Limitation of mouth opening is an important sign of temporomandibular disor
ders. It is usually measured Linearly from the incisal edge of the maxillar
y incisors to the incisal edge of the mandibular incisors. This measurement
has been queried. A new measure of mouth opening, the opening index is sug
gested. It was shown that the mean opening index differs for groups of pati
ents with a myogenous or arthrogenous temporomandibular joint problem.