## 1 Introduction  
Cervical lordosis is the anterior convexity of the cervical spine, which extends from the foramen magnum to the first thoracic vertebra. Normal cervical curvature is lordotic, and proper cervical curvature is important for good posture and function of the head and neck area [1,2].  
Loss of normal cervical curvature is relatively common. Previous studies have reported that only one-third of the adult population shows lordotic cervical curvature, while the rest show straight, kyphotic (curved in the opposite direction of lordosis), or sigmoid (which has both lordotic and kyphotic curves) cervical curvature [3, 4, 5]. Loss of the normal cervical curvature can cause neurological symptoms, neck and shoulder pain, headaches, and other disorders, thus causing functional disability [1, 6, 7, 8, 9]. Although there are many studies on the biomechanical changes that alter cervical curvature, the exact pathophysiology has not been established. It has been reported that cervical curvature can be affected by numerous factors, such as age, sex, trauma, congenital defects, cervical muscle weakness, tumors, infection, and psychosocial factors [2, 4, 10, 11, 12]. Recently, interest has been focused on the relationship between cervical curvature and posture because forward head posture is common with the use of smartphones [13,14]. Forward head posture is a habitual neck posture defined by forward translation of the cervical spine and is thought to be related to cervical curvature malalignment. As the head tilt is more forward in relation to the cervical spine, the axial load moves anteriorly. Consequently, increased compressive force can trigger a progressive degenerative process and potentially result in poor alignment of the cervical curvature [15].  
Few studies have investigated the relationship between craniofacial characteristics and cervical posture [16,17]. [PERSON] et al. [16] reported that subjects between ages 8 and 15 years with dolichocephalic faces had a forwardly inclined cervical column. Similarly, [PERSON] and [PERSON] [17] investigated adult males between the ages of 18 and 30 and reported that forward head posture was frequently associated with a large anterior facial height, maxillary and mandibular retrognathism, and large mandibular plane inclination. However, to our knowledge, there have been no studies on the relationship between vertical facial patterns and craniocortical posture in adult females.  
Cervical curvature can be associated with craniocortical posture and vertical facial patterns. A few studies have investigated cervical curvature variations according to vertical facial patterns, and the results are controversial [8, 16, 17, 18]. No studies have compared the distribution of cervical curvature type according to different vertical facial patterns. Our study is the first to establish a relationship between cervical curvature and vertical facial patterns. The purposes of this study were to (1) compare the craniocortical posture of adult females with different vertical facial patterns, (2) compare the distribution of cervical curvature variations with different vertical facial patterns, and (3) determine any correlation between the vertical facial pattern, craniocortical posture, and cervical curvature measurements.