Comparison of inclination and vertical changes between single-wire and double-wire retraction techniques in lingual orthodontics

OBJECTIVE: The Heat Induction Typodont System (HITS), used in some recent studies, has a distinct advantage over previous tooth movement simulation methods. This study aimed to compare inclination and vertical changes between the single-wire and double-wire techniques during en masse retraction with different lengths of lever arms in lingual orthodontics using an upgraded version of the HITS. METHODS: Duet lingual brackets, which have two main slots, were used in this study. Forty samples were divided into four groups according to the length of the lever arm (3-mm or 6-mm hook) and the retraction wire (single-wire or double-wire). Four millimeters of en masse retraction was performed using lingual appliances. Thereafter, 3-dimensional-scanned images of the typodont were analyzed to measure inclination and vertical changes of the anterior teeth. RESULTS: Incisor inclination presented more changes in the single-wire groups than in the double-wire groups. However, canine inclination did not differ between these groups. Regarding vertical changes, only the lateral incisors in the single-wire groups presented significantly larger values than did those in the double-wire groups. Combining the effect of hook lengths, among the four groups, the single-wire group with the 3-mm hook had the highest value, while the double-wire group with the 6-mm hook showed the least decrease in crown inclination and extrusion. CONCLUSIONS: The double-wire technique with an extended lever arm provided advantages over the single-wire technique with the same lever arm length in preventing torque loss and extrusion of the anterior teeth during en masse retraction in lingual orthodontics.