**Abstract**

Odontogenic cysts are a group of common pathological lesions of the jaw. Typically, they can be found randomly on X-rays as round benign lesions. However, some of them can behave aggressively with a tendency toward malignancy. Among odontogenic cysts with benign pathology, up to 60% of all jaw cysts are radicular cysts, which originate from root canal infection. Pathogenesis involves the interaction between osteoblasts, osteocytes, and osteoclasts as well as the expression of RANK-RANKL/OPG signaling system. Furthermore, collagenases (e.g., MMPs) are expressed in epithelial lining of the cyst. Among odontogenic cysts with potentially aggressive behavior, odontogenic keratocysts (OKCs) have a high rate of recurrence and very debatable treatment options; they can be associated with Gorlin syndrome. Keratocysts have developmental origin and show variability in their gene expression profiles. Their etiology is closely related to genetic factors, especially mutations in different members of Shh signaling pathway, including *PTCH* gene.

**Keywords:** odontogenic cysts, radicular cyst, keratocyst, RANK-RANKL/OPG, PTCH gene

#### **1. Introduction**

Odontogenic cysts are pathological cavities located in the jaw bones, filled with fluid surrounded by epithelial lining and fibrous connective tissue. Two most common odontogenic cysts with epithelial lining are inflammatory and developmental cysts (**Figure 1**). Among inflammatory cysts, the most characteristic one is the radicular cyst, which can be found in 60% of all odontogenic cysts. Radicular cyst originates from root canal infection and is of benign nature [1]. Cysts that originate from tissues involved in tooth development are called developmental cysts. Among them, the most interesting one is odontogenic keratocyst because of its unique and unexplored characteristics [2].

This chapter will deal with gene expression profiles of radicular cysts as the most common member of odontogenic cysts and keratocysts as the most debatable member of epithelial developmental cysts in order to uncover possible mechanism of pathogenesis of these two types of jaw cysts.

**Figure 1.**

*Modified classification of cysts found in oral and maxillofacial regions [1].*
