Relationships between masticatory rhythmicity, body mass and cephalometrically-determined aesthetic and functional variables during development in humans.

OBJECTIVE: We studied the relationship between chewing rhythmicity, craniomandibular morphology, and age in humans. DESIGN: Sixty subjects (10M:10F/group×three age groups, viz., 4-8, 10-14, and 17-21 years) participated. Subjects chewed gum for 2min while jaw movements in the frontal plane were videorecorded. Mean and variation in mean chewing cycle duration (TC) were quantified using maximum opening to maximum opening as cycle boundaries. Five "aesthetic" cephalometric variables (e.g., ANB) and seven "functional" variables (e.g., jaw length) were quantified from subjects' lateral cephalographs. Simple linear regression models and several multivariate analyses were used in comparisons. RESULTS: Mean TC increased and variation in TC decreased significantly with age. Body mass correlated with age, height, TC, all seven "functional" variables and only two "aesthetic" variables. Mean TC was correlated significantly with jaw length, distance from condylion to first molar point, distance from gonion to zygomatic arch, and distance from hyoid to menton. CONCLUSIONS: TC appeared to adapt with age. Although TC scaled most significantly with age, it is more likely that TC is mechanistically linked to jaw length or size. The decrease in TC variation with age suggests improved efficiency. TC did not scale with "aesthetic" variables, suggesting that these do not impact chewing rate; however, clinical procedures that impact jaw length may. The negative allometric scaling of TC with "functional" variables may reflect the pedomorphic jaw and face of humans. Further human studies will provide insights into the nature of scaling and adaptation of rhythmic chewing during development.