This study aims to evaluate the effectiveness of auxiliary segmental lingual appliances in leveling the Curve of Wilson at the second molars in patients undergoing labial fixed orthodontic treatment. Patients exhibiting an excessive (deep) Curve of Wilson at the second molar bilaterally (meaning lingually inclined mandibular second molar) will be recruited.. Using a split-mouth design, one side will receive the intervention (auxiliary segmental lingual appliances), while the other side will serve as the control. The variables measured include the Curve of Wilson at the second and first molars, and the distance from the mesiolingual and distolingual cusps of the second molar to the occlusal plane of the first molar. Measurements will be taken on digital impressions at baseline (T0), after leveling with a stainless steel labial archwire (T1), and three months after applying the auxiliary segmental lingual appliances. The effectiveness will be assessed by comparing the two groups.