Normal Maximal Incisal Opening and Associations with Physical Variables in Children

Purpose: The purpose of this investigation was to establish a normal range of maximal incisal opening (MIO) in children, and the correlation between MIO with age, height, weight, gender, race, and molar relationship. Methods: Calibrated examiners used the TheraBite Range of Motion (ROM) scale to obtain two MIO readings from 500 enrolled subjects, accounting for overbite or open bite. The subject's height, weight, molar relationship, age, gender, and race were recorded. Subjects were stratified according to age, and mean MIO +/- standard deviation for each age group was determined. Results: Mean MIO was positively correlated with age (P<.001), height (P<.001), weight (P<.001), and race (P<.001). However, height became insignificant in the multivariable regression model. On average, MIO of African-Americans was 3.66 mm larger than Whites (P<.001), and MIO of Hispanics/Latinos was 2.52mm greater than Whites (P<0.01). There was no statistically significant association with left or right molar relationships (P=.07, P=.26 respectively) or gender (P=.58). Conclusions: TheraBite ROM scale is a practical tool to clinically measure MIO. MIO mimics somatic growth, peaking at age 12-13 years for females and 14-15 years for males. African-Americans and Hispanics/Latinos have a greater mean MIO than Whites. The established norms will be useful in diagnosis and treatment.