An Investigation of Mouth Opening Forces in Adults

Objectives: Knowledge of the forces generated during mouth opening is important to elucidate the function and biomechanics of the masticatory apparatus, in addition to having clinical relevance in the management of certain diseases and conditions. This study aimed to estimate maximum mouth opening forces in a large sample of adult participants and to investigate variability in force patterns.

Methods: 39 male and 64 female participants aged 20-60 years were recruited among staff and students of the Faculty of Dentistry, University of Otago, NZ. Exclusion criteria included pain in the fascial muscles and TMJ, current orthodontic treatment and absence of the natural dentition. Opening forces were measured with an adjustable rigid extra-oral device connected to a 1 KN load cell. Seven attempts were recorded, with 10 sec interval. Data was recorded in PowerLab and analysed with LabChart7 (AD Instruments). Average maximum force values were obtained after discarding the first and last attempt.

Results: Maximum mouth opening force values averaged 77.91 N ± 42.57 for males and 48.22 N ± 31.54 for females, and this difference was statistically significant (U = 1,787, p = 0.0002). In males, maximum force values ranged from 10.64 N to 166.62 N and in females from 4.3 N to 152.77 N. Maximum force values were poorly associated with age, height and weight of the participants. A high degree of individual variation was observed in the amplitude and shape of the curves generated during mouth opening and closing.

Conclusions: It can be concluded that males had higher opening force values than females in this study. Further analyses with a larger number of participants will contribute towards the understanding of the dynamics of the masticatory apparatus. The potential of this method being used as a screening tool for TMJ disorders and other conditions still needs to be further explored.