Maximal Mouth Opening in Infants: A Single-Group Prospective Cohort Study

Detection of mandibular range of motion variations in infants may allow for early diagnosis of pathologic conditions to the temporomandibular joint. The purpose of this study was to determine the normal ranges for maximal mouth opening (MMO) in healthy infants under 12 months of age. A single-group prospective cohort study of consecutive patients below 12 months of age was conducted in an outpatient setting at the Florida Craniofacial Institute in Tampa, Florida. Patients were excluded if they had trismus, presented with signs of obstructive sleep apnea, suffered a facial fracture, or were diagnosed with a craniofacial syndrome. Age (in months) at the time of presentation, measured as a continuous variable. The main outcome variable was MMO. This was measured by placing a thumb and forefinger in the infant's mouth and applies slight pressure to encourage MMO. In older infants with erupted central incisors, MMO was measured from the gingival margins. The covariates were sex, race, and gestational age. Findings were presented as means with 95% confidence intervals. A multivariate linear regression analysis was conducted to evaluate changes in MMO with increasing age. The sample was composed of 151 infants with a mean age of 5.2 months (95% confidence interval [CI] 4.8 to 5.6), and 33% were female. The mean MMO was 32.1 mm (95% CI 31.5 to 32.7). Results of the linear regression analysis showed MMO to significantly increase with increasing age, increasing at a mean rate of approximately 1 mm per month (coefficient 1.06, 95% CI 0.88 to 1.23, P