to the increased hypoxia in these lesions. In addition, PI3K/Akt signaling may be stimulated by increased PIK3CA and decreased PTEN expression, which promote cell survival and support the mechanism of cyst formation.

Expression of epithelial growth factors and of apoptosis-regulating proteins, and presence of CD57+ cells in the development of inflammatory periapical lesions

The mechanisms that stimulate the proliferation of epithelial cells in inflammatory periapical lesions are not completely understood and the literature suggests that changes in the balance between apoptosis and immunity regulation appear to influence this process.

Proliferative and anti-apoptotic indices of unicystic ameloblastoma, odontogenic keratocyst, dentigerous cyst and radicular cyst

Objective:

The aim of this study is to compare the proliferative capacity and antiapoptotic capacity of unicystic ameloblastoma (UA), odontogenic keratocyst (OKC), dentigerous cyst (DC) and radicular cyst (RC) by assessing the Ki-67 labeling index (LI) and Bcl-2 LI, respectively.

Materials and Methods:

Formalin-fixed, paraffin-embedded tissue blocks of twenty-three histopathologically diagnosed UAs, 6 OKCs, 8 DCs and 10 RCs were selected from the archival specimens. Five micrometer thick sections of tissue blocks of the lesions were processed for immunohistochemical staining with Ki-67 and Bcl-2. The Ki-67 LI and Bcl-2 LI were determined for the cases with a positive reaction.

Results:

Ki-67 expression was seen in 6 (26.1%) cases of UA, 4 (66.7%) OKC, 1 (12.5%) DC and 1 (10.0%) RC. There was a statistically significant difference between the mean Ki-67 LI of UA and OKC (P = 0.024). Bcl-2 expression was seen in 16 (69.6%) UA, 5 (83.3%) OKC, 5 (62.5%) DC and 5 (50.0%) RC. The mean Bcl-2 LI of UA was significantly higher than that of DC (P = 0.048). Furthermore, cases of OKC had significantly higher mean Bcl-2 LI compared to DC (P = 0.026) and RC (P = 0.049).

Conclusion:

This study suggests that the Ki-67 LI may help in differentiating OKC from UA. The Bcl-2 LI may be useful in differentiating UA from DCs, and differentiating OKC from DC and RC.

A Clinicopathological Approach to Odontogenic Cysts: the Role of Cytokeratin 17 and bcl2 Immunohistochemistry in Identifying Odontogenic Keratocysts

Odontogenic keratocysts (OKCs) are developmental cysts of the jaws that require proper diagnosis due to their potential for local aggressive growth and recurrences. OKCs have a typical parakeratotic epithelium demonstrating transepithelial cytokeratin 17 (CK17) and basal bcl2 staining on immunohistochemistry (IHC), which distinguishes them from other common jaw cysts. Secondary to inflammation, the epithelial lining may be altered and loses the typical IHC phenotype. The aim of the present study was to analyse a series of consecutive jaw cysts for their expression of CK17 and bcl2 and assess how these IHC stains may help in their diagnosis. All cysts were retrospectively assessed for available clinical, radiological and pathological findings and diagnoses were revised whenever needed. 85 cysts from 72 patients were collected from two departments. The series had 21 OKCs, the remaining non-OKCs included radicular/residual, dentigerous, paradental, lateral periodontal, botryoid odontogenic cysts. OKCs with typical epithelium showed the typical IHC phenotype, which was generally lost in inflammation-associated altered epithelium. Contrarily to earlier descriptions, a wide variety of CK17 positivity was seen in the majority of non-OKCs, including focal transepithelial staining. Basal bcl2 staining was also seen in 16 non-OKCs. These stainings were never as strong in intensity as seen in OKCs. One case was histopathologically identified as OKC due to focally maintained IHC profile. CK17 and bcl2 IHC may help in the diagnosis of OKCs, but must be interpreted with caution and is not a yes or no tool in the diagnostic puzzle.

Effect of calcium hydroxide as intracanal medicament on the expression of caspase-9 located within the radicular cyst epithelium

Apoptosis (a programmed cell death mechanism) within the radicular cyst epithelium has still not been correlated with any clinical factor. This study aimed to investigate the effect of calcium hydroxide on apoptosis, via the detection of caspase-9. Thirty radicular cysts collected during apicoectomies and stored in paraffin were retrospectively retrieved. Conservative endodontic treatments had been carried out either without (group (a) n = 14), or with calcium hydroxide application (group (b), n = 16) before obturation. All cysts were immunohistochemically stained for caspase-9 to record apoptosis of the epithelium. Statistical analysis followed. The frequency of caspase-9 immunoreactivity in the cystic epithelium in the two groups was 42.86% and 93.75% of cysts respectively. This difference was statistically significant (P = 0.04 < 0.05). In cysts larger than (or equal to) 10 mm, caspase-9 was more frequently expressed. It was found calcium hydroxide appears to enhance the expression of caspase-9, especially in large lesions.

