Effect of Head Position on Vertical Mandibular Opening

STUDY DESIGN: A within-subjects repeated measures design. OBJECTIVES: To determine differences in the amount of vertical opening of the mandible among 3 different head positions. BACKGROUND: Results from several studies have suggested that the position of the head and neck may affect temporomandibular joint function. Presently no standardized position of the head and neck has been recommended for measuring vertical opening of the mandible. METHODS AND MEASURES: Twenty males and 20 females (32.9 +/- 8.3 years) participated in the study. We obtained 3 measurements of vertical mandibular opening using a millimeter ruler on each subject in the forward, neutral, and retracted head positions. RESULTS: A 1-way repeated measures analysis of variance followed by pairwise comparisons indicated that the vertical mandibular opening was significantly greater in the forward head position (44 +/- 5.3 mm) than in the neutral head position (41.5 +/- 4.8 mm) and in the retracted head position (36.2 +/- 4.5 mm). In addition, vertical mandibular opening was significantly greater in the neutral head position than in the retracted head position. Interclass correlation coefficients for the 3 head positions ranged from 0.90 to 0.97 for intrarater, interrater, and day-to-day reliability. CONCLUSIONS: Head position is an important factor in determining the amount of vertical mandibular opening in healthy adults.