2018 Volume 56 Issue 4 Pages 427-433
When the first milk molar is unilaterally lost at an early stage, a crown loop is a standard apparatus often used to maintain eruption space for the first molar. In this fundamental study, we investigated the effects of use of crown loop on periodontal tissue and also examined loop strength using the fol lowing methods. With placement of force onto the crown or a W- or U-shaped loop, stress in the periodontal ligament (PDL) of the milk canine and second milk molar was calculated using a finite element method. The alveolar bone and teeth were assumed to be rigid bodies, while the PDL was considered to be a nonlinear elastic film and the loop a linear elastic beam. Intrusive force was ap plied to the occlusal surface of the second milk molar or buccolingual force was applied to the buccal side of the loop. The following results were obtained.
1.When intrusive force was applied to the occlusal surface of the second milk molar, stress in the loop was nearly zero. In this case, the crown loop was scarcely affected by stress in the PDL of the second milk molar.
2.When intrusive force was applied to the buccal side of the loop, stress in the PDL of the second milk molar was increased by two to three times as compared to findings obtained when the same intrusive force was applied to the occlusal surface of the second milk molar. When buccolingual force was applied to the buccal side of a W-shaped loop, stress was produced in the PDL of both the second milk molar and milk canine.
Our results suggest that excessive occlusal force can produce a plastic deformation in the region soldered to the crown, leading to loop failure.