Analysis of CD57+ natural killer cells and CD8+ T lymphocytes in periapical granulomas and radicular cysts

The aim of this study was to compare the number of CD57+ natural killer (NK) cells and CD8+ T lymphocytes between periapical granulomas (PGs) and radicular cysts (RCs). Twenty-fives cases of PGs and 25 of RCs were submitted to histological analysis and immunohistochemistry using anti-CD57 and anti-CD8 biomarkers. Positive cells were counted in 10 fields (400× magnification) and the median value was calculated for each case. Statistical tests were used to evaluate differences in the number of CD57+ NK cells and CD8+ T lymphocytes according to type of lesion, intensity of the infiltrate and thickness of the lining epithelium. The number of CD57+ NK cells and CD8+ T lymphocytes was higher in PGs than in RCs (p = 0.129 and p = 0.541, respectively). Comparison of the number of CD57+ NK cells in atrophic and hyperplastic epithelium revealed a larger number of cells in the atrophic epithelium (p = 0.042). A larger number of CD57+ NK cells and CD8+ T lymphocytes were observed in grade III infiltrates compared to grade I/II (p = 0.145 and p = 0.725, respectively). CD8+ T lymphocytes were more prevalent than CD57+ NK cells in most cases when PGs and RCs were analyzed separately or in combination (p < 0.0001). CD57+ NK cells and CD8+ T lymphocytes play a key role in antiviral defense and the presence of these cells supports evidence suggesting the participation of these microorganisms in the pathogenesis of PGs and RCs. The response mediated by CD8+ T lymphocytes was more frequent, indicating greater participation of the adaptive immunity in these chronic lesions.

Role of HIF-1α and CASPASE-3 in cystogenesis of odontogenic cysts and tumors

OBJECTIVES

Odontogenic cysts and tumors are the most relevant lesions that affect the gnathic bones. These lesions have in common the formation of cystic areas and this common feature may suggest involvement of similar mechanisms. The hypoxia inducible factor 1 alpha (HIF-1α), a responsive protein to hypoxia and caspase-3, an irreversible apoptosis marker, may contribute to cyst formation. Thus, this study aimed to investigate the immunoexpression of these proteins in odontogenic cysts and tumors.

MATERIAL AND METHODS

Twenty cases of ameloblastoma, keratocystic odontogenic tumor (KOT) (n = 20), radicular cyst (RC) (n = 18), dentigerous cyst (DC) (n = 11), calcifying cystic odontogenic tumor (n = 8), and dental follicle (DF) (n = 10) were used to investigate HIF-1α and caspase-3 expression in sequential serial cuts by immunohistochemistry.

RESULTS

HIF-1α was overexpressed in RC, DC, and ameloblastoma when compared with DF. The basal and sometimes the lower suprabasal layer showed no or very low expression in DC, KOT, and ameloblastoma, the last also showing strong expression in solid epithelial areas and initial cystic formation regions. Caspase-3 was found to be overexpressed in all lesions, with the highest expression in odontogenic cysts compared to tumors. HIF-1α and caspase-3 were localized in similar areas of the same lesions, especially in the epithelium surrounding cystic formations.

CONCLUSIONS

This study showed distinct immunoexpression of HIF-1α and caspase-3 in odontogenic cyst and tumors, with higher expression observed in odontogenic cysts.

CLINICAL RELEVANCE

These findings suggest a possible correlation between hypoxia, apoptosis, and cystogenesis, leading to understand the mechanisms responsible to cystic formation in odontogenic lesions.

Comparative immunoexpression of ICAM-1, TGF-β1 and ki-67 in periapical and residual cysts

Background

This study compared the immunohistochemical expression of ki-67, transforming growth factor beta 1 (TGF-β1) and intercellular adhesion molecule-1 (ICAM-1) in inflammatory periapical cysts and residual cysts.

Material and Methods

The study sample was composed by 25 periapical cysts and 25 residual cysts and immunohistochemical reactions were carried out using antibodies directed against ICAM-1, TGF-β1 and ki-67. Clinical, radiological, gross, histological and immunohistochemical data were tabulated for descriptive and comparative analysis using the SPSS software and differences were considered statistically significant when p<0.05%.

