Analysis of maximum mouth opening and its related factors in 3- to 5-year-old Taiwanese children.

Maximum mouth opening (MMO) can reflect the function of the dentofacial musculature and joint system, and routine oral examinations should include its assessment. To diagnose abnormalities using MMO measurements, it is necessary to establish the normal range of MMO; however, few studies have investigated this subject in Taiwan. Therefore, the purposes of this study were to determine the normal MMO range in 3- to 5-year-old preschool children and to investigate the factors correlated with MMO. We examined the interincisal distance, defined as the distance between the edges of the upper and lower incisors, in 518 preschool children (age range 3-5 years; 271 boys and 247 girls) with a plastic sliding caliper. The MMO on both sides of the mouth and mouth width (MW) was measured 3 times. No differences in MMO were found between the genders. The interincisal distance was 37.47 (±4.11) mm for boys and 36.93 (±3.85) mm for girls, whereas the mean MMO was 37.21 (±3.99) mm. The MMO increased with the increasing age of the children, and the mean value of MMO in children aged 3, 4, and 5 was 35.31 (±4.03), 36.61 (±3.79), and 38.31 (±3.88) mm, respectively. Furthermore, MMO was found to correlate with weight and MW. MMO increased by 0.19 mm per increased weight and 0.37 mm per increased MW. The mean value of MMO in 3- to 5-year-old preschool children was 37.21 (±3.99) mm. MMO in 3- to 5-year-old preschool children increased with age and was correlated with weight and MW.