The linear intra-articular motions of the temporomandibular joint in individuals with severe forward head posture: A cross-sectional study

Background: The cervical vertebrae and the temporomandibular joint (TMJ) may be linked through their common muscles. Objectives: The aim of the present study was to compare the linear intra-articular motions of the TMJ between individuals with the normal craniocervical posture (CCP) and severe forward head posture (FHP). Design: Cross-sectional study. Methods: Volunteers (N = 38) were equally assigned to either the severe FHP group or the normal CCP group according to their craniovertebral angle (CVA). The CVA angles greater than 49 were considered as the normal CCP while angles between 44 and 40 were regarded as the severe FHP. The TMJ was imaged at the closed, median, and maximum open positions of the mouth using an ultrasound machine with a 7.5 MHz linear transducer in the sitting position. The best -fitting curve in the contour registration method was employed to measure displacement of the mandibular condyle on the transverse and vertical axes. Results: The forward displacement of the mandibular condyle in the severe FHP group was significantly (p -value = 0.037) reduced compared to the normal CCP group at maximum open position of the mouth, while no significant difference was revealed at closed (p -value = 0.937) or median open (p -value = 0.699) positions. The perpendicular displacement of the mandibular condyle exhibited no significant (p-value>0.107) difference between groups at any mouth position. Discussion: The current study demonstrated, for the first time, that severe FHP may impact the intra-articular motion of the TMJ. This study presumed that individuals with severe FHP may encounter a force imbalance in the anterior -posterior direction.