Introduction

The success of root canal therapies requires factors such as proper irrigation and instrumentation, dense obturation, and good coronal sealing. For this purpose, knowledge about the morphology of the root canal system and its variations is essential (1). Most permanent mandibular first molars typically have 2 roots- mesial and distal with 3 root canal systems. Still, variations concerning the number of roots and canal morphology are also not occasional. Radix Paramolaris (mesiobuccally) and Radix Entomolaris (distolingually) are variations determined according to the position of the third additional root (2). In the literature review, the prevalence of RE according to race and ethnic group includes a wide range from 0.6 to 29.7% (3). Radix entomolaris (RE) is often not diagnosable because of overlapping by the distal root with orthograde radiographs and it can only be discovered by a careful correlation between clinical and radiographical examination(1). Roots that have a double curvature are called S-shaped roots(4). S-shaped canals, also known as bayonet root canals(5), are found in approximately 10% of clinical cases(4). Due to the complexity of these canals, the root treatment process in these teeth is very challenging (5, 6). complex root canal curvatures or S-shaped canals in radix entomolaris create rare circumstances. Accordingly, the current study aimed at presenting three cases of management of radix entomolaris of the mandibular first molar with complex root curvature or (s-shaped canal).