Collagen Fibre orientation and behaviour of odontogenic cysts; A picrosirius red staining and polarising microscopic study

Introduction: Epithelial–mesenchymal interactions are thought to play an important role in the pathogenesis of odontogenic cysts. Odontogenic Keratocyst (OKC) is a benign cystic neoplasm with a characteristic parakeratinized epithelial lining, which differs histologically and behaviourally from the Dentigerous cyst (DC) and Radicular cyst (RC). Biological behaviour of OKC is dependent on both epithelium and the underlying stroma. Collagen plays an important role in maintaining structural integrity and in determination of tissue functions. Collagen has natural birefringence which is attributed to arrangement of its fibres; this property is enhanced by Picrosirius Red staining. Aim: The purpose of this study will be to investigate the differences in collagen fibres within the fibrous tissue walls of OKC, DC and RC. Study design: Formalin-fixed paraffin-embedded tissue samples of OKC, DC, RC was segregated from the department of Oral Pathology & Microbiology, RRDCH and cut sections was subjected to staining with Picrosirius red and was observed under polarising light microscope. Polarising colours of the collagen fibres was recorded and statistically analysed. Materials and Methods: A group of 30 histopathologically diagnosed cases of Odontogenic cysts, 10 cases of Radicular cysts, 10 cases of Dentigerous cyst, 10 cases of Odontogenic Keratocyst and 2 cases of Dental follicular tissue as controls were retrieved from files of Department of Oral Pathology and Microbiology, Rajarajeswari Dental College and Hospital. Haematoxylin and Eosin stained slides were evaluated for the existence and degree of inflammation in all the slides. Paraffin embedded tissue blocks were sectioned at 5µm thickness. Sections were deparaffinised, hydrated and stained with Picro Sirius Red stain for collagen. Statistical analysis: Level of Significance: α=0.05 Statistical test used: Chi-squared (χ2) test Results: Our study showed that in, RC and DC - yellowish orange and orange color was seen indicating dense fibrosis in case of mild and moderate inflammation. Whereas in case of OKC , greenish yellow color was dominant in subepithelial, intermediate layer in absence and mild inflammation, whereas in periphery yellowish orange was seen in mild inflammation Conclusion: This method can be used to analyze the orientation of collagen fibers and also how inflammation can induce a change in the collagen from loosely packed thin fibrils to closely packed mature collagen. It can also be used as a diagnostic tool to differentiate two lesions and to predict their nature in terms of biologic behaviour and prognosis.