Results

There were no differences between the expression of ICAM-1 (p=0.239) and TGF-β1 (p=0.258) when comparing both groups. Ki-67 labeling index was higher in residual cysts compared to periapical cysts (p=0.017).

Conclusions

Results from the present study suggest that some specific inflammatory stimuli on residual cysts would modulate their mechanisms of etiopathogenesis, growing and repair.

Key words:Periapical cyst, radicular cyst, residual cyst, transforming growth factor beta 1 (TGF-β1), intercellular adhesion molecule 1 (ICAM-1), ki-67.

Hydrogen peroxide induces apoptosis in human dental pulp cells via caspase-9 dependent pathway

INTRODUCTION

Reactive oxygen species are a group of metabolic intermediates produced during oxidative metabolism in eukaryotic cells. They include superoxide anion (O2(-)), hydrogen peroxide (H2O2), hydroxyl radical (·OH), and (1)O2. Of these intermediates, H2O2 is the most stable. Dental pulp cells can be invaded by tooth bleaching, laser radiation, and dental materials. This can influence the intracellular level of reactive oxygen species. Apoptosis, which is the best-known form of programmed cell death, is pivotal to tissue development and regeneration. Little information is available regarding the relationship between H2O2 and apoptosis of human dental pulp cells (hDPCs). The purpose of this study was to investigate whether H2O2 can induce apoptosis in hDPCs and its signaling way.

METHODS

HDPCs were obtained by using a modified tissue explant technique in vitro and cultured at 37°C, 20% O2 (5% CO2, 95% air) in Dulbecco modified Eagle medium. Cell viability was investigated by methyl-thiazol-tetrazolium assay. Cell apoptosis was detected by using the annexin V-fluorescein isothiocyanate/propidium iodide apoptosis assay and flow cytometry. Expression of activated caspase-3, cleaved caspase-9, and β-actin was analyzed by using Western blot.

RESULTS

Cell viability of hDPCs decreased more in treated groups than in the control group from days 1 to 7. The relative number of apoptotic cells and the expression of activated caspase-3 and cleaved caspase-9 were much higher in groups exposed to 20 and 50 μmol/L H2O2.

CONCLUSIONS

These results imply that low concentrations of H2O2 are cytotoxic to hDPCs and induce apoptosis in hDPCs in a caspase-9-dependent way.

Common Matrix Metalloproteinases (MMP-8, -9, -25, and -26) Cannot Explain Dentigerous Cyst Expansion

OBJECTIVE

Mechanisms of the dentigerous cyst formation from the normal eruption follicle is unknown but disturbances in the proteolytic activity have been suspected, since the growth of these cysts is accompanied by local bone destruction. The aim of the present study was to evaluate the expression of matrix metalloproteinases (MMP) in human dental dentigerous cysts and healthy dental follicles.

MATERIALS AND METHODS

We studied 10 patients with dentigerous cysts and 10 healthy dental follicles from the lower jaw in respect to their immunoexpression of MMPs -8, -9, -25, and -26 and tissue inhibitor of metalloproteinases -1 (TIMP-1).

RESULTS

MMP-8 was expressed slightly more in cyst epithelium than in odontogenic epithelium of healthy controls dental follicle but the difference lacked statistical difference. Other MMPs and TIMP-1 did not differ regarding the studied specimens.

CONCLUSION

Differences in MMP expression cannot solely explain the cyst expansion suggesting the potential involvement of other osteolytic mechanisms.

Avaliação do metabolismo epitelial em cistos radiculares pela técnica de AgNORS

Introdução: A formação do Cisto Radicular (CR) está associada à proliferação dos restos epiteliais de Malassez por estímulos inflamatórios, provenientes da proliferação bacteriana do canal radicular de um dente não vital. Quando o dente é removido, esse cisto passa a ser denominado Cisto Residual (CRe). O tratamento de escolha para o CR é endodôntico, com o objetivo de eliminar a inflamação presente no periápice. No entanto, em alguns casos, o cisto pode continuar a crescer, necessitando de tratamento cirúrgico, o que ocorre na maioria dos casos de CRe. Objetivo: Avaliar o metabolismo do epitélio de revestimento de CR e CRe, utilizando a quantificação das AgNORs, e verificar a influência da presença de inflamação sobre o crescimento desses cistos. Material e método: Vinte casos de CR e dez de CRe foram submetidos à técnica de AgNOR. A análise quantitativa das NORs foi realizada utilizando-se o software 'Contando células'. O teste estatístico pós-hock de Newman-keuls foi realizado para a comparação do número médio de AgNORs entre CR e CRe, e entre áreas inflamadas e não inflamadas. Resultado: Diferença estatisticamente significante (p=0,0094) foi observada entre áreas inflamadas (1,86±0,26) e não inflamadas (1,65±0,20). Na comparação entre CR (1,81±0,28) e CRe (1,73±0,16), não houve diferença estatisticamente significante (p=0,37). Conclusão: A inflamação interfere no metabolismo epitelial de CR e CRe, o que reflete a ação de fatores de crescimento na proliferação do epitélio, contribuindo para o crescimento do cisto, independentemente da presença do fator etiológico associado com a origem da lesão.

