2017 Volume 55 Issue 4 Pages 451-457
When the mandibular first milk molar teeth are lost at an early stage, crown loops are often applied for space maintenance. However, depending on the shape of the tip of the crown loop, it has been reported to cut into the gingiva or detach from the tooth in some cases. In the present study, we simulated the influence of crown loops on tooth and crown loop movement using a finite element method for simulation with 3 different loop tip shapes (W-, I-, U-shape). The experimental methods were as follows. When force was applied to the second milk molar teeth in a mesial direction, another force was simultaneously applied in a lingual direction with the crown loop. The following results were obtained.
1.When a force in a mesial direction was applied to the crown loop, the second milk molar teeth inclined in a mesial direction. As a result, the tip of the crown loop was distracted towards the distal cervical gingiva. The amount of distraction was increased in the order of W-, I-, and U-shape.
2.When a force was applied to the crown loop in a lingual direction simultaneously with that in a mesial direction, the tip of the loop sank and moved in a lingual manner in the U-shape group. As a result, the tip of the loop became detached from the milk canine tooth.
3.With the same forces were applied as in section 2 above to the W-shaped loop, lingual movement was extremely limited and it was possible to prevent detachment from the milk canine tooth.
