The tip and torque of the cases that support the straight wire appliance were evaluated to determine the theoretical strength, the normal distribution of the information, the homogeneity of variances and the symmetrical behavior of the means in the dental arches. The 120 cases were analyzed in statistical program and underwent to tests the Kolmogórov-Smirnov, Levene and t Student. The torque of each upper teeth was compared with its pair on the opposite side and the probability to be equal to 95% of confidence was for the canine, first premolar and second premolar and lower teeth for the central incisor and lateral incisor. Tip was only normal for the lower right canine. It was concluded that the hypotheses of theory of straight wire appliance has not confirmed. Therefore, asymmetry is a constant between the right and left dental arches and has been confirmed even in this group of ideal occlusion. The characteristics of straight wire appliance should not be generalized to normal group because they are data from a sample that does not represent them.
(Rev Esp Ortod. 2011;41(3):164-168)