Symmetry evaluation in the dental arch: the IXS index.

The aim of the present geometrical analysis is to find a method to evaluate the symmetrical position of the teeth inside the dental arch and the symmetry of the dental curve in general. The biggest problem was the identification of the symmetry axis of the upper and the lower dental arches, since there is an absence of certain anatomic landmarks in the centre of palate and mandibular body. Therefore the theorems of symmetrical figures have been applied in order to research the relationship between the dental arch points and to obtain an index: the Ixs Index. The Ixs Index gives a result of 1 when 2 couples, such as the cusps of the canines and the mesio-buccal cusps of the first molars, are in symmetric position. In contrast with a result unequal to 1, the teeth lie asymmetrically.