Immunohistochemical analysis of factors related to apoptosis and cellular proliferation in relation to inflammation in dentigerous and odontogenic keratocyst

Background:

The effect of inflammation on pathogenesis and biological behavior of odontogenic keratocyst (OKC) and dentigerous cyst (DC) is not completely understood. Hence, we aimed to analyze the effect of inflammation on biological behavior of OKC and DC using a proliferative and anti-apoptotic marker, i.e., proliferative cellular nuclear antigen (PCNA) and Bcl-2, respectively.

Materials and Methods:

Immunohistochemical staining was performed using anti-PCNA and Bcl-2 antibody in 10 cases each of classical OKC, inflamed OKC and classical DC and inflamed DC.

Results:

Inflamed OKC and DC showed a significant increase in PCNA expression and decrease in Bcl-2 expression when compared with non-inflamed cyst. Correlation between inflammation and proliferative and anti-apoptotic activity was found to be statistically non-significant.

Conclusion:

Inflammation is responsible for change in behavior of neoplastic epithelium of OKC and hence should be treated meticulously, whereas in DC it is responsible for changes in the epithelial lining.

A molecular insight into the role of inflammation in the behavior and pathogenesis of odontogenic cysts

Background:

Although, odontogenickeratocyst (OKC) and dentigerous cyst (DC) are considered asdevelopmental cysts inflammation has been seen in its connective tissue wall. Inflammation is seen to alter the epithelial lining of both OKC and DC butwhether it plays in altering the behavior of these cysts is not fully understood.

Aim:

The present study is conducted with the help of molecular marker proliferating cellular nuclear antigen (PCNA) to assess the proliferative activity of OKC and DC and to further evaluate and correlate the effect of inflammation on the proliferative activity and hence on biological behavior of these cysts.

Materials and Methods:

Immunohistochemicalstaining was performed using anti-PCNA antibody in 10 cases each of classical OKC, inflamed OKC, classical DC, and inflamed DC. The resulting data was tabulated on Microsoft excel and subjected to statistical analysis using two-way analysis of variance test, t test and post-hoc test followed by Bonferroni test with the application of statistical package for social sciences (SPSS) (SPSS, Chicago, IL, USA) and Epi-Info 6.04 d, Atlanta, Georgia (USA).

Results:

Total mean PCNA expression is statistically higher in inflamed OKC than classical OKC and inflamed DC also showed significantly higher PCNA expression than classical DC (P < 0.001). Correlation between inflammation and PCNA expression was not statistically significant (P ≥ 0.05).

Conclusion:

Inflammation is responsible for change in behavior of neoplastic epithelium of OKC, whereas in dentigerous it is responsible for changes in epithelial lining and hence should be treated meticulously.

Distribution of mast cells and macrophages and expression of interleukin-6 in periapical cysts

INTRODUCTION

Mast cells and macrophages are important components of the inflammatory infiltrate found in inflammatory periapical diseases. Several cytokines participate in the mechanisms of inflammation, tissue repair, and bone resorption associated with periapical cysts. The aim of the present study was to evaluate the distribution of mast cells and macrophages and the expression of interleukin-6 (IL-6) in periapical cysts.

METHODS

Thirty periapical cysts were selected for the study, and clinical, demographic, and gross information from the cases was obtained from the laboratory records. Five-micrometer sections stained with hematoxylin-eosin were reviewed for analysis of the microscopic features of the cysts, and 3-μm sections on silanized slides were used for immunohistochemical reactions with anti-tryptase, anti-CD68, and anti-IL-6.

RESULTS

There was no statistically significant difference in the mean number of mast cells and macrophages when comparing superficial and deep regions of the fibrous capsule of the cysts. Mean number of mast cells on the superficial region of the fibrous capsule was higher in cysts showing intense superficial inflammation and exocytosis. Macrophages were more commonly found in areas showing IL-6 expression, and IL-6 was less expressed in deep regions of the fibrous capsule in cysts showing greater gross volume.

