Effect of Starting Posture on Three-Dimensional Jaw and Head Movement

OBJECTIVES: The effect of body posture on movement of the jaw and head has not yet been clearly established. The relationship between jaw and head movement has implications for conditions such as temporomandibular joint disorders which can be associated with neck pain. The purpose of this quasi-experimental study was to examine the effect of starting posture on three-dimensional movement of the jaw and head, and to examine the relationship between head and jaw movement during mouth opening. MATERIAL AND METHODS: Fourteen healthy participants performed jaw opening to comfortable and maximal amounts from three starting body postures (neutral, slumped, upright) while three-dimensional movement of the head, jaw, and trunk was tracked. Separate repeated measures analyses of variance analyses examined the effect of posture on jaw and head rotation and translation, and Pearson product moment correlations examined the relationship between jaw opening and head rotation. RESULTS: Body posture significantly influenced maximal opening but not comfortable opening (P < 0.0033). There was a positive relationship between head extension and maximum opening in an upright posture (r = 0.74, P = 0.006), and head extension and comfortable opening in neutral and upright postures (r = 0.75 to 0.93, P < 0.0033), although there was no relationship between head extension and jaw opening in a slumped posture when opening comfortably. CONCLUSIONS: Posture can affect three-dimensional movement of the jaw when opening. Negating the normal head extension that occurs with mouth opening when in a slumped posture has implications for the development of temporomandibular and neck problems in some individuals.