Lower Incisor Inclination in Relation to Head Posture, Tongue and Hyoid Positions

Abstract

Objectives: To investigate the relationship between head posture, hyoid bone, tongue position and lower incisor inclination. Materials and Methods: The study sample consisted of 98 subjects (35 males, 63 females), who had a mean age of 17.7 years in the permanent dentition and with a skeletal Class I relationship. Lower incisor inclination, craniovertical, craniocervical and craniohorizontal postural variables, tongue and hyoid position and airway measurements were evaluated on lateral cephalograms taken in natural head position. The study sample was divided into two groups according to lower incisor inclination (48 had IMPA<90 ⁰ with a mean degree of 88.09 and 50 had IMPA>90 ⁰ with a mean degree of 102.84) and a Student-t test was performed to compare and describe head posture, tongue and hyoid bone positions.Results: The subjects with upright incisors had a more posteriorly positioned hyoid bone relative to the mandibular symphysis compared with the subjects with flared incisors (p<0.05). Tongue length was greater in the flared incisor group than in the upright incisor group (p<0.05). In relation to head posture measurements, the upright incisor group had 3-3.5° larger cranio-cervical angles (NSL-OPT, NSL-CVT, NL-OPT, NL-CVT angles, p<0.05) than the flared incisor group. The airway measurements revealed no statistically significant difference between the groups.Conclusions: The position of the hyoid bone, tongue length and craniocervical head posture showed significant differences between upright and flared lower incisors.