Characteristics of masticatory behavior of patients with mandibular prognathism.

Background: Patients with mandibular prognathism exhibit not only its characteristic maxillofacial morphology but also discrepancies in stomatognathic function, and understanding this morphology and function is vital for establishing a plan for surgical orthodontic treatment or providing guidance for recovery after orthognathic surgery. However, few studies have yet addressed the objective evaluation of masticatory function before and after surgical orthodontic treatment. In particular, the masticatory behaviors that show how you chew in your daily meals, including the number of chews, chewing rate, and posture during chewing, has not yet been fully studied in patients with mandibular prognathism. The aim of this study was to compare the masticatory behaviors of patients with mandibular prognathism with that of patients with individualized normal occlusion, to clarify the characteristics of masticatory behaviors in mandibular prognathism and to search for a relationship with maxillofacial morphology.

Methods: Participants were 23 patients (12 men, 11 women; mean age 17.9 years) with mandibular prognathism (patient group) and 23 patients (12 men, 11 women; mean age 24.4 years) with normal occlusion that had been achieved by orthodontic treatment (control group). Masticatory behaviors were measured by a wearable device fitted to each participant's right ear. Parameters such as number of chews, chewing rate, number of chews per bite, mealtime, and head and neck posture were recorded, while participants consumed a 100-g rice ball. Body mass index, occlusal contact area, and lateral cephalograms were also measured, and their associations with masticatory behaviors were investigated.

Results: In patient group, the number of chews was lower, mealtime was shorter, and the head and neck were tilted further forward. There was a significant positive correlation between overjet and anteroposterior head and neck posture and a significant negative correlation between overbite and anteroposterior head and neck posture.

Conclusion: Due to morpho/functional discrepancies in the stomatognathic system, patient group chewed fewer times and for a shorter time and leaned further forward while chewing. The characteristics of the masticatory behaviors of patients with mandibular prognathism identified in the present study may be helpful when devising plans for changing behavior before and after orthodontic treatment or orthognathic surgery.