The effect of the gonial angle, ramus length, age and gender on the temporomandibular opening index.

Linear mouth opening is often used to assess the limitation of mandibular movement. However, this has a number of limitations. It is dependent on variables such as age, gender and ramus length. A new measure of movement has been developed previously, called the temporomandibular opening index (TOI). Forty-two subjects who did not exhibit signs and symptoms of temporomandibular disorder (TMD) were recruited to this study. The relationship of age, gender, gonial angle, ramus length and the TOI was studied. Linear regression analysis showed that the TOI was not dependent on gender (P > 0.644), gonial angle (P > 0.327), ramus length (P > 0.248) and age (P > 0.690). The index may therefore be a better measure of mandibular movement.