Purpose: Emerging evidence shows that changes in the bone and its microenvironment following radiotherapy are associated with either an inhibition or a state of low bone formation. Ionizing radiation is damaging to the jawbone as it increases the complication rate due to the development of hypovascular, hypocellular, and hypoxic tissue. This review summarizes and correlates the current knowledge on the effects of irradiation on the bone with an emphasis on jawbone, as these have been a less extensively studied area. Conclusions: The stringent regulation of bone formation and bone resorption can be influenced by radiation, causing detrimental effects at structural, cellular, vascular, and molecular levels. It is also associated with a high risk of damage to surrounding healthy tissues and an increased risk of fracture. Technological advances and research on animal models as well as a few human bone tissue studies have provided novel insights into the ways in which bone can be affected by high, low and sublethal dose of radiation. The influence of radiation on bone metabolism, cellular properties, vascularity, collagen, and other factors like inflammation, reactive oxygen species are discussed.

Oral Lichen planus (OLP) is a chronic autoimmune cellmediated inflammatory disease. Most OLP patients complain of xerostomia/dry mouth due to changes in the oral mucosal protective barrier. Mucin 5B (MUC5B) is the predominate gelforming mucin in the oral cavity that protects the underlying tissue from mechanical damage, chemical insult, and pathogenic microbes. This study aims to assess MUC5B in OLP subjects and correlate its role in etiopathogenesis. The study included 20 OLP subjects and 10 healthy controls. OLP subjects were divided further into 10 keratotic (reticular) and 10 nonkeratotic (atrophic/erythematous) groups based on the clinical criteria. Dryness of mouth was confirmed by the subjective (Xerostomia Inventory, XI; Bother Index, BI) and clinical testing (Clinical Oral Dryness Score, CODS) method. Stimulated, unstimulated saliva and blood samples were collected from subjects. Samples were centrifuged and analysed for MUC5B level using an ELISA kit. The subjective and clinical testing methods which clinically define xerostomia are correlated with the age and sex of the OLP subjects. The stimulated and unstimulated salivary flow rate of OLP subjects was lower (p<0.05) than controls and was associated with the XI, BI, and CODS (p<0.01) . In contrast, the MUC5B level was increased in the serum of OLP subjects compared to controls (p<0.05) . OLP subjects with xerostomia, displayed lower salivary flow, decrease MUC5B in saliva and increase MUC5B in serum. Alteration of MUC5B in the saliva causes oral mucosal alterations affecting the protection of the oral cavity and increase xerostomia in OLP.

Heat shock proteins (Hsp) or the molecular chaperones are observed in most cells of humans, microbes, and in extracellular and intracellular fluids. Hsps plays an essential role under most stress conditions at the cellular and subcellular levels. It presents cytoprotective properties by the modulation of cytokine release and immunity and is involved in various physiological and pathological events. A tight regulation of molecular chaperones monitors the folding/misfolding, internal localization, and proteolytic turnover of proteins. Despite their advantageous effects, Hsps also has disadvantageous role in intensifying the inflammation. They are potential mediators of oncogenesis as they are the key regulators of cellular growth and differentiation. The authors reviewed, an overview of the role of chaperones, with respect to the lesions affecting oral and para-oral structures.