CONCLUSIONS

The results reinforced the participation of mast cells and macrophages in the pathogenesis of periapical cysts and suggested that IL-6 is not the major bone resorption mediator in larger periapical cysts.

Immunoexpression of interleukin 17, transforming growth factor β1, and forkhead box P3 in periapical granulomas, radicular cysts, and residual radicular cysts

INTRODUCTION

Different cell types and cytokines have been identified as contributors to the formation of periapical lesions. In this perspective, this study aimed to evaluate the immunoexpression of interleukin (IL)-17, transforming growth factor (TGF)-β1, and the forkhead box P3 (FoxP3) in periapical lesions, correlating them with the type of lesion, the intensity of the inflammatory infiltrate, and the thickness of the cystic epithelial lining.

METHODS

Twenty periapical granulomas (PGs), 20 radicular cysts (RCs), and 20 residual radicular cysts (RRCs) were submitted to immunohistochemical analysis using anti-IL-17, anti-TGF-β1, and anti-FoxP3 antibodies.

RESULTS

In comparison with PGs and RCs, RRCs exhibited a lower immunoexpression of IL-17 and TGF-β1 (P = .021 and P < .001, respectively). The number of FoxP3+ cells increased in this order: RRCs, RCs, and PGs (P < .001). In comparison with lesions with inflammatory infiltrates grades I and II, lesions with inflammatory infiltrate grade III exhibited a higher number of FoxP3+ cells (P = .002). Similarly, in comparison with lesions with inflammatory infiltrates grades II and III, lesions with inflammatory infiltrate grade I showed a tendency for a lower expression of IL-17 and TGF-β1 (P = .085 and P = .051, respectively). For all groups, there was a positive correlation between the immunoexpressions of IL-17 and TGF-β1 (P < .05). Positive correlations between the number of FoxP3+ cells and the immunoexpressions of IL-17 and TGF-β1 (P < .05) were found only in PGs.

CONCLUSIONS

Th17 and Treg cells seem to interact at the site of injury, suggesting the involvement of proinflammatory and immunoregulatory cytokines in the pathogenesis of periapical lesions.

Presence of myofibroblasts and matrix metalloproteinase 2 in radicular cysts, dentigerous cysts, and keratocystic odontogenic tumors: a comparative immunohistochemical study

INTRODUCTION

The aim of this study was to analyze the presence of myofibroblasts and matrix metalloproteinase 2 (MMP-2) in radicular cysts (RCs), dentigerous cysts (DCs), and keratocystic odontogenic tumors (KOTs).

METHODS

For the study, 29 RCs, 19 DCs, and 15 KOTs were selected. Immunohistochemical reactions were performed by using anti-MMP-2 and anti-α-smooth muscle actin (SMA) antibodies. For the analysis, 10 high-power fields were observed in each case to determine the percentage of positive cells, which was classified as negative, weak, or strong.

RESULTS

The presence of myofibroblasts (α-SMA-positive cells) was most common in KOTs (46.67%), followed by DCs (36.84%) and RCs (31.04%); however, it was not statistically significant (P = .8). The stromal MMP-2 expression was positive in all lesions but 1 case of KOT. Most cases of RC and DC presented strong MMP-2 expression in the stroma, whereas half of the KOTs showed similar classification. The MMP-2 expression was commonly found in the epithelial lining of the lesions; it was strong in almost all KOTs. No correlation between epithelial and stromal MMP-2 and α-SMA expressions was observed.

CONCLUSIONS

Myofibroblasts and MMP-2 are frequent in RCs, DCs, and KOTs and eventually can contribute to bone resorption, favoring the progression and growth of these lesions.

Apoptotic signaling in mouse odontogenesis

Apoptosis is an important morphogenetic event in embryogenesis as well as during postnatal life. In the last 2 decades, apoptosis in tooth development (odontogenesis) has been investigated with gradually increasing focus on the mechanisms and signaling pathways involved. The molecular machinery responsible for apoptosis exhibits a high degree of conservation but also organ and tissue specific patterns. This review aims to discuss recent knowledge about apoptotic signaling networks during odontogenesis, concentrating on the mouse, which is often used as a model organism for human dentistry. Apoptosis accompanies the entire development of the tooth and corresponding remodeling of the surrounding bony tissue. It is most evident in its role in the elimination of signaling centers within developing teeth, removal of vestigal tooth germs, and in odontoblast and ameloblast organization during tooth mineralization. Dental apoptosis is caspase dependent and proceeds via mitochondrial mediated cell death with possible amplification by Fas-FasL signaling modulated by Bcl-2 family members.