Influence of bolus hardness on masticatory function and nutrition

Objectives: To evaluate the effect of bolus hardness on chewing pattern and masticatory muscles activity in subjects with normal dental occlusion. Methods: 40 subjects (mean age ± SD: 26±5 years) with normal dental occlusion were selected for this study. Inclusion criteria: age range 18–30 years, fully functional erupted teeth, 2 mm overbite and overjet, absence of prosthesis, malocclusion and symptoms of temporomandibular joint dysfunction. Two standardized soft (chewing gum) and hard (wine gum) boluses with same size (20 mm length, 1.2 mm height, and 0.5 mm width) but different weights (2g soft and 3g hard) and puncture forces (0.36 N soft and 1.85 N hard) were used. Mandibular motion was tracked with a K7 Kinesiograph (Myotronics, USA). From each cycle were evaluated: opening amplitude; closure angle; cycle width; maximum lateral excursion; maximum velocity. Surface EMG signals were simultaneously recorded from masseter and anterior temporalis muscles with a multichannel electromyography. The relative increase in EMG peak value between soft and hard bolus was computed and expressed in percentage. Kinematic and EMG data were analyzed with a three-way and four-way ANOVA respectively with statistical significance of P<0.05. Results: Chewing pattern in the frontal plane was significantly higher and wider (P<0.001), with smaller closure angle(P<0.05) and higher peak velocity (P<0.01) during chewing the hard bolus. EMG peak amplitude of both masseter and anterior temporalis muscles was higher for both sides, but the contralateral side increased its activity significantly more than the ipsilateral side with the hard bolus(P<0.001). Conclusions: Results showed different EMG amplitude and coordination between sides with soft versus hard boluses. Masticatory forces improve bone growth and maintain patency of facial sutures during adulthood and ageing. Results provide kinematic and EMG adaptations to bolus hardness in healthy subjects and can be used as normative data for realizing foods able to improve physiological function.