Harikrishnan Pandurangan, Magesh Varadaraju, Ajayan Akhil Minu, JebaSingh Devadhas Kingsly
Craniofacial Orthodontist, Division of Orthodontics, Teeth "N" Jaws Center, Lake Areaa 1st Cross Street, Nungambakkam, Chennai 600034, Tamil Nadu, India.
Department of mechanical engineering, SRM Institute of Science and Technology, Kattankulathur, Chengalpattu 603203, Tamil Nadu, India.
Comput Methods Programs Biomed. 2020 Dec;197:105748. doi: 10.1016/j.cmpb.2020.105748. Epub 2020 Sep 9.
Orthodontic fixed appliance therapy involves alignment of teeth through the bracket and archwires. The archwire twist (torque) imparts significant forces inside the bracket slot in refining the teeth position at the end of treatment. The objective of this in- silico study was to evaluate the torque induced bracket slot deformation in the commonly used 0.018 inch (") and 0.022" conventional Stainless Steel (SS) brackets with clinically relevant archwires during various angles of twist.
SS maxillary central incisor brackets of 0.018" width × 0.022" depth (0.457 mm × 0.558 mm) and 0.022" width × 0.028" depth (0.558 mm × 0.711 mm) were used. The SS archwires of 0.016" width × 0.022" depth (0.406 mm × 0.558 mm), 0.017" width × 0.025" depth (0.431 mm × 0.635 mm), 0.019" width × 0.025" depth (0.482 mm × 0.635 mm) and 0.021" width × 0.025" depth (0.533 mm × 0.635 mm) were engaged in the respective bracket slots. The assembled bracket-archwire Finite Element (FE) models were constructed. The archwire torque, the top, middle and bottom slot deformations (TSD, MSD, BSD) were obtained for the bracket-archwire combinations for various angles of archwire twist using FE Analysis (FEA).
The torque, TSD, MSD and BSD for 30 twist of 0.016" × 0.022" archwire in 0.018" slot were 28.13 Nmm, 35.71 µm, 21.51 µm and 15.67 µm respectively, and for 0.017" × 0.025" archwire were 50.18 Nmm, 54.52 µm, 32.47 µm and 19.11 µm respectively. Similarly for 0.019" × 0.025" archwire in 0.022" slot and 0.021" × 0.025" archwire in 0.022" slot they were 38.82 Nmm, 50.78 µm, 31.47 µm and 16.82 µm, and 60.22 Nmm, 65.22 µm, 36.44 µm and 22.68 µm respectively.
The slot deformation was present in both 0.018" and 0.022" brackets which increased as the angle of twist increased. The TSD were higher than the MSD and BSD in all the bracket-archwire combinations. We conclude that there is only elastic deformation of bracket slots upto 30 angle of twist and clinicians could maintain within this torque limits to avoid plastic deformation leading to improper teeth position.
正畸固定矫治器治疗通过托槽和弓丝使牙齿排齐。在治疗末期，弓丝扭转（转矩）会在托槽槽沟内施加显著力以精细调整牙齿位置。本计算机模拟研究的目的是评估在不同扭转角度下，常用的0.018英寸（"）和0.022英寸传统不锈钢（SS）托槽与具有临床相关性的弓丝之间相互作用时，转矩引起的托槽槽沟变形情况。
使用宽度为0.018英寸×深度为0.022英寸（0.457毫米×0.558毫米）以及宽度为0.022英寸×深度为0.028英寸（0.558毫米×0.711毫米）的上颌中切牙SS托槽。将宽度为0.016英寸×深度为0.022英寸（0.406毫米×0.558毫米）、0.017英寸×深度为0.025英寸（0.431毫米×0.635毫米）、0.019英寸×深度为0.025英寸（0.482毫米×0.635毫米）以及0.021英寸×深度为0.025英寸（0.533毫米×0.635毫米）的SS弓丝分别放入各自的托槽槽沟中。构建组装好的托槽 - 弓丝有限元（FE）模型。使用有限元分析（FEA）获取不同弓丝扭转角度下托槽 - 弓丝组合的弓丝转矩、托槽槽沟顶部、中部和底部变形（TSD、MSD、BSD）。
0.016英寸×0.022英寸弓丝在0.018英寸托槽中扭转30°时的转矩、TSD、MSD和BSD分别为28.13牛毫米、35.71微米、21.51微米和15.67微米，0.017英寸×0.025英寸弓丝的分别为50.18牛毫米、54.52微米、32.47微米和19.11微米。同样，0.019英寸×0.025英寸弓丝在0.022英寸托槽中以及0.021英寸×0.025英寸弓丝在0.022英寸托槽中扭转30°时，它们分别为38.82牛毫米、50.78微米、31.47微米和16.82微米，以及60.22牛毫米、65.22微米、36.44微米和22.68微米。
0.018英寸和0.022英寸托槽均存在槽沟变形，且随着扭转角度增加而增大。在所有托槽 - 弓丝组合中，TSD均高于MSD和BSD。我们得出结论，在扭转角度达30°时托槽槽沟仅发生弹性变形，临床医生可将转矩维持在该限度内以避免塑性变形导致牙齿位置不当。
