Comparison between lingual and labial orthodontics based on treatment of overbite by using rocking chair archwire- A biomechanical study

Background Lingual orthodontics (LiO) has developed rapidly in recent years and research on treatment of overbite by using Rocking Chair Arch (RCA) wire of different curve depths is still limited, especially with 3-dimensional Finite Element (FE) models. The main objectives are to study the biomechanical differences in maxillary anterior teeth between lingual and labial orthodontics and observe the lingual mechanics on different inclinations of teeth. Methods The force produced by Nickel-Titanium, Stainless Steel (SS) RCA for both sides was measured using Electromechanical Universal Testing Machine. 6 FE models were constructed and divided into 2 groups according to SS wire of 0.016×0.022-inch standard and mushroom arch shaped RCA of curve depth 2, 4, 6 mm. Additional 9 FE models were constructed and divided into 3 groups based on Retroclination (-5°, -10°) and Proclination (+10°). Results Use of same diameter of SS RCA with same curve depth but on different sides shows more stress and strain, displacement of teeth in lingual mechanics. Also, stress-strain, displacement increased with increasing RCA curve depth. In LiO, intrusion of normally inclined or proclined teeth are accompanied by little or no labial tipping whereas that of retroclined teeth is accompanied by further lingual tipping. Conclusion In the intrusion using Lingual RCA, to avoid the traumatic force to teeth, the curve depth should be lesser than Labial RCA or apply more elastic arch material; Aligning different inclined teeth into normal inclination firstly and proceed with the application of intrusive force can be the best approach.