Clinical measurement of normal maximum mouth opening in children

This study was designed to find a method of assessing maximum mouth opening (MMO), using a tool that is proportional to the body size. One hundred two (102) children were selected to participate in the study. MMO, the width of three fingers (index, middle and ring fingers), four fingers (index, middle, ring and little fingers), body height, weight and age of each child were recorded, and the ability of each subject to position the fingers, vertically aligned between the upper and lower central incisors with the mouth maximally open, was documented. All subjects were able to position three fingers between the upper and lower central incisors, while only 37 (36.3%) were able to position four fingers. MMO was significantly different from the width of three and four fingers and was positively correlated with both weight and height and with age. Height, weight, and age showed a moderate to strong correlation with all finger measurements; no gender significant difference was observed for MMO. The findings of this study suggest that the ability to position three fingers between the upper and lower incisors with the mouth wide open can be considered a simple method to quickly evaluate MMO, but that it is not highly reliable.